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PODjango - Count a subset of related models - Need to annotate count of active Coupons for each Item
 

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  1. PODjango - Count a subset of related models - Need to annotate count of active Coupons for each Item
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    <p>I have a Coupon model that has some fields to define if it is active, and a custom manager which returns only live coupons. Coupon has an FK to Item.</p> <p>In a query on Item, I'm trying to annotate the number of active coupons available. However, the Count aggregate seems to be counting all coupons, not just the active ones.</p> <pre><code># models.py class LiveCouponManager(models.Manager): """ Returns only coupons which are active, and the current date is after the active_date (if specified) but before the valid_until date (if specified). """ def get_query_set(self): today = datetime.date.today() passed_active_date = models.Q(active_date__lte=today) | models.Q(active_date=None) not_expired = models.Q(valid_until__gte=today) | models.Q(valid_until=None) return super(LiveCouponManager,self).get_query_set().filter(is_active=True).filter(passed_active_date, not_expired) class Item(models.Model): # irrelevant fields class Coupon(models.Model): item = models.ForeignKey(Item) is_active = models.BooleanField(default=True) active_date = models.DateField(blank=True, null=True) valid_until = models.DateField(blank=True, null=True) # more fields live = LiveCouponManager() # defined first, should be default manager # views.py # this is the part that isn't working right data = Item.objects.filter(q).distinct().annotate(num_coupons=Count('coupon', distinct=True)) </code></pre> <p>The <code>.distinct()</code> and <code>distinct=True</code> bits are there for other reasons - the query is such that it will return duplicates. That all works fine, just mentioning it here for completeness.</p> <p>The problem is that <code>Count</code> is including inactive coupons that are filtered out by the custom manager.</p> <p>Is there any way I can specify that <code>Count</code> should use the <code>live</code> manager?</p> <hr> <h3>EDIT</h3> <p>The following SQL query does exactly what I need:</p> <pre><code>SELECT data_item.title, COUNT(data_coupon.id) FROM data_item LEFT OUTER JOIN data_coupon ON (data_item.id=data_coupon.item_id) WHERE ( (is_active='1') AND (active_date &lt;= current_timestamp OR active_date IS NULL) AND (valid_until &gt;= current_timestamp OR valid_until IS NULL) ) GROUP BY data_item.title </code></pre> <p>At least on sqlite. Any SQL guru feedback would be greatly appreciated - I feel like I'm programming by accident here. Or, even better, a translation back to Django ORM syntax would be awesome.</p>
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    1. USChris Lawlor
    1. USChris Lawlor
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      1. PODjango - Count a subset of related models - Need to annotate count of active Coupons for each Item
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    1. CODid you try `use_for_related_fields`? (http://docs.djangoproject.com/en/dev/topics/db/managers/#manager-types)
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      1. USWill Hardy
    2. COThere's a big "DO NOT FILTER AWAY ANY RESULTS IN THIS TYPE OF MANAGER SUBCLASS" disclaimer - kinda scares me away from trying it. I'm thinking I may need to take a raw SQL approach, which I'd really rather avoid if at all possible.
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      1. PODjango - Count a subset of related models - Need to annotate count of active Coupons for each Item
      1. USChris Lawlor
    3. COtried `use_for_related_fields` anyway, didn't help.
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      1. USChris Lawlor
 

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