Question

I have a MessageThread entity which contains Message entities. The foreign key is set up so I can navigate from MessageThread to all the messages easily. Each message has a from and to address. I want to write a query to retrieve all message threads for which a particular address has either written or received a message.

MessageThread
{
    EntityCollection<Message> messages;
}

Message
{
    long FromAccount;
    long ToAccount;
}

The query should be something like this, but I can’t figure out how to navigate to the To and From addresses all the way from the MessageThread class.

public IQueryable<MessageThread> GetMessageThreads(long userAccount)
{
    return from messageThread in this.ObjectContext.MessageThreads
           where messageThread.Messages.ToAddress == userAccount || 
                 messageThread.Messages.FromAddress == userAccount
           select messageThread;
}

That query won’t work because messageThread.Messages is a collection and both ToAddress and FromAddress are not directly accessible from the collection.

Answer 1

Select the child items first and then include the parent. Then at the end, just select a list of the parent entity that you were after.

Messages.Include("MessageThread")
        .Where(m => m.FromAccount == userAccount
                 || m.ToAccount == userAccount)
        .Select(m => m.MessageThread)

If you leave the select off the end you get a list of messages with the parents included. It depends on what you where after.

OR…. (this, which is a bit neater)

MessageThreads.Where(s => s.Messages.Any( m => m.FromAccount == userAccount
                                            || m.ToAccount == userAccount))