Set up Dataloader to improve database queries via batching

README.md

@@ -1,20 +1,36 @@
-# AbsintheDemo
+# GraphQL server with Dataloader Example
 
-To start your Phoenix server:
+I've left a trail of [commit messages](https://github.com/denvaar/absinthe_graphql_dataloader/commits/master) that is hopefully easy to follow. I might try to make a video soon.
 
-  * Install dependencies with `mix deps.get`
-  * Create and migrate your database with `mix ecto.setup`
-  * Install Node.js dependencies with `cd assets && npm install`
-  * Start Phoenix endpoint with `mix phx.server`
+- [Create a new Phoenix app](https://github.com/denvaar/absinthe_graphql_dataloader/commit/5fa2681f8797aa9317e223437eaf6fbd51e39bfb).
+- [Install Absinthe and configure it to work with Phoenix](https://github.com/denvaar/absinthe_graphql_dataloader/commit/51bd434b832091ca394ee2f977bdfe63b5e38ab6).
+- [Create a database schema with some basic relations; Hook it up to GraphQL schema](https://github.com/denvaar/absinthe_graphql_dataloader/commit/1b523986f5698eeb7c2dfa8dc12dd357e771d245). At this point we have a naive GraphQL schema. The resolvers cause some horrible database queries to happen.
+- [Set up Dataloader with Absinthe to improve performance of database queries](https://github.com/denvaar/absinthe_graphql_dataloader/commit/dbbaae5828ffc1a403ce0cea3bc901e048288e0f).
 
-Now you can visit [`localhost:4000`](http://localhost:4000) from your browser.
+### Setup Instructions
 
-Ready to run in production? Please [check our deployment guides](https://hexdocs.pm/phoenix/deployment.html).
+1. Install dependencies `mix deps.get`
+1. Create database `mix ecto.setup`
+1. Create database schema and populate with data `mix ecto.drop; mix ecto.create; mix ecto.migrate; mix run priv/repo/seeds.exs`
+1. Start the Phoenix server `mix phx.server`
+1. Run GraphQL queries (and browse schema documentation) from your web browser at `http://localhost:4000/api/graphiql`
 
-## Learn more
+### Learn more about Dataloader (Efficiently load data in batches)
 
-  * Official website: http://www.phoenixframework.org/
-  * Guides: https://hexdocs.pm/phoenix/overview.html
-  * Docs: https://hexdocs.pm/phoenix
-  * Mailing list: http://groups.google.com/group/phoenix-talk
-  * Source: https://github.com/phoenixframework/phoenix
+- [Elixir Dataloader GitHub repo](https://github.com/absinthe-graphql/dataloader)
+- [Elixir Dataloader Hex docs](https://hexdocs.pm/dataloader/Dataloader.html)
+- [A helpful blog post](https://schneider.dev/blog/elixir-phoenix-absinthe-graphql-react-apollo-followup/)
+- [Original Dataloader JavaScript implementation](https://github.com/graphql/dataloader)
+
+### Learn more about Absinthe (Elixir implementation of GraphQL spec)
+
+- [Absinthe GitHub Repo](https://github.com/absinthe-graphql/absinthe)
+- [Absinthe Hex docs](https://hexdocs.pm/absinthe/overview.html)
+
+### Learn more about Phoenix (Elixir Web Framework)
+
+- [Official website](http://www.phoenixframework.org/)
+- [Guides](https://hexdocs.pm/phoenix/overview.html)
+- [Docs](https://hexdocs.pm/phoenix)
+- [Mailing list](http://groups.google.com/group/phoenix-talk)
+- [Source](https://github.com/phoenixframework/phoenix)

lib/absinthe_demo_web/data_source.ex

@@ -0,0 +1,9 @@
+defmodule AbsintheDemo.DataSource do
+  def data() do
+    Dataloader.Ecto.new(AbsintheDemo.Repo, query: &query/2)
+  end
+
+  def query(queryable, _params) do
+    queryable
+  end
+end

lib/absinthe_demo_web/graphql/schema.ex

@@ -5,6 +5,18 @@ defmodule AbsintheDemoWeb.GraphQL.Schema do
 
   alias AbsintheDemoWeb.GraphQL.Resolvers
 
+  def context(ctx) do
+    loader =
+      Dataloader.new()
+      |> Dataloader.add_source(:blog_context, AbsintheDemo.DataSource.data())
+
+    Map.put(ctx, :loader, loader)
+  end
+
+  def plugins do
+    [Absinthe.Middleware.Dataloader] ++ Absinthe.Plugin.defaults()
+  end
+
   query do
     @desc "Get all posts"
     field :posts, list_of(:post) do

lib/absinthe_demo_web/graphql/typedefs.ex

@@ -1,50 +1,32 @@
 defmodule AbsintheDemoWeb.GraphQL.Typedefs do
   use Absinthe.Schema.Notation
 
