Preloaded data lost when turned into JSON

Question

in my context I have the below to preload owner and assignee both which belong to users

  def list_tasks do
    Repo.all(Task)
    |> Repo.preload([:owner, :assignee])
  end

in my controller for index I have something like this:

def index(conn, _params) do
    tasks = Issue.list_tasks()
    IO.inspect(tasks)
    render(conn, "index.json", tasks: tasks)
end

the IO.inspect(tasks) prints out

[
  %Task3.Issue.Task{
    __meta__: #Ecto.Schema.Metadata<:loaded, "tasks">,
    assignee: %Task3.Accounts.User{
      __meta__: #Ecto.Schema.Metadata<:loaded, "users">,
      email: "[email protected]",
      id: 2,
      inserted_at: ~N[2018-04-02 18:22:21.699478],
      updated_at: ~N[2018-04-02 18:22:21.699486],
      username: "Jill"
    },
    assignee_id: 2,
    details: nil,
    id: 1,
    inserted_at: ~N[2018-04-02 18:22:21.711588],
    owner: %Task3.Accounts.User{
      __meta__: #Ecto.Schema.Metadata<:loaded, "users">,
      email: "[email protected]",
      id: 1,
      inserted_at: ~N[2018-04-02 18:22:21.677877],
      updated_at: ~N[2018-04-02 18:22:21.677887],
      username: "Jack"
    },
    owner_id: 1,
    status: "COMPLETE",
    timespent: nil,
    title: "test",
    updated_at: ~N[2018-04-02 18:22:21.711598]
  }
]

However the json data I get on the front end is

{"data":[{"title":"test","timespent":null,"status":"COMPLETE","id":1,"details":null}]}

I have lost assignee and owner. Am I missing anything? Was there an extra step to be taken to get the preloaded data to json form?

I think you will want to take a look at your view for that controller. By default, we cannot take a struct and turn it into JSON because of certain fields (like __meta__). Because of this, we need to take out only the fields we want. In your view, you will most likely have a render function that does this. — Justin Wood

emoragaf emoragaf · Accepted Answer · 2018-04-03T18:27:51

You need to check your task_view.ex file

If it's the default file generated with phx.gen.json it'll look something like this:

defmodule MyAppWeb.TaskView do
    use MyAppWeb, :view
    alias MyAppWeb.TaskView

    def render("index.json", %{tasks: tasks}) do
        %{data: render_many(tasks, TaskView, "task.json")}
    end

    def render("show.json", %{task: task}) do
        %{data: render_one(task, TaskView, "task.json")}
    end

    def render("task.json", %{task: task}) do
        %{
            id: task.id,
            title: task.title,
            timespent: task.timespent,
            details: task.details,
            status: task.status
        }
    end
end

You need to edit this file and add the extra fields you want to show.

e.g. for assignee you could reuse your autogenerated view like this:

defmodule MyAppWeb.TaskView do
    use MyAppWeb, :view
    alias MyAppWeb.{TaskView, AsigneeView}

    ...

    def render("task.json", %{task: task} do
        %{
            id: task.id,
            ...
            asignee: render_one(task.asignee, AsigneeView, "asignee.json"),
        }
    end
end

Preloaded data lost when turned into JSON

1 Answers