Database Migration

Database Migration

掌握跨 ORM（Sequelize、TypeORM、Prisma）的数据库模式和数据迁移，包括回滚策略和零停机部署。

何时不使用此技能

• 任务与数据库迁移无关
• 需要此范围之外的其他领域或工具

使用说明

• 明确目标、约束和所需输入。
• 应用相关最佳实践并验证结果。
• 提供可执行的步骤和验证方法。
• 如需详细示例，请打开 resources/implementation-playbook.md。

何时使用此技能

• 在不同 ORM 之间迁移
• 执行模式转换
• 在数据库之间移动数据
• 实现回滚流程
• 零停机部署
• 数据库版本升级
• 数据模型重构

ORM 迁移

Sequelize 迁移

// migrations/20231201-create-users.js
module.exports = {
  up: async (queryInterface, Sequelize) => {
    await queryInterface.createTable('users', {
      id: {
        type: Sequelize.INTEGER,
        primaryKey: true,
        autoIncrement: true
      },
      email: {
        type: Sequelize.STRING,
        unique: true,
        allowNull: false
      },
      createdAt: Sequelize.DATE,
      updatedAt: Sequelize.DATE
    });
  },

  down: async (queryInterface, Sequelize) => {
    await queryInterface.dropTable('users');
  }
};

// 运行: npx sequelize-cli db:migrate
// 回滚: npx sequelize-cli db:migrate:undo

TypeORM 迁移

// migrations/1701234567-CreateUsers.ts
import { MigrationInterface, QueryRunner, Table } from 'typeorm';

export class CreateUsers1701234567 implements MigrationInterface {
  public async up(queryRunner: QueryRunner): Promise<void> {
    await queryRunner.createTable(
      new Table({
        name: 'users',
        columns: [
          {
            name: 'id',
            type: 'int',
            isPrimary: true,
            isGenerated: true,
            generationStrategy: 'increment'
          },
          {
            name: 'email',
            type: 'varchar',
            isUnique: true
          },
          {
            name: 'created_at',
            type: 'timestamp',
            default: 'CURRENT_TIMESTAMP'
          }
        ]
      })
    );
  }

  public async down(queryRunner: QueryRunner): Promise<void> {
    await queryRunner.dropTable('users');
  }
}

// 运行: npm run typeorm migration:run
// 回滚: npm run typeorm migration:revert

Prisma 迁移

// schema.prisma
model User {
  id        Int      @id @default(autoincrement())
  email     String   @unique
  createdAt DateTime @default(now())
}

// 生成迁移: npx prisma migrate dev --name create_users
// 应用迁移: npx prisma migrate deploy

模式转换

添加带默认值的列

// 安全迁移：添加带默认值的列
module.exports = {
  up: async (queryInterface, Sequelize) => {
    await queryInterface.addColumn('users', 'status', {
      type: Sequelize.STRING,
      defaultValue: 'active',
      allowNull: false
    });
  },

  down: async (queryInterface) => {
    await queryInterface.removeColumn('users', 'status');
  }
};

重命名列（零停机）

// 步骤 1：添加新列
module.exports = {
  up: async (queryInterface, Sequelize) => {
    await queryInterface.addColumn('users', 'full_name', {
      type: Sequelize.STRING
    });

    // 从旧列复制数据
    await queryInterface.sequelize.query(
      'UPDATE users SET full_name = name'
    );
  },

  down: async (queryInterface) => {
    await queryInterface.removeColumn('users', 'full_name');
  }
};

// 步骤 2：更新应用程序以使用新列

// 步骤 3：删除旧列
module.exports = {
  up: async (queryInterface) => {
    await queryInterface.removeColumn('users', 'name');
  },

  down: async (queryInterface, Sequelize) => {
    await queryInterface.addColumn('users', 'name', {
      type: Sequelize.STRING
    });
  }
};

更改列类型

module.exports = {
  up: async (queryInterface, Sequelize) => {
    // 对于大表，使用多步骤方法

    // 1. 添加新列
    await queryInterface.addColumn('users', 'age_new', {
      type: Sequelize.INTEGER
    });

    // 2. 复制并转换数据
    await queryInterface.sequelize.query(`
      UPDATE users
      SET age_new = CAST(age AS INTEGER)
      WHERE age IS NOT NULL
    `);

    // 3. 删除旧列
    await queryInterface.removeColumn('users', 'age');

    // 4. 重命名新列
    await queryInterface.renameColumn('users', 'age_new', 'age');
  },

  down: async (queryInterface, Sequelize) => {
    await queryInterface.changeColumn('users', 'age', {
      type: Sequelize.STRING
    });
  }
};

数据转换

复杂数据迁移

module.exports = {
  up: async (queryInterface, Sequelize) => {
    // 获取所有记录
    const [users] = await queryInterface.sequelize.query(
      'SELECT id, address_string FROM users'
    );

    // 转换每条记录
    for (const user of users) {
      const addressParts = user.address_string.split(',');

      await queryInterface.sequelize.query(
        `UPDATE users
         SET street = :street,
             city = :city,
             state = :state
         WHERE id = :id`,
        {
          replacements: {
            id: user.id,
            street: addressParts[0]?.trim(),
            city: addressParts[1]?.trim(),
            state: addressParts[2]?.trim()
          }
        }
      );
    }

