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+---
+title: .NET 开发知识库
+tags:
+  - dotNET
+  - CSharp
+  - ASPNET
+  - Microsoft
+  - Backend
+created: 2026-04-21
+---
+
+# .NET 开发知识库
+
+## .NET 技术栈概述
+
+| 技术 | 说明 |
+|------|------|
+| **.NET Framework** | 旧版 Windows 专用（4.8 已停止更新） |
+| **.NET Core** | 跨平台版本，已合并入 .NET 5+ |
+| **.NET 5/6/7/8** | 统一跨平台版本，推荐使用 |
+| **ASP.NET Core** | Web API / MVC 框架 |
+| **Blazor** | 使用 C# 的 WebAssembly 框架 |
+| **MAUI** | 跨平台移动应用框架 |
+| **EF Core** | 轻量级 ORM |
+
+## C# 核心语法
+
+### 基础类型
+
+```csharp
+// 值类型
+int num = 42;
+double price = 19.99;
+decimal money = 99.99m;
+bool isActive = true;
+char grade = 'A';
+DateTime now = DateTime.Now;
+
+// 引用类型
+string name = "张三";
+var list = new List<string>();
+
+// 可空类型
+int? nullableNum = null;
+string? nullableStr = null;
+
+// 集合初始化
+var nums = new[] { 1, 2, 3, 4, 5 };
+var names = new List<string> { "张三", "李四" };
+
+// 字典
+var dict = new Dictionary<string, int>
+{
+    ["a"] = 1,
+    ["b"] = 2
+};
+```
+
+### 类与接口
+
+```csharp
+// 类
+public class User
+{
+    public int Id { get; set; }
+    public string Name { get; set; }
+    
+    // 只读属性
+    public DateTime CreatedAt { get; }
+    
+    // 构造函数
+    public User(string name)
+    {
+        Name = name;
+        CreatedAt = DateTime.UtcNow;
+    }
+    
+    // 方法
+    public string GetDisplayName() => $"用户: {Name}";
+}
+
+// 接口
+public interface IRepository<T>
+{
+    T GetById(int id);
+    IEnumerable<T> GetAll();
+    void Add(T entity);
+    void Update(T entity);
+    void Delete(int id);
+}
+
+// 继承
+public class UserRepository : IRepository<User>
+{
+    public User GetById(int id) { /* ... */ return null; }
+    public IEnumerable<User> GetAll() { /* ... */ yield break; }
+    public void Add(User entity) { }
+    public void Update(User entity) { }
+    public void Delete(int id) { }
+}
+```
+
+### 异步编程
+
+```csharp
+// async/await
+public async Task<User> GetUserAsync(int id)
+{
+    // 异步等待，不阻塞线程
+    var data = await _context.Users.FindAsync(id);
+    return data;
+}
+
+// 并行任务
+public async Task<(User, Order)> GetUserAndOrderAsync(int userId, int orderId)
+{
+    var userTask = _userRepo.GetByIdAsync(userId);
+    var orderTask = _orderRepo.GetByIdAsync(orderId);
+    
+    await Task.WhenAll(userTask, orderTask);
+    
+    return (userTask.Result, orderTask.Result);
+}
+
+// IAsyncEnumerable（流式数据）
+public async IAsyncEnumerable<User> StreamUsersAsync()
+{
+    await using var conn = new SqlConnection(_connectionString);
+    await using var reader = await conn.ExecuteReaderAsync("SELECT * FROM Users");
+    
+    while (await reader.ReadAsync())
+    {
+        yield return new User { Id = reader.GetInt32(0), Name = reader.GetString(1) };
+    }
+}
+```
+
+### LINQ 查询
+
+```csharp
+var users = new List<User>
+{
+    new User { Id = 1, Name = "张三", Age = 25 },
+    new User { Id = 2, Name = "李四", Age = 30 },
+    new User { Id = 3, Name = "王五", Age = 25 }
+};
+
+// 条件查询
+var adults = users.Where(u => u.Age >= 18);
+
+// 投影
+var names = users.Select(u => u.Name);
+
+// 排序
+var sorted = users.OrderByDescending(u => u.Age).ThenBy(u => u.Name);
+
+// 分组
+var grouped = users.GroupBy(u => u.Age)
+                   .Select(g => new { Age = g.Key, Count = g.Count() });
+
+// 联接
+var joined = from u in users
+             join o in orders on u.Id equals o.UserId
+             select new { u.Name, o.OrderNo };
+
+// 聚合
+var count = users.Count();
+var avgAge = users.Average(u => u.Age);
+```
+
+## ASP.NET Core Web API
+
+### 最小模板
+
+```csharp
+var builder = WebApplication.CreateBuilder(args);
+
+// 添加服务
+builder.Services.AddControllers();
+builder.Services.AddEndpointsApiExplorer();
+builder.Services.AddSwaggerGen();
+
+// 注册依赖
+builder.Services.AddScoped<IUserRepository, UserRepository>();
+
+var app = builder.Build();
+
+// 中间件管道
+if (app.Environment.IsDevelopment())
+{
