我是 C# 和 ASP.NET Core 的新手。我的 Web 应用程序与 PostgreSQL 连接时遇到问题

Question

我正在开发一个简单的测试 Web 应用程序，具有注册和登录功能。我尝试使用此 POST 请求通过 Postman 向数据库添加新行：

https://localhost:7239/api/Auth/Register

但我收到此错误：

System.InvalidOperationException：尝试激活“WebApplication1.Controllers.AuthController”时无法解析类型“WebApplication1.Data.AppDbContext”的服务。

   at lambda_method13(Closure, IServiceProvider, Object[])
   at Microsoft.AspNetCore.Mvc.Controllers.ControllerFactoryProvider.<>c__DisplayClass6_0.<CreateControllerFactory>g__CreateController|0(ControllerContext controllerContext)
   at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.Next(State& next, Scope& scope, Object& state, Boolean& isCompleted)
   at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.InvokeInnerFilterAsync()
--- End of stack trace from previous location ---
   at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.<InvokeNextResourceFilter>g__Awaited|25_0(ResourceInvoker invoker, Task lastTask, State next, Scope scope, Object state, Boolean isCompleted)
   at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.Rethrow(ResourceExecutedContextSealed context)
   at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.Next(State& next, Scope& scope, Object& state, Boolean& isCompleted)
   at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.InvokeFilterPipelineAsync()
--- End of stack trace from previous location ---
   at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.<InvokeAsync>g__Awaited|17_0(ResourceInvoker invoker, Task task, IDisposable scope)
   at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.<InvokeAsync>g__Awaited|17_0(ResourceInvoker invoker, Task task, IDisposable scope)
   at Microsoft.AspNetCore.Authorization.AuthorizationMiddleware.Invoke(HttpContext context)
   at Microsoft.AspNetCore.Authentication.AuthenticationMiddleware.Invoke(HttpContext context)
   at Microsoft.AspNetCore.Diagnostics.DeveloperExceptionPageMiddlewareImpl.Invoke(HttpContext context)

数据库已启动并正在运行。

这是我的

AuthController.cs

：

using Microsoft.AspNetCore.Mvc;
using Microsoft.EntityFrameworkCore;
using WebApplication1.Data;
using WebApplication1.Models;
using System.Threading.Tasks;

namespace WebApplication1.Controllers
{
    [Route("api/[controller]")]
    [ApiController]
    public class AuthController : ControllerBase
    {
        private readonly AppDbContext _context;

        public AuthController(AppDbContext context)
        {
            _context = context;
        }

        [HttpPost("register")]
        public async Task<IActionResult> Register(User user)
        {
            if (ModelState.IsValid)
            {
                _context.Users.Add(user);
                await _context.SaveChangesAsync();
                return Ok("User registered successfully.");
            }
            return BadRequest("Invalid model state.");
        }

        [HttpPost("login")]
        public async Task<IActionResult> Login(User user)
        {
            var existingUser = await _context.Users.FirstOrDefaultAsync(u => u.Username == user.Username && u.Password == user.Password);

            if (existingUser != null)
            {
                return Ok("Login successful.");
            }

            return BadRequest("Invalid username or password.");
        }
    }
}

AppDbContext.cs

：

using Microsoft.EntityFrameworkCore;
using WebApplication1.Models;

namespace WebApplication1.Data
{
    public class AppDbContext(DbContextOptions<AppDbContext> options) : DbContext(options)
    {
        public DbSet<User> Users { get; set; }
    }
}

Startup.cs

的一部分：

public void ConfigureServices(IServiceCollection services)
{
    services.AddDbContext<AppDbContext>(options =>
        options.UseNpgsql(Configuration.GetConnectionString("DefaultConnection")));

    services.AddControllers();
}

appsettings.json

：

{
  "ConnectionStrings": {
    "DefaultConnection": "Host=localhost;Port=5432;Database=database;Username=postgres;Password=qwertyps4;"
  },
  "Logging": {
    "LogLevel": {
      "Default": "Information",
      "Microsoft.AspNetCore": "Warning"
    }
  },
  "AllowedHosts": "*"
}

最后是模型

User.cs

：

using System.ComponentModel.DataAnnotations;

namespace WebApplication1.Models
{
    public class User
    {
        public int Id { get; set; }

        [Required]
        public string Username { get; set; }

        [Required]
        public string Password { get; set; }
    }
}

我已经检查了所有文件好几次了，但就是无法找出问题所在。

Answer 1

将您的 AppContext.cs 修改为此并添加无参数构造函数。

    public class AppDbContext : DbContext
 {
    // Constructor with DbContextOptions
    public AppDbContext(DbContextOptions<AppDbContext> options) : base(options)
    {
    }

    // Parameterless constructor
    public AppDbContext()
    {
    }
   
    public DbSet<User> Users { get; set; }
}