How to use Mixins?

[lovetoburnswhen]

First Check

• I added a very descriptive title to this issue.
• I used the GitHub search to find a similar issue and didn't find it.
• I searched the SQLModel documentation, with the integrated search.
• I already searched in Google "How to X in SQLModel" and didn't find any information.
• I already read and followed all the tutorial in the docs and didn't find an answer.
• I already checked if it is not related to SQLModel but to Pydantic.
• I already checked if it is not related to SQLModel but to SQLAlchemy.

Commit to Help

• I commit to help with one of those options 👆

Example Code

class TimeStampMixin:
    """Provides last created/modified timestamps"""

    created_at: Optional[datetime] = Field(
        sa_column=Column(
            DateTime,
            default=datetime.utcnow,
            nullable=False,
        )
    )

    updated_at: Optional[datetime] = Field(
        sa_column=Column(
            DateTime,
            default=datetime.utcnow,
            onupdate=datetime.utcnow,
        )
    )


class MyModel(SQLModel, TimestampMixin, table=True):
    id: Optional[int] = Field(default=None, primary_key=True)
    name: str

Description

• Utilize mixins that don't necessarily need to subclass SQLModel
  • Perhaps something that resembles @declarative_mixin from SQLAlchemy?

The above example errors with:

AttributeError: type object 'TimeStampMixin' has no attribute '__config__'

Operating System

Linux

Operating System Details

No response

SQLModel Version

0.0.4

Python Version

3.9.0

Additional Context

No response

[elben10]

Try this out

from datetime import datetime
from typing import Optional

from pydantic import BaseModel
from sqlmodel import SQLModel, Column, DateTime, Field, Session, create_engine, select

        
class TimeStampMixin(BaseModel):
    created_at: Optional[datetime] = Field(
        sa_column=Column(
            DateTime,
            default=datetime.utcnow,
            nullable=False,
        )
    )

    updated_at: Optional[datetime] = Field(
        sa_column=Column(
            DateTime,
            default=datetime.utcnow,
            onupdate=datetime.utcnow,
        )
    )
    


class MyModel(SQLModel, TimeStampMixin, table=True):
    id: Optional[int] = Field(default=None, primary_key=True)
    name: str
        
engine = create_engine("sqlite:///database.db")
SQLModel.metadata.create_all(engine)

with Session(bind=engine) as session:
    session.add(MyModel(name="A Name"))
    session.commit()

[lovetoburnswhen]

Try this out

from datetime import datetime
from typing import Optional

from pydantic import BaseModel
from sqlmodel import SQLModel, Column, DateTime, Field, Session, create_engine, select

        
class TimeStampMixin(BaseModel):
    created_at: Optional[datetime] = Field(
        sa_column=Column(
            DateTime,
            default=datetime.utcnow,
            nullable=False,
        )
    )

    updated_at: Optional[datetime] = Field(
        sa_column=Column(
            DateTime,
            default=datetime.utcnow,
            onupdate=datetime.utcnow,
        )
    )
    


class MyModel(SQLModel, TimeStampMixin, table=True):
    id: Optional[int] = Field(default=None, primary_key=True)
    name: str
        
engine = create_engine("sqlite:///database.db")
SQLModel.metadata.create_all(engine)

with Session(bind=engine) as session:
    session.add(MyModel(name="A Name"))
    session.commit()

That works! This also enables a Generic[_T] base class

[vi-klaas]

Why do we need to extend the Mixins from pydantic BaseModel and not SQLModel? Or is both possible? Also, with SQLModel, the definition would be simpler:

class TimeStampMixin(SQLModel):
    created_at: Optional[datetime] = Field(default=datetime.utcnow(), nullable=False)
    updated_at: Optional[datetime] = Field(default_factory=datetime.utcnow, nullable=False)