Isolate Recipe defaults to prevent modification via instances

With this change, every baked instance holds an isolated copy of the
recipe default attributes of any Container class (e.g., dict or list).
This prevents from affecting the parent recipe, and other (existing or
future) instances, when such fields are modified on an instance.

model_bakery/recipe.py

@@ -1,4 +1,5 @@
 import collections
+import copy
 import itertools
 from typing import (
     Any,
@@ -79,6 +80,8 @@ def _mapping(  # noqa: C901
                     mapping[k] = v.recipe.prepare(_using=_using, **recipe_attrs)
             elif isinstance(v, related):
                 mapping[k] = v.make
+            elif isinstance(v, collections.abc.Container):
+                mapping[k] = copy.deepcopy(v)
 
         mapping.update(new_attrs)
         mapping.update(rel_fields_attrs)

tests/test_recipes.py

@@ -4,6 +4,7 @@
 from random import choice  # noqa
 from unittest.mock import patch
 
+from django.db import connection
 from django.utils.timezone import now
 
 import pytest
@@ -34,6 +35,7 @@
     "blog": "https://joe.example.com",
     "days_since_last_login": 4,
     "birth_time": now(),
+    "data": {"one": 1},
 }
 person_recipe = Recipe(Person, **recipe_attrs)
 user_recipe = Recipe(User)
@@ -68,6 +70,8 @@ def test_flat_model_make_recipe_with_the_correct_attributes(self):
         assert person.appointment == recipe_attrs["appointment"]
         assert person.blog == recipe_attrs["blog"]
         assert person.days_since_last_login == recipe_attrs["days_since_last_login"]
+        assert person.data is not recipe_attrs["data"]
+        assert person.data == recipe_attrs["data"]
         assert person.id is not None
 
     def test_flat_model_prepare_recipe_with_the_correct_attributes(self):
@@ -80,6 +84,8 @@ def test_flat_model_prepare_recipe_with_the_correct_attributes(self):
         assert person.appointment == recipe_attrs["appointment"]
         assert person.blog == recipe_attrs["blog"]
         assert person.days_since_last_login == recipe_attrs["days_since_last_login"]
+        assert person.data is not recipe_attrs["data"]
+        assert person.data == recipe_attrs["data"]
         assert person.id is None
 
     def test_accepts_callable(self):
@@ -171,6 +177,34 @@ def test_defining_recipes_str(self):
         except AttributeError as e:
             pytest.fail(f"{e}")
 
+    def test_recipe_dict_attribute_isolation(self):
+        person1 = person_recipe.make()
+        person2 = person_recipe.make()
+        person2.data["two"] = 2
+        person3 = person_recipe.make()
+
+        # Mutation on instances must have no side effect on their recipe definition,
+        # or on other instances of the same recipe.
+        assert person1.data == {"one": 1}
+        assert person2.data == {"one": 1, "two": 2}
+        assert person3.data == {"one": 1}
+
+    @pytest.mark.skipif(
+        connection.vendor != "postgresql", reason="PostgreSQL specific tests"
+    )
+    def test_recipe_list_attribute_isolation(self):
+        pg_person_recipe = person_recipe.extend(acquaintances=[1, 2, 3])
+        person1 = pg_person_recipe.make()
+        person2 = pg_person_recipe.make()
+        person2.acquaintances.append(4)
+        person3 = pg_person_recipe.make()
+
+        # Mutation on instances must have no side effect on their recipe definition,
+        # or on other instances of the same recipe.
+        assert person1.acquaintances == [1, 2, 3]
+        assert person2.acquaintances == [1, 2, 3, 4]
+        assert person3.acquaintances == [1, 2, 3]
+
 
 @pytest.mark.django_db
 class TestExecutingRecipes: