fix: Config.copy_on_model_validation does a deep copy and not a sha…

…llow one

closes pydantic#3641

changes/3641-PrettyWood.md

@@ -0,0 +1 @@
+`Config.copy_on_model_validation\` does a deep copy and not a shallow one

pydantic/main.py

@@ -666,7 +666,7 @@ def __get_validators__(cls) -> 'CallableGenerator':
     def validate(cls: Type['Model'], value: Any) -> 'Model':
         if isinstance(value, cls):
             if cls.__config__.copy_on_model_validation:
-                return value._copy_and_set_values(value.__dict__, value.__fields_set__, deep=False)
+                return value._copy_and_set_values(value.__dict__, value.__fields_set__, deep=True)
             else:
                 return value
 

tests/test_main.py

@@ -1561,12 +1561,28 @@ class Config:
 
     assert t.user is not my_user
     assert t.user.hobbies == ['scuba diving']
-    assert t.user.hobbies is my_user.hobbies  # `Config.copy_on_model_validation` only does a shallow copy
+    assert t.user.hobbies is not my_user.hobbies  # `Config.copy_on_model_validation` does a deep copy
     assert t.user._priv == 13
     assert t.user.password.get_secret_value() == 'hashedpassword'
     assert t.dict() == {'id': '1234567890', 'user': {'id': 42, 'hobbies': ['scuba diving']}}
 
 
+def test_validation_deep_copy():
+    """By default, Config.copy_on_model_validation should do a deep copy"""
+
+    class A(BaseModel):
+        name: str
+
+    class B(BaseModel):
+        list_a: List[A]
+
+    a = A(name='a')
+    b = B(list_a=[a])
+    assert b.list_a == [A(name='a')]
+    a.name = 'b'
+    assert b.list_a == [A(name='a')]
+
+
 @pytest.mark.parametrize(
     'kinds',
     [