当分组的bY列在一个表中并且项目在另一表中时，如何计算写linq查询

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();