Forem: Wei

MiniWord easy and effective .NET Word Template library

Wei — Sun, 25 Sep 2022 15:34:32 +0000

Github Link : https://github.com/mini-software/MiniWord

Introduction

MiniWord is an easy and effective .NET Word Template library.

Getting Started

Installation

nuget link : https://www.nuget.org/packages/MiniWord
Packge xml <PackageReference Include="MiniWord" Version="0.4.0" />
Or .NET CLI : dotnet add package MiniWord --version 0.4.0

Quick Start

Template follow "WHAT you see is what you get" design，and the template tag styles are completely preserved.

var value = new Dictionary<string, object>(){["title"] = "Hello MiniWord"};
MiniSoftware.MiniWord.SaveAsByTemplate(outputPath, templatePath, value);

Input, Output

Input support file path, byte[]
Output support file path, byte[], stream

SaveAsByTemplate(string path, string templatePath, Dictionary<string, object> value)
SaveAsByTemplate(string path, byte[] templateBytes, Dictionary<string, object> value)
SaveAsByTemplate(this Stream stream, string templatePath, Dictionary<string, object> value)
SaveAsByTemplate(this Stream stream, byte[] templateBytes, Dictionary<string, object> value)

Other

POCO or dynamic parameter

v0.5.0 support POCO or dynamic parameter

var value = new { title = "Hello MiniWord" };
MiniWord.SaveAsByTemplate(outputPath, templatePath, value);

FontColor and HighlightColor

var value = new
{
    Company_Name = new MiniWordColorText { Text = "MiniSofteware", FontColor = "#eb70AB" },
    Name = new MiniWordColorText { Text = "Jack", HighlightColor = "#eb70AB" },
    CreateDate = new MiniWordColorText { Text = new DateTime(2021, 01, 01).ToString(), HighlightColor = "#eb70AB", FontColor = "#ffffff" },
    VIP = true,
    Points = 123,
    APP = "Demo APP",
};

HyperLink

If value type is MiniWordHyperLink system will replace template string by hyperlink.

Url： HyperLink URI target path
Text：Description

var value = new 
{
    ["Name"] = new MiniWordHyperLink(){
        Url = "https://google.com",
        Text = "Test Link!!"
    },
    ["Company_Name"] = "MiniSofteware",
    ["CreateDate"] = new DateTime(2021, 01, 01),
    ["VIP"] = true,
    ["Points"] = 123,
    ["APP"] = "Demo APP",
};
MiniWord.SaveAsByTemplate(path, templatePath, value);

Examples

ASP.NET Core 3.1 API Export

using Microsoft.AspNetCore.Builder;
using Microsoft.AspNetCore.Hosting;
using Microsoft.AspNetCore.Mvc;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Hosting;
using System;
using System.Collections.Generic;
using System.IO;
using System.Net;
using MiniSoftware;

public class Program
{
    public static void Main(string[] args) => CreateHostBuilder(args).Build().Run();

    public static IHostBuilder CreateHostBuilder(string[] args) => Host.CreateDefaultBuilder(args).ConfigureWebHostDefaults(webBuilder => webBuilder.UseStartup<Startup>());
}

public class Startup
{
    public void ConfigureServices(IServiceCollection services) => services.AddMvc();
    public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
    {
        app.UseStaticFiles();
        app.UseRouting();
        app.UseEndpoints(endpoints =>
        {
            endpoints.MapControllerRoute(
                name: "default",
                pattern: "{controller=api}/{action=Index}/{id?}");
        });
    }
}

public class ApiController : Controller
{
    public IActionResult Index()
    {
        return new ContentResult
        {
            ContentType = "text/html",
            StatusCode = (int)HttpStatusCode.OK,
            Content = @"<html><body>
<a href='api/DownloadWordFromTemplatePath'>DownloadWordFromTemplatePath</a><br>
<a href='api/DownloadWordFromTemplateBytes'>DownloadWordFromTemplateBytes</a><br>
</body></html>"
        };
    }

    static Dictionary<string, object> defaultValue = new Dictionary<string, object>()
    {
        ["title"] = "FooCompany",
        ["managers"] = new List<Dictionary<string, object>> {
            new Dictionary<string, object>{{"name","Jack"},{ "department", "HR" } },
            new Dictionary<string, object> {{ "name", "Loan"},{ "department", "IT" } }
        },
        ["employees"] = new List<Dictionary<string, object>> {
            new Dictionary<string, object>{{ "name", "Wade" },{ "department", "HR" } },
            new Dictionary<string, object> {{ "name", "Felix" },{ "department", "HR" } },
            new Dictionary<string, object>{{ "name", "Eric" },{ "department", "IT" } },
            new Dictionary<string, object> {{ "name", "Keaton" },{ "department", "IT" } }
        }
    };

    public IActionResult DownloadWordFromTemplatePath()
    {
        string templatePath = "TestTemplateComplex.docx";

        Dictionary<string, object> value = defaultValue;

        MemoryStream memoryStream = new MemoryStream();
        MiniWord.SaveAsByTemplate(memoryStream, templatePath, value);
        memoryStream.Seek(0, SeekOrigin.Begin);
        return new FileStreamResult(memoryStream, "application/vnd.openxmlformats-officedocument.wordprocessingml.document")
        {
            FileDownloadName = "demo.docx"
        };
    }

    private static Dictionary<string, Byte[]> TemplateBytesCache = new Dictionary<string, byte[]>();

    static ApiController()
    {
        string templatePath = "TestTemplateComplex.docx";
        byte[] bytes = System.IO.File.ReadAllBytes(templatePath);
        TemplateBytesCache.Add(templatePath, bytes);
    }

    public IActionResult DownloadWordFromTemplateBytes()
    {
        byte[] bytes = TemplateBytesCache["TestTemplateComplex.docx"];

        Dictionary<string, object> value = defaultValue;

        MemoryStream memoryStream = new MemoryStream();
        MiniWord.SaveAsByTemplate(memoryStream, bytes, value);
        memoryStream.Seek(0, SeekOrigin.Begin);
        return new FileStreamResult(memoryStream, "application/vnd.openxmlformats-officedocument.wordprocessingml.document")
        {
            FileDownloadName = "demo.docx"
        };
    }
}

.NET Miniexcel Dynamic Query Totuial

Wei — Mon, 18 Apr 2022 01:32:00 +0000

DOTNET Develop Simple Disk Key Value Cache

Wei — Tue, 05 Apr 2022 09:23:51 +0000

Trace Dapper.NET Source Code - The Underlying Logic Of Parameterization

Wei — Thu, 17 Dec 2020 00:24:16 +0000

Github Link : Trace-Dapper.NET-Source-Code

20. The Underlying Logic Of Parameterization

One key function of Dapper: "Parameterization"

Main logic: GetCacheInfo checks whether there is a dynamic method in the cache > If there is no cache, use the CreateParamInfoGenerator method Emit IL to create the AddParameter dynamic method > Save it in the cache after creation

Next, we will focus on the underlying logic and "exquisite detail processing" in the CreateParamInfoGenerator method, using the result reverse code method, ignoring the "unused fields" and not generating the corresponding IL code to avoid resource waste. This is also the reason why the previous caching algorithm has to check different SQL strings.

The following are the key parts of the source code I picked:

internal static Action<IDbCommand, object> CreateParamInfoGenerator(Identity identity, bool checkForDuplicates, bool removeUnused, IList<LiteralToken> literals)
{
  //...
  if (filterParams)
  {
    props = FilterParameters(props, identity.sql);
  }

  var callOpCode = isStruct ? OpCodes.Call : OpCodes.Callvirt;
  foreach (var prop in props)
  {
    //Emit IL action
  }
  //...
}


private static IEnumerable<PropertyInfo> FilterParameters(IEnumerable<PropertyInfo> parameters, string sql)
{
  var list = new List<PropertyInfo>(16);
  foreach (var p in parameters)
  {
    if (Regex.IsMatch(sql, @"[?@:]" + p.Name + @"([^\p{L}\p{N}_]+|$)", RegexOptions.IgnoreCase | RegexOptions.Multiline | RegexOptions.CultureInvariant))
      list.Add(p);
  }
  return list;
}

Then check IL to verify, the query code is as follows

var result = connection.Query("select @Name name ", new { Name = "Wei", Age = 26}).First();

The IL code of the CreateParamInfoGenerator AddParameter dynamic method is as below:

IL_0000: ldarg.1    
IL_0001: castclass  <>f__AnonymousType1`2[System.String,System.Int32]
IL_0006: stloc.0    
IL_0007: ldarg.0    
IL_0008: callvirt   System.Data.IDataParameterCollection get_Parameters()/System.Data.IDbCommand
IL_000d: dup        
IL_000e: ldarg.0    
IL_000f: callvirt   System.Data.IDbDataParameter CreateParameter()/System.Data.IDbCommand
IL_0014: dup        
IL_0015: ldstr      "Name"
IL_001a: callvirt   Void set_ParameterName(System.String)/System.Data.IDataParameter
IL_001f: dup        
IL_0020: ldc.i4.s   16
IL_0022: callvirt   Void set_DbType(System.Data.DbType)/System.Data.IDataParameter
IL_0027: dup        
IL_0028: ldc.i4.1   
IL_0029: callvirt   Void set_Direction(System.Data.ParameterDirection)/System.Data.IDataParameter
IL_002e: dup        
IL_002f: ldloc.0    
IL_0030: callvirt   System.String get_Name()/<>f__AnonymousType1`2[System.String,System.Int32]
IL_0035: dup        
IL_0036: brtrue.s   IL_0042
IL_0038: pop        
IL_0039: ldsfld     System.DBNull Value/System.DBNull
IL_003e: ldc.i4.0   
IL_003f: stloc.1    
IL_0040: br.s       IL_005a
IL_0042: dup        
IL_0043: callvirt   Int32 get_Length()/System.String
IL_0048: ldc.i4     4000
IL_004d: cgt        
IL_004f: brtrue.s   IL_0058
IL_0051: ldc.i4     4000
IL_0056: br.s       IL_0059
IL_0058: ldc.i4.m1  
IL_0059: stloc.1    
IL_005a: callvirt   Void set_Value(System.Object)/System.Data.IDataParameter
IL_005f: ldloc.1    
IL_0060: brfalse.s  IL_0069
IL_0062: dup        
IL_0063: ldloc.1    
IL_0064: callvirt   Void set_Size(Int32)/System.Data.IDbDataParameter
IL_0069: callvirt   Int32 Add(System.Object)/System.Collections.IList
IL_006e: pop        
IL_006f: pop        
IL_0070: ret

