dotnet-backend-patterns

.NET 后端开发模式

掌握 C#/.NET 模式，运用现代最佳实践（2024/2025）构建生产级 API、MCP 服务和企业后端。

何时使用此技能

• 开发新的 .NET Web API 或 MCP 服务
• 审查 C# 代码的质量和性能
• 使用依赖注入设计服务架构
• 使用 Redis 实现缓存策略
• 编写单元测试和集成测试
• 使用 EF Core 或 Dapper 优化数据库访问
• 使用 IOptions 模式配置应用程序
• 处理错误并实现弹性模式

核心概念

1. 项目结构（整洁架构）

src/
├── Domain/                     # Core business logic (no dependencies)
│   ├── Entities/
│   ├── Interfaces/
│   ├── Exceptions/
│   └── ValueObjects/
├── Application/                # Use cases, DTOs, validation
│   ├── Services/
│   ├── DTOs/
│   ├── Validators/
│   └── Interfaces/
├── Infrastructure/             # External implementations
│   ├── Data/                   # EF Core, Dapper repositories
│   ├── Caching/                # Redis, Memory cache
│   ├── External/               # HTTP clients, third-party APIs
│   └── DependencyInjection/    # Service registration
└── Api/                        # Entry point
    ├── Controllers/            # Or MinimalAPI endpoints
    ├── Middleware/
    ├── Filters/
    └── Program.cs

2. 依赖注入模式

// Service registration by lifetime
public static class ServiceCollectionExtensions
{
    public static IServiceCollection AddApplicationServices(
        this IServiceCollection services,
        IConfiguration configuration)
    {
        // Scoped: One instance per HTTP request
        services.AddScoped<IProductService, ProductService>();
        services.AddScoped<IOrderService, OrderService>();

        // Singleton: One instance for app lifetime
        services.AddSingleton<ICacheService, RedisCacheService>();
        services.AddSingleton<IConnectionMultiplexer>(_ =>
            ConnectionMultiplexer.Connect(configuration["Redis:Connection"]!));

        // Transient: New instance every time
        services.AddTransient<IValidator<CreateOrderRequest>, CreateOrderValidator>();

        // Options pattern for configuration
        services.Configure<CatalogOptions>(configuration.GetSection("Catalog"));
        services.Configure<RedisOptions>(configuration.GetSection("Redis"));

        // Factory pattern for conditional creation
        services.AddScoped<IPriceCalculator>(sp =>
        {
            var options = sp.GetRequiredService<IOptions<PricingOptions>>().Value;
            return options.UseNewEngine
                ? sp.GetRequiredService<NewPriceCalculator>()
                : sp.GetRequiredService<LegacyPriceCalculator>();
        });

        // Keyed services (.NET 8+)
        services.AddKeyedScoped<IPaymentProcessor, StripeProcessor>("stripe");
        services.AddKeyedScoped<IPaymentProcessor, PayPalProcessor>("paypal");

        return services;
    }
}

// Usage with keyed services
public class CheckoutService
{
    public CheckoutService(
        [FromKeyedServices("stripe")] IPaymentProcessor stripeProcessor)
    {
        _processor = stripeProcessor;
    }
}

3. Async/Await 模式

// ✅ CORRECT: Async all the way down
public async Task<Product> GetProductAsync(string id, CancellationToken ct = default)
{
    return await _repository.GetByIdAsync(id, ct);
}

// ✅ CORRECT: Parallel execution with WhenAll
public async Task<(Stock, Price)> GetStockAndPriceAsync(
    string productId,
    CancellationToken ct = default)
{
    var stockTask = _stockService.GetAsync(productId, ct);
    var priceTask = _priceService.GetAsync(productId, ct);

    await Task.WhenAll(stockTask, priceTask);

    return (await stockTask, await priceTask);
}

// ✅ CORRECT: ConfigureAwait in libraries
public async Task<T> LibraryMethodAsync<T>(CancellationToken ct = default)
{
    var result = await _httpClient.GetAsync(url, ct).ConfigureAwait(false);
    return await result.Content.ReadFromJsonAsync<T>(ct).ConfigureAwait(false);
}

