StructureMapBuildPlanException：无法创建构建计划

Question

我正在使用AngularJS，Asp.Net Web API 2，数据访问层中的通用存储库模式（我在DAL项目中添加了IRepository和Repository）创建了一个示例应用程序，并且我有使用CodeFirst方法的UserContext类。

我在我的Web API项目中添加了StructureMap.WebAPI2 Nuget。我的IRepository代码是

public interface IRepository<C,T>
{
        IQueryable<T> GetAll();
        void Add(T entity);
        void Delete(T entity);
        void Edit(T entity);
        T GetById(int id);
        void Save();
}

My Repository类如下：

public class Repository<C, T> : IRepository<C, T> where T : class where C : DbContext,new()
{
        private C _entities = new C();
public C Context
        {
            get { return _entities; }
            set { _entities = value; }
        }
        protected DbSet<T> DbSet;

        public Repository(DbContext dataContext)
        {
            DbSet = Context.Set<T>();
        }

        public void Add(T entity)
        {

            _entities.Set<T>().Add(entity);
            Save();
        }

        public void Delete(T entity)
        {
            _entities.Set<T>().Remove(entity);
            Save();
        }

        public void Edit(T entity)
        {
            _entities.Entry(entity).State =            System.Data.Entity.EntityState.Modified;
            Save();
        }

        public IQueryable<T> GetAll()
        {
            IQueryable<T> query = _entities.Set<T>();
            return query;
        }



        public T GetById(int id)
        {
          return  DbSet.Find(id);

        }

        public void Save()
        {
            _entities.SaveChanges();
        }
}

在我的Web API项目中我的控制器有一个参数

public class UserAccountController : ApiController
    {
        private readonly IRepository<UserContext,UserAccount> _useraccount;

        [DefaultConstructor]
        public UserAccountController(IRepository<UserContext, UserAccount> useraccount)
        {
            _useraccount = useraccount;
        }



        [HttpPost]
        public int AddUser(UserAccount useracct)
        {
            UserAccount user3 = new UserAccount() { Name = "Oza", Email = "oza@email.com", Address = "Dover" };
            _useraccount.Add(user3);
            return user3.Id;
        }

        [HttpGet]
        public IHttpActionResult GetUserByID(int id)
        {
           UserAccount useracc =  _useraccount.GetById(id);            
            return Ok(useracc);
        }

        [HttpGet]
        public List<UserAccount> GetUsersList()
        {
            return _useraccount.GetAll().ToList<UserAccount>();
        }

        [HttpPut]
        public void ModifyUser(UserAccount useracc, int id)
        {
            if (useracc.Id == id)
            {
                _useraccount.Edit(useracc);
            }
        }

        [HttpDelete]
        public void DeleteUser(int id)
        {
            UserAccount useracc = _useraccount.GetById(id);
            if (useracc != null)
            {
                _useraccount.Delete(useracc);
            }

        }
    }

我的WebAPI配置有以下代码

public static class WebApiConfig
    {
        public static void Register(HttpConfiguration config)
        {
            // Web API configuration and services
            // Configure Web API to use only bearer token authentication.

            App_Start.StructuremapWebApi.Start();
            config.SuppressDefaultHostAuthentication();
            config.Filters.Add(new HostAuthenticationFilter(OAuthDefaults.AuthenticationType));

            // Web API routes
            config.MapHttpAttributeRoutes();

            config.Routes.MapHttpRoute(
                name: "DefaultApi",
                routeTemplate: "api/{controller}/{id}",
                defaults: new { id = RouteParameter.Optional }
            );



        }
    }

MyDefaultRegistry.cs（在添加nuget后添加到DependencyResolution文件夹中）

public class DefaultRegistry：Registry {         #region构造函数和析构函数

    public DefaultRegistry() {
        Scan(
            scan => {
                scan.TheCallingAssembly();
                scan.WithDefaultConventions();

                scan.Assembly("EntityFramework");
                scan.Assembly("EntityFramework.SqlServer");
                scan.Assembly("DataAccessLayer");
                scan.Assembly("DomainModels");
                scan.Assembly("DataRepositories");


            });
        //For<IExample>().Use<Example>();
        For<DataRepositories.IRepository<UserContext, UserAccount>>().Use<DataRepositories.Repository<UserContext, UserAccount>>();
    }

最后我的Global.Asax我添加了以下代码行

protected void Application_Start()
        {
            AreaRegistration.RegisterAllAreas();
            FilterConfig.RegisterGlobalFilters(GlobalFilters.Filters);
            IContainer container = DependencyResolution.IoC.Initialize();
            GlobalConfiguration.Configuration.DependencyResolver = new StructureMapWebApiDependencyResolver(container);
            GlobalConfiguration.Configure(WebApiConfig.Register);
            RouteConfig.RegisterRoutes(RouteTable.Routes);
            BundleConfig.RegisterBundles(BundleTable.Bundles);


        }

现在，当我尝试运行应用程序并从浏览器访问该服务时，它会抛出以下错误。

Unable to create a build plan for concrete type System.Data.Entity.DbContext
new DbContext(String nameOrConnectionString)
┗ String nameOrConnectionString = Required primitive dependency is not      explicitly defined
1.) Attempting to create a BuildPlan for Instance of System.Data.Entity.DbContext -- System.Data.Entity.DbContext
2.) new Repository`2(*Default of DbContext*)
3.) Repository<UserContext, UserAccount>
4.) Instance of IRepository<UserContext, UserAccount> (Repository<UserContext, UserAccount>)
5.) new UserAccountController(*Default of IRepository<UserContext, UserAccount>*)
6.) NAPService.Controllers.UserAccountController
7.) Instance of NAPService.Controllers.UserAccountController
8.) Container.GetInstance(NAPService.Controllers.UserAccountController)