IL converted to C# code:

public class TestType
{
  public static void TestMeThod(IDataReader P_0, object P_1)
  {
    var anon = (<>f__AnonymousType1<string, int>)P_1;
    IDataParameterCollection parameters = ((IDbCommand)P_0).Parameters;
    IDbDataParameter dbDataParameter = ((IDbCommand)P_0).CreateParameter();
    dbDataParameter.ParameterName = "Name";
    dbDataParameter.DbType = DbType.String;
    dbDataParameter.Direction = ParameterDirection.Input;
    object obj = anon.Name;
    int num;
    if (obj == null)
    {
      obj = DBNull.Value;
      num = 0;
    }
    else
    {
      num = ((((string)obj).Length > 4000) ? (-1) : 4000);
    }
    dbDataParameter.Value = obj;
    if (num != 0)
    {
      dbDataParameter.Size = num;
    }
    parameters.Add(dbDataParameter);
  }
}

It can be found that although the Age parameter is passed, the SQL string is not used, and Dapper will not generate the SetParameter action IL for this field. This detail processing really needs to give Dapper a thumbs up!

21. The underlying logic of IN multi-set parameterization

Why ADO.NET does not support IN parameterization, but Dapper does?

Check whether the attribute of the parameter is a subclass of IEnumerable
If yes, use the parameter name + regular format to find the parameter string in SQL (regular format: ([?@:]Parameter name)(?!\w)(\s+(?i)unknown(?- i))?)
Replace the found string with () + multiple attribute names + serial number
CreateParameter> SetValue in order of serial number

Key Code part

The following uses sys.objects to check SQL Server tables and views as an example of tracking:

var result = cn.Query(@"select * from sys.objects where type_desc In @type_descs", new { type_descs = new[] { "USER_TABLE", "VIEW" } });

Dapper will change the SQL string to the following sql to execute

select * from sys.objects where type_desc In (@type_descs1,@type_descs2)
-- @type_descs1 = nvarchar(4000) - 'USER_TABLE'
-- @type_descs2 = nvarchar(4000) - 'VIEW'

Looking at Emit IL, you can find that it is very different from the previous parameterized IL, which is very clean.

IL_0000: ldarg.1    
IL_0001: castclass  <>f__AnonymousType0`1[System.String[]]
IL_0006: stloc.0    
IL_0007: ldarg.0    
IL_0008: callvirt   System.Data.IDataParameterCollection get_Parameters()/System.Data.IDbCommand
IL_000d: ldarg.0    
IL_000e: ldstr      "type_descs"
IL_0013: ldloc.0    
IL_0014: callvirt   System.String[] get_type_descs()/<>f__AnonymousType0`1[System.String[]]
IL_0019: call       Void PackListParameters(System.Data.IDbCommand, System.String, System.Object)/Dapper.SqlMapper
IL_001e: pop        
IL_001f: ret

Turning to C# code, you will be surprised to find: This code does not need to use Emit IL at all. It is simply unnecessary.

    public static void TestMeThod(IDbCommand P_0, object P_1)
    {
        var anon = (<>f__AnonymousType0<string[]>)P_1;
        IDataParameterCollection parameter = P_0.Parameters;
        SqlMapper.PackListParameters(P_0, "type_descs", anon.type_descs);
    }

That's right, it is unnecessary, even IDataParameterCollection parameter = P_0.Parameters; this code will not be used at all.

There is a reason for Dapper, because it can be used with non-collective parameters, such as the previous example and the data logic to find the name of the order.

var result = cn.Query(@"select * from sys.objects where type_desc In @type_descs and name like @name"
    , new { type_descs = new[] { "USER_TABLE", "VIEW" }, @name = "order%" });

The corresponding generated IL conversion C# code will be the following code, which can be used together:

    public static void TestMeThod(IDbCommand P_0, object P_1)
    {
        <>f__AnonymousType0<string[], string> val = P_1;
        IDataParameterCollection parameters = P_0.Parameters;
        SqlMapper.PackListParameters(P_0, "type_descs", val.get_type_descs());
        IDbDataParameter dbDataParameter = P_0.CreateParameter();
        dbDataParameter.ParameterName = "name";
        dbDataParameter.DbType = DbType.String;
        dbDataParameter.Direction = ParameterDirection.Input;
        object obj = val.get_name();
        int num;
        if (obj == null)
        {
            obj = DBNull.Value;
            num = 0;
        }
        else
        {
            num = ((((string)obj).Length > 4000) ? (-1) : 4000);
        }
        dbDataParameter.Value = obj;
        if (num != 0)
        {
            dbDataParameter.Size = num;
        }
        parameters.Add(dbDataParameter);
    }

In addition, why does Emit IL directly call the tool method PackListParameters on Dapper? Because the number of IN parameters is not fixed, the method cannot be dynamically generated from the fixed result.

The main logic contained in this method:

Determine the type of the set parameter (if it is a string, the default size is 4000)
Regular role of SQL parameters are replaced with serial number parameter strings
Creation of DbCommand Paramter

The replacement logic of the SQL parameter string is also written here, such as the picture

22. DynamicParameter underlying logic and custom implementation

For example:

using (var cn = Connection)
{
    var paramter = new { Name = "John", Age = 25 };
    var result = cn.Query("select @Name Name,@Age Age", paramter).First();
}

We already know that String type Dapper will automatically convert to database Nvarchar and a parameter with a length of 4000. The SQL actually executed by the database is as below:

exec sp_executesql N'select @Name Name,@Age Age',N'@Name nvarchar(4000),@Age int',@Name=N'John',@Age=25

This is an intimate design that is convenient for rapid development, but if you encounter a situation where the field is of varchar type, it may cause the index to fail due to the implicit transformation, resulting in low query efficiency.

At this time, the solution can use Dapper DynamicParamter to specify the database type and size to achieve the purpose of optimizing performance

using (var cn = Connection)
{
    var paramters = new DynamicParameters();
    paramters.Add("Name","John",DbType.AnsiString,size:4);
    paramters.Add("Age",25,DbType.Int32);
    var result = cn.Query("select @Name Name,@Age Age", paramters).First();
}

Then go to the source to see how to implement it. First, pay attention to the GetCacheInfo method. You can see that DynamicParameters create a dynamic method. The code is very simple, just call the AddParameters method.

Action<IDbCommand, object> reader;
if (exampleParameters is IDynamicParameters)
{
    reader = (cmd, obj) => ((IDynamicParameters)obj).AddParameters(cmd, identity);
}

The reason why the code can be so simple is that Dapper uses an "interface-dependent" design here to increase the flexibility of the program and allow users to customize the implementation logic they want. This point will be explained below. First, let's look at the implementation logic of the AddParameters method in Dapper's default implementation class DynamicParameters.

public class DynamicParameters : SqlMapper.IDynamicParameters, SqlMapper.IParameterLookup, SqlMapper.IParameterCallbacks
{
    protected void AddParameters(IDbCommand command, SqlMapper.Identity identity)
    {
        var literals = SqlMapper.GetLiteralTokens(identity.sql);

        foreach (var param in parameters.Values)
        {
            if (param.CameFromTemplate) continue;

            var dbType = param.DbType;
            var val = param.Value;
            string name = Clean(param.Name);
            var isCustomQueryParameter = val is SqlMapper.ICustomQueryParameter;

            SqlMapper.ITypeHandler handler = null;
            if (dbType == null && val != null && !isCustomQueryParameter)
            {
#pragma warning disable 618
                dbType = SqlMapper.LookupDbType(val.GetType(), name, true, out handler);
#pragma warning disable 618
            }
            if (isCustomQueryParameter)
            {
                ((SqlMapper.ICustomQueryParameter)val).AddParameter(command, name);
            }
            else if (dbType == EnumerableMultiParameter)
            {
#pragma warning disable 612, 618
                SqlMapper.PackListParameters(command, name, val);
#pragma warning restore 612, 618
            }
            else
            {
                bool add = !command.Parameters.Contains(name);
                IDbDataParameter p;
                if (add)
                {
                    p = command.CreateParameter();
                    p.ParameterName = name;
                }
                else
                {
                    p = (IDbDataParameter)command.Parameters[name];
                }

                p.Direction = param.ParameterDirection;
                if (handler == null)
                {
#pragma warning disable 0618
                    p.Value = SqlMapper.SanitizeParameterValue(val);
#pragma warning restore 0618
                    if (dbType != null && p.DbType != dbType)
                    {
                        p.DbType = dbType.Value;
                    }
                    var s = val as string;
                    if (s?.Length <= DbString.DefaultLength)
                    {
                        p.Size = DbString.DefaultLength;
                    }
                    if (param.Size != null) p.Size = param.Size.Value;
                    if (param.Precision != null) p.Precision = param.Precision.Value;
                    if (param.Scale != null) p.Scale = param.Scale.Value;
                }
                else
                {
                    if (dbType != null) p.DbType = dbType.Value;
                    if (param.Size != null) p.Size = param.Size.Value;
                    if (param.Precision != null) p.Precision = param.Precision.Value;
                    if (param.Scale != null) p.Scale = param.Scale.Value;
                    handler.SetValue(p, val ?? DBNull.Value);
                }

                if (add)
                {
                    command.Parameters.Add(p);
                }
                param.AttachedParam = p;
            }
        }

        // note: most non-priveleged implementations would use: this.ReplaceLiterals(command);
        if (literals.Count != 0) SqlMapper.ReplaceLiterals(this, command, literals);
    }
}

It can be found that Dapper has made many conditions and actions in AddParameters for convenience and compatibility with other functions, such as Literal Replacement and EnumerableMultiParameter functions, so the amount of code will be more than the previous version of ADO.NET, so the efficiency will be slower.