// ✅ CORRECT: ValueTask for hot paths with caching
public ValueTask<Product?> GetCachedProductAsync(string id)
{
    if (_cache.TryGetValue(id, out Product? product))
        return ValueTask.FromResult(product);

    return new ValueTask<Product?>(GetFromDatabaseAsync(id));
}

// ❌ WRONG: Blocking on async (deadlock risk)
var result = GetProductAsync(id).Result;  // NEVER do this
var result2 = GetProductAsync(id).GetAwaiter().GetResult(); // Also bad

// ❌ WRONG: async void (except event handlers)
public async void ProcessOrder() { }  // Exceptions are lost

// ❌ WRONG: Unnecessary Task.Run for already async code
await Task.Run(async () => await GetDataAsync());  // Wastes thread

4. 使用 IOptions 进行配置

// Configuration classes
public class CatalogOptions
{
    public const string SectionName = "Catalog";

    public int DefaultPageSize { get; set; } = 50;
    public int MaxPageSize { get; set; } = 200;
    public TimeSpan CacheDuration { get; set; } = TimeSpan.FromMinutes(15);
    public bool EnableEnrichment { get; set; } = true;
}

public class RedisOptions
{
    public const string SectionName = "Redis";

    public string Connection { get; set; } = "localhost:6379";
    public string KeyPrefix { get; set; } = "mcp:";
    public int Database { get; set; } = 0;
}

// appsettings.json
{
    "Catalog": {
        "DefaultPageSize": 50,
        "MaxPageSize": 200,
        "CacheDuration": "00:15:00",
        "EnableEnrichment": true
    },
    "Redis": {
        "Connection": "localhost:6379",
        "KeyPrefix": "mcp:",
        "Database": 0
    }
}

// Registration
services.Configure<CatalogOptions>(configuration.GetSection(CatalogOptions.SectionName));
services.Configure<RedisOptions>(configuration.GetSection(RedisOptions.SectionName));

// Usage with IOptions (singleton, read once at startup)
public class CatalogService
{
    private readonly CatalogOptions _options;

    public CatalogService(IOptions<CatalogOptions> options)
    {
        _options = options.Value;
    }
}

// Usage with IOptionsSnapshot (scoped, re-reads on each request)
public class DynamicService
{
    private readonly CatalogOptions _options;

    public DynamicService(IOptionsSnapshot<CatalogOptions> options)
    {
        _options = options.Value;  // Fresh value per request
    }
}

// Usage with IOptionsMonitor (singleton, notified on changes)
public class MonitoredService
{
    private CatalogOptions _options;

    public MonitoredService(IOptionsMonitor<CatalogOptions> monitor)
    {
        _options = monitor.CurrentValue;
        monitor.OnChange(newOptions => _options = newOptions);
    }
}

5. Result 模式（避免将异常用于流程控制）

// Generic Result type
public class Result<T>
{
    public bool IsSuccess { get; }
    public T? Value { get; }
    public string? Error { get; }
    public string? ErrorCode { get; }

    private Result(bool isSuccess, T? value, string? error, string? errorCode)
    {
        IsSuccess = isSuccess;
        Value = value;
        Error = error;
        ErrorCode = errorCode;
    }

    public static Result<T> Success(T value) => new(true, value, null, null);
    public static Result<T> Failure(string error, string? code = null) => new(false, default, error, code);

    public Result<TNew> Map<TNew>(Func<T, TNew> mapper) =>
        IsSuccess ? Result<TNew>.Success(mapper(Value!)) : Result<TNew>.Failure(Error!, ErrorCode);

    public async Task<Result<TNew>> MapAsync<TNew>(Func<T, Task<TNew>> mapper) =>
        IsSuccess ? Result<TNew>.Success(await mapper(Value!)) : Result<TNew>.Failure(Error!, ErrorCode);
}

// Usage in service
public async Task<Result<Order>> CreateOrderAsync(CreateOrderRequest request, CancellationToken ct)
{
    // Validation
    var validation = await _validator.ValidateAsync(request, ct);
    if (!validation.IsValid)
        return Result<Order>.Failure(
            validation.Errors.First().ErrorMessage,
            "VALIDATION_ERROR");

    // Business rule check
    var stock = await _stockService.CheckAsync(request.ProductId, request.Quantity, ct);
    if (!stock.IsAvailable)
        return Result<Order>.Failure(
            $"Insufficient stock: {stock.Available} available, {request.Quantity} requested",
            "INSUFFICIENT_STOCK");

