alembic-migrations

Alembic Migrations

• Migrations must stay compatible with offline SQL generation.
• Pass the session connection into helpers rather than opening a new connection.
• Prefer Alembic's enum integration over hand-written enum migrations when it works.
• Migration logic should not use model classes.

Default Content for New Non-Nullable Columns

To add a non-nullable column and set a specific value for all existing rows without a persistent server default:

# 1. Add the column as nullable (no default needed):
op.add_column(
    "distribution",
    sa.Column(
        "default_campaign_ending_date", sa.DateTime(timezone=True), nullable=True
    ),
)
# 2. Update existing rows with your desired value (e.g., a specific datetime)
op.execute(
    "UPDATE distribution SET default_campaign_ending_date = %s", [datetime.utcnow()]
)
# 3. Alter the column to non-nullable:
op.alter_column("distribution", "default_campaign_ending_date", nullable=False)

Record Backfill Operations

For migrations that include data mutation, and not only schema modifications, use this pattern to setup a session:

from alembic import op
from sqlmodel import Session
from activemodel.session_manager import global_session
from app import log


def run_migration_helper():
    pass


def upgrade() -> None:
    session = Session(bind=op.get_bind())

    with global_session(session):
        run_migration_helper()
        flip_point_coordinates()
        backfill_screening_host_data()

    # flush before running any other operations, otherwise not all changes will persist to the transaction
    session.flush()

However, if you don't need the business logic attached to the models, you can execute a query using op.execute:

op.execute(
    TheModel.__table__.update().values({"a_field": "a_value"})  # type: ignore
)