CODEWITHSUNDEEP
entity-frameworklinq-to-entities
Pawel
Pawel

Reputation: 2646

How to write this Linq query for this scenario?

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...

Upvotes: 0

Views: 44

Answers (2)

Pawel
Pawel

Reputation: 2646

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

`

Upvotes: 0

J.W.
J.W.

Reputation: 18181

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

Upvotes: 1

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