c# - Entity Framework InvalidOperationException when updating an item

Question

I get an System.InvalidOperationException error which states:

Additional information: Member 'IsModified' cannot be called for property 'state' because the entity of type 'BatteryItem' does not exist in the context. To add an entity to the context call the Add or Attach method of DbSet.

Haven't I done exactly this? That is my method below:

public void UpdateBatteryState(BatteryItem batItem, BatteryState state)
{
    try
    {
        batItem.state = state.ToString();
        context.BatteryItem.Attach(batItem);
        var entry = context.Entry(batItem);
        entry.Property(x => x.state).IsModified = true;

        Save();
     }
     catch (Exception e)
     {
         Console.WriteLine(e.Message);
     }
}

Answer 1

from that info you should do it this way:

public void UpdateBatteryState(BatteryItem batItem, BatteryState state)
{
    try
    {

        context.BatteryItem.Add(batItem);
        batItem.state = state.ToString();

        context.SaveChanges()
     }
     catch (Exception e)
     {
         Console.WriteLine(e.Message);
     }
}