首先通过 composer 安装，注意：tp5.1必须指定2.*版本

    1. composer require topthink/think-migration=2.*

    注意事项，不支持修改文件配置目录

    在命令行下运行查看帮助，可以看到新增的命令

    1. php think
    1. migrate
    2.   migrate:create     Create a new migration
    3.   migrate:rollback   Rollback the last or to a specific migration
    4.   migrate:run        Migrate the database
    5.   migrate:status     Show migration status
    6.  optimize
    7.   optimize:autoload  Optimizes PSR0 and PSR4 packages to be loaded wit
    8. h classmaps too, good for production.
    9.   optimize:config    Build config and common file cache.
    10.   optimize:route     Build route cache.
    11.   optimize:schema    Build database schema cache.
    12.  seed
    13.   seed:create        Create a new database seeder
    14.   seed:run           Run database seeders

    migrate:数据库迁移工具 seed:数据库填充工具

    创建迁移类，首字母必须为大写

    1. php think migrate:create Users

    可以看到目录下有新文件 .\database\migrations\20161117144043_users.php

    主要讨论migrate:
    migrate:create : 创建一个新的数据迁移类,php think migrate:create ,文件名须采用驼峰命名法
    forexample:php think migrate:create ScProductImage 文件会在制定目录下生成一个php文件
    数据迁移(think-migration) - 图1
    ＊＊＊＊＊＊＊＊＊＊＊＊＊＊＊＊＊＊＊＊＊＊＊＊＊＊＊＊＊＊＊＊＊＊＊＊＊＊＊＊＊＊＊＊＊＊＊＊＊＊＊＊＊＊＊＊＊＊＊
    migrate:run : 完成数据迁移工作 php think migrate:run
    ＊＊＊＊＊＊＊＊＊＊＊＊＊＊＊＊＊＊＊＊＊＊＊＊＊＊＊＊＊＊＊＊＊＊＊＊＊＊＊＊＊＊＊＊＊＊＊＊＊＊＊＊＊＊＊＊＊＊＊
    migrate:status:查看migrate工作状态 php think migrate:status
    数据迁移(think-migration) - 图2


    *
    migrate:rollback : 回滚数据到指定的一个数据迁移版本 php think migrate:rollback -t
    就是我们上图上面红框表示的值

    三：migrate文件编写
    在migrate中有三个方法
    up:在migrate:run时执行(前提是文件中不存在change方法)
    down:在migrate:rollback时执行(前提是文件中不存在change方法)
    change:migrate:run 和migrate:rollback时执行 (如果存在该方法 则不会去执行up 与down)