How to count write the linq query when the grouped bY column is in one table and the items are in another table

Question

I'm trying to write this simple Linq query without success. Here's the original SQL Query:

SELECT os.OSName, COUNT(d.DOperatingSystemId)
FROM [dbo].[Device_OperatingSystem] os
LEFT JOIN [dbo].[Device_DeviceDetails] d
ON os.OperatingSystemID = d.DOperatingSystemId
GROUP BY os.OSName

Which return result like:

Windows     131
Linux         7
iOS          51

This is my linq query:

public List<KeyValue> GetNumberOFDevicesByOperatingSystem()
{
   var numberOFDevicesByOperatingSystem = new List<KeyValue>();
   var rawQuery = GetAll()
       .GroupBy(
        os => os.OSName,
        os => os.Devices,
            (key, g) => new { key, g });

  foreach (var item in rawQuery)
  {
     numberOFDevicesByOperatingSystem.Add(new KeyValue
     {
         Key = item.key,
         Value = item.g.Count().ToString()
     });
  }

  return numberOFDevicesByOperatingSystem.ToList();
}

This return the following result:

Windows     1
Linux       1
iOS         1

Thanks for helping

Answer 1

Try something like this:

var osDevicesList = (
    from os in context.Device_OperatingSystem

    let devicesWithOSCount = (
        from d in context.Device_DeviceDetails
        where d.DOperatingSystemId == os.OperatingSystemID
        select d.Id
    ).Count()

    group devicesWithOSCount by os.OSName into g

    select new {
        OS = g.Key,
        value = g.First()
    }
);

Answer 2

return (from d in Device_DeviceDetails
group d by d.DOperatingSystemId into dddg
join os in Device_OperatingSystem on dddg.Key equals os.OperatingSystemID
select new KeyValue { Key = os.OSName, Value = dddg.Count()}).ToList();