除了的加载顺序

Question

I have these two tables.

var cardtagtable = (from u in db.CardTagTables
                    where u.FKCardTagID == cardtable.cardID
                    select u.CardTagName).ToList();

var tagtable = (from u in db.TagTables
                select u.TagName).ToList();

Where in cardtagtable all names are selected to match with tagtable 's name.

Condition-

I want names from tagtable except names coming from cardtagtable list.

so I tried here-

 var list = tagtable.Except(cardtagtable);

This list is a sequence of all names except from cardtagtable .

Everything is all right till now.

Now I will use this list and pass it through the model.

var taglist = (from u in list
               select new TagModel {
                   tagId = u.TagID,
                   tagName = u.TagName,
                   tagCount = Convert.ToInt32(u.TagCount) == null ? 0 : Convert.ToInt32(u.TagCount),
               }).ToList();

But this query says me no definition found for Model values from u .

How do I use this list here in this case?

Answer 1

Because u is probably a string because your list is a IEnumerable<string> .The reason is that you are only selecting your TagNames , so your list contains only tag names , not your TagTables .Instead you need to select your elements instead of just tag names :

var cardtagtable = (from u in db.CardTagTables
                    where u.FKCardTagID == cardtable.cardID
                    select u).ToList();

var tagtable = (from u in db.TagTables
                select u).ToList();

Then use Where and Any instead of Except like this:

var list = tagtable.Where(c => !cardtagtable
                             .Any(x => x.CardTagName == c.TagName));

Then your last query should work fine.

Update: Also there is a more elegant and optimized way to do that (especially if this is LINQ to SQL ).You can select only CardtagNames from cardtagtable and use Contains method:

var cardtagtable = (from u in db.CardTagTables
                    where u.FKCardTagID == cardtable.cardID
                    select u.CardTagName).ToList();

var tagtable = (from u in db.TagTables
                select u).ToList();

var list = tagtable.Where(c => !cardtagtable.Contains(c.TagName));