If you have demanding requirements for efficiency, you can implement the logic yourself, because this section of Dapper is specially designed to "depend on the interface", and you only need to implement the IDynamicParameters interface.

The following is a demo I made, you can use ADO.NET SqlParameter to establish parameters to cooperate with Dapper

public class CustomPraameters : SqlMapper.IDynamicParameters
{
  private SqlParameter[] parameters;
  public void Add(params SqlParameter[] mParameters)
  {
    parameters = mParameters;
  }

  void SqlMapper.IDynamicParameters.AddParameters(IDbCommand command, SqlMapper.Identity identity)
  {
    if (parameters != null && parameters.Length > 0)
      foreach (var p in parameters)
        command.Parameters.Add(p);
  }
}

Trace Dapper.NET Source Code - Detailed processing of CommandBehavior

Wei — Wed, 16 Dec 2020 15:32:49 +0000

Github Link : Trace-Dapper.NET-Source-Code

19. Detailed processing of CommandBehavior

This article will take readers to understand how Dapper uses CommandBehavior to optimize query efficiency, and how to choose the correct Behavior at a specific time.

I have compiled the Behavior table corresponding to each method here:

method	Behavior
Query	CommandBehavior.SequentialAccess & CommandBehavior.SingleResult
QueryFirst	CommandBehavior.SequentialAccess & CommandBehavior.SingleResult & CommandBehavior.SingleRow
QueryFirstOrDefault	CommandBehavior.SequentialAccess & CommandBehavior.SingleResult & CommandBehavior.SingleRow
QuerySingle	CommandBehavior.SingleResult & CommandBehavior.SequentialAccess
QuerySingleOrDefault	CommandBehavior.SingleResult & CommandBehavior.SequentialAccess
QueryMultiple	CommandBehavior.SequentialAccess

SequentialAccess, SingleResult optimization logic

First, you can see that each method uses CommandBehavior.SequentialAccess. The main function of this tag is to make the DataReader read rows and columns sequentially without buffering. After reading a column, it will be deleted from memory. It has the following advantages:

Resources can be read in order to avoid binary large resources from being read into memory at one time, especially Blob or Clob will cooperate with GetBytes or GetChars methods to limit the buffer size, Microsoft officials also have special attention:

Actual environment testing show it can speed up query efficiency. But it is not the default behavior of DataReader, the system default is CommandBehavior.Default

CommandBehavior.Default has the below behaviors:

Can return multiple result sets
Read row data to memory at once

These two features are much different from the production environment. After all, most of the time,only a set of result sets are needed with limited memory, so in addition to SequentialAccess, Dapper also uses CommandBehavior.SingleResult in most methods, so that only one set of results is required. To avoid wasting resources.

There is also a detailed processing of this paragraph. Looking at the source code, you can find that in addition to marking SingleResult, Dapper also specially adds code at the end while(reader.NextResult()){} instead of directly Return (such as the picture)

Earlier, I specifically posted an Issue (Link #1210) to ask author, here is the answer: mainly to avoid ignoring errors, such as when the DataReader is closed early.

QueryFirst with SingleRow

Sometimes we will encounter a situation where select top 1 knows that only one row of data will be read. At this time, QueryFirst can be used. It uses CommandBehavior.SingleRow to avoid wasting resources and only read one row of data.

In addition, it can be found that in addition to while (reader.NextResult()){}, Dapper also has while (reader.Read()) {}, which is also to avoid ignoring errors. This is something that some companies’ self-make ORMs will ignore.

Differences with QuerySingle

The difference between the two is that QuerySingle does not use CommandBehavior.SingleRow. As for why it is not used, it is because multiple rows of data are needed to determine whether the conditions are not met and an Exception is thrown to inform the user.

There is a particularly fun trick to learn in Dapper. The error handling directly uses the Exception corresponding to LINQ. For example: more than one line of data is wrong, use new int[2].Single(), so you don't need to maintain the Exception class separately, and you can also have more i18N language message.

Trace Dapper.NET Source Code - TypeHandler custom Mapping logic & its underlying logic

Wei — Sun, 13 Dec 2020 14:16:33 +0000

Github Link : Trace-Dapper.NET-Source-Code

18. TypeHandler custom Mapping logic & its underlying logic

When you want to customize some attribute Mapping logic, you can use TypeHandler in Dapper

Create a class to inherit SqlMapper.TypeHandler
Assign the class to be customized to the generic, e.g: JsonTypeHandler<custom_type>: SqlMapper.TypeHandler<custom_type>
Override Parse method to custom Query logic, and override SetValue method to custom Create,Delete,Updte logic
If there are multiple class Parse and SetValue share the same logic, you can change the implementation class to a generic method. The custom class can be specified in AddTypeHandler, which can avoid creating a lot of class, eg: JsonTypeHandler<T>: SqlMapper.TypeHandler< T> where T: class

Example : when User level is changed, the change action will be automatically recorded in the Log field.



public class JsonTypeHandler<T> : SqlMapper.TypeHandler<T> 
  where T : class
{
  public override T Parse(object value)
  {
    return JsonConvert.DeserializeObject<T>((string)value);
  }

  public override void SetValue(IDbDataParameter parameter, T value)
  {
    parameter.Value = JsonConvert.SerializeObject(value);
  }
}

public void Main()
{
  SqlMapper.AddTypeHandler(new JsonTypeHandler<List<Log>>()); 

  using (var ts = new TransactionScope())
  using (var cn = new SqlConnection(@"Data Source=(localdb)\MSSQLLocalDB;Integrated Security=SSPI;Initial Catalog=master;"))
  {

    cn.Execute("create table [User] (Name nvarchar(200),Age int,Level int,Logs nvarchar(max))");

    var user = new User()
    {
      Name = "Wei",
      Age = 26,
      Level = 1,
      Logs = new List<Log>() {
        new Log(){Time=DateTime.Now,Remark="CreateUser"}
      }
    };

    // add
    {
      cn.Execute("insert into [User] (Name,Age,Level,Logs) values (@Name,@Age,@Level,@Logs);", user);

      var result = cn.Query("select * from [User]");
      Console.WriteLine(result);
    }

    // Level up
    {
      user.Level = 9;
      user.Logs.Add(new Log() {Remark="UpdateLevel"});
      cn.Execute("update [User] set Level = @Level,Logs = @Logs where Name = @Name", user);
      var result = cn.Query("select * from [User]");
      Console.WriteLine(result);
    }

    ts.Dispose();

  }
}

public class User
{
  public string Name { get; set; }
  public int Age { get; set; }
  public int Level { get; set; }
  public List<Log> Logs { get; set; }

}
public class Log
{
  public DateTime Time { get; set; } = DateTime.Now;
  public string Remark { get; set; }
}

Then trace the TypeHandler source code logic, which needs to be traced in two parts: SetValue, Parse

The underlying logic of SetValue

AddTypeHandlerImpl method to manage the addition of cache
When creating a dynamic AddParameter method in the CreateParamInfoGenerator method Emit, if there is data in the TypeHandler cache of the Mapping type, Emit adds an action to call the SetValue method.



if (handler != null)
{
  il.Emit(OpCodes.Call, typeof(TypeHandlerCache<>).MakeGenericType(prop.PropertyType).GetMethod(nameof(TypeHandlerCache<int>.SetValue))); // stack is now [parameters] [[parameters]] [parameter]
}

LookupDbType will be used when calling the AddParameters method at Runtime to determine whether there is a custom TypeHandler

Then pass the created Parameter to the custom TypeHandler.SetValue method

Finally, the C# code converted from IL



    public static void TestMeThod(IDbCommand P_0, object P_1)
    {
        User user = (User)P_1;
        IDataParameterCollection parameters = P_0.Parameters;
        //...
        IDbDataParameter dbDataParameter3 = P_0.CreateParameter();
        dbDataParameter3.ParameterName = "Logs";
        dbDataParameter3.Direction = ParameterDirection.Input;
        SqlMapper.TypeHandlerCache<List<Log>>.SetValue(dbDataParameter3, ((object)user.Logs) ?? ((object)DBNull.Value));
        parameters.Add(dbDataParameter3);
        //...
    }

It can be found that the generated Emit IL will get our implemented TypeHandler from TypeHandlerCache, and then call the implemented SetValue method to run the set logic, and TypeHandlerCache uses generic type to save different handlers in Singleton mode according to different generics. This has the following advantages :

Same handler can be obtained to avoid repeated creation of objects
Because it is a generic type, reflection actions can be avoided when the handler is taken, and efficiency can be improved

Parse corresponds to the underlying principle

The main logic is when the GenerateDeserializerFromMap method Emit establishes the dynamic Mapping method, if it is judged that the TypeHandler cache has data, the Parse method replaces the original Set attribute action.

