Hi
If I'm understanding the question properly I think what is being asked is the following
1) You've created your own class based off esEntityCollection - i.e. this class is manually crafted and has not been generated by MyGeneration so you have an empty class that inherits from esEntityCollection,.
2) You want to fill this collection from a datatable or other source. As the class doesn't include the regular generated entityspaces code you're trying to do this with methods that are defined and implemented in esEntityCollection.
Unfortunately I don't have time to look into this personally but I thought it might help to rephrase the question (if I've understood it correctly) so that someone else may better answer it.
Hope that helps but apologies if I've completely misunderstood
Cheers
Martin