I like the Django database API a lot. It makes writing SQL statements quite clean. However, I ran into a little snag recently on something that I would expect to be different.
First a quick refresher for those who are not familiar with the Django API. Essentially you use a filter or get function to do all your queries.
[python]
post=Post.objects.get(title='python is great')
comments = Comment.objects.filter(post=post,author_name='Jehiah')
[/python]
As you can see, all the parameters to the filter command get combined with a sql AND
Django also has a syntax for more complex queries using Q objects.
The problem I ran into was in grouping things together. I expected all the parameters passed to a Q object to be ANDd together just like they are in a filter method, and then I could OR those groups.
With this block of code
[python]
posts = Post.objects.filter( Q(author='A1',datetime__range=(start,end) |
Q(author='A2',datetime__range=(start2,end2)))
[/python]
You would expect this
[sql]
WHERE (author = 'A1' and datetime between start and end)
OR (author = 'A2' and datetime between start2 and end)
[/sql]
However it really yields this
[sql]
WHERE author = 'A1' OR author = 'A2' OR datetime between start and end
OR datetime between start2 and end2
[/sql]
I don’t really see the logic in not making it behave like a filter object does when it’s passed multiple parameters.
Anyway, what I wanted to do needed code like this
[python]
posts = Post.objects.filter( (Q(author='A1') & Q(datetime__range=(start,end) )|
(Q(author='A2') & Q(datetime__range=(start2,end2))))
[/python]
Which does not seem as clear to me. It makes use of the & operator to call __and__ between the two Q objects just like the | operator calls __or__ on two Q objects.
Just thought I’d share