Run Multiple Alembic Environments from one .ini file

Long before Alembic had the “multiple bases” feature described in Working with Multiple Bases, projects had a need to maintain more than one Alembic version history in a single project, where these version histories are completely independent of each other and each refer to their own alembic_version table, either across multiple databases, schemas, or namespaces. A simple approach was added to support this, the --name flag on the commandline.

早在 Alembic 拥有使用多个base中描述的“多base”功能之前，项目需要在单个项目中维护多个 Alembic 版本历史，其中这些版本历史完全相互独立，并且每个都引用自己的 alembic_version 表，可以跨多个数据库、模式或命名空间。 添加了一种简单的方法来支持这一点，即命令行上的 --name 标志。

First, one would create an alembic.ini file of this form:

首先，创建一个这种形式的 alembic.ini 文件：

[DEFAULT]
# all defaults shared between environments go here

sqlalchemy.url = postgresql://scott:tiger@hostname/mydatabase


[schema1]
# path to env.py and migration scripts for schema1
script_location = myproject/revisions/schema1

[schema2]
# path to env.py and migration scripts for schema2
script_location = myproject/revisions/schema2

[schema3]
# path to env.py and migration scripts for schema3
script_location = myproject/revisions/db2

# this schema uses a different database URL as well
sqlalchemy.url = postgresql://scott:tiger@hostname/myotherdatabase

Above, in the [DEFAULT] section we set up a default database URL. Then we create three sections corresponding to different revision lineages in our project. Each of these directories would have its own env.py and set of versioning files. Then when we run the alembic command, we simply give it the name of the configuration we want to use:

如上所示，在 [DEFAULT] 部分中，我们设置了默认的 数据库URL。 然后我们在我们的项目中创建三个对应于不同修订沿袭的部分。 这些目录中的每一个都有自己的 env.py 和一组版本控制文件。 然后当我们运行 alembic 命令时，我们只需给它指定我们要使用的配置的名称：

alembic --name schema2 revision -m "new rev for schema 2" --autogenerate

Above, the alembic command makes use of the configuration in [schema2], populated with defaults from the [DEFAULT] section.

上面， alembic 命令使用 [schema2] 中的配置，填充了 [DEFAULT] 部分的默认值。

The above approach can be automated by creating a custom front-end to the Alembic commandline as well.

上述方法也可以通过为 Alembic 命令行创建自定义前端来实现自动化。