基本说明

用alembic --help命令查看使用说明

(py38-fastapi) ➜  面向 alembic --help
usage: alembic [-h] [--version] [-c CONFIG] [-n NAME] [-x X] [--raiseerr]
               {branches,current,downgrade,edit,ensure_version,heads,history,init,list_templates,merge,revision,show,stamp,upgrade}
               ...

positional arguments:
  {branches,current,downgrade,edit,ensure_version,heads,history,init,list_templates,merge,revision,show,stamp,upgrade}
    branches            Show current branch points.
    current             Display the current revision for a database.
    downgrade           Revert to a previous version.
    edit                Edit revision script(s) using $EDITOR.
    ensure_version      Create the alembic version table if it doesn't exist already .
    heads               Show current available heads in the script directory.
    history             List changeset scripts in chronological order.
    init                Initialize a new scripts directory.
    list_templates      List available templates.
    merge               Merge two revisions together. Creates a new migration file.
    revision            Create a new revision file.
    show                Show the revision(s) denoted by the given symbol.
    stamp               'stamp' the revision table with the given revision; don't run any
                        migrations.
    upgrade             Upgrade to a later version.

optional arguments:
  -h, --help            show this help message and exit
  --version             show program's version number and exit
  -c CONFIG, --config CONFIG
                        Alternate config file; defaults to value of ALEMBIC_CONFIG environment
                        variable, or "alembic.ini"
  -n NAME, --name NAME  Name of section in .ini file to use for Alembic config
  -x X                  Additional arguments consumed by custom env.py scripts, e.g. -x
                        setting1=somesetting -x setting2=somesetting
  --raiseerr            Raise a full stack trace on error

看着与git比较类似，有init merge不用的是有upgrade

-c命令，指自定义ini文件的名字

因此若生成指定的ini文件，及使用指定的ini文件进行迁移，需要使用如下命令：

# 初始化
alembic -c test1.ini init test1
# 提交更改
alembic -c test1.ini revision --autogenerate -m "height commit"
# 执行更改
alembic  -c test1.ini upgrade head

更详细的执行可查看SQLAlchemy + alembic版本迁移数据库 - 简书 (jianshu.com)

若需要不同的迁移目录对应不同的数据库，需要对数据库的Base进行分割

拆分Base

说是拆分Base，其实是将建表的类继承自不同的对象基类

# models/base.py

from sqlalchemy.ext.declarative import declarative_base
# 创建对象基类
Base1 = declarative_base()
Base2 = declarative_base()

创建表时继承对应的基类即可

举例：User表

# models/user/models.py

from sqlalchemy import Column, String

from models.base import Base2 as Base


class User(Base):
    """
    用户表
    """
    __tablename__ = "users"
    __table_args__ = {"comment": "用户表"}
    user_id = Column(String(80), primary_key=True, unique=True, comment="用户id")
    username = Column(String(30), nullable=False, unique=True, comment="登陆用户名")
    create_time = Column(String(20), default="", comment="创建时间")

    def __repr__(self):
        return f"<User(username={self.username})>"

Product表：

# models/product/models.py


from sqlalchemy import Column, Integer, String

from models.base import Base1 as Base


class ProductInfo(Base):
    """
    用户表
    """
    __tablename__ = "product_info"
    __table_args__ = {"comment": "项目表"}
    product_id = Column(Integer, primary_key=True,
                        autoincrement=True, comment="项目id")
    user_id = Column(String(80), index=True, comment="创建项目用户id")
    product_name = Column(String(30), nullable=False,
                          unique=True, comment="项目名")
    create_time = Column(String(20), default="", comment="创建时间")

    def __repr__(self):
        return (
            f"<ProductInfo(product_name={self.product_name}, user_id={self.user_id})>"
        )

以下解决方案来自 alembic + sqlalchemy 多个数据库答案 - 爱码网 (likecs.com)

Alembic 提供了一个模板来处理多个数据库：

alembic init --template multidb ./multidb

1. 修改ini

#alembic.ini

databases = engine1, engine2

[engine1]
sqlalchemy.url = driver://user:pass@localhost/dbname

[engine2]
sqlalchemy.url = driver://user:pass@localhost/dbname2

2. 将multidb/env.py 中的target_metadata 指向对应模型【有更改】

# multidb/env.py

# 添加以下代码
import os
import sys
# 把当前项目路径加入到path中
sys.path.append(os.path.dirname(os.path.dirname(__file__)))
from models.base import Base1
from models.base import Base2

target_metadata = {
      'engine1':Base1.metadata,
      'engine2':Base2.metadata
}

2. 测试Alembic设置

alembic revision --autogenerate -m "test"

3. 使用Alembic迁移

alembic revision --autogenerate -m "one more db"
alembic upgrade head

其它模式

也可以基于不同的base生成不同的迁移目录，做到脚本配置与数据库一一对应。当下我没有此需求，故未做探究