Reusable embeds in `use Params.Schema, %{}`

[astery]

Just as suggestion or maybe I missing something and this can be already achieved:

defmodule SomeIdentityParams do
  use Params.Schema
  import App.Params.Helpers

  @fields ~w(id code)
  schema do
    field :id, :id
    field :code, :string
    # more here
  end

  def changeset(changeset, params) do
    cast(changeset, params, @fields)
    |> at_least_one_should_be_present([:id, :code])
  end
end

# this one looks fine
defmodule SomeControllerParams do
  use Params.Schema
  @fields ~w(tarif_id some_identity)a

  schema do
    field :tarif_id, :id
    embeds_one :some_identity, SomeIdentityParams
  end

  def changeset(cs, params) do
    cast(cs, params, @fields)
    |> validate_required(@fields)
    |> cast_embed(:passenger, required: true)
  end
end

# but it can be much shorter
defmodule SomeControllerParams do
  use Params.Schema, %{
    tarif_id: :id,
    some_identity: SomeIdentityParams
  }
end

[vic]

Hey, using SomeIdentityParams directly would be nice, could you provide a PR? The only thing would be to check if the symbol resembles a module (ie its capitalized) then use embeds_one for it.

[astery]

Ok, I will try it in this week.

[moxley]

The challenge is that it is difficult to differentiate between an Ecto type and an Ecto schema.

Using your example, right now, params supports something like this:

  use Params.Schema, %{
    tarif_id: :id,
    some_identity: Ecto.UUID
  }

Ecto.UUID is an Ecto type, not a schema.

So if you were to assign SomeIdentityParams to :some_identity, how would params know it's a schema and not a type? If this was evaluated at runtime, it would be easy: call Kernel.function_exported?(SomeIdentityParams, :__schema__, 1) to discover that SomeIdentityParams is a schema. But it's not evaluated at runtime. It's evaluated at compile time. SomeIdentityParams is not loaded at compile time, and therefore the __schema__/1 function will not be exported.