Re: Bug when creating Q object from string representation of another Q object?

[Margie]

Yes - sorry about the typo.  As you say, the "orig" should be
filter_orig - that was a cut and paste mistake.

I was playing around and I think I just mistakenly assumed that I
could create a Q from the string representation of another Q.   Sounds
like that was a mistaken assumption.

What I have is a string representation that is a prefix notation that
is very similar to what you get when you print a Q.  IE, it is easy
for me to generate something like this:

(OR (AND: ('owner__username', 'mlevine'), ('status', 'open')),
('priority', 'critical'))

Where this means (Q(owner_username='mlevine') & Q(status='open')) | Q
(priority='critical')

Actually, what I have is just plain xml.  Through basic regexp
substitution I am able to turn it into the above prefix notation with
minimal effort.

So I was trying to figure out if there was a way I could easily create
a Q without loading my prefix notation into a tree and recursing into
the tree to create the Q from the leaves up.  I was pleasantly
surprised when I was able to construct a Q off of the string rep of
another Q, but it looks like that it is not really doing what I
thought it was doing.  Ok, back to the drawing board.

Margie




On Jul 22, 5:02 am, Russell Keith-Magee 
wrote:
> On Wed, Jul 22, 2009 at 5:52 AM, Margie wrote:
>
> > I have a situation where I want to do the following:
> >       take a bunch of POST params and from them create a Q object
> >       urlencode that Q object and turn it into a GET param, redirect
> > using that param
> >       process the GET that contains the urlencoded Q object, create a
> > Q object from it, and use it in a filter
>
> > I think this should all be possible, however, I am having trouble
> > recreating the new Q object from the string representation of the
> > original Q object. Here's an example of the problem:
>
>  filter_orig = Q(owner__username='mlevine')
>  print filter_orig
> > (AND: ('owner__username', 'mlevine'))
>  filter_new = Q("%s" % orig)
>
> This is the line that looks a bit suspect to me. Firstly - I'm
> assuming `orig` should actually be `filter_orig` - in which case...
>
>  print filter_new
> > (AND: (AND: ('owner__username', 'mlevine')))
>
> This isn't quite what you think it is. You are reading it as an AND
> whose first term is an AND. I suspect what you are actually getting is
> an AND clause whose first term is a string that starts "(AND:"
>
> When you construct filter_new, you don't pass in a string - you're
> passing in a dictionary of kwargs. The owner__username='mlevine'
> syntax is a keyword argument, not a string.
>
> Your original problem descriptions seems to suggest that you think you
> will be able to pass a string into Q() and have it interpreted as a
> query. This isn't the case - the arguments to Q() are no different to
> the arguments to filter(). If you want to serialize a query for use in
> a GET request, you'll need to find a different way to serialize your
> query.
>
> Yours,
> Russ Magee %-)
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Re: Bug when creating Q object from string representation of another Q object?

[Russell Keith-Magee]

On Wed, Jul 22, 2009 at 5:52 AM, Margie wrote:
>
> I have a situation where I want to do the following:
>       take a bunch of POST params and from them create a Q object
>       urlencode that Q object and turn it into a GET param, redirect
> using that param
>       process the GET that contains the urlencoded Q object, create a
> Q object from it, and use it in a filter
>
>
> I think this should all be possible, however, I am having trouble
> recreating the new Q object from the string representation of the
> original Q object. Here's an example of the problem:
>
 filter_orig = Q(owner__username='mlevine')
 print filter_orig
> (AND: ('owner__username', 'mlevine'))
 filter_new = Q("%s" % orig)

This is the line that looks a bit suspect to me. Firstly - I'm
assuming `orig` should actually be `filter_orig` - in which case...
 print filter_new
> (AND: (AND: ('owner__username', 'mlevine')))

This isn't quite what you think it is. You are reading it as an AND
whose first term is an AND. I suspect what you are actually getting is
an AND clause whose first term is a string that starts "(AND:"

When you construct filter_new, you don't pass in a string - you're
passing in a dictionary of kwargs. The owner__username='mlevine'
syntax is a keyword argument, not a string.

Your original problem descriptions seems to suggest that you think you
will be able to pass a string into Q() and have it interpreted as a
query. This isn't the case - the arguments to Q() are no different to
the arguments to filter(). If you want to serialize a query for use in
a GET request, you'll need to find a different way to serialize your
query.

Yours,
Russ Magee %-)

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Re: Bug when creating Q object from string representation of another Q object?

[Frédéric Hébert]

You don't give us enough explanation about your error.

 What type of error have you got ?

 What is your orig variable ?

 How do you serialize your Q object ?

 Are you sure that a Q object can be instantiated like that ?

 Frédéric

2009/7/21 Margie :
>
> I have a situation where I want to do the following:
>       take a bunch of POST params and from them create a Q object
>       urlencode that Q object and turn it into a GET param, redirect
> using that param
>       process the GET that contains the urlencoded Q object, create a
> Q object from it, and use it in a filter
>
>
> I think this should all be possible, however, I am having trouble
> recreating the new Q object from the string representation of the
> original Q object. Here's an example of the problem:
>
 filter_orig = Q(owner__username='mlevine')
 print filter_orig
> (AND: ('owner__username', 'mlevine'))
 filter_new = Q("%s" % orig)
 print filter_new
> (AND: (AND: ('owner__username', 'mlevine')))
 Task.objects.filter(filter_orig)
> [, ]
 Task.objects.filter(filter_new)
> Traceback (most recent call last):
> ...
>  File "/home/mlevine/django/django_libs/django-admin-ui-july8/lib/
> python2.6/site-packages/django/db/models/sql/query.py", line 1520, in
> add_filter
>    arg, value = filter_expr
>
>
> Note that in the above log, when I print filter_new, there is an extra
> AND at the front.  Logically this shouldn't be be a problem, but I
> suspect that it is indicative of the problem.
>
> Is what I'm doing above supposed to work?  Is this a bug?
>
> This is using 1.1 beta.
>
> Margie
>
>
>
> >
>



-- 
http://www.openidfrance.fr/fhebert

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Bug when creating Q object from string representation of another Q object?

[Margie]

I have a situation where I want to do the following:
   take a bunch of POST params and from them create a Q object
   urlencode that Q object and turn it into a GET param, redirect
using that param
   process the GET that contains the urlencoded Q object, create a
Q object from it, and use it in a filter


I think this should all be possible, however, I am having trouble
recreating the new Q object from the string representation of the
original Q object. Here's an example of the problem:

>>> filter_orig = Q(owner__username='mlevine')
>>> print filter_orig
(AND: ('owner__username', 'mlevine'))
>>> filter_new = Q("%s" % orig)
>>> print filter_new
(AND: (AND: ('owner__username', 'mlevine')))
>>> Task.objects.filter(filter_orig)
[, ]
>>> Task.objects.filter(filter_new)
Traceback (most recent call last):
...
  File "/home/mlevine/django/django_libs/django-admin-ui-july8/lib/
python2.6/site-packages/django/db/models/sql/query.py", line 1520, in
add_filter
arg, value = filter_expr


Note that in the above log, when I print filter_new, there is an extra
AND at the front.  Logically this shouldn't be be a problem, but I
suspect that it is indicative of the problem.

Is what I'm doing above supposed to work?  Is this a bug?

This is using 1.1 beta.

Margie



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