Allow associations to be cast/put inside of embedded schema changesets (

#4504)

lib/ecto/changeset.ex

@@ -1197,16 +1197,7 @@ defmodule Ecto.Changeset do
 
   """
   @spec cast_assoc(t, atom, Keyword.t()) :: t
-  def cast_assoc(changeset, name, opts \\ [])
-
-  def cast_assoc(%Changeset{data: %{} = data}, _name, _opts)
-      when not is_map_key(data, :__meta__) do
-    raise ArgumentError,
-          "cast_assoc/3 cannot be used to cast associations into embedded schemas or schemaless changesets. " <>
-            "Please modify the association independently."
-  end
-
-  def cast_assoc(changeset, name, opts) when is_atom(name) do
+  def cast_assoc(changeset, name, opts \\ []) when is_atom(name) do
     cast_relation(:assoc, changeset, name, opts)
   end
 
@@ -2104,16 +2095,7 @@ defmodule Ecto.Changeset do
 
   """
   @spec put_assoc(t, atom, term, Keyword.t()) :: t
-  def put_assoc(changeset, name, value, opts \\ [])
-
-  def put_assoc(%Changeset{data: %{} = data}, _name, _value, _opts)
-      when not is_map_key(data, :__meta__) do
-    raise ArgumentError,
-          "put_assoc/4 cannot be used to put associations into embedded schemas or schemaless changesets. " <>
-            "Please modify the association independently."
-  end
-
-  def put_assoc(%Changeset{} = changeset, name, value, opts) do
+  def put_assoc(%Changeset{} = changeset, name, value, opts \\ []) do
     put_relation(:assoc, changeset, name, value, opts)
   end
 

lib/ecto/schema.ex

@@ -549,13 +549,8 @@ defmodule Ecto.Schema do
   `@primary_key` attribute.
 
   `belongs_to/3` associations may be defined inside of
-  embedded schemas. However, they are essentially read-only.
-  This means you may preload the associations but you may
-  not modify them by using `Ecto.Changeset.cast_assoc/3`
-  or `Ecto.Changeset.put_assoc/4`. If you would like to
-  modify the associations of an embedded schema, you must
-  change them independently. Associations nested inside of
-  embedded schemas will also not be persisted to the database
+  embedded schemas. However, any association nested inside
+  of an embedded schema won't be persisted to the database
   when calling `c:Ecto.Repo.insert/2` or `c:Ecto.Repo.update/2`.
   """
   defmacro embedded_schema(do: block) do

test/ecto/changeset/belongs_to_test.exs

@@ -49,14 +49,6 @@ defmodule Ecto.Changeset.BelongsToTest do
     end
   end
 
-  defmodule Embed do
-    use Ecto.Schema
-
-    embedded_schema do
-      belongs_to :profile, Profile
-    end
-  end
-
   defp cast(schema, params, assoc, opts \\ []) do
     schema
     |> Changeset.cast(params, ~w())
@@ -328,14 +320,6 @@ defmodule Ecto.Changeset.BelongsToTest do
     assert changeset.valid?
   end
 
-  test "cast belongs_to from embedded schema" do
-    msg = ~r"cast_assoc/3 cannot be used to cast associations into embedded schemas"
-
-    assert_raise ArgumentError, msg, fn ->
-      cast(%Embed{}, %{"profile" => %{"name" => "michal"}}, :profile)
-    end
-  end
-
   ## Change
 
   test "change belongs_to" do
@@ -503,15 +487,6 @@ defmodule Ecto.Changeset.BelongsToTest do
     refute Map.has_key?(changeset.changes, :profile)
   end
 
-  test "put_assoc/4 from embedded schema" do
-    msg = ~r"put_assoc/4 cannot be used to put associations into embedded schema"
-    base_changeset = Changeset.change(%Embed{})
-
-    assert_raise ArgumentError, msg, fn ->
-      Changeset.put_assoc(base_changeset, :profile, %{name: "michal"})
-    end
-  end
-
   test "put_assoc/4 with empty" do
     # On unloaded
     changeset =