Select most recent records using LINQ to Entities

Question

I have a simple Linq to Enities table to query and get the most recent records using Date field

So I tried this code:

IQueryable<Alert> alerts = GetAlerts();
IQueryable<Alert> latestAlerts =
    from a in alerts
    group a by a.UpdateDateTime into g
    select g.OrderBy(a => a.Identifier).First();

Error: NotSupportedException: The method 'GroupBy' is not supported.

Is there any other way to get do it? Thanks a lot!

Answer 1

If there isn't a reason to group it, you could just switch your query up a little:

IQueryable<Alert> alerts = GetAlerts();
IQueryable latestAlerts = alerts.OrderByDescending(a => a.UpdateDateTime);

Answer 2

It should be

IQueryable<Alert> latestAlerts =
    (from a in alerts
    group a by a.UpdateDateTime into g
    order by g.Key
    select g).First();

GroupBy is definitely supported by Linq-to-Entities

Answer 3

So the answer is:

var query =
    from alert in m_alerts
    group alert by alert.Identifier
          into g 
          select new 
          {
        GroupIdentifier = g.Key,
        UpdateDateTime = g.Max(p => p.UpdateDateTime) 
          };

This will return the most recent records.