从表中选择第一个ID

Question

我想根据我的子类别列出所有条目。所以我想在加载主页上显示条目列表，而无需事先选择任何类别或子类别。

我做了一个查询，返回条目列表，但手动subCategoryId。

下面是该查询：

int userId = WebSecurity.GetUserId(User.Identity.Name); 

    var preQuery = (from sub in dc.SubCategory 
        join c in dc.Category on sub.SubCategoryId equals c.Id 
        join u in dc.User on c.UserId equals u.UserId 
        where u.UserId == userId 
        select sub.SubCategoryId).Take(1).FirstOrDefault(); 

     var query = (from e in dc.Entry 
        join sub in dc.SubCategory on e.SubCategoryId equals sub.SubCategoryId 
        join cat in dc.Category on sub.CategoryId equals cat.Id 
        join u in dc.User on cat.UserId equals u.UserId 
        where ((u.UserId == userId) && (cat.UserId == userId) 
         && (sub.CategoryId == cat.Id) && (e.SubCategoryId == preQuery)) 
        select e).ToList(); 

     return View(query); 

所以我的观点是，我想代替手工编写的6号，要采取子类别ID列表，并从中选择第一个ID。我做了prequery，但仍然不是所需的结果。任何建议我做错了什么？

Answer 1

我能够得到我的问题的解决方案，所以我张贴解决方案。如果有人提出优化解决方案的建议，欢迎分享。

int userId = WebSecurity.GetUserId(User.Identity.Name); 

     var preQuery = (from e in dc.Entry 
        join sub in dc.SubCategory on e.SubCategoryId equals sub.SubCategoryId 
        join cat in dc.Category on sub.CategoryId equals cat.Id 
        join u in dc.User on cat.UserId equals u.UserId 
        where u.UserId == userId 
        select e.SubCategoryId).Take(1); 

     var query = (from e in dc.Entry 
        join sub in dc.SubCategory on e.SubCategoryId equals sub.SubCategoryId 
        join cat in dc.Category on sub.CategoryId equals cat.Id 
        join u in dc.User on cat.UserId equals u.UserId 
        where ((u.UserId == userId) && (cat.UserId == userId) 
         && (sub.CategoryId == cat.Id) && (e.SubCategoryId == preQuery.FirstOrDefault())) 
        select e).ToList(); 

     return View(query);