實體或複雜類型'xyz'不能在LINQ to Entities查詢中構建

Question

我知道這已經在之前討論過了，我一直在仔細閱讀並嘗試所有這些，但每個解決方案都會返回一個List，而我明確地需要返回IQueryable才能爲已經實現的異步分頁方法提供資源。

ASP NET MVC5 Web應用程序，EF6時，Visual Studio 2015年

public partial class Product 
    { 
     public int? ID { get; set; } 
     public string Name { get; set; } 
     public string Description { get; set; } 
     public int CategoryID { get; set; } 
     public virtual Category Category { get; set; } 
     public virtual CategoryTrans CategoryTrans { get; set; } 
    } 

public partial class Category 
{ 
    public int ID { get; set; } 
    public string Name { get; set; } 
    public int? ParentID { get; set; } 
    public bool IsDeleted { get; set; } 
    public virtual ICollection<Product> Products { get; set; } 
    public virtual ICollection<CategoryTrans> CategoryTrans { get; set; } 
} 

public class ISO_Languages 
{ 
    public int ID { get; set; } 
    public string code { get; set; } 
    public bool IsEnabled { get; set; } 
    public string name_en { get; set; } 
    public string name_fr { get; set; } 
    public string name_it { get; set; } 
    public string name_de { get; set; } 
    public string name_es { get; set; } 
} 

public class CategoryTrans 
{ 
    [Key, Column(Order = 1)] 
    public int category_id { get; set; } 
    [Key, Column(Order = 2)] 
    public int language_id { get; set; } 
    [ForeignKey("category_id")] 
    public virtual Category categoryId { get; set; } 
    [ForeignKey("language_id")] 
    public virtual ISO_Languages languageId { get; set; } 
    public string name { get; set; } 
} 

下面的查詢返回p.Category.CategoryTrans ALL CategoryTrans，這意味着任何類別的轉換（這是一個起點雖然，不是我需要的）：

public static IQueryable<Product> ActiveProductsPerUser(BaseContext db,  string userid, string culture) 
{ 
    var query = (from p in db.Products 
       join ct in db.CategoryTrans 
       on p.CategoryID equals ct.category_id 
       join l in db.ISO_Languages 
       on ct.language_id equals l.ID 
       where l.code.Substring(0, 2) == culture 
       select p); 

    return query; 
} 

我想要做的是過濾，對於每個產品，單個類別translatio n，取決於文化輸入參數。喜歡的東西：

public static IQueryable<Product> ActiveProductsPerUser(BaseContext db, string userid, string culture) 
    { 
     var query = from p in db.Products 
        join ct in db.CategoryTrans 
        on p.CategoryID equals ct.category_id 
        join l in db.ISO_Languages 
        on ct.language_id equals l.ID 
        where l.code.Substring(0, 2) == culture 
        select new Product 
        { 
         ID = p.ID, 
         Name = p.Name, 
         Description = p.Description, 
         CategoryTrans = p.Category.CategoryTrans.Where(b => b.language_id.Equals(l.ID)).SingleOrDefault() 
        }; 
     return query; 
    } 

但返回錯誤：

The entity or complex type 'xyz.DAL.Product' cannot be constructed in a LINQ to Entities query.

我嘗試了好幾種方案，但沒有奏效。我的理解是返回LINQ到實體，而不是LINQ到對象，但實體需要什麼，我肯定需要一個產品的IQueryable返回負責下面的異步方法用於尋呼&排序問題：

public async Task<ActionResult> UserList(int? page, int sortBy = 1) 
    { 
     int currentPage = (page ?? 1); 
     ViewBag.CurrentPage = currentPage; 
     viewModel.productList = await userlist(sortBy).ReturnPages(currentPage, Constants.PageItems); 
     return View(viewModel);} 

在等待「用戶列表」輸入是Product IQueryable，由我努力實現的方法返回。

Answer 1

我無法找到一個答案

The entity or complex type 'xyz.DAL.Product' cannot be constructed in a LINQ to Entities query.

錯誤。我最終加入了

[NotMapped] 
public virtual string LocalizedCategoryName { get; set; } 

產品模型類，負責顯示本地化類別名稱，移動過濾到視圖模型解決了這個問題，設定兩個嵌套的foreach循環，返回的完全本地化的產品的新名單：

private List<Product> _LocalizedProductList = new List<Product>(); 

public List<Product> LocalizedProductList 
    { 
     get 
     { 
      HttpUtilities HttpHelper = new HttpUtilities(); 
      string culture = HttpHelper.getFullCulture(); 
      int IsoCode = GenericUtilities.getIsoID(culture, db); 
      List<Product> localized = new List<Product>(); 

      foreach (Product p in _LocalizedProductList) 
      { 
       foreach (CategoryTrans c in p.Category.CategoryTrans) 
       { 
        if (c.language_id.Equals(IsoCode)) 
        { 
         Product x = new Product 
         { 
          ID = p.ID, 
          LocalizedCategoryName = c.name, 
          DateCreated = p.DateCreated, 
          DateExpire = p.DateExpire, 
          DateLastModified = p.DateLastModified, 
          Name = p.Name, 
          Description = p.Description, 
          IsApproved = p.IsApproved, 
          IsDeleted = p.IsDeleted, 
          ProductImages = p.ProductImages, 
          User = p.User 
         }; 
         localized.Add(x); 
        }; 
       } 
      } 
      return localized; 
     } 

     set { _LocalizedProductList = value; } 
    } 

不知道這是否是最好的或唯一的方法，但按預期工作。 我現在可以繼續使用簡單的查詢，並將返回的Product的IQueryable傳遞給排序和分頁異步方法或其他任何方法。每當我完成，結果被分配給ViewModel.LocalizedProductList，其中getter負責最後的過濾。

Answer 2

我覺得這種事情會更合適。

var query = db.Products 
      .Where(p => p.CategoryTrans.languageId.code.StartWith(culture)) 
      .Include(p => p.CategoryTrans.languageId);