查询构建器

The ModelQueryBuilder extends the standard QueryBuilder and hence all of the methods are available to the model query builder as well.

This document just covers the additional methods/properties exclusive to the model query builder only.

The model query builder always returns an array of models instances and not plain objects.

Also, the model query builder is aware of the model and its relationships and hence provides an easy to use API to work with relationships.

class User extends BaseModel {}

// Returns model query builder instance
User.query()

Methods/Properties

Following is the list of the methods/properties available on the model query builder

preload

Pre-load/Eager-load relationships for the model.

const users = await User.query().preload('posts')

The preload method will perform the required queries to load the posts for all the users and then set them on the user instance.

Optionally, you can pass a callback to modify the relationship query. The callback receives the model query builder for the related model.

User.query().preload('posts', (postsQuery) => {
  postsQuery.where('status', 'published')
})

You can also preload multiple relationships by calling the preload method.

User.query().preload('posts').preload('profile')

The nested relationships can be loaded by the calling the preload method on the related model query builder. The following example fetches a tree of users -> posts -> comments -> user

const users = await User
  .query()
  .preload('posts', (postsQuery) => {
    postsQuery.preload('comments', (commentsQuery) => {
      commentsQuery.preload('user')
    })
  })

withCount

The withCount method performs a sub query to count the total number of rows for a relationship.

const users = await User.query().withCount('posts')

users.forEach((user) => {
  console.log(user.$extras.posts_count)
})

The count is added to the model $extras object, since it is not a regular model attribute and created on the fly for just one query.

Also, withCount and preload are not related to each other. If you want to load relationship rows and also get the count, then you need to call both the methods.

await User
  .query()
  .withCount('posts')
  .preload('posts')

You can also define a custom attribute name for the count value.

const user = await User
  .query()
  .withCount('posts', (query) => {
    query.as('totalPosts')
  })
  .firstOrFail()

console.log(user.$extras.totalPosts)

withAggregate

The withAggregate method allows you define a custom aggregate function. For example: sum the account balance.

const user = await User
  .query()
  .withAggregate('accounts', (query) => {
    query.sum('balance').as('accountsBalance')
  })
  .firstOrFail()

console.log(user.$extras.accountsBalance)

has

The has method allows you to limit the parent model rows by checking for the existence of a given relationship.

For example: Get a list of users who have one or more posts.

const users = await User.query().has('posts')

You can also define a custom count.

await User.query().has('posts', '>=', 2)

The has method has following variants.

whereHas

Similar to the has method. However, the whereHas method allows defining additional constraints by passing a callback as the 2nd argument.

For example: Get a list of users who have one or more posts published posts.

await User.query().whereHas('posts', (postsQuery) => {
  postsQuery.where('status', 'published')
})

The whereHas method has following variants

sideload

The sideload method works as a pipeline for passing an arbitrary object to the model instance(s) created after executing the query.

For example: Passing the currently logged in user.

const users = await User.query().sideload(auth.user)

users.forEach((user) => {
  console.log(user.$sideloaded.user === auth.user) // true
})

The sideloaded value is passed down to the preloaded relationships as well.

withScopes

The withScopes method allows you to leverage the query scopes defined on the model.

Begin by defining a query scope.

import { BaseModel, scope } from '@ioc:Adonis/Lucid/Orm'

export default class Team extends BaseModel {

  public static forUser = scope((query, user: User) => {
    const subQuery = Database
      .from('user_teams')
      .select('team_id')
      .where('user_teams.user_id', user.id)

    query.whereIn('id', subQuery)
  })

}

The forUser property is a query scope that accepts the user object to fetch the teams of the currently logged in user.

Now you can use the query scope as follows

Team
  .query()
  .withScopes((scopes) => scopes.forUser(auth.user))

apply

Alias for the withScopes method.

Team
  .query()
  .apply((scopes) => scopes.forUser(auth.user))

pojo

The pojo method returns the model results as an array of plain JavaScript objects and not an array of model instances.

Also, no lifecycle hooks are executed when using the pojo method, since hooks needs model instances to work.

const posts = await Post.query().pojo()

console.log(posts[0] instanceof Post) // false

paginate

The paginate method on the ORM query builder returns an instancer of the ModelPaginator . The Model paginator class has an additional .serialize method to serialize the models.

const posts = await Post.query().paginate(1)
const paginationJSON = posts.serialize({
  fields: ['title', 'id']
})

model

Reference to the model from which the query instance was created.

console.log(User.query().model === User) // true