How to perform Update operation in Ios using Odata Services

Hello,

I want to do PUT(update) operation on odataservice... I am using followin code to get the proper Entry property to update

SDMODataEntry * entry1=((SDMODataEntry *)[ArraySelectedCell objectAtIndex:0]);

SDMODataPropertyValueObject* obj = ((SDMODataPropertyValueObject*)[entry1getPropertyValueByPath:@"rm_comment"]);

But i am getting following error

__NSDictionaryM getPropertyValueByPath:]: unrecognized selector sent to instance 0x10166620

Please help...

Regards,

Ravindra