Autofac容器使用属性进行WebApi自动注入

背景

使用Autofac进行依赖注入时，经常遇到的场景是在容器中进行类似如下代码的注入操作：

builder.RegisterType<BackInStockSubscriptionService>().As<IBackInStockSubscriptionService>().InstancePerLifetimeScope();

builder.RegisterType<CategoryService>().As<ICategoryService>().InstancePerLifetimeScope();

builder.RegisterType<CompareProductsService>().As<ICompareProductsService>().InstancePerLifetimeScope();

builder.RegisterType<RecentlyViewedProductsService>().As<IRecentlyViewedProductsService>().InstancePerLifetimeScope();

builder.RegisterType<ManufacturerService>().As<IManufacturerService>().InstancePerLifetimeScope();

builder.RegisterType<PriceFormatter>().As<IPriceFormatter>().InstancePerLifetimeScope();

builder.RegisterType<ProductAttributeFormatter>().As<IProductAttributeFormatter>().InstancePerLifetimeScope();

builder.RegisterType<ProductAttributeParser>().As<IProductAttributeParser>().InstancePerLifetimeScope();

因为这种注入是统一进行的，随着项目规模的扩大和代码复杂度的增加，需要在注册的地方不断地增加新的类来注册类型，这样会使代码失去了开闭原则：对修改关闭，对扩展开放。

解决方案

1. 定义一个属性用于标识类的注入意图，在应用初始化时利用反射进行集中类型注册。

    public class InjectableAttribute : Attribute

    {

    }

2. 在需要注入的类型中，使用[Injectable]标记注入

 public class Employee

    {

        public string Name { get; set; }

        public string Password { get; set; }

    }

    public interface IEmployeeManager

    {

        IList<Employee> GetAllEmployess();

    }

    public interface IEmployeeRepository

    {

        IList<Employee> GetAllEmployess();

    }

    [Injectable]

    public class EmployeeRepository : IEmployeeRepository

    {

        public IList<Employee> GetAllEmployess()

        {

            List<Employee> list = new List<Employee>();

            list.Add(new Employee { Name = "a", Password = "b" });

            return list;

        }

    }

    [Injectable]

    public class EmployeeManager : IEmployeeManager

    {

        private readonly IEmployeeRepository _employeeRepository;

        public EmployeeManager(IEmployeeRepository employeeRepository)

        {

            _employeeRepository = employeeRepository;

        }

        public IList<Employee> GetAllEmployess()

        {

            var employeeData = _employeeRepository.GetAllEmployess();

            var employeeList = new List<Employee>();

            foreach (var employee in employeeData)

            {

                var employ = new Employee();

                employ.Password= employee.Password;

                employ.Name = employee.Name;

                employeeList.Add(employ);

            }

            return employeeList;

        }

    }

3. 在WebApi的Controller中进行注入操作

 public class EmployeeController : ApiController

    {

        private readonly IEmployeeManager _employeeManager;

        public EmployeeController(IEmployeeManager employeeManager)

        {

            _employeeManager = employeeManager;

        }

        [AllowAnonymous]

        [ResponseType(typeof(Employee))]

        public IHttpActionResult GetEmployees()

        {

            var employeeData = _employeeManager.GetAllEmployess();

            return Ok(employeeData);

        }

    }

4. 项目中引用 Autofac.WebApi2 and AutoFac,定义如下容器初始化类

 public static class AutofacDependecyBuilder

    {

        public static void DependencyBuilder()

        {

            // Create the builder with which components/services are registered.

            var builder = new ContainerBuilder();

            // Register your Web API controllers.

            builder.RegisterApiControllers(Assembly.GetExecutingAssembly());

            builder.RegisterAssemblyTypes(AppDomain.CurrentDomain.GetAssemblies())

                                      .Where(t => t.GetCustomAttribute<InjectableAttribute>() != null)

                                      .AsImplementedInterfaces()

                                      .InstancePerRequest();

            builder.RegisterWebApiFilterProvider(GlobalConfiguration.Configuration);

            //Build the Container

            var container = builder.Build();

            //Create the Dependency Resolver

            AutofacWebApiDependencyResolver resolver = new AutofacWebApiDependencyResolver(container);

            //Configuring WebApi with Dependency Resolver

            GlobalConfiguration.Configuration.DependencyResolver = resolver;

        }

    }

5. 在Web程序开始处调用容器注册

    public class WebApiApplication : System.Web.HttpApplication

    {

        protected void Application_Start()

        {

            GlobalConfiguration.Configure(WebApiConfig.Register);

            RouteConfig.RegisterRoutes(RouteTable.Routes);

            AutofacDependecyBuilder.DependencyBuilder();

        }

    }

6.测试效果：

请求：

结果：

巴特西

Autofac容器使用属性进行WebApi自动注入

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