这是一篇图文基础教程：适合新手练习。

开发环境VS2019+.net core 3.0

需要安装core 3.0

检验是否安装core 3.0  ----cmd   命令dotnet --info

运行vs2019

创建新项目---选择ASP.NET Core Web应用程序

配置项目

选择项目类型--API

点击创建---等一会就会有模版了

运行这个项目，会在浏览器上显示一个json数据。这个默认生成的数据。

然后下一步：

创建Models文件夹：

然后右键Models文件夹，添加一个类文件：TodoItem

namespace WebTest.Models
{
    public class TodoItem
    {
        public int Id { get; set; }
        public string Name { get; set; }
        public bool IsBlack { get; set; }
    }
}

下一步需要引用nuget扩展包

连续步骤 添加：Microsoft.EntityFrameworkCore.SqlServer

和        Microsoft.EntityFrameworkCore.InMemory

安装完之后，右键Models文件夹添加TodoContext 数据库上下文类

using Microsoft.EntityFrameworkCore;

namespace WebTest.Models
{
    public class TodoContext : DbContext
    {
        public TodoContext(DbContextOptions<TodoContext> options) : base(options)
        { }
        public DbSet<TodoItem> TodoItems { get; set; }
    }
}

上下文添加完之后需要Startup.cs修改一下：向依赖关系注入 (DI) 容器进行注册

using Microsoft.AspNetCore.Builder;
using Microsoft.AspNetCore.Hosting;
using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Hosting;
using Microsoft.EntityFrameworkCore;
using WebTest.Models;

namespace WebTest
{
    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.AddDbContext<TodoContext>(opt => opt.UseInMemoryDatabase("TodoList"));
            services.AddControllers();
        }

        // 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();
            });
        }
    }
}

下一步，添加控制器：右键Controllers文件夹，

继续：

继续：选择对应的项：

控制器代码：

using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;
using Microsoft.AspNetCore.Http;
using Microsoft.AspNetCore.Mvc;
using Microsoft.EntityFrameworkCore;
using WebTest.Models;

namespace WebTest.Controllers
{
    [Route("api/[controller]")]
    [ApiController]
    public class TodoItemsController : ControllerBase
    {
        private readonly TodoContext _context;

        public TodoItemsController(TodoContext context)
        {
            _context = context;
        }

        // GET: api/TodoItems
        [HttpGet]
        public async Task<ActionResult<IEnumerable<TodoItem>>> GetTodoItems()
        {
            return await _context.TodoItems.ToListAsync();
        }

        // GET: api/TodoItems/5
        [HttpGet("{id}")]
        public async Task<ActionResult<TodoItem>> GetTodoItem(int id)
        {
            var todoItem = await _context.TodoItems.FindAsync(id);

            if (todoItem == null)
            {
                return NotFound();
            }

            return todoItem;
        }

        // PUT: api/TodoItems/5
        // To protect from overposting attacks, please enable the specific properties you want to bind to, for
        // more details see https://aka.ms/RazorPagesCRUD.
        [HttpPut("{id}")]
        public async Task<IActionResult> PutTodoItem(int id, TodoItem todoItem)
        {
            if (id != todoItem.Id)
            {
                return BadRequest();
            }

            _context.Entry(todoItem).State = EntityState.Modified;

            try
            {
                await _context.SaveChangesAsync();
            }
            catch (DbUpdateConcurrencyException)
            {
                if (!TodoItemExists(id))
                {
                    return NotFound();
                }
                else
                {
                    throw;
                }
            }

            return NoContent();
        }

        // POST: api/TodoItems
        // To protect from overposting attacks, please enable the specific properties you want to bind to, for
        // more details see https://aka.ms/RazorPagesCRUD.
        [HttpPost]
        public async Task<ActionResult<TodoItem>> PostTodoItem(TodoItem todoItem)
        {
            _context.TodoItems.Add(todoItem);
            await _context.SaveChangesAsync();

            //return CreatedAtAction("GetTodoItem", new { id = todoItem.Id }, todoItem);
            //nameof是为了调用方法时不采用硬编码
            return CreatedAtAction(nameof(GetTodoItem), new { id = todoItem.Id }, todoItem);
        }

        // DELETE: api/TodoItems/5
        [HttpDelete("{id}")]
        public async Task<ActionResult<TodoItem>> DeleteTodoItem(int id)
        {
            var todoItem = await _context.TodoItems.FindAsync(id);
            if (todoItem == null)
            {
                return NotFound();
            }

            _context.TodoItems.Remove(todoItem);
            await _context.SaveChangesAsync();

            return todoItem;
        }

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

这样之后，就可以使用Postman来测试：

浏览器运行可以看到结果。使用postman的时候，程序需要运行着。

可参考：https://docs.microsoft.com/zh-cn/aspnet/core/tutorials/first-web-api?view=aspnetcore-3.0&tabs=visual-studio