Is it possible use MongoDB in UE4?
Yes, as long as you can find C++ library for that (well practically you can write your own implementation, so technically you can do everything, it’s just matter of work effort)
But problem with external libraries in UE4 is that, UE4 use it’s own standard library. Which means you either will need to convert types all the time (except some primitives), all create a wrapper functions (in UObject classes?) which will do dirty work for you.
Here you have tutorial how to include library to module:
You might consider implementing MongoDB as a plug-in first
Thanks for advice
Yes and it’s easy to do so with Nodejs, and socket.io which is also available as a plug-in with ue4.