View the IL code generated by the dynamic Mapping method:



IL_0000: ldc.i4.0   
IL_0001: stloc.0    
IL_0002: newobj     Void .ctor()/Demo.User
IL_0007: stloc.1    
IL_0008: ldloc.1    
IL_0009: dup        
IL_000a: ldc.i4.0   
IL_000b: stloc.0    
IL_000c: ldarg.0    
IL_000d: ldc.i4.0   
IL_000e: callvirt   System.Object get_Item(Int32)/System.Data.IDataRecord
IL_0013: dup        
IL_0014: stloc.2    
IL_0015: dup        
IL_0016: isinst     System.DBNull
IL_001b: brtrue.s   IL_0029
IL_001d: unbox.any  System.String
IL_0022: callvirt   Void set_Name(System.String)/Demo.User
IL_0027: br.s       IL_002b
IL_0029: pop        
IL_002a: pop        
IL_002b: dup        
IL_002c: ldc.i4.1   
IL_002d: stloc.0    
IL_002e: ldarg.0    
IL_002f: ldc.i4.1   
IL_0030: callvirt   System.Object get_Item(Int32)/System.Data.IDataRecord
IL_0035: dup        
IL_0036: stloc.2    
IL_0037: dup        
IL_0038: isinst     System.DBNull
IL_003d: brtrue.s   IL_004b
IL_003f: unbox.any  System.Int32
IL_0044: callvirt   Void set_Age(Int32)/Demo.User
IL_0049: br.s       IL_004d
IL_004b: pop        
IL_004c: pop        
IL_004d: dup        
IL_004e: ldc.i4.2   
IL_004f: stloc.0    
IL_0050: ldarg.0    
IL_0051: ldc.i4.2   
IL_0052: callvirt   System.Object get_Item(Int32)/System.Data.IDataRecord
IL_0057: dup        
IL_0058: stloc.2    
IL_0059: dup        
IL_005a: isinst     System.DBNull
IL_005f: brtrue.s   IL_006d
IL_0061: unbox.any  System.Int32
IL_0066: callvirt   Void set_Level(Int32)/Demo.User
IL_006b: br.s       IL_006f
IL_006d: pop        
IL_006e: pop        
IL_006f: dup        
IL_0070: ldc.i4.3   
IL_0071: stloc.0    
IL_0072: ldarg.0    
IL_0073: ldc.i4.3   
IL_0074: callvirt   System.Object get_Item(Int32)/System.Data.IDataRecord
IL_0079: dup        
IL_007a: stloc.2    
IL_007b: dup        
IL_007c: isinst     System.DBNull
IL_0081: brtrue.s   IL_008f
IL_0083: call       System.Collections.Generic.List`1[Demo.Log] Parse(System.Object)/Dapper.SqlMapper+TypeHandlerCache`1[System.Collections.Generic.List`1[Demo.Log]]
IL_0088: callvirt   Void set_Logs(System.Collections.Generic.List`1[Demo.Log])/Demo.User
IL_008d: br.s       IL_0091
IL_008f: pop        
IL_0090: pop        
IL_0091: stloc.1    
IL_0092: leave      IL_00a4
IL_0097: ldloc.0    
IL_0098: ldarg.0    
IL_0099: ldloc.2    
IL_009a: call       Void ThrowDataException(System.Exception, Int32, System.Data.IDataReader, System.Object)/Dapper.SqlMapper
IL_009f: leave      IL_00a4
IL_00a4: ldloc.1    
IL_00a5: ret

Convert it into C# code to verify:



 public static User TestMeThod(IDataReader P_0)
  {
    int index = 0;
    User user = new User();
    object value = default(object);
    try
    {
      User user2 = user;
      index = 0;
      object obj = value = P_0[0];
      //..
      index = 3;
      object obj4 = value = P_0[3];
      if (!(obj4 is DBNull))
      {
        user2.Logs = SqlMapper.TypeHandlerCache<List<Log>>.Parse(obj4);
      }
      user = user2;
      return user;
    }
    catch (Exception ex)
    {
      SqlMapper.ThrowDataException(ex, index, P_0, value);
      return user;
    }
  }

Trace Dapper.NET Source Code - Query Multiple Mapping

Wei — Sat, 12 Dec 2020 06:22:35 +0000

Github Link : Trace-Dapper.NET-Source-Code

How to use Query Multiple Mapping

Then explain the Dapper Multi Mapping(multi-mapping) implementation and the underlying logic. After all, there can not always one-to-one relation in work.

How to use:

You need to write your own Mapping logic and use it: Query<Func>(SQL,Parameter,Mapping Func)
Need to specify the generic parameter type, the rule is Query<Func first type,Func second type,..,Func last type> (supports up to six sets of generic parameters)
Specify the name of the cutting field ID , it is used by default , if it is different, it needs to be specified .
The order is from left to right

For example: There is an order (Order) and a member (User) form, the relationship is a one-to-many relationship, a member can have multiple orders, the following is the C# Demo code:

void Main()
{
    using (var ts = new TransactionScope())
    using (var cn = new SqlConnection(@"Data Source=(localdb)\MSSQLLocalDB;Integrated Security=SSPI;Initial Catalog=master;"))
    {
        cn.Execute(@"
      CREATE TABLE [User]([ID] int, [Name] nvarchar(10));
      INSERT INTO [User]([ID], [Name])VALUES(1, N'Jack'),(2, N'Lee');

      CREATE TABLE [Order]([ID] int, [OrderNo] varchar(13), [UserID] int);
      INSERT INTO [Order]([ID], [OrderNo], [UserID])VALUES(1, 'SO20190900001', 1),(2, 'SO20190900002', 1),(3, 'SO20190900003', 2),(4, 'SO20190900004', 2);
    ");

        var result = cn.Query<Order, User, Order>(@"
        select * from [order] T1
        left join [User] T2 on T1.UserId = T2.ID    
      ", (order, user) =>
        {
            order.User = user;
            return order;
        }
        );

        ts.Dispose();
    }
}

public class Order
{
    public int ID { get; set; }
    public string OrderNo { get; set; }
    public User User { get; set; }
}

public class User
{
    public int ID { get; set; }
    public string Name { get; set; }
}

14. Support dynamic Multi Mapping

In the initial stage, the table structure is often changed or the one-time function and does not want to declare the class. Dapper Multi Mapping also supports the dynamic method.

void  Main ()
{
  using (var ts = new TransactionScope())
  using (var connection = Connection)
  {
    const string createSql = @"
            create table Users (Id int, Name nvarchar(20))
            create table Posts (Id int, OwnerId int, Content nvarchar(20))

            insert Users values(1, N'Jack')
            insert Users values(2, N'Lee')

            insert Posts values(101, 1, N'Jack's first day diary') 
            insert Posts values(102, 1, N'Jack's second day diary') 
            insert Posts values(103, 2, N'Lee's first day diary ') 
" ;
     connection . Execute ( createSql );    

    const string sql =
      @"select * from Posts p 
      left join Users u on u.Id = p.OwnerId 
      Order by p.Id
    ";

    var data = connection.Query<dynamic, dynamic, dynamic>(sql, (post, user) => { post.Owner = user; return post; }).ToList();
    }
}

15. SplitOn distinguish type Mapping group

Split Default is used to cut the primary key, so default cut string is ID, if the table structure PK name is ID can omit parameters, for example

var result = cn.Query<Order,User,Order>(@"
  select * from [order] T1
  left join [User] T2 on T1.UserId = T2.ID    
  ", (order, user) => { 
    order.User = user;
    return order;
  }
);

If the primary key name is another name, specify the splitOn string name and it corresponds to multiple names, it can be used ,as a segmentation. For example, add a product table as Join:

var result = cn.Query<Order,User,Item,Order>(@"
  select * from [order] T1
  left join [User] T2 on T1.UserId = T2.ID  
  left join [Item] T3 on T1.ItemId = T3.ID
  "

  ,map :  (order, user,item) => { 
    order.User = user;
    order.Item = item;
    return order;
  }
  ,splitOn : "Id,Id"
);

16. Query Multi Mapping underlying principle

First, a simple Demo.

Create a Mapping FUNC collection corresponding to the number of generic class parameters
The Mapping FUNC setup logic is the same as Query Emit IL
Call the user's Custom Mapping Func, where the parameters are derived from the previously dynamically generated Mapping Func

public static class MutipleMappingDemo
{
    public static IEnumerable<TReturn> Query<T1, T2, TReturn>(this IDbConnection connection, string sql, Func<T1, T2, TReturn> map)
       where T1 : Order, new()
       where T2 : User, new() 
    {
        // 1. Create a Mapping FUNC collection corresponding to the number of generic class parameters
        var deserializers = new List<Func<IDataReader, object>>();
        {
            // 2. The Mapping FUNC setup logic is the same as Query Emit IL
            deserializers.Add((reader) =>
         {
             var newObj = new T1();
             var value = default(object);
             value = reader[0];
             newObj.ID = value is DBNull ? 0 : (int)value;
             value = reader[1];
             newObj.OrderNo = value is DBNull ? null : (string)value;
             return newObj;
         });

            deserializers.Add((reader) =>
            {
                var newObj = new T2();
                var value = default(object);
                value = reader[2];
                newObj.ID = value is DBNull ? 0 : (int)value;
                value = reader[4];
                newObj.Name = value is DBNull ? null : (string)value;
                return newObj;
            });
        }


        using (var command = connection.CreateCommand())
        {
            command.CommandText = sql;
            using (var reader = command.ExecuteReader())
            {
                while (reader.Read())
                {
                    // 3. Call the user's Custom Mapping Func, where the parameters are derived from the previously dynamically generated Mapping Func
                    yield return map(deserializers[0](reader) as T1, deserializers[1](reader) as T2);
                }
            }
        }
    }
}

Support multiple groups of type + strongly typed return values

Dapper using multiple generic parameter methods for strongly typed multi-class Mapping has disadvantage that it can not be dynamically adjusted and needs to be fixed.

