Question

I am using Entitry Framework 4.1 and I am struggling to understand how the convert the below query which uses joins and aggregate methods to a Linq to Entities call in the DomainService.

SELECT     tblTime.Period As Timeline, COUNT(tblEngineeringDashboard_ItemList.ID) AS Items
FROM         tblEngineeringDashboard_ItemList INNER JOIN
                      tblTime ON tblEngineeringDashboard_ItemList.TimeID = tblTime.ID
GROUP BY tblTime.Period
ORDER BY tblTime.Period

Can anyone provide help.

Possible Solution

Dim var = From i In ObjectContext.tblEngineeringDashboard_ItemList
                Join t In ObjectContext.tblTimes On i.TimeID Equals t.ID
                Group By i.TimeID Into Group
                Select DateStart = (From n In ObjectContext.tblTimes Where n.ID = TimeID Select n.Period), PartCount = Group.Count

Phil

Answer 1

The first thing which comes to mind is:

var q = from t in Context.Time
        group t by t.Period into g
        orderby g.Key
        select new 
        {
            Timeline = g.Key,
            Items = (from ti in g
                     from il in ti.ItemList // or whatever the property for the navigation to tblEngineeringDashboard_ItemList is called
                     select il).Count()
        };

However, the original SQL had an INNER JOIN, which would reject tblTime records without any matching records in tblEngineeringDashboard_ItemList. So you may want:

var q = from t in Context.Time
        where t.ItemList.Any()
        group t by t.Period into g
        orderby g.Key
        select new 
        {
            Timeline = g.Key,
            Items = (from ti in g
                     from il in ti.ItemList // or whatever the property for the navigation to tblEngineeringDashboard_ItemList is called
                     select il).Count()
        };

You can also flip the query around:

var q = from i in Context.EngineeringDashboardItemList
        where i.Time != null 
        group i by i.Time.Period into g
        orderby g.Key
        select new 
        {
            Timeline = g.Key,
            Items = g.Count()
        };