+  import Absinthe.Resolution.Helpers, only: [dataloader: 1]
+
   alias AbsintheDemo.Database
 
   object :post do
     field :id, :id
     field :title, :string
     field :body, :string
 
-    field :author, :author do
-      resolve(fn post, _args, _info ->
-        # Example of N+1 problem
-        {:ok, Database.get_author(post.author_id)}
-      end)
-    end
-
-    field :categories, list_of(:category) do
-      resolve(fn post, _args, _info ->
-        # Example of N+1 problem
-        {:ok, Database.get_categories_of_post(post.id)}
-      end)
-    end
+    field :author, :author, resolve: dataloader(:blog_context)
+
+    field :categories, list_of(:category), resolve: dataloader(:blog_context)
   end
 
   object :author do
     field :id, :id
     field :name, :string
     field :profile_picture_link, :string
 
-    field :posts, list_of(:post) do
-      resolve(fn author, _args, _info ->
-        # Example of N+1 problem
-        {:ok, Database.get_posts_of_author(author.id)}
-      end)
-    end
+    field :posts, list_of(:post), resolve: dataloader(:blog_context)
   end
 
   object :category do
     field :id, :id
     field :name, :string
 
-    field :posts, list_of(:post) do
-      resolve(fn category, _args, _info ->
-        # Example of N+1 problem
-        {:ok, Database.get_posts_of_category(category.id)}
-      end)
-    end
+    field :posts, list_of(:post), resolve: dataloader(:blog_context)
   end
 end

mix.exs

@@ -45,7 +45,8 @@ defmodule AbsintheDemo.MixProject do
       {:plug_cowboy, "~> 2.0"},
       # Absinthe GraphQL stuff
       {:absinthe, "~> 1.4.16"},
-      {:absinthe_phoenix, "~> 1.4.4"}
+      {:absinthe_phoenix, "~> 1.4.4"},
+      {:dataloader, "~> 1.0.7"}
     ]
   end
 

mix.lock

@@ -5,6 +5,7 @@
   "connection": {:hex, :connection, "1.0.4", "a1cae72211f0eef17705aaededacac3eb30e6625b04a6117c1b2db6ace7d5976", [:mix], [], "hexpm"},
   "cowboy": {:hex, :cowboy, "2.7.0", "91ed100138a764355f43316b1d23d7ff6bdb0de4ea618cb5d8677c93a7a2f115", [:rebar3], [{:cowlib, "~> 2.8.0", [hex: :cowlib, repo: "hexpm", optional: false]}, {:ranch, "~> 1.7.1", [hex: :ranch, repo: "hexpm", optional: false]}], "hexpm"},
   "cowlib": {:hex, :cowlib, "2.8.0", "fd0ff1787db84ac415b8211573e9a30a3ebe71b5cbff7f720089972b2319c8a4", [:rebar3], [], "hexpm"},
+  "dataloader": {:hex, :dataloader, "1.0.7", "58351b335673cf40601429bfed6c11fece6ce7ad169b2ac0f0fe83e716587391", [:mix], [{:ecto, ">= 0.0.0", [hex: :ecto, repo: "hexpm", optional: true]}], "hexpm"},
   "db_connection": {:hex, :db_connection, "2.2.1", "caee17725495f5129cb7faebde001dc4406796f12a62b8949f4ac69315080566", [:mix], [{:connection, "~> 1.0.2", [hex: :connection, repo: "hexpm", optional: false]}], "hexpm"},
   "decimal": {:hex, :decimal, "1.8.1", "a4ef3f5f3428bdbc0d35374029ffcf4ede8533536fa79896dd450168d9acdf3c", [:mix], [], "hexpm"},
   "ecto": {:hex, :ecto, "3.3.4", "95b05c82ae91361475e5491c9f3ac47632f940b3f92ae3988ac1aad04989c5bb", [:mix], [{:decimal, "~> 1.6 or ~> 2.0", [hex: :decimal, repo: "hexpm", optional: false]}, {:jason, "~> 1.0", [hex: :jason, repo: "hexpm", optional: true]}], "hexpm"},