InvalidCastException的使用LINQ

Question

查詢嵌套集合時，我有一個類似的問題，因爲在這個問題：linq question: querying nested collections

我有一個ICollection<Category>一個產品，我想通過ID的類別。我通過一個IProductsRepository。

我已經嘗試了products.SelectMany(p => p.Categories).Where(c => c.CategoryID == categoryId)和products.SelectMany(p => p.Categories).First(c => c.CategoryID == categoryId)以及我嘗試過的許多其他變體。但是我沒有得到它的工作。

在運行時我收到InvalidCastException。 Category.CategoryID和categoryId都是int。

創建一個ICategoriesRepository會更好嗎？也許它也有性能優勢？我明顯對LINQ很陌生，因此不確定如何正確執行操作。

EDIT（代碼示例）：

public interface IProductsRepository 
{ 
    IQueryable<Product> Products { get; } 
} 

public class ProductsController : Controller 
{ 
    public int PageSize = 4; 
    private IProductsRepository productsRepository; 

    public ProductsController(IProductsRepository productsRepository) 
    { 
     this.productsRepository = productsRepository; 
    } 

    public ViewResult ListById(int categoryId, int page = 1) 
    { 
     Category cat; 
     // What do I need here to get the Category with the categoryId regardless of which Product it is connected to? 
     return List(cat, page); 
    } 

    private ViewResult List(Category category, int page = 1) { //this code works } 
} 

[Table(Name = "products")] 
public class Product 
{ 
    [HiddenInput(DisplayValue = false)] 
    [Column(Name = "id", IsPrimaryKey = true, IsDbGenerated = true, AutoSync = AutoSync.OnInsert)] 
    public int ProductID { get; set; } 

    [Column] 
    public string Name { get; set; } 

    [Column(Name = "info")] 
    public string Description { get; set; } 

    public float LowestPrice 
    { 
     get { return (from product in ProductSubs select product.Price).Min(); } 
    } 

    private EntitySet<Category> _Categories = new EntitySet<Category>(); 
    [System.Data.Linq.Mapping.Association(Storage = "_Categories", OtherKey = "CategoryID")] 
    public ICollection<Category> Categories 
    { 
     get { return _Categories; } 
     set { _Categories.Assign(value); } 
    } 
} 

[Table(Name = "products_types")] 
public class Category 
{ 
    [HiddenInput(DisplayValue = false)] 
    [Column(Name = "id", IsPrimaryKey = true, IsDbGenerated = true, AutoSync = AutoSync.OnInsert)] 
    public int CategoryID { get; set; } 

    [Column(Name = "id")] // Temp solution, real name is localized in a separate table 
    public string Name { get; set; } 

    private EntitySet<Product> _Products = new EntitySet<Product>(); 
    [System.Data.Linq.Mapping.Association(Storage = "_Products", OtherKey = "ProductID")] 
    public ICollection<Product> Products 
    { 
     get { return _Products; } 
     set { _Products.Assign(value); } 
    } 
} 

