Lazy loading often fetches too little and eager loading too much. Most orms select all columns in all tables regardless of need. The query translation and hydration overhead of transforming the data into objects even in a fast language are always going to be problems, it's just a matter of how big, over a system without the orm. Since orms are superfluous, every line of code in them adds unnecessary overhead. They are indeed inherently inefficient by definition.
> The query translation and hydration overhead of transforming the data into objects even in a fast language are always going to be problems
No they are not. Have you measured this in a real-world application? This overhead is negligible compared to the cost of the query itself. And without an ORM you still have to load the data into some kind of objects or data structures before you pass it to presentation, you will just have to write the code yourself.
But yeah, lazy loading in a loop will kill performance. So don't do that.
It's definetly not always going to be a problem, but sometimes it does. ORM is always slower than writing custom code, but it might be more than fast enough.
Surely it depends on the custom code in question if it is faster or slower than the similar ORM logic?
You may be able to write faster code, but unless you are Donald Knuth, you can't guarantee that any custom code you write will always be faster than some library.
