[c# or C++] How to load feature from POSTGIS programmatically

Hi everyone, 

It is not a lot , but i worked for around ten years with the microstation SDK, and now i have to work with OpenCitiesMap SDK.

I would like to make an app , where i draw a fence from a shape (i know how to achieve that) and next, query and draw all the feature who are register in my postgis database (and i do not know how to do that)

I'm trying to find some example but lot of link are dead. Also i tried to read the documentation of OCM SDK , but i do not know which part of the sdk could help me to achieve my goal.

Is it GeoDataInterchangeApi?

ggApi?

MapSDK?

MapQueryAPI?

I tried to use xfmCmdMgr_startLocateOperation, but it seems to work only with data already draw in the dgn.

I tried to use xfmFeatureDef_XXX, but it only read feature definition (indeed :)) 

If someone have some clues, some hints for me , it would be very very helpfull 

Rgdts Arnaud