Programmatic changeset errors

Questions / Help
,
1

Is there a way to programmatically check for the existence of a specific changeset error?

If I am adding an error to the changeset like this:

      Ecto.Changeset.add_error(
        changeset,
        :age,
        "Must be more than 12"
      )

After I get the changeset back from Repo.insert how can I check that this specific error has been added? I want to add special handling for a specific error. I can use Ecto.Changeset.traverse_errors but that would require looking for the string "Must be more than 12" which seems brittle.

2

Default validators use additional keys to specify the type of the validation, you can do the same

{%{}, %{age: :integer}}
|> cast(%{}, [:age])
|> validate_required(:age)
|> add_error(:age, "Must be more than 12", validation: :too_young)

#Ecto.Changeset<
  action: nil,
  changes: %{},
  errors: [
    age: {"Must be more than 12", [validation: :too_young]},
    age: {"can't be blank", [validation: :required]}
  ],
  data: %{},
  valid?: false
>
1 Like
3

Hmmm, so I’d have a check like this:

case insert(changest) do
  {:ok, data} -> handle_data(data)
  {:error, changeset} ->
    if too_young_error?(changeset) do
      special_handling(changeset)
    else
      {:error, changeset}
    end
end

...
def too_young_error?(changeset) do
  Enum.any(changeset.errors, fn {key, {_error_message, keys} ->
    Keyword.get(keys, :validation) == :too_young
  end)
end

This is better than checking for the error message, but it would be nice to have a more straightforward way to do this check.

1 Like