C# · 12月 26, 2021

c# – 不能比较EF查询中的元素异常

我基本上是: public ActionResult MyAction(List<int> myIds){ var myList = from entry in db.Entries where (myIds == null || myIds.Contains(entry.Id)) select entry; return View(myList);}

目的是仅获取带有传递ID的项目或返回所有这些项目. (其他标准为了清楚而剪除)

当我返回myList时,我收到异常,我已经做了一些调试,并且发生在.ToList()

Cannot compare elements of type ‘System.Collections.Generic.List`1’.
Only primitive types (such as Int32,String,and Guid) and entity
types are supported.

解决方法 问题是因为myIds是空的.

我需要:

public ActionResult MyAction(List<int> myIds){ if(myIds == null) { myIds = new List<int>(); } bool ignoreIds = !myIds.Any(); var myList = from entry in db.Entries where (ignoreIds || myIds.Contains(entry.Id)) select entry; return View(myList);}