Help with Manager.

[Marc Aymerich]

Hi, 

I'm trying to make a Manager for my model "order". I want that it returns all orders that their 'active period'* is greater than a certain threshold. With "active period" I mean: (order.cancel_date - order.register_date )

My Order model looks like this:

class order(models.Model):

    register_date = models.DateTimeField(auto_now_add=True)

    cancel_date = models.DateTimeField(null=True, blank=True)

I'm wondering if is possible to achieve that using "annotate", something like that:

(this not work) 

order.objects.annotate(diff=SUB('cancel_date','register_date')).filter(diff__gt=period_threshold)

or maybe django provides another kind of tool to achieve what i want ? 

I'll appreciate any kind of orientation :) 

thanks!! 

--
Marc

[Jonathan Barratt]

Unless I'm misunderstanding what you're looking for, I think this might suit your needs:

in your model:

class order(models.Model):

...

    def get_active_period(self): return self.cancel_date - self.register_date active_period = property(get_active_period)

(you may want to add some checking that cancel_date is not null, or that active_period is not negative but you get the idea)

Then where you need to access that queryset use:

order.objects.filter(active_period__gt=period_threshold)

But others with more Django experience than I may give you better advice...

Good luck!

Jonathan

[Marc Aymerich]

2010/10/14 Jonathan Barratt <jonathan...@knifeict.com>

Hi Jonathan!, 

Thank you very much for your answer, it's a pretty good solution :)

 

--
Marc

[Marc Aymerich]

2010/10/14 Jonathan Barratt <jonathan...@knifeict.com>

jops ;(, unfortunately the Manager doesn't know what "active_period" is. 

This is my order model now:

class order(models.Model):

    [...]

    def get_active_period(self):

        if self.cancel_date:

            return self.cancel_date-self.register_date

        else:

            return datetime.datetime.now()-self.register_date

        

    active_period = property(get_active_period)    

    objects = models.Manager()

    pending_of_bill = pending_of_billManager()  

And this is my manager:

class pending_of_billManager(models.Manager):

    def get_query_set(self):

        [...]

        return super(pending_of_billManager, self).get_query_set().filter(active_period__gt=threshold)

This Works:

>>> order.objects.get(pk=1).active_period

datetime.timedelta(0, 8347, 24949)

but this doesn't:

>>> order.pending_of_bill.all()

Traceback (most recent call last):

  File "<console>", line 1, in <module>

  File "/usr/lib/python2.6/dist-packages/django/db/models/manager.py", line 117, in all

    return self.get_query_set()

  File "/home/ucp/trunk/ucp/../ucp/order/models.py", line 15, in get_query_set

    return super(pending_of_billManager, self).get_query_set().filter(active_period__gt=threshold)

  File "/usr/lib/python2.6/dist-packages/django/db/models/query.py", line 549, in filter

    return self._filter_or_exclude(False, *args, **kwargs)

  File "/usr/lib/python2.6/dist-packages/django/db/models/query.py", line 567, in _filter_or_exclude

    clone.query.add_q(Q(*args, **kwargs))

  File "/usr/lib/python2.6/dist-packages/django/db/models/sql/query.py", line 1128, in add_q

    can_reuse=used_aliases)

  File "/usr/lib/python2.6/dist-packages/django/db/models/sql/query.py", line 1026, in add_filter

    negate=negate, process_extras=process_extras)

  File "/usr/lib/python2.6/dist-packages/django/db/models/sql/query.py", line 1191, in setup_joins

    "Choices are: %s" % (name, ", ".join(names)))

FieldError: Cannot resolve keyword 'active_period' into field. Choices are: amendment_invoice, amendment_quota, bill, cancel_date, comment, contracted_pack, discount, entity, forward, htacces, htpasswd, id, included, installed_app, mailman, name, order_disk, order_memory, order_swap, ovz, pack, price, register_date, renew, service, size, system_group, system_user, system_user_related, traffic, virtual_aliase, virtual_user, virtual_user_related, virtualhost

What I'm missing ?? why super(pending_of_billManager, self).get_query_set() doesn't know about active_period?

Thanks! 

