// 我原以為的"清潔架構(gòu)"
type UserRepository interface {
    GetUser(id string) (*User, error)
    CreateUser(user *User) error
    UpdateUser(user *User) error
    DeleteUser(id string) error
    FindUsersByStatus(status string) ([]*User, error)
}

type userRepositoryImpl struct {
    db *gorm.DB
}
func (r *userRepositoryImpl) GetUser(id string) (*User, error) {
    var user User
    if err := r.db.First(&user, "id = ?", id).Error; err != nil {
        return nil, err
    }
    return &user, nil
}

// 業(yè)務(wù)需求："按分類顯示有庫(kù)存的商品變體"
// 抽象迫使我寫的代碼：
func (s *ProductService) GetAvailableProductsByCategory() ([]CategoryProducts, error) {
    categories, err := s.categoryRepo.GetAll()
    if err != nil {
        return nil, err
    }
    
    var result []CategoryProducts
    for _, category := range categories {
        products, err := s.productRepo.GetByCategory(category.ID)
        if err != nil {
            return nil, err
        }
        
        var availableProducts []Product
        for _, product := range products {
            variants, err := s.variantRepo.GetByProductID(product.ID)
            if err != nil {
                return nil, err
            }
            
            hasStock := false
            for _, variant := range variants {
                if variant.Stock > 0 {
                    hasStock = true
                    break
                }
            }
            if hasStock {
                availableProducts = append(availableProducts, product)
            }
        }
        
        result = append(result, CategoryProducts{
            Category: category,
            Products: availableProducts,
        })
    }
    
    return result, nil
}

// 我構(gòu)建的"清潔"方式
classEventRepository {
    async findEventsByTimeRange(startDate, endDate) {
        returnawait Event.find({
            timestamp: { $gte: startDate, $lte: endDate }
        });
    }
    
    async aggregateEventsByType(events) {
        // 客戶端聚合，因?yàn)?關(guān)注點(diǎn)分離"
        const aggregated = {};
        events.forEach(event => {
            aggregated[event.type] = (aggregated[event.type] || 0) + 1;
        });
        return aggregated;
    }
}

客戶端請(qǐng)求
     ↓
API網(wǎng)關(guān)
     ↓
分析服務(wù)
     ↓
事件倉(cāng)庫(kù)（抽象層）
     ↓
MongoDB（獲取200萬(wàn)+文檔）
     ↓
內(nèi)存聚合（Node.js堆溢出）
     ↓
503服務(wù)不可用

客戶端請(qǐng)求 → API網(wǎng)關(guān) → MongoDB聚合管道 → 響應(yīng)

-- 業(yè)務(wù)實(shí)際需要的
WITH monthly_revenue AS (
    SELECT
        DATE_TRUNC('month', created_at) asmonth,
        SUM(amount) as revenue,
        COUNT(*) as transaction_count
    FROM transactions t
    JOIN accounts a ON t.account_id = a.id
    WHERE a.status ='active'
      AND t.created_at >='2023-01-01'
    GROUPBY DATE_TRUNC('month', created_at)
),
growth_analysis AS (
    SELECT
        month,
        revenue,
        transaction_count,
        LAG(revenue) OVER (ORDERBYmonth) as prev_month_revenue,
        revenue /LAG(revenue) OVER (ORDERBYmonth) -1as growth_rate
    FROM monthly_revenue
)
SELECT*FROM growth_analysis WHERE growth_rate ISNOT NULL;

// 47行Go代碼復(fù)制20行SQL查詢的功能
func (s *ReportService) GenerateMonthlyGrowthReport() (*GrowthReport, error) {
    // 多個(gè)倉(cāng)庫(kù)調(diào)用
    // 手動(dòng)數(shù)據(jù)處理
    // 內(nèi)存聚合
    // 跨越3個(gè)服務(wù)的復(fù)雜業(yè)務(wù)邏輯
}

┌─────────────────┐
│   HTTP API      │
├─────────────────┤
│ 業(yè)務(wù)邏輯層       │  ← 薄層，專注于業(yè)務(wù)規(guī)則
├─────────────────┤
│ 查詢層           │  ← 直接SQL/NoSQL查詢，優(yōu)化執(zhí)行
├─────────────────┤
│   數(shù)據(jù)庫(kù)         │  ← 讓數(shù)據(jù)庫(kù)做它擅長(zhǎng)的事
└─────────────────┘

// 當(dāng)前做法：讓數(shù)據(jù)庫(kù)做數(shù)據(jù)庫(kù)的事
type FinanceService struct {
    db *sql.DB
}

func (s *FinanceService) GetMonthlyGrowthReport(ctx context.Context) (*GrowthReport, error) {
    query := `
    WITH monthly_revenue AS (
        SELECT 
            DATE_TRUNC('month', created_at) as month,
            SUM(amount) as revenue,
            COUNT(*) as transaction_count
        FROM transactions t
        JOIN accounts a ON t.account_id = a.id
        WHERE a.status = 'active'
          AND t.created_at >= $1
        GROUP BY DATE_TRUNC('month', created_at)
    ),
    growth_analysis AS (
        SELECT 
            month,
            revenue,
            transaction_count,
            LAG(revenue) OVER (ORDER BY month) as prev_month_revenue,
            revenue / LAG(revenue) OVER (ORDER BY month) - 1 as growth_rate
        FROM monthly_revenue
    )
    SELECT month, revenue, transaction_count, growth_rate 
    FROM growth_analysis WHERE growth_rate IS NOT NULL`
    
    rows, err := s.db.QueryContext(ctx, query, time.Now().AddDate(-2, 0, 0))
    if err != nil {
        return nil, fmt.Errorf("failed to execute growth report query: %w", err)
    }
    defer rows.Close()
    
    // 簡(jiǎn)單的結(jié)果映射，無(wú)業(yè)務(wù)邏輯
    return s.mapRowsToGrowthReport(rows)
}