    // Create order
    var order = await _repository.CreateAsync(request.ToEntity(), ct);

    return Result<Order>.Success(order);
}

// Usage in controller/endpoint
app.MapPost("/orders", async (
    CreateOrderRequest request,
    IOrderService orderService,
    CancellationToken ct) =>
{
    var result = await orderService.CreateOrderAsync(request, ct);

    return result.IsSuccess
        ? Results.Created($"/orders/{result.Value!.Id}", result.Value)
        : Results.BadRequest(new { error = result.Error, code = result.ErrorCode });
});

数据访问模式

Entity Framework Core

// DbContext configuration
public class AppDbContext : DbContext
{
    public DbSet<Product> Products => Set<Product>();
    public DbSet<Order> Orders => Set<Order>();

    protected override void OnModelCreating(ModelBuilder modelBuilder)
    {
        // Apply all configurations from assembly
        modelBuilder.ApplyConfigurationsFromAssembly(typeof(AppDbContext).Assembly);

        // Global query filters
        modelBuilder.Entity<Product>().HasQueryFilter(p => !p.IsDeleted);
    }
}

// Entity configuration
public class ProductConfiguration : IEntityTypeConfiguration<Product>
{
    public void Configure(EntityTypeBuilder<Product> builder)
    {
        builder.ToTable("Products");

        builder.HasKey(p => p.Id);
        builder.Property(p => p.Id).HasMaxLength(40);
        builder.Property(p => p.Name).HasMaxLength(200).IsRequired();
        builder.Property(p => p.Price).HasPrecision(18, 2);

        builder.HasIndex(p => p.Sku).IsUnique();
        builder.HasIndex(p => new { p.CategoryId, p.Name });

        builder.HasMany(p => p.OrderItems)
            .WithOne(oi => oi.Product)
            .HasForeignKey(oi => oi.ProductId);
    }
}

// Repository with EF Core
public class ProductRepository : IProductRepository
{
    private readonly AppDbContext _context;

    public async Task<Product?> GetByIdAsync(string id, CancellationToken ct = default)
    {
        return await _context.Products
            .AsNoTracking()
            .FirstOrDefaultAsync(p => p.Id == id, ct);
    }

    public async Task<IReadOnlyList<Product>> SearchAsync(
        ProductSearchCriteria criteria,
        CancellationToken ct = default)
    {
        var query = _context.Products.AsNoTracking();

        if (!string.IsNullOrWhiteSpace(criteria.SearchTerm))
            query = query.Where(p => EF.Functions.Like(p.Name, $"%{criteria.SearchTerm}%"));

        if (criteria.CategoryId.HasValue)
            query = query.Where(p => p.CategoryId == criteria.CategoryId);

        if (criteria.MinPrice.HasValue)
            query = query.Where(p => p.Price >= criteria.MinPrice);

        if (criteria.MaxPrice.HasValue)
            query = query.Where(p => p.Price <= criteria.MaxPrice);

        return await query
            .OrderBy(p => p.Name)
            .Skip((criteria.Page - 1) * criteria.PageSize)
            .Take(criteria.PageSize)
            .ToListAsync(ct);
    }
}

使用 Dapper 提升性能

public class DapperProductRepository : IProductRepository
{
    private readonly IDbConnection _connection;

    public async Task<Product?> GetByIdAsync(string id, CancellationToken ct = default)
    {
        const string sql = """
            SELECT Id, Name, Sku, Price, CategoryId, Stock, CreatedAt
            FROM Products
            WHERE Id = @Id AND IsDeleted = 0
            """;

        return await _connection.QueryFirstOrDefaultAsync<Product>(
            new CommandDefinition(sql, new { Id = id }, cancellationToken: ct));
    }

    public async Task<IReadOnlyList<Product>> SearchAsync(
        ProductSearchCriteria criteria,
        CancellationToken ct = default)
    {
        var sql = new StringBuilder("""
            SELECT Id, Name, Sku, Price, CategoryId, Stock, CreatedAt
            FROM Products
            WHERE IsDeleted = 0
            """);

        var parameters = new DynamicParameters();

        if (!string.IsNullOrWhiteSpace(criteria.SearchTerm))
        {
            sql.Append(" AND Name LIKE @SearchTerm");
            parameters.Add("SearchTerm", $"%{criteria.SearchTerm}%");
        }

