Creating JSON-API in Elixir-Phoenix with ease using ja_serializer.

Creating JSON-API in Elixir-Phoenix with ease using ja_serializer.


6 min read

Today, most of the Web application uses Modern Frontend frameworks like React, Angular, Ember, etc. These frameworks use the JSON API to interact with some back-end. JSON-API is the preferred specification for building APIs. This post will help you in creating JSON-API using ja_serializer(an Elixir library) for an Elixir-Phoenix app. We are going to create a simple Blog(everyone's favorite example ๐Ÿ˜‰ ) application. This application will generate JSON-API, which will be accessible for SPA's to use.

I'll divide this post into 3 parts for the sake of simplicity:

  • Creating the new app, along with that I'll add one resource(Post model with Context).
  • Configuring ja_serializer(Here we will configure ja_serializer).
  • Final Demo (We'll see ja_serializer into action).

Creating a new Phoenix application:

  • First, we are going to create a new Phoenix application with following command in your terminal.
    mix --no-webpack --no-html my_blog_api
  • After the project is generated run cd my_blog_api.
  • Run mix ecto.create. This will generate database along with Repo.
  • Next, we are going to add Post model along with Blog context. This can be achieved by following command.
    mix phx.gen.context Blog Post posts title:string body:text 
    //This will create `Post` model along with `Blog` context and 5 main `CRUD` operations methods.
  • You can test this by running iex -S mix phx.server and run MyBlogApi.Blog.list_posts. This is going to return all Posts. In our case its a fresh app. So, try creating few records and test this function later :) .
  • Now, we are ready with one resource, we can hop to next level.

Configuring ja_serializer:

  • To install we are going to add {:ja_serializer, "~> 0.12.0"} in mix.exs and run mix deps.get.
  • Now we need to configure our app to use ja_serializer. We need to add configuration in our app to make it use json-api specification headers.
  • We are going to install a plugin called poison to encode requests for our new json-api mime type. (To install poison add poison in mix.exs and run mix deps.get).
  • We will do this by adding a line below our app config in config/config.exs.
    config :mime, :types, %{
      "application/vnd.api+json" => ["json-api"]
    config :phoenix, :format_encoders, "json-api": Poison
  • Also update the error type in ErrorView in the same file. It has an array with only json type. Add json-api as well in it. Update the line as below

    render_errors: [view: MyBlogApiWeb.ErrorView, accepts: ~w(json json-api)],
  • Now we need to rebuild the plugin dependency by running the following command.

    mix deps.clean mime --build
  • Next, we have to do some setup to make our router to use ja_serializer:

    • To deserialize the request coming in we will add plug JaSerializer.ContentTypeNegotiation
    • Add plug jaserilaizer deserializer to convert bobcase property to underscore property. plug JaSerializer.Deserializer
    • In router.ex
      pipeline :api do
       plug :accepts, ["json", "json-api"]
       plug JaSerializer.ContentTypeNegotiation
       plug JaSerializer.Deserializer


  • Now that we have configured ja_serializer, we will now create a Post#index endpoint to see json-api response.
  • Go to router.ex add resources /posts, PostController, only: [:index]
  • Create post controller in my_blog_api_web/controllers/post_controller.ex.
  • Add an index action.

    defmodule MyBlogApiWeb.PostController do 
      use MyBlogApiWeb, :controller
      alias MyBlogApi.Blog
      def index(conn, _params) do
         posts = Blog.list_posts()
         render(conn, "index.json-api", data: posts)
  • Create a my_blog_api_web/views/post_view.ex file for post to render json and add the following code.

    defmodule MyBlogApiWeb.PostView do
      use MyBlogApiWeb, :view
      use JaSerializer.PhoenixView
     attributes [:title, :body]
  • In attributes macro, we can specify the fields we want to send in response.
  • Now, start your server and open postman and hit posts endpoint i.e localhost:4000/posts you can see the response in json-api format.

I hope you like this post. If you any questions please add the comment below.๐Ÿ‘‡

Note: If you face an error related to CORS while integrating this API into the frontend- framework follow this blog๐Ÿ‘‡


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