Why Changeset.change is skipping validation in Elixir?

Question

This is a simple function used to insert or update some data. If user data is already in db i simply update it, otherwise i insert a new row with data. Everything works fine but i have a problem with validation. Changeset definition:

  def changeset(struct, params \\ %{}) do
    struct
    |> cast(params, [:name, :surname, :user_id])
    |> validate_required([:name, :surname, :user_id])
    |> unique_constraint(:user_id)
  end

validate_required is currently working only during insert and not during update.

  def add_or_change(user_id, new_data) do
    data_from_db = data_by_user_id (user_id)
    case data_from_db do
      nil ->
        Data.changeset(%Data{}, new_data)
        |> Repo.insert()

      _ ->
        Changeset.change(data_from_db, new_data)
        |> Repo.update()
    end
  end

If i try to insert "" as :name value, i get an error (can't be blank) as expected. However if i'm updating an existing row with "" as :name value, changeset does not pass through validation and my db is updated improperly. How to force validation also on change, before Repo.update()??

Aleksei Matiushkin · Accepted Answer · 2017-11-30 11:58:07Z

1

According to the doc: Ecto.Changeset/2 is meant for internal data changes, so it bypasses validations:

The function is meant for working with data internal to the application. Because of that neither validation nor casting is performed. This means change/2 expects the keys in the changes map or keyword to be atoms.

You should use Ecto.Changeset.cast/4 to apply the validations, and then update if it is valid.

edited Nov 30, 2017 at 11:58

Aleksei Matiushkin

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answered Nov 30, 2017 at 10:38

Kernael

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Comments

notriddle · Accepted Answer · 2017-12-12 05:00:32Z

1

Don't use this:

    Changeset.change(data_from_db, new_data)

Just run the same function you were already using:

    Data.changeset(data_from_db, new_data)

By the way, you can actually simplify this function a lot:

  def add_or_change(user_id, new_data) do
    (data_by_user_id(user_id) || %Data{})
    |> Data.changeset(new_data)
    |> Repo.insert_or_update()
  end

answered Dec 12, 2017 at 5:00

notriddle

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