Question

I try to change a SQL Delete command into LINQ. this is my SQL Command:

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

and this is the LINQ code that I’ve written:

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();
}

but in this line I have an error:

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

that said:

The best overloaded method match for ‘System.Data.Linq.Table.DeleteOnSubmit(LINQ_Test.Trackpoint)’ has some invalid arguments

What should I do?

Answer 1

Use this:

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

or what is shorter:

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

because it returns Trackpoint

While your select p.TrackPointId returns 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();