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