編輯：

我試圖做到這一點通過ICategoriesRepository代替，但我得到了同樣的錯誤。這是一個完整的堆棧跟蹤：

[InvalidCastException的：指定的轉換是無效] System.Data.Linq.SqlClient.SqlProvider.Execute（表達式查詢，QueryInfo queryInfo，IObjectReaderFactory廠，對象[] parentArgs，對象[ ] userArgs，ICompiledSubQuery [] subQueries，Object lastResult）+1191 System.Data.Linq.SqlClient.SqlProvider.ExecuteAll（Expression query，QueryInfo [] queryInfos，IObjectReaderFactory factory，Object [] userArguments，ICompiledSubQuery [] subQueries）+118 System.Data.Linq.SqlClient.SqlProvider.System.Data.Linq.Provider.IProvider.Execute（表達式查詢）+342 System.Data.Linq.Table 1.System.Linq.IQueryProvider.Execute(Expression expression) +58 System.Linq.Queryable.First(IQueryable 1來源，表達式1 predicate) +287 MaxFPS.WebUI.Controllers.ProductsController.ListById(Int32 categoryId, Int32 page) in d:\Filer\Documents\Dropbox\ZkilfinG\webbutveckling\MaxFPS\VS Projects\MaxFPS\MaxFPS\Controllers\ProductsController.cs:26 lambda_method(Closure , ControllerBase , Object[]) +140 System.Web.Mvc.ActionMethodDispatcher.Execute(ControllerBase controller, Object[] parameters) +14 System.Web.Mvc.ReflectedActionDescriptor.Execute(ControllerContext controllerContext, IDictionary 2參數）+182 System.Web .Mvc.Cont rollerActionInvoker.InvokeActionMethod（ControllerContext controllerContext，ActionDescriptor actionDescriptor，IDictionary的2 parameters) +27 System.Web.Mvc.Async.<>c__DisplayClass42.<BeginInvokeSynchronousActionMethod>b__41() +28 System.Web.Mvc.Async.<>c__DisplayClass8 1.b__7（IAsyncResult的_）10 System.Web.Mvc.Async.WrappedAsyncResult 1.End() +50 System.Web.Mvc.Async.AsyncControllerActionInvoker.EndInvokeActionMethod(IAsyncResult asyncResult) +32 System.Web.Mvc.Async.<>c__DisplayClass39.<BeginInvokeActionMethodWithFilters>b__33() +58 System.Web.Mvc.Async.<>c__DisplayClass4f.<InvokeActionMethodFilterAsynchronously>b__49() +225 System.Web.Mvc.Async.<>c__DisplayClass37.<BeginInvokeActionMethodWithFilters>b__36(IAsyncResult asyncResult) +10 System.Web.Mvc.Async.WrappedAsyncResult 1.End（）50 System.Web.Mvc.Async.AsyncControllerActionInvoker。 EndInvokeActionMethodWithFilters（IAsyncResult asyncResult）+34 System.Web.Mvc.Async。 <> c__DisplayClass2a.b__20（）+24 System.Web.Mvc.Async。 <> c__DisplayClass25.b__22（IAsyncResult的asyncResult）99 System.Web.Mvc.Async.WrappedAsyncResult 1.End() +50 System.Web.Mvc.Async.AsyncControllerActionInvoker.EndInvokeAction(IAsyncResult asyncResult) +27 System.Web.Mvc.<>c__DisplayClass1d.<BeginExecuteCore>b__18(IAsyncResult asyncResult) +14 System.Web.Mvc.Async.<>c__DisplayClass4.<MakeVoidDelegate>b__3(IAsyncResult ar) +23 System.Web.Mvc.Async.WrappedAsyncResult 1.End（）55 System.Web.Mvc.Controller.EndExecuteCore（IAsyncResult的asyncResult）39 的System.Web。 Mvc.Async。 <> c__DisplayClass4.b__3（IAsyncResult的AR）23 System.Web.Mvc.Async.WrappedAsyncResult 1.End() +55 System.Web.Mvc.Controller.EndExecute(IAsyncResult asyncResult) +29 System.Web.Mvc.Controller.System.Web.Mvc.Async.IAsyncController.EndExecute(IAsyncResult asyncResult) +10 System.Web.Mvc.<>c__DisplayClass8.<BeginProcessRequest>b__3(IAsyncResult asyncResult) +25 System.Web.Mvc.Async.<>c__DisplayClass4.<MakeVoidDelegate>b__3(IAsyncResult ar) +23 System.Web.Mvc.Async.WrappedAsyncResult 1.End（）55 System.Web.Mvc.MvcHandler.EndProcessRequest（IAsyncResult的asyncResult）31 的System.Web。 Mvc.MvcHandler.System.Web.IHttpAsyncHandler.EndProcessRequest（IAsyncResult的結果）9 System.Web.CallHandlerExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute（）9629708 System.Web.HttpApplication.ExecuteStep（IExecutionStep步驟，布爾& completedSynchronously）155

