Execute resolution field asynchronously.

This is a helper function for using the Absinthe.Middleware.Async.

Forbidden in mutation fields. (TODO: actually enforce this)

Batch the resolution of several functions together.

Helper function for creating Absinthe.Middleware.Batch

Example

Raw usage:

object :post do
  field :name, :string
  field :author, :user do
    resolve fn post, _, _ ->
      batch({__MODULE__, :users_by_id}, post.author_id, fn batch_results ->
        {:ok, Map.get(batch_results, post.author_id)}
      end)
    end
  end
end

def users_by_id(_, user_ids) do
  users = Repo.all from u in User, where: u.id in ^user_ids
  Map.new(users, fn user -> {user.id, user} end)
end

Resolve a field with a dataloader source.

This function is not imported by default. To make it available in your module do

import Absinthe.Resolution.Helpers

Same as dataloader/3, but it infers the resource name from the field name.

Examples

field :author, :user, resolve: dataloader(Blog)

This is identical to doing the following.

field :author, :user, resolve: dataloader(Blog, :author, [])

Resolve a field with Dataloader

This function is not imported by default. To make it available in your module do

import Absinthe.Resolution.Helpers

While on_load/2 makes using dataloader directly easy within a resolver function, it is often unnecessary to need this level of direct control.

The dataloader/3 function exists to provide a simple API for using dataloader. It takes the name of a data source, the name of the resource you want to load, and then a variety of options.

Basic Usage

object :user do
  field :posts, list_of(:post),
    resolve: dataloader(Blog, :posts, args: %{deleted: false})

  field :organization, :organization do
    resolve dataloader(Accounts, :organization, use_parent: false)
  end
end

Key Functions

Instead of passing in a literal like :posts or :organization in as the resource, it is also possible pass in a function:

object :user do
  field :posts, list_of(:post) do
    arg :limit, non_null(:integer)
    resolve dataloader(Blog, fn user, args, info ->
      args = Map.update!(args, :limit, fn val ->
        max(min(val, 20), 0)
      end)
      {:posts, args}
    end)
  end
end

In this case we want to make sure that the limit value cannot be larger than 20. By passing a callback function to dataloader/2 we can ensure that the value will fall nicely between 0 and 20.

Options

• :args default: %{}. Any arguments you want to always pass into the Dataloader.load/4 call. Resolver arguments are merged into this value and, in the event of a conflict, the resolver arguments win.
• :use_parent default: true. This option affects whether or not the dataloader/2 helper will use any pre-existing value on the parent. IE if you return %{author: %User{...}} from a blog post the helper will by default simply use the pre-existing author. Set it to false if you always want it to load it fresh.

Ultimately, this helper calls Dataloader.load/4 using the loader in your context, the source you provide, the tuple {resource, args} as the batch key, and then the parent value of the field

def dataloader(source_name, resource) do
  fn parent, args, %{context: %{loader: loader}} ->
    args = Map.merge(opts[:args] || %{}, args)
    loader
    |> Dataloader.load(source_name, {resource, args}, parent)
    |> on_load(fn loader ->
      {:ok, Dataloader.get(loader, source_name, {resource, args}, parent)}
    end)
  end

Dataloader helper function

This function is not imported by default. To make it available in your module do

import Absinthe.Resolution.Helpers

This function helps you use data loader in a direct way within your schema. While normally the dataloader/1,2,3 helpers are enough, on_load/2 is useful when you want to load multiple things in a single resolver, or when you need fine grained control over the dataloader cache.

Examples

field :reports, list_of(:report) do
  resolve fn shipment, _, %{context: %{loader: loader}} ->
    loader
    |> Dataloader.load(SourceName, :automatic_reports, shipment)
    |> Dataloader.load(SourceName, :manaul_reports, shipment)
    |> on_load(fn loader ->
      reports =
        loader
        |> Dataloader.get(SourceName, :automatic_reports, shipment)
        |> Enum.concat(Dataloader.load(loader, SourceName, :manaul_reports, shipment))
        |> Enum.sort_by(&reported_at/1)
      {:ok, reports}
    end)
  end
end