For example, you can see that the image GenerateMapper method fix the strong transition logic in terms of the number of generic arguments, which is why Multiple Query has a maximum number of groups and can only support up to six.

Multi-Class generic caching algorithm

Dapper use Generic Classto save multiple types of data by strong-type
And cooperate with inheritance to share most of the identity verification logic
Provide available override GetType method to customize generic comparison logic to avoid non-multiple query Cache conflict.

Select order of Dapper Query Multi Mapping is important

Because of SplitOn group logic depend on Select Order, it is possible that attribute value wrong when sequence is wrong .

Example: If the SQL in the above example is changed to the following, the ID of User will become the ID of Order; the ID of Order will become the ID of User.

select T2.[ID],T1.[OrderNo],T1.[UserID],T1.[ID],T2.[Name] from [order] T1
left join [User] T2 on T1.UserId = T2.ID

The reason can be traced to Dapper's cutting algorithm

First, the field group by reverse order, the GetNextSplit method can be seen DataReader Index from large to small.
Then process the Mapping Emit IL Func of the type in reverse order
Finally, it is reversed to positive order, which is convenient for the use of Call Func corresponding to generics later.

17. QueryMultiple underlying logic

Example:

  using (var cn = Connection)
  {
    using (var gridReader = cn.QueryMultiple("select 1; select 2;"))
    {
      Console.WriteLine(gridReader.Read<int>()); //result : 1
      Console.WriteLine(gridReader.Read<int>()); //result : 2
    }
  }

Advantages of using QueryMultiple:

Mainly reduce the number of Reqeust
Multiple queries can share the same set of parameter

The underlying implementation logic of QueryMultiple:

The underlying technology is ADO.NET-DataReader-MultipleResult
QueryMultiple gets DataReader and encapsulates it into GridReader
The Mapping dynamic method is only created when the Read method is called, and the Emit IL action is the same as the Query method.
Then call ADO.NET DataReader NextResult to get the next set of query result
DataReader will be released if there is no next set of query results

Cache algorithm

The caching algorithm adds more gridIndex judgments, mainly for each result mapping action as a cache.

No delayed query feature

Note that the Read method uses buffer = true the returned result is directly stored in the ToList memory, so there is no delayed query feature.

Remember to manage the release of DataReader

When Dapper calls the QueryMultiple method, the DataReader is encapsulated in the GridReader object, and the DataReader will be recycled only after the last Read action.

Therefore, if you open a GridReader > Read before finishing reading, an error will show: a DataReader related to this Command has been opened, and it must be closed first.

To avoid the above situation, you can change to the using block, and the DataReader will be automatically released after running the block code.

Trace Dapper.NET Source Code - Wrong SQL String Concat Will Cause Slow Efficiency And Memory Leaks

Wei — Fri, 11 Dec 2020 00:32:46 +0000

Github Link : Trace-Dapper.NET-Source-Code

11. Wrong SQL string concating will cause slow efficiency and memory leaks

Here's an important concept used by Dapper. Its SQL string is one of the important key values to cache. If different SQL strings are used, Dapper will create new dynamic methods and caches for this, so even if you use StringBuilder improperly can also cause slow query & memory leaks .

Why the SQL string is used as one of keys, instead of simply using the Handle of the Mapping type, one of the reasons is order of query column . As mentioned earlier, Dapper uses the 「result convert to code」 method to create a dynamic method, which means that the order and data must be fixed , avoid using the same set of dynamic methods with different SQL Select column order, there will be a A column value to b column wrong value problem.

The most direct solution is to establish a different dynamic method for each different SQL string and save it in a different cache.

For example, the following code is just a simple query action, but the number of Dapper Caches has reached 999999, such as image display

using (var cn = new SqlConnection(@"connectionString"))
{
    for ( int  i  = 0; i  <  999999 ; i ++ )
    {
        var guid = Guid.NewGuid();
        for (int i2 = 0; i2 < 2; i2++)
        {
            var result = cn.Query<User>($"select '{guid}' ").First();
        }  
    }
}

To avoid this problem, you only need to maintain a principle Reuse SQL string , and the simplest way is parametrization , for example: Change the above code to the following code, the number of caches is reduced to 1 , to achieve the purpose of reuse:

using (var cn = new SqlConnection(@"connectionString"))
{
    for ( int  i  = 0; i  <  999999 ; i ++ )
    {
        var guid = Guid.NewGuid();
        for (int i2 = 0; i2 < 2; i2++)
        {
            var result = cn.Query<User>($"select @guid ",new { guid}).First();
        }  
    }
}

12. Dapper SQL correct string concating method: Literal Replacement

If there is a need to splice SQL strings, for example: Sometimes it is more efficient to use string concating than not to use parameterization, especially if there are only a few fixed values .

At this time, Dapper can use the Literal Replacements function, how to use it: {=Attribute_Name} replace the value string to be concated, and save the value in the Parameter, for example:

void Main()
{
  using (var cn = Connection)
  {
    var result = cn.Query("select N'Wei' Name,26 Age,{=VipLevel} VipLevel", new User{ VipLevel = 1}).First();
  }
}

13. Why Literal Replacement can avoid caching problems?

First, trace the GetLiteralTokens method under the source code GetCacheInfo, you can find that before cache Dapper will get the data SQL string that match {=Attribute_Name} role .

private static readonly Regex literalTokens = new Regex(@"(?<![\p{L}\p{N}_])\{=([\p{L}\p{N}_]+)\}", RegexOptions.IgnoreCase | RegexOptions.Multiline | RegexOptions.CultureInvariant | RegexOptions.Compiled);
internal static IList<LiteralToken> GetLiteralTokens(string sql)
{
  if (string.IsNullOrEmpty(sql)) return LiteralToken.None;
  if (!literalTokens.IsMatch(sql)) return LiteralToken.None;

  var matches = literalTokens.Matches(sql);
  var found = new HashSet<string>(StringComparer.Ordinal);
  List<LiteralToken> list = new List<LiteralToken>(matches.Count);
  foreach (Match match in matches)
  {
    string token = match.Value;
    if (found.Add(match.Value))
    {
      list.Add(new LiteralToken(token, match.Groups[1].Value));
    }
  }
  return list.Count == 0 ? LiteralToken.None : list;
}

Then generate Parameter parameterized dynamic method in the CreateParamInfoGenerator method. The method IL of this section is as below:

IL_0000: ldarg.1    
IL_0001: castclass  <>f__AnonymousType1`1[System.Int32]
IL_0006: stloc.0    
IL_0007: ldarg.0    
IL_0008: callvirt   System.Data.IDataParameterCollection get_Parameters()/System.Data.IDbCommand
IL_000d: pop        
IL_000e: ldarg.0    
IL_000f: ldarg.0    
IL_0010: callvirt   System.String get_CommandText()/System.Data.IDbCommand
IL_0015: ldstr      "{=VipLevel}"
IL_001a: ldloc.0    
IL_001b: callvirt   Int32 get_VipLevel()/<>f__AnonymousType1`1[System.Int32]
IL_0020: stloc.1    
IL_0021: ldloca.s   V_1

IL_0023: call       System.Globalization.CultureInfo get_InvariantCulture()/System.Globalization.CultureInfo
IL_0028: call       System.String ToString(System.IFormatProvider)/System.Int32
IL_002d: callvirt   System.String Replace(System.String, System.String)/System.String
IL_0032: callvirt   Void set_CommandText(System.String)/System.Data.IDbCommand
IL_0037: ret

Then generate the Mapping dynamic method. To understand this logic, I will make a simulation example here:

public  static  class  DbExtension
{
  public static IEnumerable<User> Query(this DbConnection cnn, string sql, User parameter)
  {
    using (var command = cnn.CreateCommand())
    {
      command.CommandText = sql;
      CommandLiteralReplace(command, parameter);
      using (var reader = command.ExecuteReader())
        while (reader.Read())
          yield return Mapping(reader);
    }
  }

  private static void CommandLiteralReplace(IDbCommand cmd, User parameter)
  {
    cmd.CommandText = cmd.CommandText.Replace("{=VipLevel}", parameter.VipLevel.ToString(System.Globalization.CultureInfo.InvariantCulture));
  }

  private  static  User  Mapping ( IDataReader  reader )
  {
    var user = new User();
    var value = default(object);
    value = reader[0];
    if(!(value is System.DBNull))
      user.Name = (string)value;
    value = reader[1];
    if (!(value is System.DBNull))
      user.Age = (int)value;
    value = reader[2];
    if (!(value is System.DBNull))
      user.VipLevel = (int)value;
    return user;
  }
}

After reading the above example, you can find that the underlying principle of Dapper Literal Replacements is string replace that it also belongs to the string concating way. Why can the cache problem be avoided?

