Change column types safely in SQLAlchemy

postgresqlmysqlsqlalchemymigrationsalembic
When changing a column type that requires a table rewrite, follow these steps:
1. Create a new column with the desired type
2. Write to both columns during the transition period
3. Backfill data from the old column to the new column
4. Move reads from the old column to the new column
5. Stop writing to the old column
6. Drop the old column

Install this rule for wispbit

Quick Install

Recommended
View install script

Run this one command to automatically install the rule:

curl -fsSL https://wispbit.com/api/install?rule=sqlalchemy-change-column-type | bash

Manual install

1

Copy the rule

---
include: *.py
---
When changing a column type that requires a table rewrite, follow these steps:
1. Create a new column with the desired type
2. Write to both columns during the transition period
3. Backfill data from the old column to the new column
4. Move reads from the old column to the new column
5. Stop writing to the old column
6. Drop the old column
Bad:
```python
def upgrade():
    # Directly changing a column type can cause table locks
    op.alter_column('users', 'some_column',
                    type_=sa.String(50),
                    existing_type=sa.Integer())
def downgrade():
    op.alter_column('users', 'some_column',
                    type_=sa.Integer(),
                    existing_type=sa.String(50))
```
Good:
```python
# Migration 1: Add new column
def upgrade():
    # Adding a new column first
    op.add_column('users', sa.Column('some_column_new', sa.String(50)))
def downgrade():
    op.drop_column('users', 'some_column_new')
```
```python
# Migration 2: Complete the transition (after backfilling data)
def upgrade():
    # After ensuring all data is migrated
    op.drop_column('users', 'some_column')
    op.alter_column('users', 'some_column_new',
                    new_column_name='some_column')
def downgrade():
    op.alter_column('users', 'some_column',
                    new_column_name='some_column_new')
    op.add_column('users', sa.Column('some_column', sa.Integer()))
```
2

Add the rule into your project

Save the copied content as: .wispbit/rules/sqlalchemy-change-column-type.md

Install this rule for Coderabbit

Copy the configuration below and add it to your repository as .coderabbit.yml in your project root.

reviews:
  path_instructions:
    - path: "*.py"
      instructions: |
                
        When changing a column type that requires a table rewrite, follow these steps:
        
        1. Create a new column with the desired type
        2. Write to both columns during the transition period
        3. Backfill data from the old column to the new column
        4. Move reads from the old column to the new column
        5. Stop writing to the old column
        6. Drop the old column
        
        Bad:
        
        ```python
        def upgrade():
            # Directly changing a column type can cause table locks
            op.alter_column('users', 'some_column',
                            type_=sa.String(50),
                            existing_type=sa.Integer())
        
        def downgrade():
            op.alter_column('users', 'some_column',
                            type_=sa.Integer(),
                            existing_type=sa.String(50))
        ```
        
        Good:
        
        ```python
        # Migration 1: Add new column
        
        def upgrade():
            # Adding a new column first
            op.add_column('users', sa.Column('some_column_new', sa.String(50)))
        
        def downgrade():
            op.drop_column('users', 'some_column_new')
        ```
        
        ```python
        # Migration 2: Complete the transition (after backfilling data)
        
        def upgrade():
            # After ensuring all data is migrated
            op.drop_column('users', 'some_column')
            op.alter_column('users', 'some_column_new',
                            new_column_name='some_column')
        
        def downgrade():
            op.alter_column('users', 'some_column',
                            new_column_name='some_column_new')
            op.add_column('users', sa.Column('some_column', sa.Integer()))
        ```

Install this rule for Greptile

Greptile rules can be added through the web interface. Please see this documentation for details on how to add custom rules and context.

When changing a column type that requires a table rewrite, follow these steps:
1. Create a new column with the desired type
2. Write to both columns during the transition period
3. Backfill data from the old column to the new column
4. Move reads from the old column to the new column
5. Stop writing to the old column
6. Drop the old column
Bad:
```python
def upgrade():
    # Directly changing a column type can cause table locks
    op.alter_column('users', 'some_column',
                    type_=sa.String(50),
                    existing_type=sa.Integer())
def downgrade():
    op.alter_column('users', 'some_column',
                    type_=sa.Integer(),
                    existing_type=sa.String(50))
```
Good:
```python
# Migration 1: Add new column
def upgrade():
    # Adding a new column first
    op.add_column('users', sa.Column('some_column_new', sa.String(50)))
def downgrade():
    op.drop_column('users', 'some_column_new')
```
```python
# Migration 2: Complete the transition (after backfilling data)
def upgrade():
    # After ensuring all data is migrated
    op.drop_column('users', 'some_column')
    op.alter_column('users', 'some_column_new',
                    new_column_name='some_column')
def downgrade():
    op.alter_column('users', 'some_column',
                    new_column_name='some_column_new')
    op.add_column('users', sa.Column('some_column', sa.Integer()))
```

File Path Patterns:

*.py

Install this rule for GitHub Copilot

Copilot instructions can be added through the interface. See the documentation for details on how to create coding guidelines.

When changing a column type that requires a table rewrite, follow these steps:
1. Create a new column with the desired type
2. Write to both columns during the transition period
3. Backfill data from the old column to the new column
4. Move reads from the old column to the new column
5. Stop writing to the old column
6. Drop the old column
Bad:
```python
def upgrade():
    # Directly changing a column type can cause table locks
    op.alter_column('users', 'some_column',
                    type_=sa.String(50),
                    existing_type=sa.Integer())
def downgrade():
    op.alter_column('users', 'some_column',
                    type_=sa.Integer(),
                    existing_type=sa.String(50))
```
Good:
```python
# Migration 1: Add new column
def upgrade():
    # Adding a new column first
    op.add_column('users', sa.Column('some_column_new', sa.String(50)))
def downgrade():
    op.drop_column('users', 'some_column_new')
```
```python
# Migration 2: Complete the transition (after backfilling data)
def upgrade():
    # After ensuring all data is migrated
    op.drop_column('users', 'some_column')
    op.alter_column('users', 'some_column_new',
                    new_column_name='some_column')
def downgrade():
    op.alter_column('users', 'some_column',
                    new_column_name='some_column_new')
    op.add_column('users', sa.Column('some_column', sa.Integer()))
```

File Path Patterns:

*.py

Install this rule for Graphite Diamond

Diamond custom rules can be added through the interface. See the documentation for details on how to create custom rules.

When changing a column type that requires a table rewrite, follow these steps:
1. Create a new column with the desired type
2. Write to both columns during the transition period
3. Backfill data from the old column to the new column
4. Move reads from the old column to the new column
5. Stop writing to the old column
6. Drop the old column
Bad:
```python
def upgrade():
    # Directly changing a column type can cause table locks
    op.alter_column('users', 'some_column',
                    type_=sa.String(50),
                    existing_type=sa.Integer())
def downgrade():
    op.alter_column('users', 'some_column',
                    type_=sa.Integer(),
                    existing_type=sa.String(50))
```
Good:
```python
# Migration 1: Add new column
def upgrade():
    # Adding a new column first
    op.add_column('users', sa.Column('some_column_new', sa.String(50)))
def downgrade():
    op.drop_column('users', 'some_column_new')
```
```python
# Migration 2: Complete the transition (after backfilling data)
def upgrade():
    # After ensuring all data is migrated
    op.drop_column('users', 'some_column')
    op.alter_column('users', 'some_column_new',
                    new_column_name='some_column')
def downgrade():
    op.alter_column('users', 'some_column',
                    new_column_name='some_column_new')
    op.add_column('users', sa.Column('some_column', sa.Integer()))
```

File Path Patterns:

*.py