Dataloader

GraphQL::Dataloader instances are created for each query (or multiplex) and they:

• Cache Source instances for the duration of GraphQL execution
• Run pending Fibers to resolve data requirements and continue GraphQL execution

During a query, you can access the dataloader instance with:

• GraphQL::Query::Context#dataloader (context.dataloader, anywhere that query context is available)
• GraphQL::Schema::Object#dataloader (dataloader inside a resolver method)
• GraphQL::Schema::Resolver#dataloader (dataloader inside def resolve of a Resolver, Mutation, or Subscription class.)

Fiber Lifecycle Hooks

Under the hood, Dataloader creates Fibers as-needed and uses them to run GraphQL and load data from Source classes. You can hook into these Fibers through several lifecycle hooks. To implement these hooks, create a custom subclass and provide new implementation for these methods:

class MyDataloader < GraphQL::Dataloader # or GraphQL::Dataloader::AsyncDataloader
  # ...
end

Then, use your customized dataloader instead of the built-in one:

  class MySchema < GraphQL::Schema
-   use GraphQL::Dataloader
+   use MyDataloader
  end

• GraphQL::Dataloader#get_fiber_variables is called before creating a Fiber. By default, it returns a hash containing the parent Fiber’s variables (from Thread.current[...]). You can add to this hash in your own implementation of this method.
• GraphQL::Dataloader#set_fiber_variables is called inside the new Fiber. It’s passed the hash returned from get_fiber_variables. You can use this method to initialize “global” state inside the new Fiber.
• GraphQL::Dataloader#cleanup_fiber is called just before a Dataloader Fiber exits. You can use this methods to teardown any state that you prepared in set_fiber_variables.