Question

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filter using Q object with dynamic from user?

I am working on a filter feature in my app. I send a comma separated string via jquery to Django (within jquery I replace the space with a +, so that it can be sent over the wire).

/?ajax&sales_item=t2,+t1

Now in the view when I retrieve the GET parameters, I can see Django has already replaced the + with a space, which is great. Then I split the keywords by comma and strip the whitespace.

sales_item_raw = request.GET['sales_item']
sales_item_keywords = sales_item_raw.split(',')            

I need first to check if the given names even exist as sales item. I have to use a icontains, hence sales_items can be more than one item.

for item in sales_item_keywords:
        sales_items = profile.company.salesitem_set.filter(item_description__icontains=item.strip())            

Last but not least the queryset is used to filter deals for the given sales_items:

deals_queryset = deals_queryset.filter(sales_item__in=sales_items)

If the user filters for only one keyword that would work fine, however if there are two keywords the sales_items will be obviously overwritten in each loop iteration.

What is the most performant way to solve this? Shall I just append the content of sales_itemsin each iteration to a list outside the loop? And eventually send the new list to the final deals_queryset.filter?

I am not sure if this is a good way to solve this…

Answer 1

Use Django’s Q object to create “or” logic in your filter.

# create a chain of Qs, one for each item, and "or" them together 
q_filters = Q(item_description__icontains=sales_item_keywords[0].strip())
for item in sales_item_keywords[1:]:
    q_filters = q_filters | Q(item_description__icontains=item.strip())   

# do a single filter with the chained Qs
profile.company.salesitem_set.filter(q_filters)

This is ugly code, as I’m not sure how to handle the initial Q elegantly, as I’m not sure what is an “empty” Q to which you can chain all other Qs, including the first one. (I’m guessing you could use Q(pk=pk) but that’s ugly in a different way.)

EDIT: Ignacio’s link above shows the way, i.e.

q_filters = reduce(operator.or_, (Q(item_description__icontains=item.strip()) for item in sales_items_keywords))
profile.company.salesitem_set.filter(q_filters)