c# - 使用LINQ删除记录时出错

Question

我尝试将SQL Delete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)

这是我编写的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();
}

但在这一行中我有一个错误：

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

那说：


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


我该怎么办？

Answer 1

用这个：

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

或更短：

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

因为它返回 Trackpoint

而您的 select p.TrackPointId返回 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();