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1---
2description: Alembic Migrations
3globs: migrations/versions/*.py
4alwaysApply: false
5---
6## Alembic Migrations
7 
8 
9### Default Content for New Non-Nullable Columns
10 
11To add a non-nullable column and set a specific value for all existing rows without a persistent server default:
12 
13```python
14# 1. Add the column as nullable (no default needed):
15op.add_column('distribution', sa.Column('default_campaign_ending_date', sa.DateTime(timezone=True), nullable=True))
16# 2. Update existing rows with your desired value (e.g., a specific datetime)
17op.execute("UPDATE distribution SET default_campaign_ending_date = %s", [datetime.utcnow()])
18# 3. Alter the column to non-nullable:
19op.alter_column('distribution', 'default_campaign_ending_date', nullable=False)
20```
21 
22### Record Backfill Operations
23 
24For migrations that include data mutation, and not only schema modifications, use this pattern to setup a session:
25 
26```python
27from alembic import op
28from sqlmodel import Session
29from activemodel.session_manager import global_session
30from app import log
31 
32def run_migration_helper():
33  pass
34 
35def upgrade() -> None:
36  session = Session(bind=op.get_bind())
37 
38  with global_session(session):
39      run_migration_helper()
40      flip_point_coordinates()
41      backfill_screening_host_data()
42 
43  # flush before running any other operations, otherwise not all changes will persist to the transaction
44  session.flush()
45```
46 
47However, if you don't need the business logic attached to the models, you can execute a query using `op.execute`:
48 
49```python
50op.execute(
51  TheModel.__table__.update().values({"a_field": "a_value"}) # type: ignore
52)
53```
54