Ecto.Changeset.traverse_errors

You're seeing just the function traverse_errors, go back to Ecto.Changeset module for more information.
Link to this function

traverse_errors(changeset, msg_func)

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Specs

traverse_errors(
  t(),
  (error() -> String.t()) | (t(), atom(), error() -> String.t())
) :: %{required(atom()) => [String.t() | map()]}

Traverses changeset errors and applies the given function to error messages.

This function is particularly useful when associations and embeds are cast in the changeset as it will traverse all associations and embeds and place all errors in a series of nested maps.

A changeset is supplied along with a function to apply to each error message as the changeset is traversed. The error message function receives an error tuple {msg, opts}, for example:

{"should be at least %{count} characters", [count: 3, validation: :length, min: 3]}

Examples

iex> traverse_errors(changeset, fn {msg, opts} ->
...>   Enum.reduce(opts, msg, fn {key, value}, acc ->
...>     String.replace(acc, "%{#{key}}", to_string(value))
...>   end)
...> end)
%{title: ["should be at least 3 characters"]}

Optionally function can accept three arguments: changeset, field and error tuple {msg, opts}. It is useful whenever you want to extract validations rules from changeset.validations to build detailed error description.