---
applyTo: "migrations/versions/*.py"
---
## Alembic Migrations


### 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:

```python
# 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:

```python
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`:

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