问AutoMapper on .Net Core 3.1

EN

using AutoMapper;
using Project.Content.EntityFrameWork;
using Project.Content.Dto;
using Microsoft.AspNetCore.Builder;
using Microsoft.AspNetCore.Hosting;
using Microsoft.EntityFrameworkCore;
using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Hosting;

namespace Project.Content
{
    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.AddControllers();
            // Auto Mapper Configurations
            services.AddAutoMapper(typeof(AutoMapping));

            string connectionString = Configuration["ConnectionString:Default"];
            services.AddDbContext<ProjectContext>(options =>
        options.UseSqlServer(connectionString));
        }

        // This method gets called by the runtime. Use this method to configure the HTTP request pipeline.
        public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
        {
            if (env.IsDevelopment())
            {
                app.UseDeveloperExceptionPage();
            }

            app.UseHttpsRedirection();

            app.UseRouting();

            app.UseAuthorization();

            app.UseEndpoints(endpoints =>
            {
                endpoints.MapControllers();
            });
        }
    }
}

using AutoMapper;
using Project.Content.Core.Domain.Model;

namespace Project.Content.Dto
{
    class AutoMapping : Profile
    {
        public AutoMapping()
        {
            CreateMap<Exercise, ExerciseDto>();
            CreateMap<ExerciseDto, Exercise>();
        }
    }
}

using AutoMapper;
using Project.Content.EntityFrameWork;
using Project.Content.Dto;
using Microsoft.AspNetCore.Mvc;
using Microsoft.Extensions.Logging;
using System;
using System.Collections.Generic;
using System.Linq;

namespace Project.Content.Controllers
{
    [ApiController]
    [Route("/exercise")]
    public class ExercisesController : ControllerBase
    {
        private readonly ILogger<ExercisesController> _logger;
        private ProjectContext _dbContext;
        private IMapper _mapper;

        public ExercisesController(ILogger<ExercisesController> logger, ProjectContext dbContext, IMapper mapper)
        {
            _logger = logger;
            _dbContext = dbContext;
            _mapper = mapper;
        }

        [HttpGet("{id}")]
        public ExerciseDto GetById(int id)
        {

            var exercise =  _mapper.Map<ExerciseDto>(_dbContext.Exercises.Where(x => x.Id == id));
            return exercise;
        }
    }
}