編輯：

當類標識符是已設定爲一個id是不在數據庫中，我得到一個空序列。這對我來說表明比較代碼是正確的，但我不明白爲什麼或什麼是無效投射。

[InvalidOperationException異常：序列不包含任何元素] System.Data.Linq.SqlClient.SqlProvider.Execute（表達式查詢，QueryInfo queryInfo，IObjectReaderFactory工廠，對象[] parentArgs，對象[] userArgs，ICompiledSubQuery []子查詢，對象+1191 System.Data.Linq.SqlClient.SqlProvider.ExecuteAll（表達式查詢，QueryInfo [] queryInfos，IObjectReaderFactory工廠，Object [] userArguments，ICompiledSubQuery []子查詢）+118 System.Data.Linq.SqlClient.SqlProvider .System.Data.Linq.Provider.IProvider.Execute（表達式查詢）+342 System.Data.Linq.Table 1.System.Linq.IQueryProvider.Execute(Expression expression) +58 System.Linq.Queryable.First(IQueryable 1 source，Expression 1 predicate) +287 MaxFPS.WebUI.Controllers.ProductsController.ListById(Int32 categoryId, Int32 page) in d:\Filer\Documents\Dropbox\ZkilfinG\webbutveckling\MaxFPS\VS Projects\MaxFPS\MaxFPS\Controllers\ProductsController.cs:28 lambda_method(Closure , ControllerBase , Object[]) +140 System.Web.Mvc.ActionMethodDispatcher.Execute(ControllerBase controller, Object[] parameters) +14 System.Web.Mvc.ReflectedActionDescriptor.Execute(ControllerContext controllerContext, IDictionary 2 parameters）+182 System.Web.Mvc.ControllerActionInvo ker.InvokeActionMethod（ControllerContext controllerContext，ActionDescriptor actionDescriptor，IDictionary的2 parameters) +27 System.Web.Mvc.Async.<>c__DisplayClass42.<BeginInvokeSynchronousActionMethod>b__41() +28 System.Web.Mvc.Async.<>c__DisplayClass8 1.b__7（IAsyncResult的_）10 System.Web.Mvc.Async.WrappedAsyncResult 1.End() +50 System.Web.Mvc.Async.AsyncControllerActionInvoker.EndInvokeActionMethod(IAsyncResult asyncResult) +32 System.Web.Mvc.Async.<>c__DisplayClass39.<BeginInvokeActionMethodWithFilters>b__33() +58 System.Web.Mvc.Async.<>c__DisplayClass4f.<InvokeActionMethodFilterAsynchronously>b__49() +225 System.Web.Mvc.Async.<>c__DisplayClass37.<BeginInvokeActionMethodWithFilters>b__36(IAsyncResult asyncResult) +10 System.Web.Mvc.Async.WrappedAsyncResult 1.End（）50 System.Web.Mvc.Async.AsyncControllerActionInvoker。 EndInvokeActionMethodWithFilters（IAsyncResult asyncResult）+34 System.Web.Mvc.Async。 <> c__DisplayClass2a.b__20（）+24 System.Web.Mvc.Async。 <> c__DisplayClass25.b__22（IAsyncResult的asyncResult）99 System.Web.Mvc.Async.WrappedAsyncResult 1.End() +50 System.Web.Mvc.Async.AsyncControllerActionInvoker.EndInvokeAction(IAsyncResult asyncResult) +27 System.Web.Mvc.<>c__DisplayClass1d.<BeginExecuteCore>b__18(IAsyncResult asyncResult) +14 System.Web.Mvc.Async.<>c__DisplayClass4.<MakeVoidDelegate>b__3(IAsyncResult ar) +23 System.Web.Mvc.Async.WrappedAsyncResult 1.End（）55 System.Web.Mvc.Controller.EndExecuteCore（IAsyncResult的asyncResult）39 的System.Web。 Mvc.Async。 <> c__DisplayClass4.b__3（IAsyncResult的AR）23 System.Web.Mvc.Async.WrappedAsyncResult 1.End() +55 System.Web.Mvc.Controller.EndExecute(IAsyncResult asyncResult) +29 System.Web.Mvc.Controller.System.Web.Mvc.Async.IAsyncController.EndExecute(IAsyncResult asyncResult) +10 System.Web.Mvc.<>c__DisplayClass8.<BeginProcessRequest>b__3(IAsyncResult asyncResult) +25 System.Web.Mvc.Async.<>c__DisplayClass4.<MakeVoidDelegate>b__3(IAsyncResult ar) +23 System.Web.Mvc.Async.WrappedAsyncResult 1.End（）55 System.Web.Mvc.MvcHandler.EndProcessRequest（IAsyncResult的asyncResult）31 的System.Web。 Mvc.MvcHandler.System.Web.IHttpAsyncHandler.EndProcessRequest（IAsyncResult的結果）9 System.Web.CallHandlerExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute（）9629708 System.Web.HttpApplication.ExecuteStep（IExecutionStep步驟，布爾& completedsynchronously

Answer 1

這個錯誤很簡單，一旦我想出來在我真正的數據庫中，我有一個LocalizedCategory來獲取本地化的類別名稱，當我想我可以跳過使用它簡化事情。所以我用這段代碼給Name賦值：

[Column(Name = "id")] 
    public string Name { get; set; } 

但是，由於id在數據庫中是int，所以我得到一個異常。我現在要儘快讓它與LocalizedCategory一起工作，儘管我遇到了另一個問題：Why do I get different values from my EntitySet depending on how I LINQ to it?