caslu

Jason encode when associations not loaded

Hello guys! I’m developing an API only Phoenix project for pet donations, and at the moment i have the following schemas:

User schema:

  schema "users" do
    field :name, :string
    field :email, :string
    field :bio, :string
    field :avatar, :string
    field :website, :string
    field :phone, :string
    field :social_links, {:array, :string}
    field :roles, {:array, Ecto.Enum}, values: [:ADOPTER, :DONOR]
    has_many :pets, Announcements.Pet, foreign_key: :owner_id

    timestamps(type: :utc_datetime)
  end

Pet schema:

  schema "pets" do
    field :name, :string
    field :size, :decimal
    field :bio, :string
    field :photos, {:array, :string}
    field :age, :integer
    field :gender, Ecto.Enum, values: [:MALE, :FEMALE]
    field :species, Ecto.Enum, values: [:DOG, :CAT]
    field :vaccinated, :boolean, default: false
    field :dewormed, :boolean, default: false
    field :neutered, :boolean, default: false
    field :disability, :boolean, default: false
    field :pedigree, :boolean, default: false
    field :weight, :decimal
    belongs_to :user, Accounts.User, foreign_key: :owner_id
    belongs_to :breed, Announcements.Breed, foreign_key: :breed_id

    timestamps(type: :utc_datetime)
  end

and the Breed schema:

  schema "breeds" do
    field :name, :string
    field :temperaments, {:array, :string}
    has_many :pets, Announcements.Pet, foreign_key: :breed_id

    timestamps(type: :utc_datetime)
  end

As you can see, the relations above are pretty simple actually, users can own many pets announces and therefore each pet announcement belongs to a user, each pet belongs to a breed, and this specific breed can own a lot announcements, so another many to one relationship.

The problem is around pets and breeds, when i insert a pet, breed or user everything looks fine, but when i trigger the show action on pets_controller the Jason complains that it’s unable to encode because of NotLoaded Association. I know there's questions similars and i know i could preloadthe breeds association with pets, but the weird fact for me is that Jason does not complain if i don't preload the:userassociation, and when i triggershowaction ofuser_controller` Jason does the encoding pretty well even with not loaded pet associations, so what i want to understand is why this error is happening with only one association.

18 comments

/phoenix #ecto #jason

0 835 18

2024-05-20 15:30:35 UTC

Marked As Solved

D4no0

First of all, ideally you should have a render file where you decide what shape the return will have, it should look the following (this one was generated using mix phx.gen.json Accounts User users name:string age:integer):

defmodule PhoenixTestWeb.UserJSON do
  alias PhoenixTest.Accounts.User

  @doc """
  Renders a list of users.
  """
  def index(%{users: users}) do
    %{data: for(user <- users, do: data(user))}
  end

  @doc """
  Renders a single user.
  """
  def show(%{user: user}) do
    %{data: data(user)}
  end

  defp data(%User{} = user) do
    %{
      id: user.id,
      name: user.name,
      age: user.age
    }
  end
end

There you can dictate what you render, it also decouples your controller from your schema.

As for error you are getting, you cannot render associations that are not preloaded. There are 2 options of doing that: