Reputation: 13

Linq query help

I have 2 Lists, both are business objects.

First object is

public class Mail
{
   string id;
   string name;
   string address;
   ....
}

Second object is

public class DoNotMail
{
   string id;
   string otherinfo;
   ....
}

The lists are

List<Mail> _mailList
List<DoNotMail> _doNotMailList

I need to a linq query to get all the Mail items where the Mail.Id is not in DoNotMail.id

If this were normal sql, I think I'd do a left join where DoNotMail.id is null, but every attempt I tried to do it in linq isn't working right.

Any ideas?

Upvotes: 1

Answers (5)

Reputation: 5999

Try This:

var results = from m in _mailList
              where !(from nm in _doNotMailList select nm.Id)
              .Contains(m.Id)
              select m;

It is equal to not in un Sql.

Upvotes: 1

Reputation: 26644

If you override the Equals method in both classes you can use this:

_mailList.Except(_doNotMailList).ToList();

Upvotes: 1

Reputation: 130

Try

var query = from m in Mail where !(from d in DoNotMail select d.Id) .Contains(m.Id) select m;

Upvotes: 0

Reputation: 15242

var mailItem = _mailList.Where(x => !_doNotMailList.Contains(x.id));

Upvotes: 1

Reputation: 1500525

Simplest approach:

var doNotMailIds = new HashSet<string>(_doNotMailList.Select(x => x.id));
var mailItems = _mailList.Where(x => !doNotMailIds.Contains(x.id));

That's assuming you want want the full Mail items. If you only need their IDs, you can do it in one query:

var mailIds = _mailList.Select(x => x.id)
                       .Except(_doNotMailList.Select(x => x.id));

Upvotes: 5