backend-patterns

# 后端开发模式

适用于可扩展服务端应用程序的后端架构模式与最佳实践。

## API 设计模式

### RESTful API 结构

```typescript
// ✅ 基于资源的 URL
GET    /api/markets                 # 资源列表
GET    /api/markets/:id             # 获取单个资源
POST   /api/markets                 # 创建资源
PUT    /api/markets/:id             # 替换资源
PATCH  /api/markets/:id             # 更新资源
DELETE /api/markets/:id             # 删除资源

// ✅ 用于过滤、排序、分页的查询参数
GET /api/markets?status=active&sort=volume&limit=20&offset=0
```

### 仓库模式 (Repository Pattern)

```typescript
// 数据访问逻辑的抽象
interface MarketRepository {
  findAll(filters?: MarketFilters): Promise<Market[]>
  findById(id: string): Promise<Market | null>
  create(data: CreateMarketDto): Promise<Market>
  update(id: string, data: UpdateMarketDto): Promise<Market>
  delete(id: string): Promise<void>
}

class SupabaseMarketRepository implements MarketRepository {
  async findAll(filters?: MarketFilters): Promise<Market[]> {
    let query = supabase.from('markets').select('*')

    if (filters?.status) {
      query = query.eq('status', filters.status)
    }

    if (filters?.limit) {
      query = query.limit(filters.limit)
    }

    const { data, error } = await query

    if (error) throw new Error(error.message)
    return data
  }

  // 其他方法...
}
```

### 服务层模式 (Service Layer Pattern)

```typescript
// 将业务逻辑与数据访问分离
class MarketService {
  constructor(private marketRepo: MarketRepository) {}

  async searchMarkets(query: string, limit: number = 10): Promise<Market[]> {
    // 业务逻辑
    const embedding = await generateEmbedding(query)
    const results = await this.vectorSearch(embedding, limit)

    // 获取完整数据
    const markets = await this.marketRepo.findByIds(results.map(r => r.id))

    // 按相似度排序
    return markets.sort((a, b) => {
      const scoreA = results.find(r => r.id === a.id)?.score || 0
      const scoreB = results.find(r => r.id === b.id)?.score || 0
      return scoreA - scoreB
    })
  }

  private async vectorSearch(embedding: number[], limit: number) {
    // 向量搜索的实现
  }
}
```

### 中间件模式 (Middleware Pattern)

```typescript
// 请求/响应处理流水线
export function withAuth(handler: NextApiHandler): NextApiHandler {
  return async (req, res) => {
    const token = req.headers.authorization?.replace('Bearer ', '')

    if (!token) {
      return res.status(401).json({ error: 'Unauthorized' })
    }

    try {
      const user = await verifyToken(token)
      req.user = user
      return handler(req, res)
    } catch (error) {
      return res.status(401).json({ error: 'Invalid token' })
    }
  }
}

// 使用方法
export default withAuth(async (req, res) => {
  // 处理程序可以访问 req.user
})
```

## 数据库模式

### 查询优化

```typescript
// ✅ 推荐：仅选择必要的列
const { data } = await supabase
  .from('markets')
  .select('id, name, status, volume')
  .eq('status', 'active')
  .order('volume', { ascending: false })
  .limit(10)

// ❌ 不推荐：选择所有列
const { data } = await supabase
  .from('markets')
  .select('*')
```

### 防止 N+1 查询

```typescript
// ❌ 不推荐：N+1 查询问题
const markets = await getMarkets()
for (const market of markets) {
  market.creator = await getUser(market.creator_id)  // N 次查询
}

// ✅ 推荐：批量获取
const markets = await getMarkets()
const creatorIds = markets.map(m => m.creator_id)
const creators = await getUsers(creatorIds)  // 1 次查询
const creatorMap = new Map(creators.map(c => [c.id, c]))

markets.forEach(market => {
  market.creator = creatorMap.get(market.creator_id)
})
```

### 事务模式 (Transaction Pattern)

```typescript
async function createMarketWithPosition(
  marketData: CreateMarketDto,
  positionData: CreatePositionDto
) {
  // 使用 Supabase 事务
  const { data, error } = await supabase.rpc('create_market_with_position', {
    market_data: marketData,
    position_data: positionData
  })

  if (error) throw new Error('Transaction failed')
  return data
}

// Supabase 的 SQL 函数
CREATE OR REPLACE FUNCTION create_market_with_position(
  market_data jsonb,
  position_data jsonb
)
RETURNS jsonb
LANGUAGE plpgsql
AS $$
BEGIN
  -- 事务自动开始
  INSERT INTO markets VALUES (market_data);
  INSERT INTO positions VALUES (position_data);
  RETURN jsonb_build_object('success', true);
EXCEPTION
  WHEN OTHERS THEN
    -- 自动触发回滚
    RETURN jsonb_build_object('success', false, 'error', SQLERRM);
END;
$$;
```

## 缓存策略

### Redis 缓存层

```typescript
class CachedMarketRepository implements MarketRepository {
  constructor(
    private baseRepo: MarketRepository,
    private redis: RedisClient
  ) {}

  async findById(id: string): Promise<Market | null> {
    // 首先检查缓存
    const cached = await this.redis.get(`market:${id}`)

    if (cached) {
      return JSON.parse(cached)
    }

    // 缓存未命中 - 从数据库获取
    const market = await this.baseRepo.findById(id)

    if (market) {
      // 缓存 5 分钟
      await this.redis.setex(`market:${id}`, 300, JSON.stringify(market))
    }

    return market
  }

  async invalidateCache(id: string): Promise<void> {
    await this.redis.del(`market:${id}`)
  }
}
```

### 旁路缓存模式 (Cache-Aside Pattern)

```typescript
async function getMarketWithCache(id: string): Promise<Market> {
  const cacheKey = `market:${id}`

  // 尝试从缓存获取
  const cached = await redis.get(cacheKey)
  if (cached) return JSON.parse(cached)

  // 缓存未命中 - 从数据库获取
  const market = await db.markets.findUnique({ where: { id } })

  if (!market) throw new Error('Market not found')

  // 更新缓存
  await redis.setex(cacheKey, 300, JSON.stringify(market))

  return market
}
```

## 错误处理模式

### 集中式错误处理程序

```typescript
class ApiError extends Error {
  constructor(
    public statusCode: number,
    public message: string,
    public isOperational = true
  ) {
    super(message)
    Object.setPrototypeOf(this, ApiError.prototype)
  }
}

export function errorHandler(error: unknown, req: Request): Response {
  if (error instanceof ApiError) {
    return NextResponse.json({
      success: false,
      error: error.message
    }, { status: error.statusCode })
  }

  if (error instanceof z.ZodError) {
    return NextResponse.json({
      success: false,
      error: 'Validation failed',