Forem: Gaëtan Masson

Soft Deletion, Nested Resource and Active Admin

Gaëtan Masson — Thu, 05 Aug 2021 08:15:50 +0000

TL;DR

models/order_payments.rb

def deletable_from_admin
  !order.validated? && deleted_at.blank?
end

def destroy
  order.context == :update_from_admin_space ? update!(deleted_at: Time.current) : super
end

admin/order.rb

controller do
  def update
    resource.context = :update_from_admin_space
    super
  end
end

f.inputs do
  f.has_many :order_payments, new_record: !order.payment_accepted?, allow_destroy: :deletable_from_admin do |order_payment|
    if order_payment.object.deleted_at.blank?
      order_payment.input :expected_at,
      ...

Details

In my company, we are currently implementing a soft deletion strategy on some tables. The task seems easy: add a new field deleted_at and fill it with an update whenever destroy has normally to be called.

However, when you are using a gem doing a lot of magic (hello Active Admin) and want to do something specific, things get more tricky.

So first I had to show the data. It was quite easy, just had to call my custom has_many instead of the real association.

Then, came the edit page, the part containing forms...

After using Rails for years, there is still one thing I always have "difficulties" to play with: the nested resources/forms. Each time I have to play with it, I have to check the documentation again and again, like if it was the first time I'm doing it.

In that case of soft deletion, the main concern I had was to find a way to modify the magic of Rails about nested resource deletion. The easier thing seemed to monkey patch the destroy method in my model.

def destroy
  update(deleted_at: Time.current)
end

It worked, but I know deep inside that someday I would regret that change. I really needed this destroy new behaviour in the context of a deletion from Active Admin only. So I continued to check the code of the app to finally found an interesting line in models/order_payments.rb:

controller do
  def update
    resource.context = :update_from_admin_space
    ...

I just had to add a condition to my destroy method to use soft deletion only in the case of an update from the admin space. I'm still not fully satisfied, but it seems better than my initial solution.

def destroy
  order.context == :update_from_admin_space ? update(deleted_at: Time.current) : super
end

So from there, my record was soft deleted as planned, and I was able to only show the data that were not softly deleted. Nevertheless, I had another trouble. When I tested the edit page, the soft deleted resources were still showing. So I added a condition to no show the soft deleted:

f.inputs do
  f.has_many :order_payments, new_record: !order.payment_accepted?, allow_destroy: !order.validated? do |order_payment|
    if order_payment.object.deleted_at.blank?
      order_payment.input :expected_at,
      ...

But was actually not enough. Yes, my record wasn't showing, but that allow_destroy magically made the checkbox appear for each soft deleted record...

After some time, I checked the Active Admin documentation and a line sounded promising:

It is possible to associate :allow_destroy with a string or a symbol, corresponding to the name of a child object’s method that will get called, or with a Proc object.

It was clear, I just had to move that allow_destroy condition somewhere and change the rule to return false whenever I'm dealing with a soft deleted record:

def deletable_from_admin
  !order.validated? && deleted_at.blank?
end

After that, everything works as expected.

I know my solution is probably not the best, but it works. Did you also have this kind of problem? How did you solve it? I'm curious. 🙃

About Me

Gaëtan Masson — Thu, 30 Aug 2018 20:45:56 +0000

This is a "repost" of the initial "Hi, I'm Gaëtan Masson" that I decided to redo because many things changed (like, I'm not a student anymore).

I have been coding for many years (I started when I was a teenager) but only for few years in a serious way. I started coding on my spare time with the C language then I went into web programming with PHP. I have to admit that I also flirted with Python at that period (my first program was a port scanner, what a hacker!).

In CS school, we did low level stuff by reinventing the wheel with the C language (had to rewrite malloc, printf...) and even a bit of Assembly. Then we went into OOP with C++ and Java. At the end, I did some Swift (had to create an iOS app) for the final school project.

Today, I mostly program in Ruby (I make my living as Ruby on Rails developer) but I have a strong interest toward Elixir (what a surprise).

About my hobbies, I enjoy to do weight lifting and being lazy by doing nerd stuff like watching animes, playing video games and hugging my two cats.

I also like to read/watch/listen stuff about science in general, technology and psychology (the brain is an interesting machine, don't you find?).

I'm currently living in Lille (France). You can find me on GitHub as gaetanm and on Twitter as @gaetanm_.

To finish, here is a photo of Matz with me!

Nice to meet you.

Getting Back to an Old PostgreSQL Specific Version

Gaëtan Masson — Thu, 16 Aug 2018 09:26:17 +0000

TL;DR

Exemple about getting back to 9.6.6 from 9.6.7

brew services stop postgresql 
brew services stop postgresql@9.6

brew uninstall postgresql 
brew uninstall postgresql@9.6

rm -rf /usr/local/var/postgres .psql_history .psqlrc .psql.local .pgpass .psqlrc.local

Select the Postgres.app release having the desired version here. Install it, "Initialize" the server then run:

sudo mkdir -p /etc/paths.d && echo /Applications/Postgres.app/Contents/Versions/9.6/bin | sudo tee /etc/paths.d/postgresapp

Reboot the shell.

Details

The PostgreSQL version of the project I'm working on at work is 9.6.6. The problem is that my machine uses a later version. It results in conflicts with the db/structure file each time I run a db:migrate.

Like most dev running on macOS, I usually use Homebrew. It allows to easily switch to another installed version of a formula by running brew switch formula@version. As you guess I tried, but the problem is that Homebrew only handles major versions of each release and I need a specific minor version.

Because I also need to switch between old and recent Rails projects, I often have to change the running PostgreSQL version. My current solution is to use the Postgres.app.

If you already have PostgreSQL installed on your system via Homebrew but want to use a specific version (like a previous one) with Postgres.app, just follow these steps:

1. Remove all PostgreSQL version installed

Check running version brew services list then stop them brew services stop postgresql.
Delete all installed formulas with brew uninstall postgresql and brew uninstall postgresql@version per installed version.
Then delete the related files rm -rf /usr/local/var postgres .psql_history .psqlrc .psql.local .pgpass .psqlrc.local.

2. Install Postgres.app

Download the release having the desired version.
Install it and create a new server:

Initialize it.

3. Make PostgreSQL related tools usable with the terminal

This last step allows you to use tools like pg_dump etc. Just run:

sudo mkdir -p /etc/paths.d &&
echo /Applications/Postgres.app/Contents/Versions/9.6/bin | sudo tee /etc/paths.d/postgresapp`

(Don't forget to replace 9.6 with your version).

Relaunch your shell. Welcome back to the past!

If you have better solution to switch between specific versions of PostgreSQL without external app like I did, don't hesitate to share it! :)

Check If a File Was Uploaded with CarrierWave

Gaëtan Masson — Tue, 14 Aug 2018 14:47:49 +0000

TL;DR

Use:

user.avatar.present?

NOT:

user.avatar.file.nil?

Details

When you want to check if a file is attached to your model, the official Carrierwave documentation says:

Note: u.avatar will never return nil, even if there is no photo associated to it. To check if a photo was saved to the model, use u.avatar.file.nil? instead.

That's fine, it works. BUT! If you are using a cloud storage service like Amazon S3, each time the line file.nil? will be executed, a request will be sent to the cloud storage to check the presence of the file. As you guess, it's not cool because it can make your app slower.

The solution is simply to use u.avatar.present?. This way, no more external call.