System.InvalidOperationException：无法解析 ASP.NET Core 中的服务

Question

我是 ASP.NET Core 的初学者。 我正在创建一个 Web API 服务。 当我从数据库中获取数据时，遇到了问题。 我得到的错误是什么？ 我已经成功完成了数据库迁移部分并成功创建了数据库。

System.InvalidOperationException：尝试激活“webb.Controllers.StudentController”时无法解析类型“webb.StudentDbContext”的服务。

在 Microsoft.Extensions.DependencyInjection.ActivatorUtilities.GetService（IServiceProvider sp，类型类型，类型 requiredBy，Boolean isDefaultParameterRequired）
在 lambda_method3（闭包，IServiceProvider，对象[]）

StudentController ：

[Route("api/[controller]")]
[ApiController]
public class StudentController : ControllerBase
{
    private StudentDbContext studentDbContext;

    public StudentController(StudentDbContext studentDbContext)
    {
        studentDbContext = studentDbContext;
    }

    // GET: api/<EmployeeController>
    [HttpGet]
    public IEnumerable<Student> Get()
    {
        return studentDbContext.Student;
    }
}

Model class：

namespace webb.Model
{
    public class Student
    {
        public int id { get; set; }
        public int stname { get; set; }

        public int course { get; set; }
    }
}

StudentDbContext ：

 public class StudentDbContext : DbContext
 {
     public DbSet<Student> Student { get; set; }

     public StudentDbContext()
     {
     }

     public StudentDbContext(DbContextOptions options) : base(options)
     {
     }

     protected override void OnModelCreating(ModelBuilder modelBuilder)
     {
         modelBuilder.Entity<Student>().HasKey(e => e.id);
     }

     protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
     {
         optionsBuilder.UseSqlServer("Data Source=.;Initial Catalog=sms;Integrated Security=True; TrustServerCertificate = True");
     }
}

appsettings.json ：

{
  "Logging": {
    "LogLevel": {
      "Default": "Information",
      "Microsoft.AspNetCore": "Warning"
    }
  },
  "AllowedHosts": "*",
  "ConnectionStrings": {
    "StudentConnStr": "Data Source=.;Initial Catalog=sms;Integrated Security=True;"
  }
}

我要在哪里设置密钥。

Program.cs ：

using Microsoft.EntityFrameworkCore;
using Microsoft.Extensions.Configuration;
using webb;

var builder = WebApplication.CreateBuilder(args);

// Add services to the container.

builder.Services.AddControllers();
// Learn more about configuring Swagger/OpenAPI at https://aka.ms/aspnetcore/swashbuckle
builder.Services.AddEndpointsApiExplorer();
builder.Services.AddSwaggerGen();

var app = builder.Build();

builder.Services.AddDbContext<StudentDbContext>(options =>
   options.UseSqlServer(builder.Configuration.GetConnectionString("StudentDbContext")));

// Configure the HTTP request pipeline.
if (app.Environment.IsDevelopment())
{
    app.UseSwagger();
    app.UseSwaggerUI();
}

app.UseHttpsRedirection();

app.UseAuthorization();

app.MapControllers();

app.Run();

Answer 1

看起来您错过了将StudentDbContext注入 DI 容器的 DbContext。

将以下内容添加到您的 Program.cs：

builder.Services.AddDbContext<StudentDbContext>(options =>
   options.UseSqlServer(builder.Configuration.GetConnectionString("StudentConnStr")));

请参阅此和第 5 部分，在 ASP.NET Core MVC 应用程序中使用数据库

更新

builder.Services.AddDbContext<StudentDbContext>(options =>
   options.UseSqlServer(builder.Configuration.GetConnectionString("StudentConnStr")));

var app = builder.Build();

Answer 2

builder.Build()应该在所有AddXXX函数之后。 换句话说，您需要将其与AddDbContext()交换

builder.Services.AddDbContext<StudentDbContext>(options =>
 options.UseSqlServer(builder.Configuration.GetConnectionString("StudentDbContext")));

var app = builder.Build();