After 'mix phx.gen.json Items Item items name:string description:string info:string amount:integer factor:float type:string --no-context --no-schema'.

lib/generic_rest_server_web/controllers/changeset_json.ex

@@ -0,0 +1,25 @@
+defmodule GenericRestServerWeb.ChangesetJSON do
+  @doc """
+  Renders changeset errors.
+  """
+  def error(%{changeset: changeset}) do
+    # When encoded, the changeset returns its errors
+    # as a JSON object. So we just pass it forward.
+    %{errors: Ecto.Changeset.traverse_errors(changeset, &translate_error/1)}
+  end
+
+  defp translate_error({msg, opts}) do
+    # You can make use of gettext to translate error messages by
+    # uncommenting and adjusting the following code:
+
+    # if count = opts[:count] do
+    #   Gettext.dngettext(GenericRestServerWeb.Gettext, "errors", msg, msg, count, opts)
+    # else
+    #   Gettext.dgettext(GenericRestServerWeb.Gettext, "errors", msg, opts)
+    # end
+
+    Enum.reduce(opts, msg, fn {key, value}, acc ->
+      String.replace(acc, "%{#{key}}", fn _ -> to_string(value) end)
+    end)
+  end
+end