数据库迁移

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

何时使用此技能

• 在不同的 ORM 之间迁移
• 执行数据库架构转换
• 在数据库之间迁移数据
• 实施回滚流程
• 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：npx prisma migrate deploy

数据库架构转换

添加带有默认值的列

// 安全迁移：添加带有默认值的列
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）

// 第 1 步：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");
  },
};

// 第 2 步：更新应用程序以使用新列

// 第 3 步：移除旧列
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("迁移验证失败");
      }

      // 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：进行向后兼容的更改
module.exports = {
  up: async (queryInterface, Sequelize) => {
    // 添加新列（新旧代码都可以工作）
    await queryInterface.addColumn("users", "email_new", {
      type: Sequelize.STRING,
    });
  },
};

// 阶段 2：部署同时写入两个列的代码

// 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：移除旧列
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
        },
      });
    }
  },
};