构建 Schema 迁移 CLI

项目概述

本项目实现一个面向 database schema migration 的完整系统，核心要解决的问题是 applying ordered, reversible schema changes so a database evolves alongside code safely。整体由 Migration loader、Version tracker、Up applier、Down reverter、Status reporter 五个模块组成，每个模块单一职责、可独立测试，最后通过集成测试验证端到端正确性。设计上把 a migration that alters a large table and holds an exclusive lock long enough to block deploys 作为第一类需求先行处理，而非事后再补。

架构与关键决策

数据模型为 a directory of numbered migration files each with up and down steps, tracked by a versions table in the target database。Migration loader 定义其余阶段共同依赖的数据形状并在边界处校验输入；Version tracker 承载 database schema migration 的正确性逻辑；Up applier 专门处理 a migration that alters a large table and holds an exclusive lock long enough to block deploys，在失败路径上给出明确的拒绝、重试或降级策略；Down reverter 提供可观测性，每次操作输出带关联 id 的结构化事件；Status reporter 在过载时按既定方式降级，避免过载演变为数据损坏。配置与代码分离，使风险变更可经 diff 审阅。

实施与测试

按五个阶段依次实现 Migration loader、Version tracker、Up applier、Down reverter、Status reporter，每阶段配套聚焦单测。集成测试组合各模块并驱动真实 database schema migration 场景：先验证正常路径，再刻意触发 a migration that alters a large table and holds an exclusive lock long enough to block deploys 并断言系统降级而非损坏。所有依赖均在进程内或被桩替换，用例在 CI 中确定可复现。

限制与后续

• 单区域设计，多区域复制超出范围。
• Migration loader 默认进程内，未水平共享。
• 无鉴权层，假定部署在强制身份的边缘之后。

代码示例

# setup for schema-migration-cli
pnpm init
pnpm add pg commander
pnpm add -D typescript tsx vitest

schema_migration_cli/
├── src/index.ts
├── src/migration-loader.ts
├── src/version-tracker.ts
├── tests/schema_migration_cli.test.ts
└── package.json

// Migration loader: database schema migration core
export function migrationloader(input: MigrationloaderInput): MigrationloaderResult {
  // Build the migration loader that anchors database schema migration and defines the core data shape.
  return processMigrationloader(input);
}

// Version tracker — handles database schema migration Add the version tracker so
export class Versiontracker {
  constructor(private opts: VersiontrackerOptions) {}
  async run(ctx: Context): Promise<VersiontrackerOutput> {
    return this.execute(ctx);
  }
}

// Up applier: database schema migration stage
export const upapplier = (next: Next) => async (req: Request) => {
  const out = await transform(req);
  return next(out);
};

// Down reverter for database schema migration
export async function downreverter(stream: AsyncIterable<Chunk>): Promise<Aggregate> {
  let acc = init();
  for await (const c of stream) acc = merge(acc, c);
  return acc;
}

// Status reporter: database schema migration finalization
export function statusreporter(state: State): Result {
  validate(state);
  return finalize(state);
}

# run the database schema migration test suite
pnpm vitest run