ORMs are bad and I say that as a veteran of Hibernate, Entity Framework (almost every version, including code-first and db-first), E Bean, NHibernate and, worst of all by far, ActiveRecord.
Fast to run? Well.. no.. it's Python.
I personally care much more about development speed and time to market/customer than execution speed. It's good enough for 99% of cases.
Anyway, I disagree. Sometimes the conversion of raw data from the db to Python objects can be the bottleneck for a view. Of course, almost always when this happens it's not really a problem per se as the view is plenty fast enough.
Have you benchmarked this?
I am at the ORMs are bad club, but if you try any of the systems that encode the logic paradigm into their interface, they are a completely different kind of beast. (MS has brought some of it into C# with linq so you can use with the Entity Framework. It's not a fully logic system, and has so many attrition points with the Entity Framework that it's mostly not useful at all.)
1. keeping a log of queries per request with stack traces
2. at the end, checking if there are N+1 problems
3. print a big warning with example SQL and stack trace to the console
During dev if I miss a prefetch_related/select_related the console will start to print gigantic stack traces telling me where the problem is. I don't have these problems in production because I get alerted to them in dev.
These are not only solvable problems but EASILY solvable problems!
(Also, in iommi tables, most of the times it can automatically figure out and do the prefetch/select related for you, further diminishing the problem)
select * from book where author_id = 5
If you represent your data as objects, you'll create a Book class with an attribute of type Author. If you now want to run the query above, you'd say (in c# likelihood, but not a real Entity query):
Database.Set<Book>().filter(author.id = 5).all()
But that instructs the ORM to fetch the author attribute from all books, and only then filter it by id. So, you will end up running the following query:
select * from book join author on book.author_id = author.id where author.id = 5
There is no reasonable way to represent the difference between this query and the one on top with an object representation. And even though both have exactly the same semantics, databases have been historically bad at optimizing them so the second one can be orders of magnitude slower.
You grab all Albums. Then you make a table of the albums with name and artist name. The artist name is in a separate table linked with a foreign key.
So the code might be:
for album in Album.objects.all():
print(album.name, album.artist.name)
So "N+1" because it's N queries (every album) plus 1 (the original "all albums" query).
The fix in Django is to do `Album.objects.all().select_related('artist')`. Then there will be just one query.
var customersWithOrderDetail = context.Customers.Include("Orders").ToList();
Would generate :
SELECT * FROM Customers JOIN Orders ON Customers.Id = Orders.CustomerId
The awareness is the key imo. That's what iommi's tool gives you out of the box.