    // 删除旧列
    await queryInterface.removeColumn('users', 'address_string');
  },

  down: async (queryInterface, Sequelize) => {
    // 重建原始列
    await queryInterface.addColumn('users', 'address_string', {
      type: Sequelize.STRING
    });

    await queryInterface.sequelize.query(`
      UPDATE users
      SET address_string = CONCAT(street, ', ', city, ', ', state)
    `);

    await queryInterface.removeColumn('users', 'street');
    await queryInterface.removeColumn('users', 'city');
    await queryInterface.removeColumn('users', 'state');
  }
};

回滚策略

基于事务的迁移

module.exports = {
  up: async (queryInterface, Sequelize) => {
    const transaction = await queryInterface.sequelize.transaction();

    try {
      await queryInterface.addColumn(
        'users',
        'verified',
        { type: Sequelize.BOOLEAN, defaultValue: false },
        { transaction }
      );

      await queryInterface.sequelize.query(
        'UPDATE users SET verified = true WHERE email_verified_at IS NOT NULL',
        { transaction }
      );

      await transaction.commit();
    } catch (error) {
      await transaction.rollback();
      throw error;
    }
  },

  down: async (queryInterface) => {
    await queryInterface.removeColumn('users', 'verified');
  }
};

基于检查点的回滚

module.exports = {
  up: async (queryInterface, Sequelize) => {
    // 创建备份表
    await queryInterface.sequelize.query(
      'CREATE TABLE users_backup AS SELECT * FROM users'
    );

    try {
      // 执行迁移
      await queryInterface.addColumn('users', 'new_field', {
        type: Sequelize.STRING
      });

      // 验证迁移
      const [result] = await queryInterface.sequelize.query(
        "SELECT COUNT(*) as count FROM users WHERE new_field IS NULL"
      );

      if (result[0].count > 0) {
        throw new Error('Migration verification failed');
      }

      // 删除备份
      await queryInterface.dropTable('users_backup');
    } catch (error) {
      // 从备份恢复
      await queryInterface.sequelize.query('DROP TABLE users');
      await queryInterface.sequelize.query(
        'CREATE TABLE users AS SELECT * FROM users_backup'
      );
      await queryInterface.dropTable('users_backup');
      throw error;
    }
  }
};

零停机迁移

蓝绿部署策略

// 阶段 1：使变更向后兼容
module.exports = {
  up: async (queryInterface, Sequelize) => {
    // 添加新列（旧代码和新代码都可以工作）
    await queryInterface.addColumn('users', 'email_new', {
      type: Sequelize.STRING
    });
  }
};

// 阶段 2：部署同时写入两列的代码

// 阶段 3：回填数据
module.exports = {
  up: async (queryInterface) => {
    await queryInterface.sequelize.query(`
      UPDATE users
      SET email_new = email
      WHERE email_new IS NULL
    `);
  }
};

// 阶段 4：部署从新列读取的代码

// 阶段 5：删除旧列
module.exports = {
  up: async (queryInterface) => {
    await queryInterface.removeColumn('users', 'email');
  }
};

跨数据库迁移

PostgreSQL 到 MySQL

// 处理差异
module.exports = {
  up: async (queryInterface, Sequelize) => {
    const dialectName = queryInterface.sequelize.getDialect();

    if (dialectName === 'mysql') {
      await queryInterface.createTable('users', {
        id: {
          type: Sequelize.INTEGER,
          primaryKey: true,
          autoIncrement: true
        },
        data: {
          type: Sequelize.JSON  // MySQL JSON 类型
        }
      });
    } else if (dialectName === 'postgres') {
      await queryInterface.createTable('users', {
        id: {
          type: Sequelize.INTEGER,
          primaryKey: true,
          autoIncrement: true
        },
        data: {
          type: Sequelize.JSONB  // PostgreSQL JSONB 类型
        }
      });
    }
  }
};

资源

• references/orm-switching.md: ORM 迁移指南
• references/schema-migration.md: 模式转换模式
• references/data-transformation.md: 数据迁移脚本
• references/rollback-strategies.md: 回滚流程
• assets/schema-migration-template.sql: SQL 迁移模板
• assets/data-migration-script.py: 数据迁移工具
• scripts/test-migration.sh: 迁移测试脚本

最佳实践

1. 始终提供回滚：每个 up() 都需要对应的 down()
2. 测试迁移：先在预发环境测试
3. 使用事务：尽可能使用原子迁移
4. 先备份：迁移前始终备份
5. 小步变更：分解为小的增量步骤
6. 监控：部署期间注意观察错误
7. 文档化：解释原因和方法
8. 幂等性：迁移应该可重复运行

常见陷阱

• 未测试回滚流程
• 在没有停机策略的情况下进行破坏性变更
• 忘记处理 NULL 值
• 未考虑索引性能
• 忽略外键约束
• 一次迁移过多数据

局限性

• 仅当任务明确符合上述描述的范围时使用此技能。
• 不要将输出作为环境特定验证、测试或专家审查的替代品。
• 如果缺少所需输入、权限、安全边界或成功标准，请停止并请求澄清。