Re: Converting a string representation of query to Django object (Q).

On Wed, Feb 22, 2012 at 01:15:04PM -0800, gowthaman ramasamy wrote:
>I am trying to construct the following query at the end.
>Result.objects.filter(Q(analysis__experiment__experiment_code="PyLS24")
>|Q(analysis__experiment__experiment_code="PyLS40"))
>
>How I do now:
>The values are passed from a from(post) using checkboxes (#expcodes =
>request.POST.getlist('expcode')
>). So I get a list of:
>expcodes = ['PyLS24', 'PyLS40']
>then use the for loop to construct string representation of Q object.
>expcodes = ['PyLS24', 'PyLS40']
>k=''
>c=0
>for e in expcodes:
>j=e.join(['Q(analysis__experiment__experiment_code="','") '])
>if c == 0:
>k = j
>else:
>k='|'.join([k, j])
>c = c+1
>
>k in this gives me 'Q(analysis__experiment__experiment_code="PyLS24")
>|Q(analysis__experiment__experiment_code="PyLS40") '.
>When i use this to query the model as following... Result.objects.filter(k)I get "ValueError: too many values to unpack" error. But, exact string, if
>I copy paste into Results.object.filter(here) it works.
>
>When I checked the type, k constructed from for loop is in string format
>(obviously). But, when I copy paste the pint out of k, it automatically
>becomes Django's Q object.

The issue is that you can't use a string to generate the Q object
passed to filter(). Instead, you need to build them up in a list,
and then use the bitwise-OR operator. You can either do that in a
loop, or this way:

import operator

q_objs = [ Q(analysis__experiment__experiment_code=code) for code in expcodes ]
arg = reduce(operator.or_, q_objs) # do bitwise-OR of all objects in the list
Results.object.filter(arg)

--
You received this message because you are subscribed to the Google Groups "Django users" group.
To post to this group, send email to django-users@googlegroups.com.
To unsubscribe from this group, send email to django-users+unsubscribe@googlegroups.com.
For more options, visit this group at http://groups.google.com/group/django-users?hl=en.