LINQ return type for nested group query

David Huisman
David Huisman used Ask the Experts™
on
I have the following query working in my code and now want to move into a separate class as a method that I call with List<Logrecord>, but having trouble determining what TYPE I need to return from the method.

recsByDate is a List<LogRecord> where records have Date, Time, EventType fields etc.

var vehicleGroupedByDate =  from daterecs in recsByDate
                                        where daterecs.Event == "Detection"
                                        orderby daterecs.Date
                                        group daterecs by daterecs.Date into vrecs
                                        from vrecs2 in
                                            (
                                               from daterecs in vrecs
                                               orderby daterecs.Time
                                               group daterecs by daterecs.Vehicle
                                            )
                                        group vrecs2 by vrecs.Key;
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Top Expert 2014

Commented:
You can find what the type of vehicleGroupedByDate is by hovering the mouse over the 'var' keyword.
Assuming that Date's type is DateTime and Vehicle's type is String, it should be:
 IGrouping<DateTime, IGrouping<string, LogRecord>>

Author

Commented:
I tried using the suggested return type and get error

Error      CS0266      Cannot implicitly convert type 'System.Collections.Generic.IEnumerable<System.Linq.IGrouping<System.DateTime, System.Linq.IGrouping<string, BodyGuardDesktop.BodyGuardUserFriendlyLogRecord>>>' to 'System.Linq.IGrouping<System.DateTime, System.Linq.IGrouping<string, System.Collections.Generic.List<BodyGuardDesktop.BodyGuardUserFriendlyLogRecord>>>'. An explicit conversion exists (are you missing a cast?)


public IGrouping<DateTime, IGrouping<string, List<BodyGuardUserFriendlyLogRecord>>> GetVehicleDetections(List<BodyGuardUserFriendlyLogRecord> recsByDate)
        {
            var vehicleQuery = from daterecs in recsByDate
                                       where daterecs.Event == "Detection"
                                       orderby daterecs.Date
                                       group daterecs by daterecs.Date into vrecs
                                       from vrecs2 in
                                           (
                                              from daterecs in vrecs
                                              orderby daterecs.Time
                                              group daterecs by daterecs.Vehicle
                                           )
                                       group vrecs2 by vrecs.Key;

            return vehicleQuery;
        }
Top Expert 2014

Commented:
The error message gave you the type you were looking for:
IEnumerable<IGrouping<DateTime, IGrouping<string, List<BodyGuardUserFriendlyLogRecord>>>>

When I tried it, I checked only the items type, so the IEnumerable was missing.
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Author

Commented:
Changed to type as you suggest and get error

Severity      Code      Description      Project      File      Line      Suppression State
Error      CS0266      Cannot implicitly convert type 'System.Collections.Generic.IEnumerable<System.Linq.IGrouping<System.DateTime, System.Linq.IGrouping<string, BodyGuardDesktop.BodyGuardUserFriendlyLogRecord>>>' to 'System.Collections.Generic.IEnumerable<System.Linq.IGrouping<System.DateTime, System.Linq.IGrouping<string, System.Collections.Generic.List<BodyGuardDesktop.BodyGuardUserFriendlyLogRecord>>>>'. An explicit conversion exists (are you missing a cast?)      


public IEnumerable<IGrouping<DateTime, IGrouping<string, List<BodyGuardUserFriendlyLogRecord>>>>
        GetVehicleDetections(List<BodyGuardUserFriendlyLogRecord> recsByDate)
        {
            var vehicleQuery = from daterecs in recsByDate
                               where daterecs.Event == "Detection"
                               orderby daterecs.Date
                               group daterecs by daterecs.Date into vrecs
                               from vrecs2 in
                                   (
                                      from daterecs in vrecs
                                      orderby daterecs.Time
                                      group daterecs by daterecs.Vehicle
                                   )
                               group vrecs2 by vrecs.Key;
            return vehicleQuery;
        }
Top Expert 2014
Commented:
My fault. Should copy/paste instead of retyping.
Sorry.
The error message gives you the right type.

System.Collections.Generic.IEnumerable<System.Linq.IGrouping<System.DateTime, System.Linq.IGrouping<string, BodyGuardDesktop.BodyGuardUserFriendlyLogRecord>>>

Author

Commented:
Thanks for your help

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