[m12k]

The programmer also already had the value in book.user_id but still chose to ask the ORM to fetch all of .user so they could get .id from there instead. And they might then afterward call .name on it as well, and there would be no further queries, because the ORM has already been asked to fetch all fields of .user - so it might in fact have been sensible to fetch all of .user if so. The query builder cannot know whether all of it will be needed or not, because Python is not a compiled language, so there's no way to tell in advance when executing the book.user.id query that no further fields of .user will be needed, so it shouldn't actually do what it's been asked to do, to fetch the entire object, but rather only fetch .id which is available in a different way, so the whole query can be skipped. So yes, this is suboptimal usage, but only the programmer can know that, so it falls to them to optimize if they want to.

[lacksconfidence]

Perhaps i'm a bit odd, but when I'm going to lean on an ORM to do things I expect it to actually do them. I expect that foo.user_id does not exist, because that representation has been transformed into an object. foo.user.id should be the only viable reference to the id. foo.user.id should return the value it already knows, any other property access i would expect will do the equiv of `select * from ...` if the object has not previously been populated.

Now perhaps some ORM's prefer to be thinner, to provide more footguns via a leaky abstraction that mixes implementation details with the object mapping. I don't think those are good implementaations.

[RussianCow]

> Now perhaps some ORM's prefer to be thinner, to provide more footguns via a leaky abstraction that mixes implementation details with the object mapping. I don't think those are good implementaations.

To me, it seems like the (hypothetical?) implementation you're talking about is much more leaky and footgun-y than the more straightforward ("thinner", in your words) version. In order for foo.user.id to not execute a new query, foo.user would have to return some sort of proxy object that only fetched the user row when you tried to access a field that hasn't been loaded. That's way more magic than the more obvious solution—which is to load the row when you access the related object—and could easily cause more problems than it solves in the long run when you need to debug very specific queries.

Furthermore, how is going out of your way to hide a field that exists in the database (user_id) not the definition of a leaky abstraction? What purpose does it serve to direct you through an unnecessary layer if all you need is the ID?

[rglullis]

> I expect that foo.user_id does not exist, because that representation has been transformed into an object.

Or you can just consider user_id to be a reference pointer that is part of foo, while user.id is an attribute of user. Totally different things and I am glad that the distinction is there.

[bottled_poe]

I’m sure there are valid engineering reasons to do it this way. One that comes to mind is memory footprint in allocating the objects associate with foreign key references.

[jtdev]

Wow! Who would have thought that using an ORM would create so much uncertainty in a codebase.

[zwily]

Fancier ORMs will return a proxy for foo.user that doesn’t issue a query until the user asks for a property on it. And it can return user.id without querying.