Linq不包含’Where’的定义

我正在尝试通过if语句调整我的查询，如下所示：

IQueryable articles = null; if (User.IsInRole("Admin")) { articles = from s in db.Articles select s; } if (User.IsInRole("Educator")) { articles = from s in db.Articles where s.createdBy == WebSecurity.CurrentUserName select s; } 

这似乎没有给我任何错误。 但是，当我尝试使用where子句进行更多过滤时，它无法识别该术语。 我理解IQuerable不支持它，但有没有办法将“articles”设置为null，然后用if语句设置它？

 if (!String.IsNullOrEmpty(searchString)) { articles = articles.Where(s => s.title.ToUpper().Contains(searchString.ToUpper()) || s.content.ToUpper().Contains(searchString.ToUpper())); } switch (sortOrder) { case "name_desc": articles = articles.OrderByDescending(s => s.title); break; case "Date": articles = articles.OrderBy(s => s.dateCreated); break; case "date_desc": articles = articles.OrderByDescending(s => s.dateCreated); break; case "rating_desc": articles = articles.OrderByDescending(s => s.finalReview); break; case "Rating": articles = articles.OrderBy(s => s.finalReview); break; case "Views": articles = articles.OrderBy(s=>s.numViews); break; case "views_desc": articles = articles.OrderByDescending(s => s.numViews); break; case "Educators": articles = articles.OrderBy(s => s.educatorCRUD); break; case "educators_desc": articles = articles.OrderByDescending(s => s.educatorCRUD); break; default: articles = articles.OrderBy(s => s.title); break; } 

我知道我可以在一个大的if语句中执行此操作if（User.IsInRole（“Admin”））然后执行所有代码然后将相同的代码复制并粘贴到不同的if语句中（if（user.IsInRole（“Educator）），但我认为这种冗余且非常糟糕的编码实践。

干杯。

 IQueryable
 articles; // Initialize as before 

 IQueryable
 articles = db.Articles; if (User.IsInRole("Admin")) { // No change... } else if (User.IsInRole("Educator")) { articles = articles.Where(s => s.createdBy == WebSecurity.CurrentUserName); } else { // Throw an exception? What do you want to happen if they're neither an // educator nor an administrator? }