如何修复“AmbiguousMatchException：请求匹配多个端点。”

Question

https://i.imgur.com/JphyUEv.png

在观看此 YouTube 视频 https://youtu.be/PlW9dgU_aVM 之后，了解如何在 ASP.NET CORE 应用程序中设置实体框架核心数据库的第一个 CRUD 操作。

此时https://youtu.be/PlW9dgU_aVM?t=578在处理请求时发生了未处理的异常，我该如何解决这个问题（参考上图）。

P.S 抱歉阅读和破译

这是 REST Api 在 ASP.NET CORE 应用程序中使用实体框架核心数据库的第一个 CRUD 操作。

项目包括 ASP.NET Core 2.2 Web 应用，Entity Framework 2.2 版，Web 应用（模型-视图-控制器）

我使用本地数据库来生成模型和控制器，看看它是否与防火墙或其他连接问题有关，但我 99% 确定它是我的代码... 我是一名初级开发人员 => 没有高级/干净的基础 =<.>

//Users Model - Auto generated
namespace Demo_Api.Models
{
    public partial class Users
    {
        public int Id { get; set; }
        public string Name { get; set; }
        public string Number { get; set; }
        public string Address { get; set; }
    }
}

//UsersContext - Auto generated - snip
using System;
using Microsoft.EntityFrameworkCore;
using Microsoft.EntityFrameworkCore.Metadata;

namespace Demo_Api.Models
{
    public partial class UsersContext : DbContext
    {
        public UsersContext()
        {
        }

        public UsersContext(DbContextOptions<UsersContext> options)
            : base(options)
        {
        }

        public virtual DbSet<Users> Users { get; set; }

        protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
        {
            if (!optionsBuilder.IsConfigured)
            {
#warning To protect potentially sensitive information in your connection string, you should move it out of source code. See http://go.microsoft.com/fwlink/?LinkId=723263 for guidance on storing connection strings.
                optionsBuilder.UseSqlServer("server=(localdb)\\MSSQLLocalDB;Database=Users; Trusted_Connection=True;");
            }
        }

        protected override void OnModelCreating(ModelBuilder modelBuilder)
        {
            modelBuilder.HasAnnotation("ProductVersion", "2.2.6-servicing-10079");

            modelBuilder.Entity<Users>(entity =>
            {
                entity.Property(e => e.Id).ValueGeneratedNever();

                entity.Property(e => e.Address).HasMaxLength(10);

                entity.Property(e => e.Name).HasMaxLength(10);

                entity.Property(e => e.Number).HasMaxLength(10);
            });
        }
    }
}

// UsersController - Auto generated - snip
using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;
using Microsoft.AspNetCore.Mvc;
using Microsoft.AspNetCore.Mvc.Rendering;
using Microsoft.EntityFrameworkCore;
using Demo_Api.Models;

namespace Demo_Api.Controllers
{
    public class UsersController : Controller
    {
        private readonly UsersContext _context;

        public UsersController(UsersContext context)
        {
            _context = context;
        }

        // GET: Users
        public async Task<IActionResult> Index()
        {
            return View(await _context.Users.ToListAsync());
        }

        // GET: Users/Details/5
        public async Task<IActionResult> Details(int? id)
        {
            if (id == null)
            {
                return NotFound();
            }

            var users = await _context.Users
                .FirstOrDefaultAsync(m => m.Id == id);
            if (users == null)
            {
                return NotFound();
            }

            return View(users);
        }

        // GET: Users/Create
        public IActionResult Create()
        {
            return View();
        }

        // POST: Users/Create
        // To protect from overposting attacks, please enable the specific properties you want to bind to, for 
        // more details see http://go.microsoft.com/fwlink/?LinkId=317598.
        [HttpPost]
        [ValidateAntiForgeryToken]
        public async Task<IActionResult> Create([Bind("Id,Name,Number,Address")] Users users)
        {
            if (ModelState.IsValid)
            {
                _context.Add(users);
                await _context.SaveChangesAsync();
                return RedirectToAction(nameof(Index));
            }
            return View(users);
        }

        // GET: Users/Edit/5
        public async Task<IActionResult> Edit(int? id)
        {
            if (id == null)
            {
                return NotFound();
            }

            var users = await _context.Users.FindAsync(id);
            if (users == null)
            {
                return NotFound();
            }
            return View(users);
        }

