Flask-migrate No support for ALTER of constraints in SQLite dialect

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问题

由于sqlite不支持DROP COLUMN、ALTER COLUMN、ADD CONSTRAINT等操作，如果flask使用了sqlite做数据库，flask-migrate不能自动迁移

解决

两种途径，都来自这里

方法1

换MySql或者Postgres，也是flask-migrate作者的建议。

方法2

在创建db的地方

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from sqlalchemy import MetaData

naming_convention = {
    "ix": 'ix_%(column_0_label)s',
    "uq": "uq_%(table_name)s_%(column_0_name)s",
    "ck": "ck_%(table_name)s_%(column_0_name)s",
    "fk": "fk_%(table_name)s_%(column_0_name)s_%(referred_table_name)s",
    "pk": "pk_%(table_name)s"
}
db = SQLAlchemy(metadata=MetaData(naming_convention=naming_convention))

enabled batch mode for auto-generated migrations by adding a render_as_batch=config.get_main_option('sqlalchemy.url').startswith('sqlite:') argument to context.configure() in run_migrations_online() in migrations/env.py.

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

    connection = engine.connect()
    context.configure(
                connection=connection,
                target_metadata=target_metadata,
                render_as_batch=config.get_main_option('sqlalchemy.url').startswith('sqlite:///')
                )

    try:
        with context.begin_transaction():
            context.run_migrations()
    finally:
        connection.close()

方法2试用到现在修改column和foreign-key没遇到什么问题，但是作者不推荐，用得很心虚（sadly）