c# - 无法比较 EF 查询中的元素异常

Question

我基本上:

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);
}

目标是仅获取具有传递的 ID 的项目或返回所有项目。 (为清楚起见，删除了其他标准)

当我返回 myList 时出现异常，我已经进行了一些调试，并且在执行 .ToList() 时发生了异常

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

Answer 1

问题是因为 myIds 为空。

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);
}