        // POST: Users/Edit/5
        // To protect from overposting attacks, please enable the specific properties you want to bind to, for 
        // more details see http://go.microsoft.com/fwlink/?LinkId=317598.
        [HttpPost]
        [ValidateAntiForgeryToken]
        public async Task<IActionResult> Edit(int id, [Bind("Id,Name,Number,Address")] Users users)
        {
            if (id != users.Id)
            {
                return NotFound();
            }

            if (ModelState.IsValid)
            {
                try
                {
                    _context.Update(users);
                    await _context.SaveChangesAsync();
                }
                catch (DbUpdateConcurrencyException)
                {
                    if (!UsersExists(users.Id))
                    {
                        return NotFound();
                    }
                    else
                    {
                        throw;
                    }
                }
                return RedirectToAction(nameof(Index));
            }
            return View(users);
        }

        // GET: Users/Delete/5
        public async Task<IActionResult> Delete(int? id)
        {
            if (id == null)
            {
                return NotFound();
            }

            var users = await _context.Users
                .FirstOrDefaultAsync(m => m.Id == id);
            if (users == null)
            {
                return NotFound();
            }

            return View(users);
        }

        // POST: Users/Delete/5
        [HttpPost, ActionName("Delete")]
        [ValidateAntiForgeryToken]
        public async Task<IActionResult> DeleteConfirmed(int id)
        {
            var users = await _context.Users.FindAsync(id);
            _context.Users.Remove(users);
            await _context.SaveChangesAsync();
            return RedirectToAction(nameof(Index));
        }

        private bool UsersExists(int id)
        {
            return _context.Users.Any(e => e.Id == id);
        }
    }
}

//StartUp.cs
using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;
using Microsoft.AspNetCore.Builder;
using Microsoft.AspNetCore.Hosting;
using Microsoft.AspNetCore.Http;
using Microsoft.AspNetCore.HttpsPolicy;
using Microsoft.AspNetCore.Mvc;
using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.DependencyInjection;

namespace Demo_Api
{
    public class Startup
    {
        public Startup(IConfiguration configuration)
        {
            Configuration = configuration;
        }

        public IConfiguration Configuration { get; }

        // This method gets called by the runtime. Use this method to add services to the container.
        public void ConfigureServices(IServiceCollection services)
        {
            services.Configure<CookiePolicyOptions>(options =>
            {
                // This lambda determines whether user consent for non-essential cookies is needed for a given request.
                options.CheckConsentNeeded = context => true;
                options.MinimumSameSitePolicy = SameSiteMode.None;
            });


            services.AddMvc().SetCompatibilityVersion(CompatibilityVersion.Version_2_2);
        }

        // This method gets called by the runtime. Use this method to configure the HTTP request pipeline.
        public void Configure(IApplicationBuilder app, IHostingEnvironment env)
        {
            if (env.IsDevelopment())
            {
                app.UseDeveloperExceptionPage();
            }
            else
            {
                app.UseExceptionHandler("/Home/Error");
                // The default HSTS value is 30 days. You may want to change this for production scenarios, see https://aka.ms/aspnetcore-hsts.
                app.UseHsts();
            }

            app.UseHttpsRedirection();
            app.UseStaticFiles();
            app.UseCookiePolicy();

            app.UseMvc(routes =>
            {
                routes.MapRoute(
                    name: "default",
                    template: "{controller=Home}/{action=Index}/{id?}");
            });
        }
    }
}

预期和实际结果：拥有一个 REST Api，我可以通过影响现有数据库来执行 CRUD 操作。

错误信息：

处理请求时发生未处理的异常。 InvalidOperationException：无法解析类型的服务 'Demo_Api.Models.UsersContext' 尝试激活时 'Demo_Api.Controllers.UsersController'。

Microsoft.Extensions.DependencyInjection.ActivatorUtilities.GetService(IServiceProvider sp, Type type, Type requiredBy, bool isDefaultParameterRequired)

Answer 1

您的 UsersContext 似乎没有连接到 Asp.net 的服务容器。

如果您打开您的 Startup.cs 文件并查找您的 ConfigureServices 函数，您将要在此处连接您的数据上下文。

这是从 microsoft 文档中提取的示例：

public void ConfigureServices(IServiceCollection services)
{
    services.AddDbContext<BloggingContext>(options => options.UseSqlite("Data Source=blog.db"));
}

但是，你的看起来更像：

public void ConfigureServices(IServiceCollection services)
{
    services.AddDbContext<UsersContext>(options => options.UseSqlServer("server=(localdb)\\MSSQLLocalDB;Database=Users; Trusted_Connection=True;"));
}

为了提供更多信息，这是告诉 Asp.net 如何解析您在 Controller 的构造函数中指定的类。有关更多信息，请搜索依赖注入或控制反转 (IoC) 主题。这些是用于实现此功能的技术。