@Envek's fork of graphql-preload works very well and has a bright future. This gem, by contrast, is unmaintained.

Build a GraphQL API on Rails, without the N+1's.

Add this line to your application's Gemfile:

gem "graphql_activerecord_resolvers"

And then execute:

$ bundle

Or install it yourself as:

$ gem install graphql_activerecord_resolvers

GraphQL marks a new era in API development, one in which the clients dictate what the server should deliver. But, due to N+1 queries, using GraphQL with Rails is a pain. That's where this gem comes in.

graphql_activerecord_resolvers works with the graphql gem. It provides an ActiveRecord scope that works in tandem with the GraphQL context to automatically preload the requested associations. This takes the database performance burden off of you when writing your GraphQL API.

To use it, simply make the following change to every root field in your Query:

module Types
  QueryType = GraphQL::ObjectType.define do
    name "Query"

    field :countries do
      type types[Types::CountryType]

-     resolve ->(_, _, _) { Country.all }
+     resolve ->(_, _, ctx) { Country.preload_graphql_associations(ctx) }
    end

    field :locations do
      type types[Types::LocationType]

-     resolve ->(_, _, _) { Location.all }
+     resolve ->(_, _, ctx) { Location.preload_graphql_associations(ctx) }
    end
  end
end

You'll notice the N+1's disappear.

There's a special case that the resolver can't detect automatically, and that is when you have a field that resolves to an association but does not match the name of said association. In this case, you need to explicitly declare the association name on the field. For example:

class Pet < ActiveRecord::Base
  belongs_to :person
end

# ...

module Types
  PetType = GraphQL::ObjectType.define do
    name "Pet"

    field :owner do
      type Types::PersonType
+     association_name :person
      resolve -> (obj, _, _) { obj.person }
    end
  end
end

Research is still underway on this. The difficulty lies in determining how resolvers would need to be modified to support eager-loading when requested, but also in such a way that redundant eager loading doesn't occur.

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.

Bug reports and pull requests are welcome on GitHub.

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