How should I declare enums in SQLAlchemy using mapped_column (to enable type hinting)? – Sqlalchemy

The Problem:

How can I declare enums in SQLAlchemy version 2 using mapped_column to enable type hinting and avoid errors like 'ENUM' object has no attribute '__mro__' during class construction?

The Solutions:

Solution 1: {title}

To declare enums in SQLAlchemy using `mapped_column` (to enable type hinting), you can use the following approach:

from typing import Literal
from typing import get_args
from sqlalchemy import Enum
from sqlalchemy.orm import DeclarativeBase
from sqlalchemy.orm import Mapped
from sqlalchemy.orm import mapped_column

CampaignStatus = Literal["activated", "deactivated"]

class Base(DeclarativeBase):
    pass

class Campaign(Base):
    __tablename__ = "campaign"
    id: Mapped[int] = mapped_column(primary_key=True, autoincrement=True)
    status: Mapped[CampaignStatus] = mapped_column(Enum(
        *get_args(CampaignStatus),
        name="campaignstatus",
        create_constraint=True,
        validate_strings=True,
    ))

In this solution, we first create a CampaignStatus enum using the Literal type from the typing module. Then, we define a Campaign class that inherits from Base, which is a declarative base class. We use the mapped_column function to define the id and status columns, specifying the data types and constraints. The Enum class from SQLAlchemy is used to create an enum column for the status field, and we pass the arguments for the enum type, including the list of enum values, the name of the enum type, and the create_constraint and validate_strings flags.