How to traverse and translate nested errors

[Vladislav Shcherbin]

For example, we have Faculties and Specialities. Each Faculty has many Specialities.

If we insert Faculties and Specialities using Ecto 2.0 and have nested errors (in Specialities), how can we traverse and return translated errors?

My current code was:

changeset = Faculty.changeset(%Faculty{}, attrs["data"], :specialities, [])

case Repo.insert(changeset) do
  {:ok, _model} -> {:reply, :ok, socket}
  {:error, changeset} ->
    {:reply, {:error, %{errors: translate_errors(changeset)}}, socket}
end

defp translate_errors(changeset) do
  Ecto.Changeset.traverse_errors(changeset, &translate_error/1)
end

[José Valim]

That's it. You need to make sure to import YourApp.ErrorHelpers or reference the translate_error function in it.

José Valim

www.plataformatec.com.br

Skype: jv.ptec

Founder and Director of R&D

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[Vladislav Shcherbin]

It works, but the problem is - how to get nested errors. Let me explain:

Imagine, we have two models: Faculty, Speciality

Faculty
simple model with one required field(title), length >= 6

defmodule Universities.Faculty do
  use Universities.Web, :model

  schema "faculties" do
    field :title, :string
  
    timestamps
  
    has_many :specialities, Universities.Speciality
  end
  
  def changeset(model, params, assoc, opts \\ []) do
    model
    |> cast(params, [:title])
    |> cast_assoc(assoc, opts)
    |> validate_required([:title])
    |> validate_length(:title, min: 6)
  end
end

Speciality
simple model with one required field(title), length >= 10

defmodule Universities.Speciality do
  use Universities.Web, :model

  schema "specialities" do
    field :title, :string

    timestamps

    belongs_to :faculty, Universities.Faculty
  end

  def changeset(model, params \\ %{}) do
    model
    |> cast(params, [:faculty_id, :title])
    |> validate_required([:title])
    |> validate_length(:title, min: 10)
  end
end

Faculty can have many Specialities.

I need to validate and send response with errors if invalid.

Cases
1. Insert single Faculty and no Specialities, valid one

changeset = Faculty.changeset(%Faculty{}, %{title: "Faculty title"}, :specialities, [])

Valid, no errors.

2. Insert single Faculty and no Specialities, invalid one

changeset = Faculty.changeset(%Faculty{}, %{title: "Fac"}, :specialities, [])

Invalid, length error. So, I traverse errors and send response:

%{errors: Ecto.Changeset.traverse_errors(changeset, &translate_error/1)}

Client receives:

errors = {
  title: "should be at least 6 character(s)"
}

Works great.

3. Insert single Faculty and some Specialities, valid one's

changeset = Faculty.changeset(%Faculty{}, %{title: "Faculty", specialities: [
  %{title: "Speciality one"},
  %{title: "Speciality two"}
]}, :specialities, [])

Valid, no errors

4. [The problem one] Insert single Faculty and some Specialities, invalid one's

changeset = Faculty.changeset(%Faculty{}, %{title: "Faculty", specialities: [
  %{title: "Short one"},
  %{title: "Speciality two"}
]}, :specialities, [])

Invalid, first Speciality length error. If I use the same traverse function:

%{errors: Ecto.Changeset.traverse_errors(changeset, &translate_error/1)}

I will get:

%{errors: %{specialities: [%{}, %{}]}}

So, nested errors are not shown.

The expected output is:

errors = {
  specialities: [
    {
      title: "should be at least 10 character(s)"
    }
  ]
}

That's why the question:

How to traverse and send the output with translated errors in it?

[José Valim]

Can you provide a sample app that reproduces the error? Or it could even be a failing test case to Ecto's suite. We have tests in Ecto that ensures your exact use case works as expected, so something else is likely happening.

José Valim

www.plataformatec.com.br

Skype: jv.ptec

Founder and Director of R&D

To view this discussion on the web visit https://groups.google.com/d/msgid/elixir-ecto/5df84c52-e620-4a61-aadc-0920e6f6d3be%40googlegroups.com.

[José Valim]

Here is an example: https://github.com/elixir-lang/ecto/blob/6464da626276073495a8dcb61d37b3baafcde834/test/ecto/changeset/embedded_test.exs#L697

[Vladislav Shcherbin]

Yes, I recreated a new app and the same code worked.

So, I used deps.clean and deps.get and it worked in my app.

So strange, it didn't work the whole day, only reinstalling deps helped.

Huge thank you!