[PeterisP]

All abstractions tend to be leaky.

ORM can abstract DB/SQL for you, but if you really ignore DB/SQL, then it can happily make some queries an order (or two ) of magnitude slower than they should be.

So, you must always think in explicit SQL-query-terms anyway; and then it's just a balance for ease of coding - does the ease of ORM syntactic sugar outweigh the effort for you to double-check if any ORM-built queries don't accidentally do something stupidly slow.