Getting a better understanding of preload

Phoenix Forum Questions / Help
,
1

Thanks for stopping by. I was hoping to get some help in better understanding how we are supposed to preload a field when doing a query since that is an error I’m running into.

The query I’m trying to run which is causing #Ecto.Association.NotLoaded<association :owner is not loaded> and #Ecto.Association.NotLoaded<association :category is not loaded> is

  def products(user) do
    from(p in Product, where: p.owner == ^user.id)
    |> Repo.all()
    |> Repo.preload(category: :products)
    |> Repo.preload(owner: :products)
  end

My schema tables look like this:
Products

  schema "products" do
    field(:description, :string)
    field(:name, :string)
    field(:price, :decimal)
    belongs_to(:owner, Amoramor.Accounts.User)
    belongs_to(:category, Amoramor.Shops.Category)

    timestamps()
  end

User

  schema "users" do
    field(:email, :string)
    field(:is_admin, :boolean, default: false)
    field(:password_hash, :string)
    field(:password, :string, virtual: true)
    has_many(:products, Amoramor.Shops.Product)

    timestamps()
  end

Category

  schema "categories" do
    field(:name, :string)
    belongs_to(:owner, Amoramor.Accounts.User)
    has_many(:products, Amoramor.Shops.Product)

    timestamps()
  end

Last my product schema when I migrated the table was

  use Ecto.Migration

  def change do
    create table(:products) do
      add(:name, :string, null: false)
      add(:description, :string, null: false)
      add(:price, :decimal, null: false)
      add(:category_id, references(:categories, on_delete: :delete_all), null: false)
      add(:owner_id, references(:users, on_delete: :delete_all), null: false)

      timestamps()
    end

Is there something I’m not understanding? Thank you in advance for explaining how we should approach association/preload.

2

Figured out what was the cause. I don’t need to use a preload but the problem was I had in my Resolver this function

  def products(_, _, %{context: %{current_user: user}}) do
    case(Shops.products(user)) do
      {:ok, products} -> {:ok, products}
  end

which was causing that problem. It was fixed once I removed the case statement and instead did:

 def products(_, _, %{context: %{current_user: user}}) do
     {:ok, Shops.products(user)}
  end`