[tomsthumb]

> It turns out just treating data as sets lends to a functional style and is simpler down the road.

Could you elaborate on this or point in the direction of something that does? I'm pretty sure I get the gist but having some more meat to chew to make sure the perspective is fleshed out fully would be awesome.

[hcarvalhoalves]

The bottom line is, tying data to objects seems like an elegant idea, but in practice it sucks. ORMs introduce various problems, like statefulness (when the whole point of dealing with a database is atomicity) and mismatches (your data doesn't necessarly map to one row or one object, it doesn't have to). I'll try to give two examples.

Consider how people often write update code on Django:

    instance = Model.objects.get(id=some_id)
    instance.foo = bar
    instance.save()

This sucks a lot. It's doing two queries, and you have concurrency issues. This would be optimal, since it's atomic:

    Model.objects.filter(id=some_id).update(foo=bar)

But in this case, it's not instantiating any object nor triggering any signals, so what's the point of the ORM after all? We might as well just use a sane DB API.

Here's another place where Django's ORM fails:

    Model.objects.annotate(Count('foos')).filter(foos__lt=10)

This won't work. Django will complain 'foos' is not a field on the model - even though 'foos' is a column in the result set, and it's perfect valid to SELECT on it. I reported this as a bug, but because the ORM works with model definitions and the result set can contain any column, what the ORM is really supposed to do or not is murky, so it's WONTFIX. This is one instance where data doesn't map to an object and the ORM concept crumbles.

There are many other pain points with ORMs, and Django's in particular, but these are the highlights for me. For an elegant querying API, in my opinion, check out RethinkDB. It doesn't depend on schemas (therefore, ORMs) and it supports map/reduce semantics, which solves 100% of what you need to do with data.

[subleq]

You are mistaking about filtering an annotation.

   > Model.objects.annotate(Count('foos')).filter(foos__lt=10)

The only reason this doesn't work is because the property annotate creates isn't called `foos` by default. You just need to do this:

    Model.objects.annotate(foos=Count('foos')).filter(foos__lt=10)

and Django now knows to add a `HAVING COUNT(foos) < 10` clause.