Serializing Adonis Lucid Models with Postgis Columns

why #

I’m currently in the middle of backend rewrite for vandal from Django to Adonisjs. Overall, things have gone swimmingly and the developer experience has been wonderful – so has the type-safety. My biggest pain point has been around the lack of searchable historical knowledge, which makes sense because Adonis is still a new framework. This is the why behind this series of blog posts. I aim to add to that searchable knowledge bit by bit & encourage you to do the same!

intro #

Adonis doesn’t have first-class support for geospatial database columns, but they do offer a cookbook that shows you how to leverage knex-postgis in your Lucid ORM models. To keep this post brief, I’ll assume you’ve followed the cookbook and set up your postgis database already.

what’s the POINT #

When querying for a geo-point column in our database I kept receiving a string of characters like this (point: '0101000020E6100000276893C327A25EC0D881734694F24240',) instead of the value that was in the database (POINT(10 -20)).

This was a serialization issue. I needed to explicitly tell my query about the point field I was returning with the query so it could be properly serialized. The cookbook references a method for doing this leveraging knex-postgis:

import Database from '@ioc:Adonis/Lucid/Database'

await Database
  .from('points')
  .select(
    'id',
    Database.st().asText('point')
  )

This method works, but I want to be able to leverage the power of Lucid ORM models! After some digging around in the documentation, I found two very useful lifecycle hooks & cooked up my own solution.

lucid orm + postgis #

Lucid exposes two critical lifecycle hooks that we’ll use here to properly serialize postgis point columns: beforeFind & beforeFetch. The first applies to all ORM queries that find a single record & the latter is used for all other queries.

Below is the simple solution to the problem. Before every ORM query gets sent off, we append a select statement to get everything along with the properly formatted geopoint field point.

import { BaseModel, beforeCreate, column } from '@ioc:Adonis/Lucid/Orm'
import Database from '@ioc:Adonis/Lucid/Database'
import {
  ModelQueryBuilderContract,
  beforeFetch,
  beforeFind,
  column,
} from '@ioc:Adonis/Lucid/Orm'

type ModelQuery = ModelQueryBuilderContract<typeof Model>

export default class Model extends BaseModel {

  // query hooks
  // add properly formatted Geo point to every query
  @beforeFetch()
  @beforeFind()
  public static fetchWithFormattedPoint(query: ModelQuery) {
    query.select('*', Database.st().asText('point')) // point is the name of the geo-point column
  }

  @column()
  public point: any
}

That’s it! Now you can query for a model through the ORM and access the exact database value via point.