不能转换类型”来。这个IQueryable 的“int”

I have a problem sending data from the database to a list in the Controller. I am new to C# and MVC so any help will be useful! Code follows

将数据从数据库发送到控制器中的列表时出现了问题。我是c#和MVC的新手，所以任何帮助都是有用的!代码如下所示

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;
    }

Thanks & Happy Holidays!! :)

谢谢&节日快乐! !:)

2 个解决方案

#1

device.ID = (from a in db.FilterTree select a.ID).First();

Linq query is lazy, and executes only after you request the value

Linq查询是惰性的，只有在请求值之后才执行

BTW don't forgot to close the context, otherwise you will leak connections

顺便说一下，不要忘记关闭上下文，否则会泄漏连接。

using (var db = new FilterTreeDBContext())
{
    ...
    return userList;
}

#2

As far as the frameworks knows that query may have more than one object so use it like this:

就框架所知，查询可能有多个对象，因此可以这样使用:

device.ID = (from a in db.FilterTree select a.ID).FirstOrDefault();

#1

device.ID = (from a in db.FilterTree select a.ID).First();