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"Adding" Q objects in Django

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[开发(python) 所属分类 开发(python) | 发布者 店小二05 | 时间 2016 | 作者 红领巾 ] 0人收藏点击收藏

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(), \context_instance=RequestContext(request))

Needless to say, Q objects are quite powerful!

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