        if (criteria.CategoryId.HasValue)
        {
            sql.Append(" AND CategoryId = @CategoryId");
            parameters.Add("CategoryId", criteria.CategoryId);
        }

        if (criteria.MinPrice.HasValue)
        {
            sql.Append(" AND Price >= @MinPrice");
            parameters.Add("MinPrice", criteria.MinPrice);
        }

        if (criteria.MaxPrice.HasValue)
        {
            sql.Append(" AND Price <= @MaxPrice");
            parameters.Add("MaxPrice", criteria.MaxPrice);
        }

        sql.Append(" ORDER BY Name OFFSET @Offset ROWS FETCH NEXT @PageSize ROWS ONLY");
        parameters.Add("Offset", (criteria.Page - 1) * criteria.PageSize);
        parameters.Add("PageSize", criteria.PageSize);

        var results = await _connection.QueryAsync<Product>(
            new CommandDefinition(sql.ToString(), parameters, cancellationToken: ct));

        return results.ToList();
    }

    // Multi-mapping for related data
    public async Task<Order?> GetOrderWithItemsAsync(int orderId, CancellationToken ct = default)
    {
        const string sql = """
            SELECT o.*, oi.*, p.*
            FROM Orders o
            LEFT JOIN OrderItems oi ON o.Id = oi.OrderId
            LEFT JOIN Products p ON oi.ProductId = p.Id
            WHERE o.Id = @OrderId
            """;

        var orderDictionary = new Dictionary<int, Order>();

        await _connection.QueryAsync<Order, OrderItem, Product, Order>(
            new CommandDefinition(sql, new { OrderId = orderId }, cancellationToken: ct),
            (order, item, product) =>
            {
                if (!orderDictionary.TryGetValue(order.Id, out var existingOrder))
                {
                    existingOrder = order;
                    existingOrder.Items = new List<OrderItem>();
                    orderDictionary.Add(order.Id, existingOrder);
                }

                if (item != null)
                {
                    item.Product = product;
                    existingOrder.Items.Add(item);
                }

                return existingOrder;
            },
            splitOn: "Id,Id");

        return orderDictionary.Values.FirstOrDefault();
    }
}

缓存模式

使用 Redis 的多级缓存

public class CachedProductService : IProductService
{
    private readonly IProductRepository _repository;
    private readonly IMemoryCache _memoryCache;
    private readonly IDistributedCache _distributedCache;
    private readonly ILogger<CachedProductService> _logger;

    private static readonly TimeSpan MemoryCacheDuration = TimeSpan.FromMinutes(1);
    private static readonly TimeSpan DistributedCacheDuration = TimeSpan.FromMinutes(15);

    public async Task<Product?> GetByIdAsync(string id, CancellationToken ct = default)
    {
        var cacheKey = $"product:{id}";

        // L1: Memory cache (in-process, fastest)
        if (_memoryCache.TryGetValue(cacheKey, out Product? cached))
        {
            _logger.LogDebug("L1 cache hit for {CacheKey}", cacheKey);
            return cached;
        }

        // L2: Distributed cache (Redis)
        var distributed = await _distributedCache.GetStringAsync(cacheKey, ct);
        if (distributed != null)
        {
            _logger.LogDebug("L2 cache hit for {CacheKey}", cacheKey);
            var product = JsonSerializer.Deserialize<Product>(distributed);

            // Populate L1
            _memoryCache.Set(cacheKey, product, MemoryCacheDuration);
            return product;
        }

        // L3: Database
        _logger.LogDebug("Cache miss for {CacheKey}, fetching from database", cacheKey);
        var fromDb = await _repository.GetByIdAsync(id, ct);

        if (fromDb != null)
        {
            var serialized = JsonSerializer.Serialize(fromDb);

            // Populate both caches
            await _distributedCache.SetStringAsync(
                cacheKey,
                serialized,
                new DistributedCacheEntryOptions
                {
                    AbsoluteExpirationRelativeToNow = DistributedCacheDuration
                },
                ct);

            _memoryCache.Set(cacheKey, fromDb, MemoryCacheDuration);
        }

        return fromDb;
    }

    public async Task InvalidateAsync(string id, CancellationToken ct = default)
    {
        var cacheKey = $"product:{id}";

        _memoryCache.Remove(cacheKey);
        await _distributedCache.RemoveAsync(cacheKey, ct);

