Question

I have a table RecentChanges which holds reference to all actions done on my website. It contains the Type of the action done (e.g. edit, upload, etc.), a Revision ID foreign key (which references to the ID in the Revisions table – can be null) and a Log ID foreign key (which references to the ID in the Logs table – can be null). Both the last two tables mentioned contain a timestamp of when the action occurred.

My problem is how can I order the results from the RecentChanges table to be displayed in descending order since the timestamp values are in two separate tables?

To get an idea here is a snippet of Linq query:

var list = (from r in Entity.RecentChanges
            //where clause??
            select r);

Answer 1

Something like this? I’m projecting into an anoymous type to help with the ordering (you’ll need to add other fields that you need into the projection):

var query = (from c in Entity.RecentChanges
        from l in Entity.Logs
            .FirstOrDefault(log => log.ID == c.LogID).DefaultIfEmpty()
        from r in Entity.Revisions
            .FirstOrDefault(rev => rev.ID == c.RevisionID).DefaultIfEmpty()
        select new
               {
                   ActivityDate = l != null 
                       ? l.Timestamp 
                       : r != null
                           ? r.Timestamp
                           : DateTime.Now. //what if both are null? catching all eventualities here
                   //select your other fields here

               })
        .OrderByDescending(c => c.ActivityDate)
        .ToList();