使用linq添加项目列表

Question

我有一个拥有类别的类。

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>(); 
    } 
} 

它里面有一个列表，这是其他子类别类的列表：

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

我然后填充这个项目，但我得到一个“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的外键。每个类别都有0：n个子类别。所以，实体框架模型有一个Context.transaction_category.transaction_sub_categories集合。

因此，现在我所做的是，通过上面列表中的类别进行foreach，并填充子类别。

有没有办法在同一个链接语句中做到这一点？ Categories对象有一个List列表。它可以在上面的Linq声明中完成吗？

编辑： 这是修复的尝试，作为推荐，但呈现的错误：

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

你可以这样说：

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：为了使它更容易改变你的SubCategories和Category这样的属性：

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

public virtual CategoryDto Category { get; set; } 

然后你可以使用包括，简单地加载子类是这样的：

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