Add support for partial model validation

changes/3179-lsapan.md

@@ -0,0 +1 @@
+Add support for partial model validation

docs/usage/model_config.md

@@ -115,6 +115,9 @@ not be included in the model schemas. **Note**: this means that attributes on th
 **`copy_on_model_validation`**
 : whether or not inherited models used as fields should be reconstructed (copied) on validation instead of being kept untouched (default: `True`)
 
+**`partial`**
+: whether or not the model should allow required fields to be omitted. Useful when working with CRUD operations, and you need to use an existing model for a PATCH operation. (default: `False`)
+
 ## Change behaviour globally
 
 If you wish to change the behaviour of _pydantic_ globally, you can create your own custom `BaseModel`

pydantic/config.py

@@ -62,6 +62,7 @@ class BaseConfig:
     json_dumps: Callable[..., str] = json.dumps
     json_encoders: Dict[Type[Any], AnyCallable] = {}
     underscore_attrs_are_private: bool = False
+    partial: bool = False
 
     # Whether or not inherited models as fields should be reconstructed as base model
     copy_on_model_validation: bool = True

pydantic/main.py

@@ -756,6 +756,20 @@ def update_forward_refs(cls, **localns: Any) -> None:
         for f in cls.__fields__.values():
             update_field_forward_refs(f, globalns=globalns, localns=localns)
 
+    @classmethod
+    def partial_model(cls: Type['Model']) -> Type['Model']:
+        """
+        Create a version of the model that is suitable for partial validation.
+        Useful when working with CRUD operations, and you need to use an
+        existing model for a PATCH operation.
+        """
+
+        class PartialModel(cls):  # type: ignore
+            class Config(cls.Config):  # type: ignore
+                partial = True
+
+        return PartialModel
+
     def __iter__(self) -> 'TupleGenerator':
         """
         so `dict(model)` works
@@ -978,6 +992,9 @@ def validate_model(  # noqa: C901 (ignore complexity)
             using_name = True
 
         if value is _missing:
+            if config.partial:
+                continue
+
             if field.required:
                 errors.append(ErrorWrapper(MissingError(), loc=field.alias))
                 continue

tests/test_edge_cases.py

@@ -1892,3 +1892,17 @@ class Config:
             arbitrary_types_allowed = True
 
     assert Model().x == Foo()
+
+
+def test_config_partial():
+    class Foo(BaseModel):
+        a: str = Field(...)
+        b: str = Field(...)
+
+    Bar = Foo.partial_model()
+
+    assert Foo.Config.partial is False
+    assert Bar.Config.partial is True
+
+    b = Bar(a='x')
+    assert b.dict(exclude_unset=True) == {'a': 'x'}