How to write this Linq query for this scenario?

Question

I've got a query I need to perform:

return entity.Messages.Include(m => m.User) .Include(m => m.MessageRecipients.Select(u => u.User)) .First(m => m.MessageID == messageID);

This works fine on my local machine but it breaks on the webserver, despite the same setup. The problem is that I try to include the User

Include(m => m.User)

but the user could not exist in the database anymore so it throws "Sequence contains no elements" because I use First().

Question: Is there a way to build the query in a way, so it does not brake when a user is not in DB? Something like outer join in SQL?

EDIT: If there's no User I still need the Message to be returned...

J.W. · Accepted Answer · 2013-07-02 15:42:08Z

1

First() will throw exception like that, if you want null or default value returned when there is no element, then try to use FirstOrDefault().

answered Jul 2, 2013 at 15:42

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3 Comments

will FirstOrDefault() still return the Message with the User property null? Or will the query return null?

The query will return null.

any idea on how to write this query to still return the instance of the Message?

Pawel · Accepted Answer · 2013-07-22 10:52:50Z

it seems that the only way was to split the query in two:

`var message = entity.Messages .Include(m => m.MessageRecipients.Select(u => u.User)) .First(m => m.MessageID == messageID);

var author = entity.Users.Where(u => u.UserID == message.AuthorUserID).FirstOrDefault();

if (author != null) message.User = author;

return message

`