Apologize to my interruption even this thread has marked as answered.
Actually, "data" property inside FlattenedDataset has inherited a sorter function from bindAggregation method from SAPUI5. Please try below:
data: {
path: oPath, //+ "?$orderby=Idate asc"
sorter : new sap.ui.model.Sorter("Idate", true)
}
bindAggregation API doc can be found on SAPUI5 SDK - Demo Kit
