一、创建实体类库

1、创建单独实体类

创建DI.Entity类库，用来存放所有的实体类，新建用户实体类，其结构如下：

1 using System; 2 using System.Collections.Generic; 3 using System.Linq; 4 using System.Text; 5 using System.Threading.Tasks; 6  7 namespace DI.Entity 8 { 9     public class UserEntity10     {11         public int UserId { get; set; }12 13         public string UserName { get; set; }14 15         public int Sex { get; set; }16 17         public int Age { get; set; }18     }19 }

二、创建仓储接口类库

新建DI.Interface类库文件，存放所有接口，IUserRepository接口定义如下：

using DI.Entity;using System;using System.Collections.Generic;using System.Linq;using System.Text;using System.Threading.Tasks;namespace DI.Interface{    public interface IUserRepository    {        List
     
       GetUsers();    }}

三、创建仓储接口的实现类库

1、SQL Server数据库实现

新建DI.SqlServer类库文件，SqlServerUserRepository实现IUserRepository接口，SqlServerUserRepository类定义如下：

using DI.Entity;using DI.Interface;using System;using System.Collections.Generic;using System.Linq;using System.Text;using System.Threading.Tasks;namespace DI.SqlServer{    public class SqlServerUserRepository : IUserRepository    {        public List
     
       GetUsers()        {            List
      
        list = new List
       
        ()            {              new UserEntity(){UserId=1,UserName="王五",Sex=2,Age=21},              new UserEntity(){UserId=2,UserName="赵六",Sex=2,Age=23},            };            return list;        }    }}

2、Oracle数据库实现

新建DI.Oracle类库文件，OracleUserRepository实现IUserRepository接口，OracleUserRepository类定义如下：

using DI.Entity;using DI.Interface;using System;using System.Collections.Generic;using System.Linq;using System.Text;using System.Threading.Tasks;namespace DI.Oracle{    public class OracleUserRepository : IUserRepository    {        public List
     
       GetUsers()        {            List
      
        list = new List
       
        ()            {              new UserEntity(){UserId=1,UserName="张三",Sex=1,Age=24},              new UserEntity(){UserId=2,UserName="李四",Sex=1,Age=22},            };            return list;        }    }}

四、新建WebAPI项目

1、安装依赖项

通过NuGet安装所需的依赖项：Autofac、Autofac.WebApi2（如果使用的是WebApi1，这里需要安装WebApi）。

2、创建AutofacWebApiConfig类

AutofacWebApiConfig类定义如下：

using Autofac;using Autofac.Integration.WebApi;using DI.Interface;using DI.SqlServer;using System;using System.Collections.Generic;using System.Linq;using System.Reflection;using System.Web;using System.Web.Http;namespace WebApi.AutofacDI{    public class AutofacWebApiConfig    {        public static void RegisterDependencies()        {            SetAutofacWebapi();        }        private static void SetAutofacWebapi()        {            ContainerBuilder builder = new ContainerBuilder();            HttpConfiguration config = GlobalConfiguration.Configuration;            // Register API controllers using assembly scanning.            builder.RegisterApiControllers(Assembly.GetExecutingAssembly());            builder.RegisterAssemblyTypes(AppDomain.CurrentDomain.GetAssemblies()).Where(t => t.Name.EndsWith("Repository")).AsImplementedInterfaces();            // 使用SQLserver数据库实现            builder.RegisterType
     
      ().As
      
       ().InstancePerRequest();            var container = builder.Build();            // Set the WebApi dependency resolver.            config.DependencyResolver = new AutofacWebApiDependencyResolver(container);        }    }}

3、修改Global.asax文件

修改后的Global.asax文件定义如下：

using System;using System.Collections.Generic;using System.Linq;using System.Web;using System.Web.Http;using System.Web.Mvc;using System.Web.Optimization;using System.Web.Routing;using WebApi.AutofacDI;namespace WebApi{    public class WebApiApplication : System.Web.HttpApplication    {        protected void Application_Start()        {            AreaRegistration.RegisterAllAreas();            GlobalConfiguration.Configure(WebApiConfig.Register);            FilterConfig.RegisterGlobalFilters(GlobalFilters.Filters);            RouteConfig.RegisterRoutes(RouteTable.Routes);            BundleConfig.RegisterBundles(BundleTable.Bundles);            // 配置依赖注入            AutofacWebApiConfig.RegisterDependencies();        }    }}

