Support has_and_belongs_to_many

This support likely allows any association.

Gemfile.lock

@@ -1,7 +1,7 @@
 PATH
   remote: .
   specs:
-    graphql-sources (1.4.0)
+    graphql-sources (1.5.0)
       graphql
       rails
       zeitwerk

README.md

@@ -21,6 +21,50 @@ end
 
 ## Usage
 
+### Loading `has_and_belongs_to_many` Associations
+
+```ruby
+class Student
+  has_and_belongs_to_many :courses
+end
+```
+
+```ruby
+class Course
+  has_and_belongs_to_many :students
+end
+```
+
+```ruby
+class StudentType < GraphQL::Schema::Object
+  field :courses, [CourseType], null: false
+
+  # @return [Array<Course>]
+  def courses
+    # SELECT "courses_students".* FROM "courses_students" WHERE "courses_students"."student_id" = IN (...)
+    # SELECT "courses".* FROM "courses" WHERE "courses"."id" IN (...)
+    dataloader
+      .with(GraphQL::Sources::ActiveRecordAssociation, :courses)
+      .load(object)
+  end
+end
+```
+
+```ruby
+class CourseType < GraphQL::Schema::Object
+  field :students, [StudentType], null: false
+
+  # @return [Array<Student>]
+  def students
+    # SELECT "courses_students".\* FROM "courses_students" WHERE "courses_students"."course_id" = IN (...)
+    # SELECT "students".\* FROM "students" WHERE "students"."id" IN (...)
+    dataloader
+      .with(GraphQL::Sources::ActiveRecordAssociation, :students)
+      .load(object)
+  end
+end
+```
+
 ### Loading `belongs_to` Associations
 
 ```ruby

lib/graphql/sources/active_record_association.rb

@@ -0,0 +1,127 @@
+# frozen_string_literal: true
+
+module GraphQL
+  module Sources
+    # A class for loading an ActiveRecord association.
+    #
+    # @example `has_and_belongs_to_many`
+    #
+    #   class Student
+    #     has_and_belongs_to_many :courses
+    #   end
+    #
+    #   class Course
+    #     has_and_belongs_to_many :students
+    #   end
+    #
+    #   class StudentType < GraphQL::Schema::Object
+    #     field :courses, [CourseType], null: false
+    #
+    #     # @return [Array<Course>]
+    #     def courses
+    #       # SELECT "courses_students".* FROM "courses_students" WHERE "courses_students"."student_id" = IN (...)
+    #       # SELECT "courses".* FROM "courses" WHERE "courses"."id" IN (...)
+    #       dataloader
+    #         .with(GraphQL::Sources::ActiveRecordAssociation, :courses)
+    #         .load(object)
+    #     end
+    #   end
+    #
+    #   class CourseType < GraphQL::Schema::Object
+    #     field :students, [StudentType], null: false
+    #
+    #     # @return [Array<Student>]
+    #     def students
+    #       # SELECT "courses_students".* FROM "courses_students" WHERE "courses_students"."course_id" = IN (...)
+    #       # SELECT "students".* FROM "students" WHERE "students"."id" IN (...)
+    #       dataloader
+    #         .with(GraphQL::Sources::ActiveRecordAssociation, :students)
+    #         .load(object)
+    #     end
+    #   end
+    #
+    #
+    # @example `has_many` / `belongs_to`
+    #
+    #   class User
+    #     has_many :comments
+    #   end
+    #
+    #   class Comment
+    #     belongs_to :user
+    #   end
+    #
+    #   class UserType < GraphQL::Schema::Object
+    #     field :comments, [CommentType], null: false
+    #
+    #     # @return [Array<Comment>]
+    #     def comments
+    #       # SELECT "comments".* FROM "comments" WHERE "comments"."user_id" = IN (...)
+    #       dataloader
+    #         .with(GraphQL::Sources::ActiveRecordAssociation, :comments)
+    #         .load(object)
+    #     end
+    #   end
+    #
+    #   class CommentType < GraphQL::Schema::Object
+    #     field :user, UserType, null: false
+    #
+    #     # @return [User]
+    #     def user
+    #       # SELECT "users".* FROM "users" WHERE "users"."id" IN (...)
+    #       dataloader
+    #         .with(GraphQL::Sources::ActiveRecordAssociation, :user)
+    #         .load(object)
+    #     end
+    #   end
+    #
+    # @example `has_one` / `belongs_to`
+    #
+    #   class User
+    #     has_one :profile
+    #   end
+    #
+    #   class Profile
+    #     belongs_to :user
+    #   end
+    #
+    #   class UserType < GraphQL::Schema::Object
+    #     field :profile, ProfileType, null: false
+    #
+    #     # @return [Profile]
+    #     def profile
+    #       # SELECT "profiles".* FROM "profiles" WHERE "profiles"."user_id" = IN (...)
+    #       dataloader
+    #         .with(GraphQL::Sources::ActiveRecordAssociation, :profile)
+    #         .load(object)
+    #     end
+    #   end
+    #
+    #   class ProfileType < GraphQL::Schema::Object
+    #     field :user, UserType, null: false
+    #
+    #     # @return [User]
+    #     def user
+    #       # SELECT "users".* FROM "users" WHERE "users"."id" IN (...)
+    #       dataloader
+    #         .with(GraphQL::Sources::ActiveRecordAssociation, :user)
+    #         .load(object)
+    #     end
+    #   end
+    class ActiveRecordAssociation < GraphQL::Dataloader::Source
+      # @param association [Symbol] an association to use for loading (e.g. :user)
+      def initialize(association)
+        super()
+        @association = association
+      end
+
+      # @param records [Array<ActiveRecord::Base>] an array of records
+      def fetch(records)
+        preloader = ActiveRecord::Associations::Preloader.new(records: records, associations: [@association])
+        preloader.call
+
+        records.map { |record| record.association(@association).target }
+      end
+    end
+  end
+end

lib/graphql/sources/version.rb

@@ -2,6 +2,6 @@
 
 module GraphQL
   module Sources
-    VERSION = '1.4.0'
+    VERSION = '1.5.0'
   end
 end

spec/dummy/app/models/user.rb

@@ -2,6 +2,7 @@
 
 class User < ApplicationRecord
   has_one :profile
+  has_many :comments
   has_one_attached :avatar
   has_many_attached :photos
 end

spec/graphql/sources/active_record_association_spec.rb

@@ -0,0 +1,23 @@
+# frozen_string_literal: true
+
+require 'spec_helper'
+
+RSpec.describe GraphQL::Sources::ActiveRecordAssociation do
+  describe '#fetch' do
+    subject(:result) do
+      GraphQL::Dataloader.with_dataloading do |dataloader|
+        dataloader
+          .with(described_class, :comments)
+          .request(user)
+          .load
+      end
+    end
+
+    let!(:user) { create(:user) }
+    let!(:comments) { create_pair(:comment, user: user) }
+
+    it 'loads many records' do
+      expect(result).to match_array(comments)
+    end
+  end
+end