使用Linq to SQL删除表中的行

Question

I have a sports database with a table groupmembers which have the fields ID, groupID and memberID. I get the memberID from a textbox called txtRemoveGroupMember and the groupID from a checkboxlist. Now i want to delete the rows wich has both the groupID and the memberID. I have tried this code:

foreach(ListItem listItem in cblRemoveMemberFromGroup.Items)
{
       int memberid = Convert.ToInt32(txtRemoveGroupMember.Text);
       int groupid = Convert.ToInt32(listItem.Value);

       var removeFromGroup = from gm in dataContext.GroupMembers
            where (gm.memberID == memberid) && (gm.groupID == groupid)
            select gm;

       dataContext.GroupMembers.DeleteOnSubmit(removeFromGroup);
       dataContext.SubmitChanges();
}

But i get this error: Error 7 Argument 1: cannot convert from 'System.Linq.IQueryable' to 'GSI_side.GroupMember'

And this error: Error 6 The best overloaded method match for 'System.Data.Linq.Table.DeleteOnSubmit(GSI_side.GroupMember)' has some invalid arguments

Hope someone can help me figure this out!

Answer 1

You have to call .ToList()

var items = removeFromGroup.ToList();
foreach (var item in items)
  dataContext.GroupMembers.DeleteOnSubmit(item);

For batch deletes I use this , because LINQ to SQL first loads the entire data which is going to be deleted, then it does the deletes each by each.

https://terryaney.wordpress.com/2008/04/14/batch-updates-and-deletes-with-linq-to-sql/

https://github.com/longday/LINQ-to-SQL-Batch-Updates-Deletes

Answer 2

removeFromGroup is still of type IQuerable .

You need to specify an actual GroupMember to delete.

You could use

GroupMember removeFromGroup = (from gm in dataContext.GroupMembers
                               where (gm.memberID == memberid) && (gm.groupID == groupid)
                               select gm).SingleOrDefault();


dataContext.GroupMembers.DeleteOnSubmit(removeFromGroup);
dataContext.SubmitChanges();

Alternatively, if your query returns a collection (from the looks of it, it won't since you are filtering by memberId ) you could use

List<GroupMember> removeFromGroup = (from gm in dataContext.GroupMembers
                                     where (gm.memberID == memberid) && (gm.groupID == groupid)
                                     select gm).ToList();


dataContext.GroupMembers.DeleteAllOnSubmit(removeFromGroup);
dataContext.SubmitChanges();

Answer 3

var listToRemove=(from a in DB.Table
             where a.Equals(id)
             select a).ToList();

DB.Table.DeleteAllOnSubmit(listToRemove);
DB.SubmitChanges();