使用linq添加項目列表

Question

我有一個擁有類別的類。

public class CategoryDto 
{ 
    public int Id { get; set; } 
    public int PortfolioId { get; set; } 
    public string Description { get; set; } 
    public List<SubCategoryDto> SubCategories { get; set; } 

    public CategoryDto() 
    { 
     SubCategories = new List<SubCategoryDto>(); 
    } 
} 

它裏面有一個列表，這是其他子類別類的列表：

public class SubCategoryDto 
{ 
    public int Id { get; set; } 
    public int CategoryId { get; set; } 
    public CategoryDto Category { get; set; } 
    public string Description { get; set; } 
} 

我然後填充這個項目，但我得到一個「PortfolioId」列表基地。

var cats = (from p in Context.transaction_category 
        where p.account_portfolio_id == portfolioId 
          && p.deleted == null 
        select new CategoryDto 
         { 
          Id = p.id, 
          Description = p.description, 
          PortfolioId = p.account_portfolio_id 
         }).ToList(); 

Categories表具有SubCategories的外鍵。每個類別都有0：n個子類別。所以，實體框架模型有一個Context.transaction_category.transaction_sub_categories集合。

因此，現在我所做的是，通過上面列表中的類別進行foreach，並填充子類別。

有沒有辦法在同一個鏈接語句中做到這一點？ Categories對象有一個List列表。它可以在上面的Linq聲明中完成嗎？

編輯： 這是修復的嘗試，作爲推薦，但呈現的錯誤：

var cats = (from p in Context.transaction_category 
         where p.account_portfolio_id == portfolioId 
           && p.deleted == null 
         select new CategoryDto 
          { 
           Id = p.id, 
           Description = p.description, 
           PortfolioId = p.account_portfolio_id, 
           SubCategories = (from s in Context.transaction_sub_category where s.transaction_category_id == p.id 
               && s.deleted == null 
                select new SubCategoryDto 
                 { 
                  Id = s.id, 
                  Description = s.description, 
                  CategoryId = s.transaction_category_id 
                 }).ToList() 
          }).ToList(); 

LINQ to Entities does not recognize the method 'System.Collections.Generic.List 1[Objects.SubCategoryDto] ToList[SubCategoryDto](System.Collections.Generic.IEnumerable 1[Objects.SubCateg‌​oryDto])' method, and this method cannot be translated into a store expression.

Answer 1

你可以這樣說：

var cats = (from p in Context.transaction_category 
       where p.account_portfolio_id == portfolioId 
         && p.deleted == null 
       select new CategoryDto 
        { 
         Id = p.id, 
         Description = p.description, 
         PortfolioId = p.account_portfolio_id, 
         SubCategories = (from s in Context.transaction_category.transaction_sub_categories 
          where s.CategoryId == p.Id 
           select new SubCategoryDto { 
            Id = s.Id, 
            Description = s.Decription  
         }).ToList() 
        }).ToList(); 

更新：爲了使它更容易改變你的SubCategories和Category這樣的屬性：

public virtual List<SubCategoryDto> SubCategories { get; set; } 

public virtual CategoryDto Category { get; set; } 

然後你可以使用包括，簡單地加載子類是這樣的：

var cats = Context.transaction_category 
       .Where(p => p.account_portfolio_id == portfolioId && p.deleted == null) 
       .Include(p => p.SubCategories);