Add initial implementation for dataloader.

README.md

@@ -443,52 +443,79 @@ Note: This tutorial was updated on macOS 11.6.3.
 
       import_types(ZeroPhoenixWeb.GraphQL.Schemas.Queries.Person)
 
+      alias ZeroPhoenix.Accounts
+      alias ZeroPhoenix.Repo
+
       query do
         import_fields(:person_queries)
       end
+
+      def context(ctx) do
+        loader =
+          Dataloader.new
+          |> Dataloader.add_source(Accounts, Accounts.datasource())
+
+        Map.put(ctx, :loader, loader)
+      end
+
+      def plugins do
+        [Absinthe.Middleware.Dataloader] ++ Absinthe.Plugin.defaults()
+      end
+    end
+    ```
+
+22. update the `Accounts` context by adding the following after the `change_person` function:
+
+    `lib/zero_phoenix/accounts.ex`:
+
+    ```elixir
+    # Dataloader
+
+    def datasource() do
+      Dataloader.Ecto.new(Repo, query: &query/2)
+    end
+
+    def query(queryable, _) do
+      queryable
     end
     ```
 
-22. add our Person type which will be performing queries against:
+23. add our Person type which will be performing queries against:
 
     `lib/zero_phoenix_web/graphql/types/person.ex`:
 
     ```elixir
     defmodule ZeroPhoenixWeb.GraphQL.Types.Person do
       use Absinthe.Schema.Notation
 
-      import Ecto
+      import Absinthe.Resolution.Helpers, only: [dataloader: 1]
 
-      alias ZeroPhoenix.Repo
+      alias ZeroPhoenix.Accounts
 
       @desc "a person"
       object :person do
         @desc "unique identifier for the person"
-        field :id, non_null(:string)
+        field(:id, non_null(:string))
 
         @desc "first name of a person"
-        field :first_name, non_null(:string)
+        field(:first_name, non_null(:string))
 
         @desc "last name of a person"
-        field :last_name, non_null(:string)
+        field(:last_name, non_null(:string))
 
         @desc "username of a person"
-        field :username, non_null(:string)
+        field(:username, non_null(:string))
 
         @desc "email of a person"
-        field :email, non_null(:string)
+        field(:email, non_null(:string))
 
         @desc "a list of friends for our person"
-        field :friends, list_of(:person) do
-          resolve fn _, %{source: person} ->
-            {:ok, Repo.all(assoc(person, :friends))}
-          end
-        end
+        field :friends, list_of(:person), resolve: dataloader(Accounts)
       end
     end
     ```
 
-23. add the `person_queries` object to contain all the queries for a person:
+24. add the `person_queries` object to contain all the queries for a person:
 
     `lib/zero_phoenix_web/graphql/schemas/queries/person.ex`:
 
@@ -506,7 +533,7 @@ Note: This tutorial was updated on macOS 11.6.3.
     end
     ```
 
-24. add the `PersonResolver` to fetch the individual fields of our person object:
+25. add the `PersonResolver` to fetch the individual fields of our person object:
 
     `lib/zero_phoenix_web/graphql/resolvers/person_resolver.ex`:
 
@@ -515,7 +542,7 @@ Note: This tutorial was updated on macOS 11.6.3.
       alias ZeroPhoenix.Accounts
       alias ZeroPhoenix.Accounts.Person
 
-      def find(_parent, %{id: id}, _info) do
+      def find(_parent, %{id: id}, _resolution) do
         case Accounts.get_person(id) do
           %Person{} = person ->
             {:ok, person}
@@ -527,7 +554,7 @@ Note: This tutorial was updated on macOS 11.6.3.
     end
     ```
 
-25. add routes for our GraphQL API and GraphiQL browser endpoints:
+26. add routes for our GraphQL API and GraphiQL browser endpoints:
 
     `lib/zero_phoenix_web/router.ex`:
 
@@ -559,19 +586,19 @@ Note: This tutorial was updated on macOS 11.6.3.
     end
     ```
 
-26. start the server
+27. start the server
 
     ```zsh
     mix phx.server
     ```
 
-27. navigate to our application within the browser
+28. navigate to our application within the browser
 
     ```zsh
     open http://localhost:4000/graphiql
     ```
 
-28. enter the below GraphQL query on the left side of the browser window
+29. enter the below GraphQL query on the left side of the browser window
 
     ```graphql
     {
@@ -590,7 +617,7 @@ Note: This tutorial was updated on macOS 11.6.3.
     }
     ```
 
-29. run the GraphQL query
+30. run the GraphQL query
 
     ```text
     Control + Enter

lib/zero_phoenix/accounts.ex

@@ -21,6 +21,28 @@ defmodule ZeroPhoenix.Accounts do
     Repo.all(Person)
   end
 
+  @doc """
+  Returns a list of people matching the given `criteria`.
+
+  Example Criteria:
+
+  [{:limit, 15}, {:order, :asc}]
+  """
+
+  def list_people(criteria) do
+    query = from p in Person
+
+    Enum.reduce(criteria, query, fn
+      {:limit, limit}, query ->
+        from p in query, limit: ^limit
+
+      {:order, order}, query ->
+        from p in query, order_by: [{^order, :id}]
+    end)
+    |> Repo.all
+  end
+
+
   @doc """
   Gets a single person.
 
