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OnPoint Vietnam profile image Dung Nguyen
Dung Nguyen for OnPoint Vietnam

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Elixir phoenix - Render Ecto schema to json with relationships

#elixir

When writing API with Phoenix and render json to client,

  • For some fields I want to keep it original value.
  • For some fields, I want to do some calculation or format data before returning.
  • And I want to render Ecto association too.

An while working on an project at OnPoint I have build a little module that helps to do this easier.

I have extract that module and release as a package named JsonView. Its source code is hosted on github:

https://github.com/bluzky/json_view

You can use it with Phoenix.View or use it independently. It helps to manipulate data, and handle rendering association automatically.

I have published an article on how to write it
A better way to render json response in Elixir Phoenix

Let's take a look.

First define view modules

 defmodule MyApp.UserView do use JsonView def render("user.json", %{user: user}) do render_json(user, [:first_name, :last_name, :vatar], [], []) end end defmodule MyApp.PostView do use JsonView # define which fields return without modifying @fields [:title, :content, :excerpt, :cover] # define which fields that need to format or calculate, you have to define `render_field/2` below @custom_fields [:like_count] # define which view used to render relationship @relationships [author: MyApp.UserView] def render("post.json", %{post: post}) do # 1st way if `use JsonView` render_json(post, @fields, @custom_fields, @relationships) end def render_field(:like_count, item) do # load like_count from some where end end
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And then use it

post = %Post{ title: "Hello JsonView", excerpt: "Now you can render Json easier", content: "Install and put it to work", cover: nil, inserted_at: ~N[2021-07-05 00:00:00], updated_at: ~N[2021-07-09 00:00:00], author: %User{ first_name: "Daniel", last_name: "James", email: "daniel@example.com", avatar: nil, inserted_at: ~N[2021-06-30 00:00:00] updated_at: ~N[2021-07-02 00:00:00] } } MyApp.PostView.render("post.json", %{post: post}) # or invoke from PostController render(conn, "post.json", post: post)
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This is the result that you can use to return from PhoenixController

%{ title: "Hello JsonView", excerpt: "Now you can render Json easier", content: "Install and put it to work", cover: nil, like_count: nil, author: %{ first_name: "Daniel", last_name: "James" } }
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If you have any feedback, please comment or create an issue.

In the next post I will go through step by step to write this library.

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