gitlab-org--gitlab-foss/doc/development/api_graphql_styleguide.md

GraphQL API

Authentication

Authentication happens through the GraphqlController, right now this uses the same authentication as the Rails application. So the session can be shared.

It is also possible to add a private_token to the querystring, or add a HTTP_PRIVATE_TOKEN header.

Authorization

Fields can be authorized using the same abilities used in the Rails app. This can be done using the authorize helper:

module Types
  class QueryType < BaseObject
    graphql_name 'Query'

    field :project, Types::ProjectType, null: true, resolver: Resolvers::ProjectResolver do
      authorize :read_project
    end
  end

The object found by the resolve call is used for authorization.

This works for authorizing a single record, for authorizing collections, we should only load what the currently authenticated user is allowed to view. Preferably we use our existing finders for that.

Types

When exposing a model through the GraphQL API, we do so by creating a new type in app/graphql/types.

When exposing properties in a type, make sure to keep the logic inside the definition as minimal as possible. Instead, consider moving any logic into a presenter:

class Types::MergeRequestType < BaseObject
  present_using MergeRequestPresenter

  name 'MergeRequest'
end

An existing presenter could be used, but it is also possible to create a new presenter specifically for GraphQL.

The presenter is initialized using the object resolved by a field, and the context.

Resolvers

To find objects to display in a field, we can add resolvers to app/graphql/resolvers.

Arguments can be defined within the resolver, those arguments will be made available to the fields using the resolver.

We already have a FullPathLoader that can be included in other resolvers to quickly find Projects and Namespaces which will have a lot of dependant objects.

To limit the amount of queries performed, we can use BatchLoader.

Testing

full stack tests for a graphql query or mutation live in spec/requests/api/graphql.

When adding a query, the a working graphql query shared example can be used to test if the query renders valid results.

Using the GraphqlHelpers#all_graphql_fields_for-helper, a query including all available fields can be constructed. This makes it easy to add a test rendering all possible fields for a query.