"Dataclasses with Declarative Table" with inheritance not working as expected

Describe the bug Using inheritance with dataclasses I get an error.

Expected behavior

The ability to use some base classes with the “Dataclasses with Declarative Table” approach.

To Reproduce

import dataclasses
from typing import TYPE_CHECKING

from sqlalchemy import Column, Integer, String, Table
from sqlalchemy.orm import registry

mapper_registry = registry()


# From Mike Bayer's "Building the app" talk, adapted to use dataclasses style mapping
# https://speakerdeck.com/zzzeek/building-the-app
@dataclasses.dataclass
class SurrogatePK:
    """
    A mixin that adds a surrogate integer 'primary key' column named ``id``
    to any declarative-mapped dataclasses.
    """

    if TYPE_CHECKING:
        # populated by the sqlalchemy at mapping time, defined here to help IDEs only
        __table__: Table

    __sa_dataclass_metadata_key__ = "sa"

    id: int = dataclasses.field(
        init=False,
        metadata={"sa": Column(Integer, primary_key=True)},
    )


# https://docs.sqlalchemy.org/en/14/orm/mapping_styles.html#example-two-dataclasses-with-declarative-table
@mapper_registry.mapped
@dataclasses.dataclass
class User(SurrogatePK):
    __tablename__ = "user"
    full_name: str = dataclasses.field(
        metadata={"sa": Column(String, primary_key=True)},
    )

Error

---------------------------------------------------------------------------
AttributeError                            Traceback (most recent call last)
<ipython-input-1-c9dca729fc03> in <module>
     32 @mapper_registry.mapped
     33 @dataclasses.dataclass
---> 34 class User(SurrogatePK):
     35     __tablename__ = "user"
     36     full_name: str = dataclasses.field(

~/Development/Personal/fastapi-postgres/.venv/lib/python3.9/site-packages/sqlalchemy/orm/decl_api.py in mapped(self, cls)
    570 
    571         """
--> 572         _as_declarative(self, cls, cls.__dict__)
    573         return cls
    574 

~/Development/Personal/fastapi-postgres/.venv/lib/python3.9/site-packages/sqlalchemy/orm/decl_base.py in _as_declarative(registry, cls, dict_)
    123     # args passed separately.
    124 
--> 125     return _MapperConfig.setup_mapping(registry, cls, dict_, None, {})
    126 
    127 

~/Development/Personal/fastapi-postgres/.venv/lib/python3.9/site-packages/sqlalchemy/orm/decl_base.py in setup_mapping(cls, registry, cls_, dict_, table, mapper_kw)
    174             cfg_cls = _ClassScanMapperConfig
    175 
--> 176         return cfg_cls(registry, cls_, dict_, table, mapper_kw)
    177 
    178     def __init__(self, registry, cls_):

~/Development/Personal/fastapi-postgres/.venv/lib/python3.9/site-packages/sqlalchemy/orm/decl_base.py in __init__(self, registry, cls_, dict_, table, mapper_kw)
    296         self._setup_declared_events()
    297 
--> 298         self._scan_attributes()
    299 
    300         with mapperlib._CONFIGURE_MUTEX:

~/Development/Personal/fastapi-postgres/.venv/lib/python3.9/site-packages/sqlalchemy/orm/decl_base.py in _scan_attributes(self)
    362 
    363             if not class_mapped and base is not cls:
--> 364                 self._produce_column_copies(attributes_for_class, base)
    365 
    366             for name, obj in attributes_for_class(base):

~/Development/Personal/fastapi-postgres/.venv/lib/python3.9/site-packages/sqlalchemy/orm/decl_base.py in _produce_column_copies(self, attributes_for_class, base)
    497         for name, obj in attributes_for_class(base):
    498             if isinstance(obj, Column):
--> 499                 if getattr(cls, name) is not obj:
    500                     # if column has been overridden
    501                     # (like by the InstrumentedAttribute of the

AttributeError: type object 'User' has no attribute 'id'

Versions.

• OS: macOS 11.0.1
• Python: 3.9
• SQLAlchemy: 1.4.0b2.dev0dev 7bdb1f3
• Database: PostgreSQL
• DBAPI: asyncpg

Additional context

Have a nice day!

[zzzeek]

thanks for testing! thought I had merged it, merged now.

[michaeloliverx]

Actually I just tested with that patch file, can confirm it works now:

import dataclasses
from datetime import datetime
from typing import TYPE_CHECKING

from sqlalchemy import Column, DateTime, Integer, String, Table
from sqlalchemy.orm import registry

mapper_registry = registry()


@dataclasses.dataclass
class SQLAlchemyDataclass:
    if TYPE_CHECKING:
        __table__: Table
    __sa_dataclass_metadata_key__ = "sa"


@dataclasses.dataclass
class SurrogatePK:
    __sa_dataclass_metadata_key__ = "sa"
    id: int = dataclasses.field(
        init=False,
        metadata={"sa": Column(Integer, primary_key=True)},
    )


@dataclasses.dataclass
class TimeStampMixin:
    __sa_dataclass_metadata_key__ = "sa"
    created_at: datetime = dataclasses.field(
        init=False, metadata={"sa": Column(DateTime, default=datetime.utcnow)}
    )
    updated_at: datetime = dataclasses.field(
        init=False,
        metadata={
            "sa": Column(DateTime, default=datetime.utcnow, onupdate=datetime.utcnow)
        },
    )


@mapper_registry.mapped
@dataclasses.dataclass
class User(SQLAlchemyDataclass, SurrogatePK, TimeStampMixin):
    __tablename__ = "user"

    auth0_id: str = dataclasses.field(
        metadata={"sa": Column(String, primary_key=True)},
    )


User(auth0_id="auth0-id")