ASP.NET MVC中的UnitOfWork错误

Question

我在mvc5项目中使用UnitOfWork模式。

我有一个带有服务的BLL层。

 public class StudentService
    {
        private readonly IUnitOfWork _db;

        public StudentService(IUnitOfWork uow)
        {
            _db = uow;
        }

        public IEnumerable<StudentView> GetStudentViews()
        {
            List<Student> students = _db.Students.GetAll().ToList();
            return Mapper.Map<List<Student>, List<StudentView>>(students);
        }
}

但是，当我尝试在mvc控制器中使用此服务时，出现错误：“没有为此对象定义无参数构造函数。”

public class StudentController : Controller
    {
        private readonly StudentService _service;

        public StudentController(StudentService service)
        {
            _service = service;
        }

        // GET: Student
        public ActionResult Index()
        {
            IEnumerable<StudentView> studentViews = _service.GetStudentViews();
            return View("Index", studentViews);
        }
}

我没有无参数构造函数，但是如何在控制器中将我的服务与无参数构造函数一起使用？

我将DI用于UnitOf工作：

 public class ServiceModule : NinjectModule
    {
        private string connection;
        public ServiceModule(string connection)
        {
            this.connection = connection;
        }

        public override void Load()
        {
            Bind<IUnitOfWork>().To<UnitOfWork>().WithConstructorArgument(connection);
        }
    }

Answer 1

“没有为此对象定义无参数构造函数。”

此消息表示您忘记注册StudentService的依赖项。 这就是为什么它忽略了构造函数

public StudentController(StudentService service)
        {
            _service = service;
        }

然后它开始寻找另一个无参数构造函数。

我建议您应该创建IStudentService接口

public class IStudentService

并使StudentService实现IStudentService

public class StudentService: IStudentService

然后在您的ServiceModule中

public class ServiceModule : NinjectModule
    {
        private string connection;
        public ServiceModule(string connection)
        {
            this.connection = connection;
        }

        public override void Load()
        {
            Bind<IUnitOfWork>().To<UnitOfWork>().WithConstructorArgument(connection);
            Bind<IStudentService>().To<StudentService>();
        }
    }

Answer 2

我已经解决了这个问题：

学生模块

public class StudentModule : NinjectModule
    {
        public override void Load()
        {
            Bind<IStudentService>().To<StudentService>();
        }
    }
}

Global.asax：

 public class MvcApplication : System.Web.HttpApplication
    {
        protected void Application_Start()
        {
           ///

            //dependencies
            NinjectModule serviceModule = new ServiceModule("connection");
            NinjectModule studentModule = new StudentModule();
            var kernel = new StandardKernel(studentModule, serviceModule);
            DependencyResolver.SetResolver(new NinjectDependencyResolver(kernel));
        }
    }

Answer 3

此错误不是由于UnitOfWork。 由于您的控制器StudentController发生了这种情况，并检查了该控制器的构造函数

public StudentController(StudentService service)

您的控制器需要StudentService实例，并且您没有为该StudentService类注册任何依赖项。 Asp.Net MVC控制器不需要参数构造函数，或者如果您有任何依赖关系，则需要在创建控制器之前解决该问题。

解决方案是为StudentService类创建一个Interface。

public interface IStudentService
{
     IEnumerable<StudentView> GetStudentViews();
}

并更新您的StudentService类以实现该接口

public class StudentService : IStudentService
{
    private readonly IUnitOfWork _db;

    public StudentService(IUnitOfWork uow)
    {
        _db = uow;
    }

    public IEnumerable<StudentView> GetStudentViews()
    {
        List<Student> students = _db.Students.GetAll().ToList();
        return Mapper.Map<List<Student>, List<StudentView>>(students);
    }
}

更新您的DI注册代码以注册此依赖关系。

public class ServiceModule : NinjectModule
    {
        private string connection;
        public ServiceModule(string connection)
        {
            this.connection = connection;
        }

        public override void Load()
        {
            Bind<IUnitOfWork>().To<UnitOfWork>().WithConstructorArgument(connection);
            Bind<IStudentService>().To<StudentService>();
        }
    }

更新您的StudentController和使用IStudentService代替StudentService 。

public class StudentController : Controller
    {
        private readonly IStudentService _service;

        public StudentController(IStudentService service)
        {
            _service = service;
        }

        // GET: Student
        public ActionResult Index()
        {
            IEnumerable<StudentView> studentViews = _service.GetStudentViews();
            return View("Index", studentViews);
        }
}