The ORM is bad because it is a poor abstraction of SQL. This manifests itself in several ways, the largest being little control over the SQL queries generated.
The poor abstraction really causes problems when you need to do anything beyond the simplest of use cases. To achieve even modest performance gains, you're better off hand writing your SQL. Additionally, doing even the most trivial of trivial aggregate queries will also mean that you're hand writing SQL.
SQLAlchemy is light years beyond the django ORM in this regard.
I think the most important difference between Alchemy and Django is the separation between the SQL abstraction layer and the ORM. There is no separation with django, making it very difficult to really get in there and make changes.
But I don't think this makes the django ORM bad. It is very easy for beginners to get up and running. It is very easy to understand the models and the query language.
As an FYI - 1.8 should make it possible to use .annotate() for constructs that aren't aggregates - like functions and extra select columns. You'll also be able to write more complex aggregates. It should give you greater control over your SQL, removing the need for .extra() in most cases (but not .raw()). It's what I've been working on recently: https://github.com/django/django/pull/2496
>The poor abstraction really causes problems when you need to do anything beyond the simplest of use cases. To achieve even modest performance gains, you're better off hand writing your SQL. Additionally, doing even the most trivial of trivial aggregate queries will also mean that you're hand writing SQL.
This isn't really a big deal - you can just hand-write your sql directly using .raw() and just pull out the corresponding result set and use it as you were doing before.
I've had to do what you're suggesting, but not a huge amount. Maybe 10-15 times on large, high scale projects.
SQLAlchemy is better but the number of times I have to break out of its abstraction layer are not enough for me to feel like I really have a desperate need to use alchemy instead. It's a minor inconvenience, nothing more.
Here's a gist I made the other day demonstrating this. https://gist.github.com/jawnb/cd7a899cac5300c01709
The poor abstraction really causes problems when you need to do anything beyond the simplest of use cases. To achieve even modest performance gains, you're better off hand writing your SQL. Additionally, doing even the most trivial of trivial aggregate queries will also mean that you're hand writing SQL.
SQLAlchemy is light years beyond the django ORM in this regard.
Don't take just my word for it though, here's a talk Alex Gaynor gave saying the same things. https://www.youtube.com/watch?v=GxL9MnWlCwo