Fix add_field_serializer_for_reverse_relations clearing validators (#1302)

* Fix add_field_serializer_for_reverse_relations clearing validators

* add test to check that validators are not removed

* compatibility with old python

* fix test default values

* fix coverage and cleanup

---------

Co-authored-by: collerek <collerek@gmail.com>

ormar/models/helpers/relations.py

@@ -5,9 +5,7 @@ from typing import TYPE_CHECKING, Any, List, Optional, Type, Union, cast
 from pydantic import BaseModel, create_model, field_serializer
 from pydantic._internal._decorators import DecoratorInfos
 from pydantic.fields import FieldInfo
-from pydantic_core.core_schema import (
-    SerializerFunctionWrapHandler,
-)
+from pydantic_core.core_schema import SerializerFunctionWrapHandler
 
 import ormar
 from ormar import ForeignKey, ManyToMany
@@ -174,8 +172,8 @@ def add_field_serializer_for_reverse_relations(
                     "ignore", message="Pydantic serializer warnings"
                 )
                 return handler(children)
-        except ValueError as exc:
-            if not str(exc).startswith("Circular reference"):  # pragma: no cover
+        except ValueError as exc:  # pragma: no cover
+            if not str(exc).startswith("Circular reference"):
                 raise exc
 
             result = []
@@ -188,7 +186,18 @@ def add_field_serializer_for_reverse_relations(
         serialize
     )
     setattr(to_model, f"serialize_{related_name}", decorator)
-    DecoratorInfos.build(to_model)
+    # DecoratorInfos.build will overwrite __pydantic_decorators__ on to_model,
+    # deleting the previous decorators. We need to save them and then merge them.
+    prev_decorators = getattr(to_model, "__pydantic_decorators__", DecoratorInfos())
+    new_decorators = DecoratorInfos.build(to_model)
+    prev_decorators.validators.update(new_decorators.validators)
+    prev_decorators.field_validators.update(new_decorators.field_validators)
+    prev_decorators.root_validators.update(new_decorators.root_validators)
+    prev_decorators.field_serializers.update(new_decorators.field_serializers)
+    prev_decorators.model_serializers.update(new_decorators.model_serializers)
+    prev_decorators.model_validators.update(new_decorators.model_validators)
+    prev_decorators.computed_fields.update(new_decorators.computed_fields)
+    setattr(to_model, "__pydantic_decorators__", prev_decorators)
 
 
 def replace_models_with_copy(

tests/test_fastapi/test_relations_with_nested_defaults.py

@@ -97,7 +97,25 @@ async def test_related_with_defaults(sample_data):
                         "year": 2021,
                     }
                 ],
-                "country": {"authors": [{"id": 1}], "id": 1},
+                "country": {
+                    "authors": [
+                        {
+                            "books": [
+                                {
+                                    "author": {"id": 1},
+                                    "id": 1,
+                                    "title": "Bug caused by " "default value",
+                                    "year": 2021,
+                                }
+                            ],
+                            "country": {"id": 1},
+                            "id": 1,
+                            "name": "bug",
+                            "rating": 5,
+                        }
+                    ],
+                    "id": 1,
+                },
                 "id": 1,
                 "name": "bug",
                 "rating": 5,

tests/test_relations/test_reverse_relation_preserves_validator.py

@@ -0,0 +1,48 @@
+from typing import List, Optional, Union
+
+import ormar
+import pytest_asyncio
+from pydantic import field_validator
+
+from tests.lifespan import init_tests
+from tests.settings import create_config
+
+base_ormar_config = create_config()
+
+
+class Author(ormar.Model):
+    ormar_config = base_ormar_config.copy()
+
+    id: int = ormar.Integer(primary_key=True)
+    name: str = ormar.String(max_length=80)
+
+    @field_validator("name", mode="before")
+    @classmethod
+    def validate_name(cls, v: Union[str, List[str]]) -> str:
+        if isinstance(v, list):
+            v = " ".join(v)
+        return v
+
+
+class Post(ormar.Model):
+    ormar_config = base_ormar_config.copy()
+
+    id: int = ormar.Integer(primary_key=True)
+    title: str = ormar.String(max_length=200)
+    author: Optional[Author] = ormar.ForeignKey(Author)
+
+
+create_test_database = init_tests(base_ormar_config)
+
+
+@pytest_asyncio.fixture(scope="function", autouse=True)
+async def cleanup():
+    yield
+    async with base_ormar_config.database:
+        await Post.objects.delete(each=True)
+        await Author.objects.delete(each=True)
+
+
+def test_validator():
+    author = Author(name=["Test", "Author"])
+    assert author.name == "Test Author"