使用LINQ删除记录时出错

Question

我尝试将SQL删除命令更改为LINQ.这是我的SQL命令:

DELETE FROM [TrackPoints]
WHERE [RouteFK] IN (SELECT RouteId
                    FROM Routes
                    WHERE UserId = @UserId)

这是我写的LINQ代码:

int UID =1;
FirstDataContext aspnetdb = new FirstDataContext();
var res1 = from q1 in aspnetdb.Routes
           where q1.UserId == UID
           select q1.RouteId;
foreach (var k in res1)
{
    var eigen = from p in aspnetdb.Trackpoints
                where p.RouteFK == k
                select p.TrackPointId;

    aspnetdb.Trackpoints.DeleteOnSubmit(eigen.First());
    aspnetdb.SubmitChanges();
}

但在这一行我有一个错误:

aspnetdb.Trackpoints.DeleteOnSubmit(eigen.First());

那说:

'System.Data.Linq.Table.DeleteOnSubmit(LINQ_Test.Trackpoint)'的最佳重载方法匹配有一些无效的参数

我该怎么办？

Answer 1

用这个:

var eigen = (from p in aspnetdb.Trackpoints
            where p.RouteFK == k
            select p).First();

或者更短的:

var eigen = aspnetdb.Trackpoints.First(p => p.RouteFK == k);

因为它返回 Trackpoint

虽然你的select p.TrackPointId回报Int.

var r = from r in aspnetdb.Routes
        join p in aspnetdb.Trackpoints on p.RouteId equals r.RouteFK
        where r.UserId == UID
        select p;

foreach (var x in r)
{
    aspnetdb.Trackpoints.DeleteOnSubmit(x);
}
aspnetdb.SubmitChanges();