> when using Entity Framework or the Mongo linq driver? They would both give you the same result but one is much more efficient.
The competent developer with knowledge of systems know that the first step when using any form of ORM or sql generation tool is to figure out how to look at generated queries.
Also in that particular example, you're dealing with a reasonably common concept across all languages (generators). While LINQ works by letting you introspect the AST and its a reasonably unique concept, when looking at the snippets here it actually doesn't matter if you don't know that: in basically any data structure manipulation code, doing a data structure conversion followed by a predicate operation is almost always a mistake, because the whole point of "toSomething()" functions is to go from the specialized domain into the language's generic's constructs. LINQ is a particularly accessible implementation of concepts that are age old. The Rx family of tools (which do exist in java) follow similar semantics, and then most ecosystems have very similar constructs even outside of RxWhatever.
Those fundamentals won't let you figure out edge cases, but they're pretty easy to pick up once you get it. The system building aspect is what takes a lot of experience to catch. Other examples would involve how to debug a server's memory dump: it's very different between C++ and .NET, but very few people know how to do it in EITHER environments, while anyone who knows how to do it in one can pick it up in another by skimming a blog post in the middle of an outage.
Probably a reason why people should learn Category Theory too. Not quite the same thing, but it would help people make more solid assumptions.