+    app.UseSwagger();
+    app.UseSwaggerUI();
+}
+
+app.UseAuthorization();
+app.MapControllers();
+
+app.Run();
+```
+
+### Controller 示例
+
+```csharp
+[ApiController]
+[Route("api/[controller]")]
+public class UsersController : ControllerBase
+{
+    private readonly IUserRepository _repo;
+    
+    public UsersController(IUserRepository repo)
+    {
+        _repo = repo;
+    }
+    
+    [HttpGet]
+    public async Task<ActionResult<IEnumerable<UserDto>>> GetAll()
+    {
+        var users = await _repo.GetAllAsync();
+        return Ok(users.Select(u => new UserDto(u)));
+    }
+    
+    [HttpGet("{id}")]
+    public async Task<ActionResult<UserDto>> GetById(int id)
+    {
+        var user = await _repo.GetByIdAsync(id);
+        if (user == null) return NotFound();
+        return Ok(new UserDto(user));
+    }
+    
+    [HttpPost]
+    public async Task<ActionResult<UserDto>> Create([FromBody] CreateUserDto dto)
+    {
+        var user = new User { Name = dto.Name, Email = dto.Email };
+        await _repo.AddAsync(user);
+        return CreatedAtAction(nameof(GetById), new { id = user.Id }, new UserDto(user));
+    }
+    
+    [HttpPut("{id}")]
+    public async Task<IActionResult> Update(int id, [FromBody] UpdateUserDto dto)
+    {
+        var user = await _repo.GetByIdAsync(id);
+        if (user == null) return NotFound();
+        
+        user.Name = dto.Name;
+        user.Email = dto.Email;
+        await _repo.UpdateAsync(user);
+        
+        return NoContent();
+    }
+    
+    [HttpDelete("{id}")]
+    public async Task<IActionResult> Delete(int id)
+    {
+        await _repo.DeleteAsync(id);
+        return NoContent();
+    }
+}
+```
+
+## Entity Framework Core
+
+```csharp
+// DbContext
+public class AppDbContext : DbContext
+{
+    public DbSet<User> Users { get; set; }
+    public DbSet<Order> Orders { get; set; }
+    
+    protected override void OnConfiguring(DbContextOptionsBuilder options)
+    {
+        options.UseNpgsql("Host=localhost;Database=mydb;Username=user;Password=pass");
+    }
+    
+    protected override void OnModelCreating(ModelBuilder modelBuilder)
+    {
+        // 配置
+        modelBuilder.Entity<User>(entity =>
+        {
+            entity.HasKey(u => u.Id);
+            entity.HasIndex(u => u.Email).IsUnique();
+            entity.Property(u => u.Name).HasMaxLength(50).IsRequired();
+        });
+    }
+}
+
+// 使用
+using var context = new AppDbContext();
+
+// 添加
+context.Users.Add(new User { Name = "张三" });
+await context.SaveChangesAsync();
+
+// 查询
+var user = await context.Users.FirstOrDefaultAsync(u => u.Id == 1);
+
+// 更新
+user.Name = "李四";
+await context.SaveChangesAsync();
+
+// 删除
+context.Users.Remove(user);
+await context.SaveChangesAsync();
+
+// 原始 SQL
+var users = await context.Users
+    .FromSqlRaw("SELECT * FROM users WHERE age > {0}", 18)
+    .ToListAsync();
+```
+
+## 依赖注入
+
+```csharp
+// 注册方式
+builder.Services.AddScoped<IUserRepository, UserRepository>();     // 每次请求新实例
+builder.Services.AddTransient<IMailService, MailService>();          // 每次注入新实例
+builder.Services.AddSingleton<ISettings, AppSettings>();              // 全局单例
+
+// 在类中注入
+public class UserService
+{
+    private readonly IUserRepository _userRepo;
+    private readonly IUnitOfWork _unitOfWork;
+    
+    // 构造函数注入（推荐）
+    public UserService(IUserRepository userRepo, IUnitOfWork unitOfWork)
+    {
+        _userRepo = userRepo;
+        _unitOfWork = unitOfWork;
+    }
+}
+```
+
+## 常用命令
+
+```bash
+# 创建项目
+dotnet new webapi -n MyApi
+dotnet new blazor -n MyBlazorApp
+dotnet new classlib -n MyLibrary
+
+# 添加包
+dotnet add package Npgsql.EntityFrameworkCore.PostgreSQL
+dotnet add package AutoMapper.Extensions.Microsoft.DependencyInjection
+
+# 运行
+dotnet run
+
+# 构建
+dotnet build
+
+# 发布
+dotnet publish -c Release -o ./publish
+
+# 测试
+dotnet test
+
+# 查看依赖
+dotnet list package
+```