@@ -124,4 +146,14 @@ defmodule ZeroPhoenix.Accounts do
   def change_person(%Person{} = person) do
     Person.changeset(person, %{})
   end
+
+  # Dataloader
+
+  def datasource() do
+    Dataloader.Ecto.new(Repo, query: &query/2)
+  end
+
+  def query(queryable, _) do
+    queryable
+  end
 end

lib/zero_phoenix_web/graphql/resolvers/person_resolver.ex

@@ -1,9 +1,6 @@
 defmodule ZeroPhoenixWeb.GraphQL.Resolvers.PersonResolver do
-  import Ecto
-
   alias ZeroPhoenix.Accounts
   alias ZeroPhoenix.Accounts.Person
-  alias ZeroPhoenix.Repo
 
   def find(_parent, %{id: id}, _resolution) do
     case Accounts.get_person(id) do
@@ -28,8 +25,4 @@ defmodule ZeroPhoenixWeb.GraphQL.Resolvers.PersonResolver do
         {:error, "Could not create person"}
     end
   end
-
-  def friends(parent, _args, _resolution) do
-    {:ok, Repo.all(assoc(parent, :friends))}
-  end
 end

lib/zero_phoenix_web/graphql/schema.ex

@@ -2,9 +2,11 @@ defmodule ZeroPhoenixWeb.GraphQL.Schema do
   use Absinthe.Schema
 
   import_types(ZeroPhoenixWeb.GraphQL.Types.Person)
-  
+
   import_types(ZeroPhoenixWeb.GraphQL.Schemas.Queries.Person)
 
+  alias ZeroPhoenix.Accounts
+
   query do
     import_fields(:person_queries)
   end
@@ -14,4 +16,16 @@ defmodule ZeroPhoenixWeb.GraphQL.Schema do
   mutation do
     import_fields(:person_mutations)
   end
+
+  def context(ctx) do
+    loader =
+      Dataloader.new
+      |> Dataloader.add_source(Accounts, Accounts.datasource())
+
+    Map.put(ctx, :loader, loader)
+  end
+
+  def plugins do
+    [Absinthe.Middleware.Dataloader] ++ Absinthe.Plugin.defaults()
+  end
 end

lib/zero_phoenix_web/graphql/types/person.ex

@@ -1,7 +1,9 @@
-defmodule ZeroPhoenixWeb.Graphql.Types.Person do
+defmodule ZeroPhoenixWeb.GraphQL.Types.Person do
   use Absinthe.Schema.Notation
 
-  alias ZeroPhoenixWeb.Graphql.Resolvers
+  import Absinthe.Resolution.Helpers, only: [dataloader: 1]
+
+  alias ZeroPhoenix.Accounts
 
   @desc "a person"
   object :person do
@@ -21,9 +23,7 @@ defmodule ZeroPhoenixWeb.Graphql.Types.Person do
     field(:email, non_null(:string))
 
     @desc "a list of friends for our person"
-    field :friends, list_of(:person) do
-      resolve &Resolvers.PersonResolver.friends/3
-    end
+    field :friends, list_of(:person), resolve: dataloader(Accounts)
   end
 
   @desc "a person input"

mix.exs

@@ -47,7 +47,8 @@ defmodule ZeroPhoenix.Mixfile do
       {:plug_cowboy, "~> 2.5.2"},
       {:absinthe, "~> 1.7.0"},
       {:absinthe_plug, "~> 1.5.8"},
-      {:cors_plug, "~> 2.0.3"}
+      {:cors_plug, "~> 2.0.3"},
+      {:dataloader, "~> 1.0.10"}
     ]
   end
 

priv/repo/dataloader_example.exs

@@ -1,6 +1,6 @@
 alias ZeroPhoenix.Accounts
 
-# Fetch 3 places we want to get the bookings for:
+# Fetch 3 people we want to get the friends for:
 
 [person1, person2, person3] = Accounts.list_people([limit: 3])
 
@@ -18,7 +18,7 @@ source = Dataloader.Ecto.new(ZeroPhoenix.Repo)
 
 loader = loader |> Dataloader.add_source(Accounts, source)
 
-# Create a batch of bookings to be loaded (does not query the database):
+# Create a batch of friends to be loaded (does not query the database):
 
 loader =
   loader
@@ -30,9 +30,9 @@ loader =
 
 loader = loader |> Dataloader.run
 
-# 🔥 This runs one Ecto query to fetch all the bookings for all the places!
+# 🔥 This runs one Ecto query to fetch all the friends for all the people!
 
-# Now you can get the bookings for a particular place:
+# Now you can get the friends for a particular person:
 
 loader |> Dataloader.load(Accounts, :friends, person1) |> IO.inspect
 loader |> Dataloader.load(Accounts, :friends, person2) |> IO.inspect