GraphQL::Preload

Provides a DSL for the graphql gem that allows ActiveRecord associations to be preloaded in field definitions. Based on a gist by @theorygeek.

Installation

Add this line to your application's Gemfile:

gem 'graphql-preload'

And then execute:

$ bundle

Or install it yourself as:

$ gem install graphql-preload

Usage

First, enable preloading in your GraphQL::Schema:

Schema = GraphQL::Schema.define do
  use GraphQL::Batch

  enable_preloading
end

There are two approaches available to config the caching for the field. Using currently supported GraphQL gem Field Extension interface or Field Instrument interface which is no longer supported as of graphql 1.10.0.

Call preload when defining your field:

Field Instrument:

PostType = GraphQL::ObjectType.define do
  name 'Post'

  field :comments, !types[!CommentType] do
    # Post.includes(:comments)
    preload :comments

    # Post.includes(:comments, :authors)
    preload [:comments, :authors]

    # Post.includes(:comments, authors: [:followers, :posts])
    preload [:comments, { authors: [:followers, :posts] }]

    resolve ->(obj, args, ctx) { obj.comments }
  end
end

preload_scope

Starting with Rails 4.1, you can scope your preloaded records by passing a valid scope to ActiveRecord::Associations::Preloader. Scoping can improve performance by reducing the number of models to be instantiated and can help with certain business goals (e.g., only returning records that have not been soft deleted).

This functionality is surfaced through the preload_scope option:

PostType = GraphQL::ObjectType.define do
  name 'Post'

  field :comments, !types[!CommentType] do
    preload :comments
    preload_scope ->(args, ctx) { Comment.where(deleted_at: nil) }

    # Resolves with records returned from the following query:
    # SELECT "comments".*
    # FROM "comments"
    # WHERE "comments"."deleted_at" IS NULL
    #   AND "comments"."post_id" IN (1, 2, 3)
    resolve ->(obj, args, ctx) { obj.comments }
  end
end

Field Extension:

PostType = GraphQL::ObjectType.define do
  name 'Post'

  field :comments, [CommentType], null: false do
    # Post.includes(:comments)
    extension GraphQL::Preload::FieldExtension, preload: :comments

    # Post.includes(:comments, :authors)
    extension GraphQL::Preload::FieldExtension, preload: [:comments, :authors]

    # Post.includes(:comments, authors: [:followers, :posts])
    extension GraphQL::Preload::FieldExtension, preload: [:comments, { authors: [:followers, :posts] }]

    resolve ->(obj, args, ctx) { obj.comments }
  end
end

preload_scope

Starting with Rails 4.1, you can scope your preloaded records by passing a valid scope to ActiveRecord::Associations::Preloader. Scoping can improve performance by reducing the number of models to be instantiated and can help with certain business goals (e.g., only returning records that have not been soft deleted).

This functionality is surfaced through the preload_scope option:

PostType = GraphQL::ObjectType.define do
  name 'Post'

  field :comments, [CommentType], null: false do
    extension GraphQL::Preload::FieldExtension, { preload: :comments, preload_scope: ->(args, ctx) { Comment.where(deleted_at: nil) } }

    # Resolves with records returned from the following query:
    # SELECT "comments".*
    # FROM "comments"
    # WHERE "comments"."deleted_at" IS NULL
    #   AND "comments"."post_id" IN (1, 2, 3)
    resolve ->(obj, args, ctx) { obj.comments }
  end
end

Development

After checking out the repo, run bin/setup to install dependencies. Then, run rake test to run the tests. You can also run bin/console for an interactive prompt that will allow you to experiment.

To install this gem onto your local machine, run bundle exec rake install. To release a new version, update the version number in version.rb, and then run bundle exec rake release, which will create a git tag for the version, push git commits and tags, and push the .gem file to rubygems.org.

Contributing

Bug reports and pull requests are welcome on GitHub at https://github.com/ConsultingMD/graphql-preload.

License

The gem is available as open source under the terms of the MIT License.