LinqJoin.cs

  List<Device> childDevices = new List<Device>
        {
            new Device { Id = 1 },
  
        };

        List<Device> parentDevices = new List<Device>
        {
            new Device { Id = 1 }, // Parent device with ID 1
            new Device { Id = 4 }  // Parent device with ID 4
        };

        // Find matches between childDevices and parentDevices based on the ID
        var matches = childDevices.Join(
            parentDevices,
            childDevice => childDevice.Id,
            parentDevice => parentDevice.Id,
            (childDevice, parentDevice) => new { ChildDevice = childDevice, ParentDevice = parentDevice }
        );

        // Parent the child devices to their corresponding parent devices
        foreach (var match in matches)
        {
            // Assuming your Device class has a property to store the parent device
            match.ChildDevice.ParentDevice = match.ParentDevice;
        }

        // Now you can access the parent device 
        foreach (var childDevice in childDevices)
        {
            if (childDevice.ParentDevice != null)
            {
                Console.WriteLine($"Child Device ID: {childDevice.Id}, Parent Device ID: {childDevice.ParentDevice.Id}");
            }
            else
            {
                Console.WriteLine($"Child Device ID: {childDevice.Id}, No Parent Device");
            }
        }