Sometimes in TypeORM you want to save location/coordinates in a type that can take advantage of GIS functions like distance, closeness etc MySQL and Postgres have these functions that get this information when you have geometry data column types.
This was surprisingly difficult to find information on so here's my implementation.
I assume you already have a TypeORM project set up.
Install these packages:
npm install wkx geojson
npm install @types/geojson --save-dev
Then add this custom transformer that converts GeoJSON to WKT and WKT back to GeoJSON
Example GeoJSON:
const location = {
type: 'point',
coordinates: [-74.534, 39.123]
}
Example WKT (like you would use in MySQL query):
POINT(-74.534, 39.123)
This would be saved as BLOB type in MySQL
Files
First you need to add the transformer class
// ./src/lib/transformers.ts
import * as wkx from 'wkx'
import { Geometry } from 'geojson'
import { ValueTransformer } from 'typeorm/decorator/options/ValueTransformer'
/**
* TypeORM transformer to convert GeoJSON to MySQL WKT (Well Known Text) e.g. POINT(LAT, LON) and back
*/
export class GeometryTransformer implements ValueTransformer {
to(geojson: Geometry): string {
return wkx.Geometry.parseGeoJSON(geojson).toWkt()
}
from(wkb: string): Record<string, any> | undefined {
if(!wkb) return
return wkx.Geometry.parse(wkb).toGeoJSON()
}
}
Then inside your target entity class:
// ./src/entities/user.ts
import {
Entity,
PrimaryGeneratedColumn,
Column,
BaseEntity
} from 'typeorm'
import { GeometryTransformer } from '../transformers'
import { Geometry } from 'geojson'
@Entity({ name: 'user' })
export class User extends BaseEntity {
@PrimaryGeneratedColumn()
idUser!: number
@Column({
type: 'geometry',
spatialFeatureType: 'Point',
srid: 4326, // WGS84 reference system
transformer: new GeometryTransformer(),
})
location?: Geometry
}
Insert GeoJSON
And then finally if you want to insert location data, insert geoJSON:
// ./src/services/user.service.ts
import { Geometry } from 'geojson'
import { getRepository } from 'typeorm'
import { User } from '../entities/user'
export const createUser = async (): Promise<User|undefined> => {
const location: Geometry = {
type: 'Point',
coordinates: [-74.534, 39.123]
}
// you should validate the geojson here
// https://www.npmjs.com/package/geojson-validation
// if(!validGeoJson(location))throw new Error('invalid GeoJSON')
return getRepository(User)
.create({ location })
.save()
}
Retrieve GeoJSON
And then when you query the object you will get location as type Geometry.
That's it!
Hi I'm Emmanuel! I write about Software and DevOps.
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