"Adding" Q objects in Django

Published on 2009-06-26 09:47:00+00:00
Python   django   web  

I've got a Django app with the following Model:

class Story(models.Model):  
    title = models.CharField(max_length=255)  
    content = models.TextField()  

The Problem:
I wanted to build a simple search feature that OR'ed all the search terms. Essentially, I wanted SQL resembling the following:

SELECT \* from myapp_stories where   
    title LIKE '%term1%' OR content LIKE '%term1%' OR   
    title LIKE '%term2%' OR content LIKE '%term2%';   

The Solution:
You can add django's Q objects together! This is a feature not currently discussed in the docs, but I dug through the source code and I discovered that a Q object is really just a node in a Tree! More specifically, Q is a subclass of django.utils.tree.Node (check it out, it's cool!) A Node has a attribute called a connector. Q objects have two possible connectors: AND and OR. But how do we connect Q objects? Well, a Node has a handy add(node, conn_type) method whose parameters include another Node and a connection type.

As previously mentioned, the possible connection types for Q objects are AND and OR, so Q objects can be added together by doing something like this:

# ANDing Q objects  
q_object = Q()  
q_object.add(Q(), Q.AND)  
# ORing Q objects  
q_object = Q()  
q_object.add(Q(), Q.OR)  

So, the solution to my Search view is as follows:

from django.db.models import Q  
from models import Story  
def search(request):  
 Generic Search: GET should contain the following:   
 terms - the search keywords separated by spaces  
    terms = request.GET.get('terms', None)  
    term_list = terms.split(' ')  
    stories = Story.objects.all()  
    q = Q(content__icontains=term_list[0]) | Q(title__icontains=term_list[0])  
    for term in term_list[1:]:  
        q.add((Q(content__icontains=term) | Q(title__icontains=term)), q.connector)  
    stories = stories.filter(q)  
    return render_to_response('myapp/search.html', locals(), \  

Needless to say, Q objects are quite powerful!