Support Field in dataclass + 'metadata' kwarg of `dataclasses.f…

…ield`

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changes/2384-PrettyWood.md

@@ -0,0 +1 @@
+Improve field declaration for _pydantic_ `dataclass` by allowing the usage of _pydantic_ `Field` or `'metadata'` kwarg of `dataclasses.field`

docs/examples/dataclasses_default_schema.py

@@ -1,5 +1,7 @@
 import dataclasses
-from typing import List
+from typing import List, Optional
+
+from pydantic import Field
 from pydantic.dataclasses import dataclass
 
 
@@ -8,6 +10,11 @@ class User:
     id: int
     name: str = 'John Doe'
     friends: List[int] = dataclasses.field(default_factory=lambda: [0])
+    age: Optional[int] = dataclasses.field(
+        default=None,
+        metadata=dict(title='The age of the user', description='do not lie!')
+    )
+    height: Optional[int] = Field(None, title='The height in cm', ge=50, le=300)
 
 
 user = User(id='42')

pydantic/dataclasses.py

@@ -3,14 +3,14 @@
 from .class_validators import gather_all_validators
 from .error_wrappers import ValidationError
 from .errors import DataclassTypeError
-from .fields import Required
+from .fields import Field, FieldInfo, Required, Undefined
 from .main import create_model, validate_model
 from .typing import resolve_annotations
 from .utils import ClassAttribute
 
 if TYPE_CHECKING:
     from .main import BaseConfig, BaseModel  # noqa: F401
-    from .typing import CallableGenerator
+    from .typing import CallableGenerator, NoArgAnyCallable
 
     DataclassT = TypeVar('DataclassT', bound='Dataclass')
 
@@ -103,7 +103,11 @@ def _process_class(
     def _pydantic_post_init(self: 'Dataclass', *initvars: Any) -> None:
         if post_init_original is not None:
             post_init_original(self, *initvars)
-        d, _, validation_error = validate_model(self.__pydantic_model__, self.__dict__, cls=self.__class__)
+
+        # We need to remove `FieldInfo` values since they are not valid as input
+        # It's ok since they are obviously the default values
+        input_data = {k: v for k, v in self.__dict__.items() if not isinstance(v, FieldInfo)}
+        d, _, validation_error = validate_model(self.__pydantic_model__, input_data, cls=self.__class__)
         if validation_error:
             raise validation_error
         object.__setattr__(self, '__dict__', d)
@@ -144,22 +148,30 @@ def _pydantic_post_init(self: 'Dataclass', *initvars: Any) -> None:
     )
     cls.__processed__ = ClassAttribute('__processed__', True)
 
-    fields: Dict[str, Any] = {}
+    field_definitions: Dict[str, Any] = {}
     for field in dataclasses.fields(cls):
+        default: Any = Undefined
+        default_factory: Optional['NoArgAnyCallable'] = None
+        field_info: FieldInfo
 
-        if field.default != dataclasses.MISSING:
-            field_value = field.default
+        if field.default is not dataclasses.MISSING:
+            default = field.default
         # mypy issue 7020 and 708
-        elif field.default_factory != dataclasses.MISSING:  # type: ignore
-            field_value = field.default_factory()  # type: ignore
+        elif field.default_factory is not dataclasses.MISSING:  # type: ignore
+            default_factory = field.default_factory  # type: ignore
+        else:
+            default = Required
+
+        if isinstance(default, FieldInfo):
+            field_info = default
         else:
-            field_value = Required
+            field_info = Field(default=default, default_factory=default_factory, **field.metadata)
 
-        fields[field.name] = (field.type, field_value)
+        field_definitions[field.name] = (field.type, field_info)
 
     validators = gather_all_validators(cls)
     cls.__pydantic_model__ = create_model(
-        cls.__name__, __config__=config, __module__=_cls.__module__, __validators__=validators, **fields
+        cls.__name__, __config__=config, __module__=_cls.__module__, __validators__=validators, **field_definitions
     )
 
     cls.__initialised__ = False

tests/test_dataclasses.py

@@ -429,7 +429,7 @@ class User:
     assert fields['id'].default is None
 
     assert fields['aliases'].required is False
-    assert fields['aliases'].default == {'John': 'Joey'}
+    assert fields['aliases'].default_factory() == {'John': 'Joey'}
 
 
 def test_default_factory_singleton_field():
@@ -456,6 +456,10 @@ class User:
         name: str = 'John Doe'
         aliases: Dict[str, str] = dataclasses.field(default_factory=lambda: {'John': 'Joey'})
         signup_ts: datetime = None
+        age: Optional[int] = dataclasses.field(
+            default=None, metadata=dict(title='The age of the user', description='do not lie!')
+        )
+        height: Optional[int] = pydantic.Field(None, title='The height in cm', ge=50, le=300)
 
     user = User(id=123)
     assert user.__pydantic_model__.schema() == {
@@ -466,11 +470,21 @@ class User:
             'name': {'title': 'Name', 'default': 'John Doe', 'type': 'string'},
             'aliases': {
                 'title': 'Aliases',
-                'default': {'John': 'Joey'},
                 'type': 'object',
                 'additionalProperties': {'type': 'string'},
             },
             'signup_ts': {'title': 'Signup Ts', 'type': 'string', 'format': 'date-time'},
+            'age': {
+                'title': 'The age of the user',
+                'description': 'do not lie!',
+                'type': 'integer',
+            },
+            'height': {
+                'title': 'The height in cm',
+                'minimum': 50,
+                'maximum': 300,
+                'type': 'integer',
+            },
         },
         'required': ['id'],
     }