alembic-pg-enum-generator 0.2.0

Lightweight Alembic extension for PostgreSQL enum value additions using ALTER TYPE ... ADD VALUE

Alembic PostgreSQL Enum Generator

A lightweight Alembic extension for PostgreSQL enum value additions.

Why Use This?

Unlike complex enum sync libraries that use heavy "replace-and-cast" approaches causing table locks and full table scans, this library uses PostgreSQL's efficient ALTER TYPE ... ADD VALUE statement for:

• ✅ No table locking - only brief enum type locks
• ✅ Production-safe - minimal database impact
• ✅ Lightning fast - no data conversion required
• ✅ Add-only operations - perfect for compatibility-focused environments

Installation

pip install alembic-pg-enum-generator

Usage

1. Import in your Alembic env.py

# In your alembic/env.py file
import alembic_pg_enum_generator

# The import automatically registers with Alembic's autogenerate system

2. Define your enums in SQLAlchemy

from sqlalchemy import Column, Integer, String, Enum
from sqlalchemy.ext.declarative import declarative_base

Base = declarative_base()

class UserStatus(Enum):
    ACTIVE = "active"
    INACTIVE = "inactive"
    PENDING = "pending"  # Add this new value

class User(Base):
    __tablename__ = 'users'
    
    id = Column(Integer, primary_key=True)
    name = Column(String(50))
    status = Column(Enum(UserStatus, name='user_status'))

3. Generate migration

alembic revision --autogenerate -m "Add pending status to user_status enum"

4. Generated migration

"""Add pending status to user_status enum

Revision ID: abc123
Revises: def456
Create Date: 2024-01-01 12:00:00.000000

"""
from alembic import op

def upgrade():
    # Simple, efficient ALTER TYPE statement
    op.add_enum_value('public', 'user_status', 'pending')

def downgrade():
    # Downgrade not supported for compatibility
    pass

Configuration

Filter enum names

import alembic_pg_enum_generator

# Only process enums matching certain patterns
config = alembic_pg_enum_generator.Config(
    include_name=lambda name: name.startswith('app_')
)
alembic_pg_enum_generator.set_configuration(config)

Features

✅ What it does

• Automatically detects new enum values in SQLAlchemy models
• Generates efficient ALTER TYPE ... ADD VALUE statements
• Integrates seamlessly with Alembic's autogenerate
• Works with multiple schemas
• Supports TypeDecorator wrapped enums
• Handles array columns with enums

❌ What it doesn't do

• No enum value deletion (use manual migrations for compatibility)
• No enum value reordering (PostgreSQL doesn't support this anyway)
• No enum renaming (use manual migrations)
• No downgrade support (enum additions are permanent for compatibility)

Performance Comparison

Operation	Alembic PG Enum Generator	Heavy Sync Libraries
SQL Command	ALTER TYPE enum_name ADD VALUE 'new_value'	Complex replace-and-cast with temp types
Table Lock	✅ None	❌ ACCESS EXCLUSIVE (blocks all operations)
Data Scan	✅ None	❌ Full table scan + rewrite
Production Impact	🟢 Minimal (milliseconds)	🔴 High (minutes on large tables)

Example: Adding Multiple Values

# Before
class Priority(Enum):
    LOW = "low"
    HIGH = "high"

# After  
class Priority(Enum):
    LOW = "low"
    MEDIUM = "medium"    # New value 1
    HIGH = "high"
    CRITICAL = "critical"  # New value 2

Generated migration:

def upgrade():
    op.add_enum_value('public', 'priority', 'medium')
    op.add_enum_value('public', 'priority', 'critical')

Requirements

• Python 3.8+ (including 3.13)
• Alembic 1.0+
• SQLAlchemy 1.4+
• PostgreSQL (any version supporting ALTER TYPE ... ADD VALUE)

Contributing

We welcome contributions! Please see our Contributing Guide for details.

Development Setup

1. Clone the repository:

git clone https://github.com/xiang9156/alembic-pg-enum-generator.git
cd alembic-pg-enum-generator

2. Install dependencies with uv:

uv sync --all-extras --dev

3. Set up pre-commit hooks:

uv run pre-commit install

4. Run tests:

uv run pytest

Code Quality

• Linting: uv run ruff check .
• Formatting: uv run ruff format .
• Type checking: uv run mypy alembic_pg_enum_generator
• Tests: uv run pytest --cov=alembic_pg_enum_generator

Changelog

See CHANGELOG.md for details about changes in each version.

License

MIT License - see LICENSE file for details.