public void ConfigureServices(IServiceCollection services)

{

            //services.AddMvc(); core 3.0以前是这样写的，这个服务包括了    TageHelper等 WebApi不需要的东西，所有3.0以后可以不这样写

            services.AddControllers();

}

public void Configure(IApplicationBuilder app, IWebHostEnvironment env)

{

            if (env.IsDevelopment())

            {

                app.UseDeveloperExceptionPage();

            }

            app.UseRouting();

            app.UseAuthorization();

            app.UseEndpoints(endpoints =>

            {

                endpoints.MapControllers();

            });

}

using Microsoft.AspNetCore.Mvc;

using Routine.Api.Service;

using System;

using System.Threading.Tasks;

namespace Routine.Api.Controllers

{

    [ApiController] //好处：ApiController不是强制的

                    //1.会启用使用属性路由（Attribute Routing）

                    //2.自动HTTP 400响应

                    //3.推断参数的绑定源

                    //4.Multipart/form-data 请求推断

                    //5.错误状态代码的问题详细信息

    [Route("api/companies")]    //写法一

    //[Route("api/[controller]")]   //写法二：意思是相当于刨除了Controller后缀，获取前面的 Companies C可以是小写，如果你改名了那么你路由的uri也跟着变了（不建议这样写）

    public class CompaniesController:ControllerBase

    {

        private readonly ICompanyRepository _companyRepository;

        public CompaniesController(ICompanyRepository companyRepository)

        {

            _companyRepository = companyRepository ??

                                 throw new ArgumentNullException(nameof(companyRepository));

        }

        [HttpGet]

        //IActionResult定义了一些合约，它可以代表ActionResult返回的结果

        public async Task<IActionResult> GetCompanies()

        {

            var companies =await _companyRepository.GetCompaniesAsync();//读取出来的是List

            return Ok(companies);

        }

        [HttpGet("{companyId}")] // Controller标注了ApiController => uri=> api/companies/{companyId}

        public async Task<IActionResult> GetCompany(Guid companyId)

        {

            //判断该公司是否存在方法一：这种方法在处理并发请求时可能会出现错误，原因是查到之后，进行删除，进入company后也可能是404找不到了

            //var exists =await _companyRepository.CompanyExistsAsync(compamyId);

            //if (!exists)

            //{

            //    //不存在应该返回404

            //    return NotFound();

            //}

            var company = await _companyRepository.GetCompanyAsync(companyId);//读取出来的是List

            //方法二

            if (company==null)

            {

                return NotFound();

            }

            return Ok(company);

        }

    }

}

using System;

using System.Collections.Generic;

using System.Linq;

using System.Threading.Tasks;

using Microsoft.AspNetCore.Builder;

using Microsoft.AspNetCore.Hosting;

using Microsoft.AspNetCore.Mvc;

using Microsoft.AspNetCore.Mvc.Formatters;

using Microsoft.EntityFrameworkCore;

using Microsoft.Extensions.Configuration;

using Microsoft.Extensions.DependencyInjection;

using Microsoft.Extensions.Hosting;

using Microsoft.Extensions.Logging;

using Routine.Api.Data;

using Routine.Api.Service;

namespace Routine.Api

{

    public class Startup

    {

        public Startup(IConfiguration configuration)

        {

            Configuration = configuration;

        }

        public IConfiguration Configuration { get; }

        public void ConfigureServices(IServiceCollection services)

        {

            //services.AddMvc(); core 3.0以前是这样写的，这个服务包括了TageHelper等 WebApi不需要的东西，所有3.0以后可以不这样写

            services.AddControllers(setup =>

            {

                //setup.ReturnHttpNotAcceptable=false;//如果客户端默认为xml格式，服务器端为json，false就不会返回406

                setup.ReturnHttpNotAcceptable = true;//如果请求的类型和服务器请求的类型不一致就返回406

                //setup.OutputFormatters.Add(new XmlDataContractSerializerOutputFormatter());

                //setup.OutputFormatters.Insert(0, new XmlDataContractSerializerOutputFormatter());

            }).AddXmlDataContractSerializerFormatters();

            //配置接口服务:涉及到这个服务注册的生命周期这里采用AddScoped，表示每次的Http请求

            services.AddScoped<ICompanyRepository, CompanyRepository>();

            //获取配置文件中的数据库字符串连接

            var sqlConnection = Configuration.GetConnectionString("SqlServerConnection");

            //配置上下文类DbContext，因为它本身也是一套服务

            services.AddDbContext<RoutineDbContext>(options =>

            {

                options.UseSqlServer(sqlConnection);

            });

        }

        public void Configure(IApplicationBuilder app, IWebHostEnvironment env)

        {

            if (env.IsDevelopment())

            {

                app.UseDeveloperExceptionPage();

            }

            app.UseRouting();

            app.UseAuthorization();

            app.UseEndpoints(endpoints =>

            {

                endpoints.MapControllers();

            });

        }

    }

}