c# – 无法将类型’System.Linq.IQueryable’转换为’int’

我在将数据从数据库发送到Controller中的列表时遇到问题.我是C#和MVC的新手,所以任何帮助都会有用！代码如下

public static List<FilterTree> GetAllUsers()
    {
        FilterTreeDBContext db = new FilterTreeDBContext();
        var userList = new List<FilterTree>();
        var device =  new FilterTree();
        //This is the line where I get the error
        device.ID = from a in db.FilterTree select a.ID;

        userList.Add(device);
        return userList;
    }

谢谢&节日快乐！！