Is there any alternatives to Ecto.Model.Callbacks?

Questions / Help
1

I need to convert some data after every query.
ex) Change id to negative

I can add converting function for every query, but it’s pretty heavy when loading that model with preload.

defmodule MyApp.Model do
  use Ecto.Schema
  alias MyApp.Repo

  schema "models" do
  end

  def get(id) do
    __MODULE__
    |> Repo.get(id)
    |> convert_id_to_negative()
  end

  def list() do
    __MODULE__
    |> Repo.all()
    |> Enum.map(&convert_id_to_negative/1)
  end

  def convert_id_to_negative(%__MODULE__{id: id} = struct) do
    %__MODULE__{struct | id: -id}
  end
end

defmodule MyApp.ParentModel do
  use Ecto.Schema
  alias MyApp.Repo

  schema "parent_models" do
    has_many :models, MyApp.Model
  end

  def get(id) do
    __MODULE__
    |> Repo.get(id)
    |> Repo.preload(:models)
    # missing converting
  end
end

I found old codes that can be useful for this situation, like after_load/2.

But it’s gone now. Is there any alternatives to this callback functions?

1 Like
2

Adding a function is the way to go. If you load that schema with preloads you can look into preload functions to not need to traverse the nested results.

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