4、创建Users控制器

创建UsersController类，并在构造函数中注入，UsersController类定义如下：

using DI.Entity;using DI.Interface;using System;using System.Collections.Generic;using System.Linq;using System.Net;using System.Net.Http;using System.Web.Http;namespace WebApi.Controllers{    public class UsersController : ApiController    {        private IUserRepository _userRepository;        ///         /// 构造函数中注入        /// 
        ///         public UsersController(IUserRepository userRepository)        {            this._userRepository = userRepository;        }        public IHttpActionResult Get()        {            return Json 
     
      
       >( _userRepository.GetUsers());        }    }}

5、测试

启动程序，然后在浏览器里面输入：http://localhost:51157/api/users，结果如下：

从结果中可以看出：这里使用的是SQLserver实现的。

修改AutofacWebApiConfig文件，用oracle实现，修改后的代码如下：

using Autofac;using Autofac.Integration.WebApi;using DI.Interface;using DI.Oracle;using DI.SqlServer;using System;using System.Collections.Generic;using System.Linq;using System.Reflection;using System.Web;using System.Web.Http;namespace WebApi.AutofacDI{    public class AutofacWebApiConfig    {        public static void RegisterDependencies()        {            SetAutofacWebapi();        }        private static void SetAutofacWebapi()        {            ContainerBuilder builder = new ContainerBuilder();            HttpConfiguration config = GlobalConfiguration.Configuration;            // Register API controllers using assembly scanning.            builder.RegisterApiControllers(Assembly.GetExecutingAssembly());            builder.RegisterAssemblyTypes(AppDomain.CurrentDomain.GetAssemblies()).Where(t => t.Name.EndsWith("Repository")).AsImplementedInterfaces();            // 使用SQLserver数据库实现            //builder.RegisterType
     
      ().As
      
       ().InstancePerRequest();            // 使用oracle数据库实现            builder.RegisterType
       
        ().As
        
         ().InstancePerRequest();            var container = builder.Build();            // Set the WebApi dependency resolver.            config.DependencyResolver = new AutofacWebApiDependencyResolver(container);        }    }}

运行结果：

从结果中可以看出：这里使用的是oracle实现的。

五、将Autofac的实现放到单独的类库中

新建DI.Server类库，将Autofac的注册单独放在类库中，AutofacWebApiConfig类定义如下：

using Autofac;using Autofac.Integration.WebApi;using DI.Interface;using DI.SqlServer;using System;using System.Collections.Generic;using System.Linq;using System.Reflection;using System.Text;using System.Threading.Tasks;using System.Web.Http;using System.Web.Mvc;namespace DI.Server{    public class AutofacWebApiConfig    {        public static void RegisterDependencies()        {            SetAutofacWebapi();        }        private static void SetAutofacWebapi()        {            ContainerBuilder builder = new ContainerBuilder();            HttpConfiguration config = GlobalConfiguration.Configuration;            // Register API controllers using assembly scanning.            builder.RegisterApiControllers(Assembly.LoadFrom(@"F:\Practice\WebAPI\WebApi依赖注入\DI\WebApiDIDemo\WebApi\bin\WebApi.dll"));            builder.RegisterAssemblyTypes(AppDomain.CurrentDomain.GetAssemblies()).Where(t => t.Name.EndsWith("Repository")).AsImplementedInterfaces();            builder.RegisterType
     
      ().As
      
       ().InstancePerRequest();            var container = builder.Build();            // Set the WebApi dependency resolver.            config.DependencyResolver = new AutofacWebApiDependencyResolver(container);        }    }}

注意：

如果是在单独的类库项目中，注册Api控制器的时候要加载WebApi项目所有的程序集文件，不要使用builder.RegisterApiControllers(Assembly.GetExecutingAssembly())，这里找到的当前程序集是类库文件，不是WebApi项目的程序集文件，在控制器里面不会实现注入。

2、修改Global.asax文件

修改后的Global.asax文件定义如下：

using DI.Server;using System;using System.Collections.Generic;using System.Linq;using System.Web;using System.Web.Http;using System.Web.Mvc;using System.Web.Optimization;using System.Web.Routing;namespace WebApi{    public class WebApiApplication : System.Web.HttpApplication    {        protected void Application_Start()        {            AreaRegistration.RegisterAllAreas();            GlobalConfiguration.Configure(WebApiConfig.Register);            FilterConfig.RegisterGlobalFilters(GlobalFilters.Filters);            RouteConfig.RegisterRoutes(RouteTable.Routes);            BundleConfig.RegisterBundles(BundleTable.Bundles);            // 配置依赖注入(注意：这里使用的是单独类库里面的AutofacWebApiConfig类)            AutofacWebApiConfig.RegisterDependencies();        }    }}

运行程序，效果和上面的一样。

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