fixed casting empty embedded schemas with use_parent_field_for_type

Author: dimakula

lib/polymorphic_embed.ex

@@ -172,9 +172,6 @@ defmodule PolymorphicEmbed do
       {:ok, nil} when not required ->
         Ecto.Changeset.put_change(changeset, field, nil)
 
-      {:ok, map} when map == %{} and not array? ->
-        changeset
-
       {:ok, params_for_field} when array? ->
         create_sort_default = fn -> sort_create(Enum.into(cast_opts, %{}), field_opts) end
         params_for_field = apply_sort_drop(params_for_field, sort, drop, create_sort_default)

test/polymorphic_embed_test.exs

@@ -228,6 +228,49 @@ defmodule PolymorphicEmbedTest do
              insert_result
   end
 
+  test "infer type from parent field and cast an empty embed" do
+    generator = :polymorphic
+    reminder_module = get_module(Reminder, generator)
+
+    reminder_attrs = %{
+      date: DateTime.utc_now(),
+      text: "This is a reminder #{generator}",
+      type: "not_provided",
+      channel4: %{}
+    }
+
+    insert_result =
+      struct(reminder_module)
+      |> reminder_module.changeset(reminder_attrs)
+      |> Repo.insert()
+
+    assert {:ok, %{id: id, channel4: %PolymorphicEmbed.Channel.NotProvided{}}} =
+             insert_result
+
+    assert %{channel4: %PolymorphicEmbed.Channel.NotProvided{}} = Repo.get!(reminder_module, id)
+  end
+
+  test "cannot cast an empty embed when no type can be inferred" do
+    generator = :polymorphic
+    reminder_module = get_module(Reminder, generator)
+
+    reminder_attrs = %{
+      date: DateTime.utc_now(),
+      text: "This is a reminder #{generator}",
+      channel2: %{}
+    }
+
+    insert_result =
+      struct(reminder_module)
+      |> reminder_module.changeset(reminder_attrs)
+      |> Repo.insert()
+
+    assert {:error, changeset} = insert_result
+
+    assert changeset.errors == [channel2: {"is invalid", []}]
+    refute changeset.valid?
+  end
+
   test "validations before casting polymorphic embed still work" do
     for generator <- @generators do
       reminder_module = get_module(Reminder, generator)

test/support/models/polymorphic/channel/not_provided.ex

@@ -0,0 +1,11 @@
+defmodule PolymorphicEmbed.Channel.NotProvided do
+  use Ecto.Schema
+  import Ecto.Changeset
+
+  embedded_schema do
+  end
+
+  def changeset(struct, attrs) do
+    cast(struct, attrs, [])
+  end
+end

test/support/models/polymorphic/reminder.ex

@@ -45,7 +45,8 @@ defmodule PolymorphicEmbed.Reminder do
     polymorphic_embeds_one(:channel4,
       types: [
         sms: PolymorphicEmbed.Channel.SMS,
-        email: PolymorphicEmbed.Channel.Email
+        email: PolymorphicEmbed.Channel.Email,
+        not_provided: PolymorphicEmbed.Channel.NotProvided
       ],
       on_replace: :update,
       use_parent_field_for_type: :type