使用 ASP.NET Core 创建 Web API（基于Net.Core 3.1和Visual Studio 2019）

使用 ASP.NET Core 创建 Web API

创建Web项目

打开Visual Studio 2019，点击创建新项目

选择ASP.NET Core Web API

输入项目名称，勾选将解决方案和项目房租同一目录中

选择目标框架为.NET Core 3.1，勾选配置HTTPS

生成的项目目录结构如下图所示

运行项目会在浏览器中跳转出如下内容

添加模型类

在项目根目录下新建Models文件夹

点击右键，选择添加，选择类。

将类命名为TodoItem

新建的TodoItem类如图所示

替换TodoItem为如下内容：

public class TodoItem
{
    public long Id { get; set; }
    public string Name { get; set; }
    public bool IsComplete { get; set; }
}

添加数据库上下文

点击工具，选择NuGet包管理器，选择管理解决方案的NuGet程序包

搜索Microsoft.EntityFrameworkCore.InMemory

右键单击 Models 文件夹，然后选择“添加” > “类” 。 将类命名为 TodoContext，然后单击“添加”。

输入如下代码：

using Microsoft.AspNetCore.Builder;
using Microsoft.AspNetCore.Hosting;
using Microsoft.AspNetCore.HttpsPolicy;
using Microsoft.AspNetCore.Mvc;
using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Hosting;
using Microsoft.Extensions.Logging;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;
using Microsoft.EntityFrameworkCore;
using TodoApi.Models;

namespace TodoApi
{
    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();
            });
        }
    }
}

注册数据库上下文

在 ASP.NET Core 中，服务（如数据库上下文）必须向依赖关系注入容器进行注册。 该容器向控制器提供服务。

using Microsoft.AspNetCore.Builder;
using Microsoft.AspNetCore.Hosting;
using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Hosting;
using Microsoft.EntityFrameworkCore; // 导入依赖
using TodoApi.Models; // 导入依赖

namespace TodoApi
{
    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)
        {
            // 将数据库上下文添加到 DI 容器。
            // 指定数据库上下文将使用内存中数据库。
            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();
            });
        }
    }
}

构建控制器

右键Controller文件夹。

选择添加，选择控制器

选择其操作使用Entity Framework的API控制器

• 在“模型类”中选择“TodoItem (TodoApi.Models)” 。
• 在“数据上下文类”中选择“TodoContext (TodoApi.Models)” 。
• 选择“添加”。

生成文件结构下图所示

代码如下：

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 TodoApi.Models;

namespace TodoApi.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(long id)
        {
            var todoItem = await _context.TodoItems.FindAsync(id);

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

            return todoItem;
        }

        // PUT: api/TodoItems/5
        // To protect from overposting attacks, enable the specific properties you want to bind to, for
        // more details, see https://go.microsoft.com/fwlink/?linkid=2123754.
        [HttpPut("{id}")]
        public async Task<IActionResult> PutTodoItem(long 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, enable the specific properties you want to bind to, for
        // more details, see https://go.microsoft.com/fwlink/?linkid=2123754.
        [HttpPost]
        public async Task<ActionResult<TodoItem>> PostTodoItem(TodoItem todoItem)
        {
            _context.TodoItems.Add(todoItem);
            await _context.SaveChangesAsync();

            return CreatedAtAction("GetTodoItem", new { id = todoItem.Id }, todoItem);
        }

        // DELETE: api/TodoItems/5
        [HttpDelete("{id}")]
        public async Task<ActionResult<TodoItem>> DeleteTodoItem(long 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(long id)
        {
            return _context.TodoItems.Any(e => e.Id == id);
        }
    }
}

使用Postman进行测试