Python使用Alembic框架进行数据库版本管理

　　安装

pip install alembic

　　初始化

alembic init alembic

　　修改配置alembic.ini

sqlalchemy.url = driver://user:pass@localhost/dbname

　　修改env.py

import sys
from logging.config import fileConfig
from os.path import abspath, dirname

from alembic import context
from sqlalchemy import engine_from_config
from sqlalchemy import pool

sys.path.append(dirname(dirname(abspath(__file__))))
from models.models import Base

# this is the Alembic Config object, which provides
# access to the values within the .ini file in use.
config = context.config

# Interpret the config file for Python logging.
# This line sets up loggers basically.
fileConfig(config.config_file_name)

# add your model's MetaData object here
# for 'autogenerate' support
# from myapp import mymodel
# target_metadata = mymodel.Base.metadata
target_metadata = Base.metadata


# other values from the config, defined by the needs of env.py,
# can be acquired:
# my_important_option = config.get_main_option("my_important_option")
# ... etc.


def run_migrations_offline():
    """Run migrations in 'offline' mode.

    This configures the context with just a URL
    and not an Engine, though an Engine is acceptable
    here as well.  By skipping the Engine creation
    we don't even need a DBAPI to be available.

    Calls to context.execute() here emit the given string to the
    script output.

    """
    url = config.get_main_option("sqlalchemy.url")
    context.configure(
        url=url,
        target_metadata=target_metadata,
        literal_binds=True,
        dialect_opts={"paramstyle": "named"},
    )

    with context.begin_transaction():
        context.run_migrations()


def run_migrations_online():
    """Run migrations in 'online' mode.

    In this scenario we need to create an Engine
    and associate a connection with the context.

    """
    connectable = engine_from_config(
        config.get_section(config.config_ini_section),
        prefix="sqlalchemy.",
        poolclass=pool.NullPool,
    )

    with connectable.connect() as connection:
        context.configure(
            connection=connection, target_metadata=target_metadata
        )

        with context.begin_transaction():
            context.run_migrations()


if context.is_offline_mode():
    run_migrations_offline()
else:
    run_migrations_online()

　　创建第一个版本

alembic revision --autogenerate -m "init"  

　　修改模型

alembic revision --autogenerate -m "update"

　　升级

alembic upgrade head  #每次要创建新的版本，需要执行数据库升级到新版本的命令，才能继续更新版本

　　降级

alembic downgrade 版本号