        _logger.LogInformation("Invalidated cache for {CacheKey}", cacheKey);
    }
}

// Stale-while-revalidate pattern
public class StaleWhileRevalidateCache<T>
{
    private readonly IDistributedCache _cache;
    private readonly TimeSpan _freshDuration;
    private readonly TimeSpan _staleDuration;

    public async Task<T?> GetOrCreateAsync(
        string key,
        Func<CancellationToken, Task<T>> factory,
        CancellationToken ct = default)
    {
        var cached = await _cache.GetStringAsync(key, ct);

        if (cached != null)
        {
            var entry = JsonSerializer.Deserialize<CacheEntry<T>>(cached)!;

            if (entry.IsStale && !entry.IsExpired)
            {
                // Return stale data immediately, refresh in background
                _ = Task.Run(async () =>
                {
                    var fresh = await factory(CancellationToken.None);
                    await SetAsync(key, fresh, CancellationToken.None);
                });
            }

            if (!entry.IsExpired)
                return entry.Value;
        }

        // Cache miss or expired
        var value = await factory(ct);
        await SetAsync(key, value, ct);
        return value;
    }

    private record CacheEntry<TValue>(TValue Value, DateTime CreatedAt)
    {
        public bool IsStale => DateTime.UtcNow - CreatedAt > _freshDuration;
        public bool IsExpired => DateTime.UtcNow - CreatedAt > _staleDuration;
    }
}

测试模式

使用 xUnit 和 Moq 进行单元测试

public class OrderServiceTests
{
    private readonly Mock<IOrderRepository> _mockRepository;
    private readonly Mock<IStockService> _mockStockService;
    private readonly Mock<IValidator<CreateOrderRequest>> _mockValidator;
    private readonly OrderService _sut; // System Under Test

    public OrderServiceTests()
    {
        _mockRepository = new Mock<IOrderRepository>();
        _mockStockService = new Mock<IStockService>();
        _mockValidator = new Mock<IValidator<CreateOrderRequest>>();

        // Default: validation passes
        _mockValidator
            .Setup(v => v.ValidateAsync(It.IsAny<CreateOrderRequest>(), It.IsAny<CancellationToken>()))
            .ReturnsAsync(new ValidationResult());

        _sut = new OrderService(
            _mockRepository.Object,
            _mockStockService.Object,
            _mockValidator.Object);
    }

    [Fact]
    public async Task CreateOrderAsync_WithValidRequest_ReturnsSuccess()
    {
        // Arrange
        var request = new CreateOrderRequest
        {
            ProductId = "PROD-001",
            Quantity = 5,
            CustomerOrderCode = "ORD-2024-001"
        };

        _mockStockService
            .Setup(s => s.CheckAsync("PROD-001", 5, It.IsAny<CancellationToken>()))
            .ReturnsAsync(new StockResult { IsAvailable = true, Available = 10 });

        _mockRepository
            .Setup(r => r.CreateAsync(It.IsAny<Order>(), It.IsAny<CancellationToken>()))
            .ReturnsAsync(new Order { Id = 1, CustomerOrderCode = "ORD-2024-001" });

        // Act
        var result = await _sut.CreateOrderAsync(request);

        // Assert
        Assert.True(result.IsSuccess);
        Assert.NotNull(result.Value);
        Assert.Equal(1, result.Value.Id);

        _mockRepository.Verify(
            r => r.CreateAsync(It.Is<Order>(o => o.CustomerOrderCode == "ORD-2024-001"),
            It.IsAny<CancellationToken>()),
            Times.Once);
    }

    [Fact]
    public async Task CreateOrderAsync_WithInsufficientStock_ReturnsFailure()
    {
        // Arrange
        var request = new CreateOrderRequest { ProductId = "PROD-001", Quantity = 100 };

        _mockStockService
            .Setup(s => s.CheckAsync(It.IsAny<string>(), It.IsAny<int>(), It.IsAny<CancellationToken>()))
            .ReturnsAsync(new StockResult { IsAvailable = false, Available = 5 });

        // Act
        var result = await _sut.CreateOrderAsync(request);

        // Assert
        Assert.False(result.IsSuccess);
        Assert.Equal("INSUFFICIENT_STOCK", result.ErrorCode);
        Assert.Contains("5 available", result.Error);

        _mockRepository.Verify(
            r => r.CreateAsync(It.IsAny<Order>(), It.IsAny<CancellationToken>()),
            Times.Never);
    }