This is because the replacement timing is in the SetParameter dynamic method, so the Cache SQL Key is unchanged can reuse the same SQL string and cache.

Also because it is a string replace method, only support basic value type if you use the String type, the system will inform you The type String is not supported for SQL literals.to avoid SQL Injection problems.

Trace Dapper.NET Source Code - Fast Efficiency Key: Cache Principle

Wei — Wed, 09 Dec 2020 16:26:52 +0000

Github Link : Trace-Dapper.NET-Source-Code

10. One of the keys to Dapper's fast efficiency: Cache principle

Why can Dapper be so fast?

I introduced the dynamic use of Emit IL to establish the ADO.NET Mapping method, but this function cannot make Dapper the king of lightweight ORM efficiency.

Because the dynamic create method is Cost and time consuming action, simply using it will slow down the speed. But when it cooperates with Cache, it is different. By storing the established method in Cache, you can use the 『Space for time』 concept to speed up the efficiency of the query .

Then trace the Dapper source code. This time, we need to pay special attention to Identity and GetCacheInfo under the QueryImpl method.

Identity、GetCacheInfo

Identity mainly encapsulates the comparison Key attribute of each cache:

sql: distinguish different SQL strings
type: distinguish Mapping type
commandType: Responsible for distinguishing different databases
gridIndex: Mainly used in QueryMultiple, explained later.
connectionString: Mainly distinguish the same database manufacturer but different DB situation
parametersType: Mainly distinguish parameter types
typeCount: Mainly used in Multi Query multi-mapping, it needs to be used with the override GetType method, which will be explained later

Then match the cache type used by Dapper in the GetCacheInfo method. When ConcurrentDictionary<Identity, CacheInfo> using the TryGetValue method, it will first compare the HashCode and then compare the Equals features, such as the image source code.

Using the Key type Identity to override Equals implement the cache comparison algorithm, you can see the following Dapper implementation logic. As long as one attribute is different, a new dynamic method and cache will be created.

public bool Equals(Identity other)
{
  if (ReferenceEquals(this, other)) return true;
  if (ReferenceEquals(other, null)) return false;

  int typeCount;
  return gridIndex == other.gridIndex
    && type == other.type
    && sql == other.sql
    && commandType == other.commandType
    && connectionStringComparer.Equals(connectionString, other.connectionString)
    && parametersType == other.parametersType
    && (typeCount = TypeCount) == other.TypeCount
    && (typeCount == 0 || TypesEqual(this, other, typeCount));
}

With this concept, the previous Emit version is modified into a simple Cache Demo :

public class Identity
{
    public string sql { get; set; }
    public CommandType? commandType { get; set; }
    public string connectionString { get; set; }
    public Type type { get; set; }
    public Type parametersType { get; set; }
    public Identity(string sql, CommandType? commandType, string connectionString, Type type, Type parametersType)
    {
        this.sql = sql;
        this.commandType = commandType;
        this.connectionString = connectionString;
        this.type = type;
        this.parametersType = parametersType;
        unchecked
        {
            hashCode = 17; // we *know* we are using this in a dictionary, so pre-compute this
            hashCode = (hashCode * 23) + commandType.GetHashCode();
            hashCode = (hashCode * 23) + (sql?.GetHashCode() ?? 0);
            hashCode = (hashCode * 23) + (type?.GetHashCode() ?? 0);
            hashCode = (hashCode * 23) + (connectionString == null ? 0 : StringComparer.Ordinal.GetHashCode(connectionString));
            hashCode = (hashCode * 23) + (parametersType?.GetHashCode() ?? 0);
        }
    }

    public readonly int hashCode;
    public override int GetHashCode() => hashCode;

    public override bool Equals(object obj) => Equals(obj as Identity);
    public bool Equals(Identity other)
    {
        if (ReferenceEquals(this, other)) return true;
        if (ReferenceEquals(other, null)) return false;

        return type == other.type
          && sql == other.sql
          && commandType == other.commandType
          && StringComparer.Ordinal.Equals(connectionString, other.connectionString)
          && parametersType == other.parametersType;
    }
}

public static class DemoExtension
{
    private static readonly Dictionary<Identity, Func<DbDataReader, object>> readers = new Dictionary<Identity, Func<DbDataReader, object>>();

    public static IEnumerable<T> Query<T>(this IDbConnection cnn, string sql, object param = null) where T : new()
    {
        using (var command = cnn.CreateCommand())
        {
            command.CommandText = sql;
            using (var reader = command.ExecuteReader())
            {
                var identity = new Identity(command.CommandText, command.CommandType, cnn.ConnectionString, typeof(T), param?.GetType());

                // 2. If the cache has data, use it, and if there is no data, create a method dynamically and save it in the cache 
                if (!readers.TryGetValue(identity, out Func<DbDataReader, object> func))
                {
                    //The dynamic creation method 
                    func = GetTypeDeserializerImpl(typeof(T), reader);
                    readers[identity] = func;
                    Console.WriteLine(" No cache, create a dynamic method and put it in the cache ");
                }
                else
                {
                    Console.WriteLine(" Use cache ");
                }


                // 3. Call the generated method by reader, read the data and return 
                while (reader.Read())
                {
                    var result = func(reader as DbDataReader);
                    yield return result is T ? (T)result : default(T);
                }
            }

        }
    }

    private static Func<DbDataReader, object> GetTypeDeserializerImpl(Type type, IDataReader reader, int startBound = 0, int length = -1, bool returnNullIfFirstMissing = false)
    {
        // ..
    }
}

Trace Dapper.NET Source Code - Emit IL Mapping

Wei — Tue, 08 Dec 2020 16:10:39 +0000

Github Link : Trace-Dapper.NET-Source-Code

8. Strongly Typed Mapping Part5: Emit IL convert to C# code

With the concept of the previous Expression version, we can then enter the core technology of Dapper: Emit.

First of all, there must be a concept, MSIL (CIL) is intended for JIT compiler, so the readability will be poor and difficult to debug, but more detailed logical operations can be done compared to Expression.

In the actual environment development and use Emit, usually c# code > Decompilation to IL > use Emit to build dynamic methods , for example:

First create a simple printing example:

void SyaHello()
{
  Console.WriteLine("Hello World");  
}

Decompile and view IL

SyaHello:
IL_0000:  nop         
IL_0001:  ldstr       "Hello World"
IL_0006:  call        System.Console.WriteLine
IL_000B:  nop         
IL_000C:  ret

Use DynamicMethod + Emit to create a dynamic method

void Main()
{
  // 1. create void method()
  DynamicMethod methodbuilder = new DynamicMethod("Deserialize" + Guid.NewGuid().ToString(),typeof(void),null);

  // 2. Create the content of the method body by Emit
  var il = methodbuilder.GetILGenerator();
  il.Emit(OpCodes.Ldstr, "Hello World");
  Type[] types = new Type[1]
  {
    typeof(string)
  };
  MethodInfo method = typeof(Console).GetMethod("WriteLine", types);
  il.Emit(OpCodes.Call,method);
  il.Emit(OpCodes.Ret);

  // 3. Convert the specified type of Func or Action 
  var action = (Action)methodbuilder.CreateDelegate(typeof(Action));

  action(); 
}

But this is not the process for a project that has been written. Developers may not kindly tell you the logic of the original design.

How to check like Dapper, only Emit IL doesn’t have C# Source Code Project

My solution is: 「Since only Runtime can know IL, save IL as a static file and decompile and view」

You can use the MethodBuild + Save method here Save IL as static exe file > Decompile view , but you need to pay special attention

Please correspond to the parameters and return type, otherwise it will compile error.
netstandard does not support this method, Dapper needs to be used region if yourversion to distinguish, otherwise it cannot be used, such as picture

code show as below :

  //Use MethodBuilder to view Emit IL that others have written 
  //1. Create MethodBuilder 
  AppDomain ad = AppDomain.CurrentDomain;
  AssemblyName am = new AssemblyName();
  am.Name = "TestAsm";
  AssemblyBuilder ab = ad.DefineDynamicAssembly(am, AssemblyBuilderAccess.Save);
  ModuleBuilder mb = ab.DefineDynamicModule("Testmod", "TestAsm.exe");
  TypeBuilder tb = mb.DefineType("TestType", TypeAttributes.Public);
  MethodBuilder dm = tb.DefineMethod("TestMeThod", MethodAttributes.Public |
  MethodAttributes.Static, type, new[] { typeof(IDataReader) });
  ab.SetEntryPoint(dm);

  // 2. the IL code 
  //..

  // 3. Generate static files 
  tb.CreateType();
  ab.Save("TestAsm.exe");

Then use this method to decompile Dapper Query Mapping IL in the GetTypeDeserializerImpl method, and you can get the C# code:

public static User TestMeThod(IDataReader P_0)
{
  int index = 0;
  User user = new User();
  object value = default(object);
  try
  {
    User user2 = user;
    index = 0;
    object obj = value = P_0[0];
    if (!(obj is DBNull))
    {
      user2.Name = (string)obj;
    }
    index = 1;
    object obj2 = value = P_0[1];
    if (!(obj2 is DBNull))
    {
      user2.Age = (int)obj2;
    }
    user = user2;
    return user;
  }
  catch (Exception ex)
  {
    SqlMapper.ThrowDataException(ex, index, P_0, value);
    return user;
  }
}

After having the C# code, it will be much faster to understand the Emit logic.

