Writing Migration Scripts to Support Script Generation

编写支持生成脚本的迁移脚本

The challenge of SQL script generation is that the scripts we generate can’t rely upon any client/server database access. This means a migration script that pulls some rows into memory via a SELECT statement will not work in --sql mode. It’s also important that the Alembic directives, all of which are designed specifically to work in both “live execution” as well as “offline SQL generation” mode, are used.

SQL 脚本生成的挑战在于我们生成的脚本不能依赖于任何客户端/服务器数据库访问。 这意味着通过 SELECT 语句将一些行拉入内存的迁移脚本将无法在 --sql 模式下工作。 同时 Alembic 指令也很重要，所有这些指令都是专门为在 “live execution”(实时执行)和 “offline SQL generation”(离线SQL生成) 模式下工作而设计的。