    [Theory]
    [InlineData(0)]
    [InlineData(-1)]
    [InlineData(-100)]
    public async Task CreateOrderAsync_WithInvalidQuantity_ReturnsValidationError(int quantity)
    {
        // Arrange
        var request = new CreateOrderRequest { ProductId = "PROD-001", Quantity = quantity };

        _mockValidator
            .Setup(v => v.ValidateAsync(request, It.IsAny<CancellationToken>()))
            .ReturnsAsync(new ValidationResult(new[]
            {
                new ValidationFailure("Quantity", "Quantity must be greater than 0")
            }));

        // Act
        var result = await _sut.CreateOrderAsync(request);

        // Assert
        Assert.False(result.IsSuccess);
        Assert.Equal("VALIDATION_ERROR", result.ErrorCode);
    }
}

使用 WebApplicationFactory 进行集成测试

public class ProductsApiTests : IClassFixture<WebApplicationFactory<Program>>
{
    private readonly WebApplicationFactory<Program> _factory;
    private readonly HttpClient _client;

    public ProductsApiTests(WebApplicationFactory<Program> factory)
    {
        _factory = factory.WithWebHostBuilder(builder =>
        {
            builder.ConfigureServices(services =>
            {
                // Replace real database with in-memory
                services.RemoveAll<DbContextOptions<AppDbContext>>();
                services.AddDbContext<AppDbContext>(options =>
                    options.UseInMemoryDatabase("TestDb"));

                // Replace Redis with memory cache
                services.RemoveAll<IDistributedCache>();
                services.AddDistributedMemoryCache();
            });
        });

        _client = _factory.CreateClient();
    }

    [Fact]
    public async Task GetProduct_WithValidId_ReturnsProduct()
    {
        // Arrange
        using var scope = _factory.Services.CreateScope();
        var context = scope.ServiceProvider.GetRequiredService<AppDbContext>();

        context.Products.Add(new Product
        {
            Id = "TEST-001",
            Name = "Test Product",
            Price = 99.99m
        });
        await context.SaveChangesAsync();

        // Act
        var response = await _client.GetAsync("/api/products/TEST-001");

        // Assert
        response.EnsureSuccessStatusCode();
        var product = await response.Content.ReadFromJsonAsync<Product>();
        Assert.Equal("Test Product", product!.Name);
    }

    [Fact]
    public async Task GetProduct_WithInvalidId_Returns404()
    {
        // Act
        var response = await _client.GetAsync("/api/products/NONEXISTENT");

        // Assert
        Assert.Equal(HttpStatusCode.NotFound, response.StatusCode);
    }
}

最佳实践

应该做

1. 在调用堆栈中全程使用 async/await
2. 通过构造函数注入依赖项
3. 使用 IOptions 进行类型化配置
4. 返回 Result 类型，而不是在业务逻辑中抛出异常
5. 在所有异步方法中使用 CancellationToken
6. 对于读取密集、性能关键的查询，优先使用 Dapper
7. 对于具有变更跟踪的复杂领域模型，使用 EF Core
8. 积极缓存，并配合适当的失效策略
9. 为业务逻辑编写单元测试，为 API 编写集成测试
10. 为 DTO 和不可变数据使用 record 类型

不应该做

1. 不要用 .Result 或 .Wait() 阻塞异步操作
2. 不要使用 async void，事件处理程序除外
3. 不要捕获泛型 Exception 而不重新抛出或记录日志
4. 不要硬编码配置值
5. 不要直接暴露 EF 实体（使用 DTO）
6. 对于只读查询，不要忘记 AsNoTracking()
7. 不要忽略 CancellationToken 参数
8. 不要手动创建 new HttpClient()（使用 IHttpClientFactory）
9. 不要不必要地混用同步和异步代码
10. 不要跳过 API 边界处的验证

常见陷阱

• N+1 查询：使用 .Include() 或显式联接
• 内存泄漏：释放 IDisposable 资源，使用 using
• 死锁：不要混用同步和异步，在库中使用 ConfigureAwait(false)
• 过度获取：仅选择需要的列，使用投影
• 缺少索引：检查查询计划，为常见筛选条件添加索引
• 超时问题：为 HTTP 客户端配置适当的超时时间
• 缓存击穿：使用分布式锁进行缓存填充