Object-relational mapping has been well discussed, including on here. I have experience with a few approaches and the pitfalls and compromises. True resolution seems like it requires changes to the OO or relational models themselves.
If using a functional language, does the same problem present itself? It seems to me that these two paradigms should fit together better than OO and RDBMS. The idea of thinking in sets in an RDBMS seems to mesh with the automatic parallelism that functional approaches seem to promise.
Does anyone have any interesting opinions or insights? What’s the state of play in the industry?
The hard problems of extending the relational database are extended transactions, data-type mismatches, automated query translation and things like N+1 Select that are fundamental problems of leaving the relational system and — in my opinion — do not change by changing the receiving programming paradigm.