9. Strongly Typed Mapping Principle Part6: Emit Version

The following code is the Emit version, I wrote the corresponding IL part of C# code

public static class DemoExtension
{
  public static IEnumerable<T> Query<T>(this IDbConnection cnn, string sql) where T : new()
  {
    using (var command = cnn.CreateCommand())
    {
      command.CommandText = sql;
      using (var reader = command.ExecuteReader())
      {
        var func = GetTypeDeserializerImpl(typeof(T), reader);

        while (reader.Read())
        {
          var result = func(reader as DbDataReader);
          yield return result is T ? (T)result : default(T);
        }
      }

    }
  }

  private static Func<DbDataReader, object> GetTypeDeserializerImpl(Type type, IDataReader reader, int startBound = 0, int length = -1, bool returnNullIfFirstMissing = false)
  {
    var returnType = type.IsValueType ? typeof(object) : type;

    var dm = new DynamicMethod("Deserialize" + Guid.NewGuid().ToString(), returnType, new[] { typeof(IDataReader) }, type, true);
    var il = dm.GetILGenerator();

    //C# : User user = new User();
    //IL : 
    //IL_0001:  newobj      
    //IL_0006:  stloc.0         
    var constructor = returnType.GetConstructors(BindingFlags.Instance | BindingFlags.Public | BindingFlags.NonPublic)[0]; 
    il.Emit(OpCodes.Newobj, constructor);
    var returnValueLocal = il.DeclareLocal(type);
    il.Emit(OpCodes.Stloc, returnValueLocal); //User user = new User();

    // C# : 
    //object value = default(object);
    // IL :
    //IL_0007: ldnull
    //IL_0008:  stloc.1     // value  
    var valueLoacl = il.DeclareLocal(typeof(object));
    il.Emit(OpCodes.Ldnull);
    il.Emit(OpCodes.Stloc, valueLoacl);


    int index = startBound;
    var getItem = typeof(IDataRecord).GetProperties(BindingFlags.Instance | BindingFlags.Public)
            .Where(p => p.GetIndexParameters().Length > 0 && p.GetIndexParameters()[0].ParameterType == typeof(int))
            .Select(p => p.GetGetMethod()).First();

    foreach (var p in type.GetProperties())
    {
      //C# : value = P_0[0];
      //IL:
      //IL_0009:  ldarg.0      
      //IL_000A: ldc.i4.0
      //IL_000B: callvirt System.Data.IDataRecord.get_Item
      //IL_0010:  stloc.1     // value        
      il.Emit(OpCodes.Ldarg_0); 
      EmitInt32(il, index);
      il.Emit(OpCodes.Callvirt, getItem);
      il.Emit(OpCodes.Stloc, valueLoacl);


      //C#: if (!(value is DBNull)) user.Name = (string)value;
      //IL:
      // IL_0011:  ldloc.1     // value
      // IL_0012:  isinst      System.DBNull
      // IL_0017:  ldnull      
      // IL_0018:  cgt.un      
      // IL_001A:  ldc.i4.0   
      // IL_001B:  ceq         
      // IL_001D:  stloc.2    
      // IL_001E:  ldloc.2     
      // IL_001F:  brfalse.s   IL_002E
      // IL_0021:  ldloc.0     // user
      // IL_0022:  ldloc.1     // value
      // IL_0023:  castclass   System.String
      // IL_0028:  callvirt    UserQuery+User.set_Name      
      il.Emit(OpCodes.Ldloc, valueLoacl);
      il.Emit(OpCodes.Isinst, typeof(System.DBNull));
      il.Emit(OpCodes.Ldnull);

      var tmpLoacl = il.DeclareLocal(typeof(int));
      il.Emit(OpCodes.Cgt_Un);
      il.Emit(OpCodes.Ldc_I4_0);
      il.Emit(OpCodes.Ceq);

      il.Emit(OpCodes.Stloc,tmpLoacl);
      il.Emit(OpCodes.Ldloc,tmpLoacl);


      var labelFalse = il.DefineLabel();
      il.Emit(OpCodes.Brfalse_S,labelFalse);
      il.Emit(OpCodes.Ldloc, returnValueLocal);
      il.Emit(OpCodes.Ldloc, valueLoacl);
      if (p.PropertyType.IsValueType)
        il.Emit(OpCodes.Unbox_Any, p.PropertyType);
      else
        il.Emit(OpCodes.Castclass, p.PropertyType);
      il.Emit(OpCodes.Callvirt, p.SetMethod);

      il.MarkLabel(labelFalse);

      index++;
    }

    // IL_0053:  ldloc.0     // user
    // IL_0054:  stloc.s     04  
    // IL_0056:  br.s        IL_0058
    // IL_0058:  ldloc.s     04  
    // IL_005A:  ret         
    il.Emit(OpCodes.Ldloc, returnValueLocal);
    il.Emit(OpCodes.Ret);

    var funcType = System.Linq.Expressions.Expression.GetFuncType(typeof(IDataReader), returnType);
    return (Func<IDataReader, object>)dm.CreateDelegate(funcType);
  }

  private static void EmitInt32(ILGenerator il, int value)
  {
    switch (value)
    {
      case -1: il.Emit(OpCodes.Ldc_I4_M1); break;
      case 0: il.Emit(OpCodes.Ldc_I4_0); break;
      case 1: il.Emit(OpCodes.Ldc_I4_1); break;
      case 2: il.Emit(OpCodes.Ldc_I4_2); break;
      case 3: il.Emit(OpCodes.Ldc_I4_3); break;
      case 4: il.Emit(OpCodes.Ldc_I4_4); break;
      case 5: il.Emit(OpCodes.Ldc_I4_5); break;
      case 6: il.Emit(OpCodes.Ldc_I4_6); break;
      case 7: il.Emit(OpCodes.Ldc_I4_7); break;
      case 8: il.Emit(OpCodes.Ldc_I4_8); break;
      default:
        if (value >= -128 && value <= 127)
        {
          il.Emit(OpCodes.Ldc_I4_S, (sbyte)value);
        }
        else
        {
          il.Emit(OpCodes.Ldc_I4, value);
        }
        break;
    }
  }
}

There are many detailed of Emit here. First pick out the important concepts to explain.

Emit Label

In Emit if/else, you need to use Label positioning, tell the compiler which position to jump to when the condition is true/false, for example: boolean to integer, assuming that you want to simply convert Boolean to Int, C# code can use If it is True Return 1 otherwise return 0 logic to write:

public static int BoolToInt(bool input) => input ? 1 : 0;

When converting to Emit, the following logic is required:

Consider the label dynamic positioning problem
The label must be established first to let Brtrue_S know which label position to set when the conditions are true (Note:at this time the label position has not been determined yet)
Continue to build IL from top to bottom in order
Wait until match condition you want to run the block previous line , use it MarkLabel to position Label .

The final c # Emit Code:

public class Program
{
  public static void Main(string[] args)
  {
    var func = CreateFunc();
    Console.WriteLine(func(true)); //1
    Console.WriteLine(func(false)); //0
  }

  static Func<bool, int> CreateFunc()
  {
    var dm = new DynamicMethod("Test" + Guid.NewGuid().ToString(), typeof(int), new[] { typeof(bool) });

    var il = dm.GetILGenerator();
    var labelTrue = il.DefineLabel();

    il.Emit(OpCodes.Ldarg_0);
    il.Emit(OpCodes.Brtrue_S, labelTrue);
    il.Emit(OpCodes.Ldc_I4_0);
    il.Emit(OpCodes.Ret);
    il.MarkLabel(labelTrue);
    il.Emit(OpCodes.Ldc_I4_1);
    il.Emit(OpCodes.Ret);

    var funcType = System.Linq.Expressions.Expression.GetFuncType(typeof(bool), typeof(int));
    return (Func<bool, int>)dm.CreateDelegate(funcType);
  }
}

Here you can find the Emit version, which has the advantage of:

Can do more detailed operations
Because the detail granularity is small, the efficiency that can be optimized is better

Disadvantages:

Difficult to debug
Poor readability
The amount of code becomes larger and the complexity increases

Then look at the suggestions of the author of Dapper. Now there is no need to use Emit in general projects. Using Expression + Func/Action can solve most of the needs of dynamic methods, especially when Expression supports Block and other methods. Link c#-What's faster: expression trees or manually emitting IL

Having said that, there are some powerful open source projects that use Emit to manage details If you want to understand them, you need the basic Emit IL concept .

Trace Dapper.NET Source Code - Expression version

Wei — Mon, 07 Dec 2020 23:56:30 +0000

Github Link : Trace-Dapper.NET-Source-Code

7. Strongly Typed Mapping Part4: Expression version

With the previous logic, we use Expression to implement dynamic creation methods, and then we can think Why use Expression implementation first instead of Emit?

In addition to the ability to dynamically build methods, compared to Emit, it has the following advantages:

Readadable, You can use familiar keywords, such as the Variable corresponds to Expression.Variable, and the creation of object New corresponds to Expression.New
Easy Runtime Debug, You can see the logic code corresponding to Expression in Debug mode

So it is especially suitable for introducing dynamic method establishment, but Expression cannot do some detailed operations compared to Emit, which will be explained by Emit later.