--
Marc

[Marc Aymerich]

2010/10/14 Marc Aymerich <glic...@gmail.com>

Seems that we can't use a property as a queryset 'filter', in other words we can't use property like this:  order.objects.filter(active_time__gt=whatever)

--
Marc

[Alec Shaner]

See this:

http://ifacethoughts.net/2009/07/14/calculated-fields-in-django/

So perhaps the 'extra' query filter is what you need.

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[Marc Aymerich]

On Thu, Oct 14, 2010 at 10:08 PM, Alec Shaner <ash...@chumpland.org> wrote:

See this:

http://ifacethoughts.net/2009/07/14/calculated-fields-in-django/

So perhaps the 'extra' query filter is what you need.

Yep, I got a success using extra filter :) Thanks Alec for sharing this! 

by the way, just right now I found the way to reference field on filter and operates with it. It can be achieved using instances of F()  

 http://docs.djangoproject.com/en/dev/topics/db/queries/#filters-can-reference-fields-on-the-model

it could be more 'elegant' than using an extra filter, all I need is something like that:

order.objects.filter(Q(cancel_date__isnull=False, cancel_date__lt=F('register_date') + Threshold) | Q(cancel_date__isnull=True, register_date__gt=Threshold) )

but i couldn't get working this part: "F('register_date')+Threshold" ,(threshold is a datetime.datetime object, and also 'register_date' field. Anyone knows the correct way to use instances of F() with date field?  

  

--
Marc

[Alec Shaner]

You can't add a datetime to another datetime - you want to add a
datetime.timedelta instance instead. Out of curiosity I just tested it
on one of my models and it does work, e.g.,

MyModel.objects.filter(update_date__gt=F('entry_date')+timedelta(days=5))

[Marc Aymerich]

On Fri, Oct 15, 2010 at 3:39 AM, Alec Shaner <ash...@chumpland.org> wrote:

You can't add a datetime to another datetime - you want to add a
datetime.timedelta instance instead. Out of curiosity I just tested it
on one of my models and it does work, e.g.,

MyModel.objects.filter(update_date__gt=F('entry_date')+timedelta(days=5))

Hi Alec, thanks again for your answer :) 

When you executes this filter on a shell you don't get a warning ? 

This is what happens to me: 

>>> order.objects.filter(cancel_date__isnull=False).filter(cancel_date__lt=F('register_date') + timedelta(days=3))

Traceback (most recent call last):

  File "<console>", line 1, in <module>

  File "/usr/lib/python2.6/dist-packages/django/db/models/query.py", line 67, in __repr__

    data = list(self[:REPR_OUTPUT_SIZE + 1])

  File "/usr/lib/python2.6/dist-packages/django/db/models/query.py", line 82, in __len__

    self._result_cache.extend(list(self._iter))

  File "/usr/lib/python2.6/dist-packages/django/db/models/query.py", line 268, in iterator

    for row in compiler.results_iter():

  File "/usr/lib/python2.6/dist-packages/django/db/models/sql/compiler.py", line 672, in results_iter

    for rows in self.execute_sql(MULTI):

  File "/usr/lib/python2.6/dist-packages/django/db/models/sql/compiler.py", line 727, in execute_sql

    cursor.execute(sql, params)

  File "/usr/lib/python2.6/dist-packages/django/db/backends/util.py", line 18, in execute

    return self.cursor.execute(sql, params)

  File "/usr/lib/python2.6/dist-packages/django/db/backends/mysql/base.py", line 86, in execute

    return self.cursor.execute(query, args)

  File "/usr/lib/pymodules/python2.6/MySQLdb/cursors.py", line 168, in execute

    if not self._defer_warnings: self._warning_check()

  File "/usr/lib/pymodules/python2.6/MySQLdb/cursors.py", line 82, in _warning_check

    warn(w[-1], self.Warning, 3)

Warning: Truncated incorrect DOUBLE value: '3 0:0:0'

It's only a warning, but I can't see the output queryset result, maybe it's a ""fatal"" warning? you know why this is happening? 

Thanks again!!

 

--
Marc

[Alec Shaner]

Sorry, not sure about that warning because I'm using a postgresql database.