Dataclasses and schema attribute

[blfpd]

When creating a model with the dataclasses backport, the model doesn’t have the schema() method, but it’s still forbidden to create a model with this attribute name. Is this a desired behaviour?

>>> from pydantic.dataclasses import dataclass
>>> 
>>> @dataclass
... class Card:
...     number: str
... 
>>> card = Card(number="1234")
>>> card.schema()
Traceback (most recent call last):
  File "<input>", line 1, in <module>
    card.schema()
AttributeError: 'Card' object has no attribute 'schema'
>>> card.__pydantic_model__.schema()
Traceback (most recent call last):
  File "<input>", line 1, in <module>
    card.__pydantic_model__.schema()
  File "~/env/lib/python3.6/site-packages/pydantic/main.py", line 402, in schema
    s = model_schema(cls, by_alias=by_alias)
  File "~/env/lib/python3.6/site-packages/pydantic/schema.py", line 204, in model_schema
    model, by_alias=by_alias, model_name_map=model_name_map, ref_prefix=ref_prefix
  File "~/env/lib/python3.6/site-packages/pydantic/schema.py", line 488, in model_process_schema
    model, by_alias=by_alias, model_name_map=model_name_map, ref_prefix=ref_prefix
  File "~/env/lib/python3.6/site-packages/pydantic/schema.py", line 514, in model_type_schema
    f, by_alias=by_alias, model_name_map=model_name_map, ref_prefix=ref_prefix
  File "~/env/lib/python3.6/site-packages/pydantic/schema.py", line 243, in field_schema
    s['default'] = encode_default(field.default)
  File "~/env/lib/python3.6/site-packages/pydantic/schema.py", line 693, in encode_default
    return pydantic_encoder(dft)
  File "~/env/lib/python3.6/site-packages/pydantic/json.py", line 40, in pydantic_encoder
    raise TypeError(f"Object of type '{obj.__class__.__name__}' is not JSON serializable")
TypeError: Object of type '_MISSING_TYPE' is not JSON serializable
>>> 
>>> @dataclass
... class Card:
...     schema: str
... 
Traceback (most recent call last):
  File "<input>", line 1, in <module>
    @dataclass
  File "~/env/lib/python3.6/site-packages/pydantic/dataclasses.py", line 118, in dataclass
    return wrap(_cls)
  File "~/env/lib/python3.6/site-packages/pydantic/dataclasses.py", line 113, in wrap
    return _process_class(cls, init, repr, eq, order, unsafe_hash, frozen, config)
  File "~/env/lib/python3.6/site-packages/pydantic/dataclasses.py", line 77, in _process_class
    cls.__pydantic_model__ = create_model(cls.__name__, __config__=config, __module__=_cls.__module__, **fields)
  File "~/env/lib/python3.6/site-packages/pydantic/main.py", line 562, in create_model
    return type(model_name, (__base__,), namespace)  # type: ignore
  File "~/env/lib/python3.6/site-packages/pydantic/main.py", line 184, in __new__
    validate_field_name(bases, var_name)
  File "~/env/lib/python3.6/site-packages/pydantic/utils.py", line 194, in validate_field_name
    f'Field name "{field_name}" shadows a BaseModel attribute; '
NameError: Field name "schema" shadows a BaseModel attribute; use a different field name with "alias='schema'".
>>> 

[samuelcolvin]

card.__pydantic_model__.schema() should work, I'm not sure why it doesn't. PR welcome to fix that.

Regarding Field name "schema" shadows a BaseModel attribute; use a different field name with "alias='schema' that's harder to fix since the underlying model __pydantic_model__ is a normal pydantic model, so won't play nicely with schema as a field. Maybe we should change the error message, to make more sense in this context.

As mentioned before, perhaps all those methods should have had other names, but it's too late now.