Rewrite Expression version

Logic:

Get all field names of sql select
Obtain the attribute data of the mapping type > encapsulate the index, sql field and class attribute data in a variable for later use
Dynamic create method: Read the data we want from the database Reader in order, the code logic:

User dynamic method ( IDataReader  reader )
{
  var user = new User();
  var value = reader[0];
  if( !(value is System.DBNull) )
    user.Name = (string)value;
  value = reader[1];
  if( !(value is System.DBNull) )
    user.Age = (int)value;  
  return user;
}

Finally, the following Exprssion version code

public static class DemoExtension
{
  public static IEnumerable<T> Query<T>(this IDbConnection cnn, string sql) where T : new()
  {
    using (var command = cnn.CreateCommand())
    {
      command.CommandText = sql;
      using (var reader = command.ExecuteReader())
      {
        var func = CreateMappingFunction(reader, typeof(T));
        while (reader.Read())
        {
          var result = func(reader as DbDataReader);
          yield return result is T ? (T)result : default(T);
        }

      }
    }
  }

  private static Func<DbDataReader, object> CreateMappingFunction(IDataReader reader, Type type)
  {
    // 1. Get all field names in sql select 
    var  names  =  Enumerable . Range ( 0 , reader . FieldCount ). Select ( index  =>  reader . GetName ( index )). ToArray ();

    // 2. Get the attribute data of the mapping type > encapsulate the index, sql fields, and class attribute data in a variable for later use 
    var  props  =  type . GetProperties (). ToList ();
     var  members  =  names . Select (( columnName , index ) =>
    {
      var property = props.Find(p => string.Equals(p.Name, columnName, StringComparison.Ordinal))
      ?? props.Find(p => string.Equals(p.Name, columnName, StringComparison.OrdinalIgnoreCase));
      return new
      {
        index,
        columnName,
        property
      };
    });

    // 3. Dynamic creation method: read the data we want from the database Reader in order 
    /*Method logic: 
      User dynamic method (IDataReader reader) 
      { 
        var user = new User(); 
        var value = reader[0]; 
        if( !(value is System.DBNull)) 
          user.Name = (string)value; 
        value = reader[1]; 
        if( !(value is System.DBNull)) 
          user.Age = (int)value;   
        return user; 
      } 
    */ 
    var exBodys = new List < Expression >();    

    {
      // method(IDataReader reader)
      var exParam = Expression.Parameter(typeof(DbDataReader), "reader");

      // Mapping class object = new Mapping class(); 
      var  exVar  =  Expression . Variable ( type , " mappingObj " );
       var  exNew  =  Expression . New ( type );
      {
        exBodys.Add(Expression.Assign(exVar, exNew));
      }

      // var value = defalut(object);
      var exValueVar = Expression.Variable(typeof(object), "value");
      {
        exBodys.Add(Expression.Assign(exValueVar, Expression.Constant(null)));
      }


      var getItemMethod = typeof(DbDataReader).GetMethods().Where(w => w.Name == "get_Item")
        .First(w => w.GetParameters().First().ParameterType == typeof(int));
      foreach (var m in members)
      {
        //reader[0]
        var exCall = Expression.Call(
          exParam, getItemMethod,
          Expression.Constant(m.index)
        );

        // value = reader[0];
        exBodys.Add(Expression.Assign(exValueVar, exCall));

        //user.Name = (string)value;
        var exProp = Expression.Property(exVar, m.property.Name);
        var exConvert = Expression.Convert(exValueVar, m.property.PropertyType); //(string)value
        var exPropAssign = Expression.Assign(exProp, exConvert);

        //if ( !(value is System.DBNull))
        //    (string)value
        var exIfThenElse = Expression.IfThen(
          Expression.Not(Expression.TypeIs(exValueVar, typeof(System.DBNull)))
          , exPropAssign
        );

        exBodys.Add(exIfThenElse);
      }


      // return user;  
      exBodys.Add(exVar);

      // Compiler Expression 
      var lambda = Expression.Lambda<Func<DbDataReader, object>>(
        Expression.Block(
          new[] { exVar, exValueVar },
          exBodys
        ), exParam
      );

      return lambda.Compile();
    }
  }
}

Finally, check Expression.Lambda > DebugView (note that it is a non-public attribute) :

.Lambda #Lambda1<System.Func`2[System.Data.Common.DbDataReader,System.Object]>(System.Data.Common.DbDataReader $reader) {
    .Block(
        UserQuery+User $mappingObj,
        System.Object $value) {
        $mappingObj = .New UserQuery+User();
        $value = null;
        $value = .Call $reader.get_Item(0);
        .If (
            !($value .Is System.DBNull)
        ) {
            $mappingObj.Name = (System.String)$value
        } .Else {
            .Default(System.Void)
        };
        $value = .Call $reader.get_Item(1);
        .If (
            !($value .Is System.DBNull)
        ) {
            $mappingObj.Age = (System.Int32)$value
        } .Else {
            .Default(System.Void)
        };
        $mappingObj
    }
}

Trace Dapper.NET Source Code - The important concept of dynamic create method "code from result" optimizes efficiency

Wei — Mon, 07 Dec 2020 00:32:06 +0000

Github Link : Trace-Dapper.NET-Source-Code

6. Strongly Typed Mapping Part3: The important concept of dynamic create method "code from result" optimizes efficiency

Then use Expression to solve the Reflection version problem, mainly using Expression features: 「Methods can be dynamically created during Runtime」 to solve the problem.

Before this, we need to have an important concept: 「Reverse the most concise code from the result」 optimizing efficiency. For example: In the past, a classic topic of "printing regular triangle stars'' when learning a program to make a regular triangle of length 3, the common practice would be loop + recursion the way

void  Main ()
{
  Print(3,0);
}

static void Print(int length, int spaceLength)
{
  if (length < 0)
    return;
  else
    Print(length - 1, spaceLength + 1);
  for (int i = 0; i < spaceLength; i++)
    Console.Write(" ");
  for (int i = 0; i < length; i++)
    Console.Write("* ");
  Console.WriteLine("");
}

But in fact, this topic can be changed to the following code when the length is already known

Console.WriteLine("  * ");
Console.WriteLine(" * * ");
Console.WriteLine("* * * ");

This concept is very important, because the code is reversed from the result, so the logic is straightforward and efficient , and Dapper uses this concept to dynamically build methods.

Example:

The Name property of User Class corresponds to Reader Index 0, the type is String, and the default value is null
The Age attribute of User Class corresponds to Reader Index 1, the type is int, and the default value is 0

void  Main ()
{
  using (var cn = Connection)
  {
    var result = cn.Query<User>("select N'Wei' Name,26 Age").First();
  }
}

class User
{
  public string Name { get; set; }
  public int Age { get; set; }
}

If the system can help generate the following logical methods, then the efficiency will be the best

User dynamic method ( IDataReader  reader )
{
  var user = new User();
  var value = reader[0];
  if( !(value is System.DBNull) )
    user.Name = (string)value;
  value = reader[1];
  if( !(value is System.DBNull) )
    user.Age = (int)value;  
  return user;
}

In addition, the above example can be seen for Dapper SQL Select corresponds to the Class attribute order is very important , so the algorithm of Dapper in the cache will be explained later, which is specifically optimized for this.

Forem: Wei

MiniWord easy and effective .NET Word Template library

Github Link : https://github.com/mini-software/MiniWord

Introduction

Getting Started

Installation

Quick Start

Input, Output

Tags

Text

Example

Template

Result

Image

Example

Template

Result

List

Example

Result

Table

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Template

Result

Other

POCO or dynamic parameter

FontColor and HighlightColor

HyperLink

Examples

ASP.NET Core 3.1 API Export

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DOTNET Develop Simple Disk Key Value Cache

Trace Dapper.NET Source Code - The Underlying Logic Of Parameterization

20. The Underlying Logic Of Parameterization

21. The underlying logic of IN multi-set parameterization

22. DynamicParameter underlying logic and custom implementation

Trace Dapper.NET Source Code - Detailed processing of CommandBehavior

19. Detailed processing of CommandBehavior

SequentialAccess, SingleResult optimization logic

QueryFirst with SingleRow

Differences with QuerySingle

Trace Dapper.NET Source Code - TypeHandler custom Mapping logic & its underlying logic

18. TypeHandler custom Mapping logic & its underlying logic

The underlying logic of SetValue

Parse corresponds to the underlying principle

Trace Dapper.NET Source Code - Query Multiple Mapping

How to use Query Multiple Mapping

14. Support dynamic Multi Mapping

15. SplitOn distinguish type Mapping group

16. Query Multi Mapping underlying principle

Support multiple groups of type + strongly typed return values

Multi-Class generic caching algorithm

Select order of Dapper Query Multi Mapping is important

17. QueryMultiple underlying logic

Cache algorithm

No delayed query feature

Remember to manage the release of DataReader

Trace Dapper.NET Source Code - Wrong SQL String Concat Will Cause Slow Efficiency And Memory Leaks

11. Wrong SQL string concating will cause slow efficiency and memory leaks

12. Dapper SQL correct string concating method: Literal Replacement

13. Why Literal Replacement can avoid caching problems?

Trace Dapper.NET Source Code - Fast Efficiency Key: Cache Principle

10. One of the keys to Dapper's fast efficiency: Cache principle

Trace Dapper.NET Source Code - Emit IL Mapping

8. Strongly Typed Mapping Part5: Emit IL convert to C# code

How to check like Dapper, only Emit IL doesn’t have C# Source Code Project

9. Strongly Typed Mapping Principle Part6: Emit Version

Trace Dapper.NET Source Code - Expression version

7. Strongly Typed Mapping Part4: Expression version

Rewrite Expression version

Trace Dapper.NET Source Code - The important concept of dynamic create method "code from result" optimizes efficiency

6. Strongly Typed Mapping Part3: The important concept of dynamic create method "code from result" optimizes efficiency