Django queryset - Adding HAVING constraint

Question

I have been using Django for a couple of years now but I am struggling today with adding a HAVING constraint to a GROUP BY.

My queryset is the following:

crm_models.Contact.objects\
.filter(dealercontact__dealer__pk__in=(265,),
         dealercontact__activity='gardening',
         date_data_collected__gte=datetime.date(2012,10,1),
         date_data_collected__lt=datetime.date(2013,10,1))\
.annotate(nb_rels=Count('dealercontact'))

which gives me the following MySQL query:

SELECT *
FROM `contact` 
LEFT OUTER JOIN `dealer_contact` ON (`contact`.`id_contact` = `dealer_contact`.`id_contact`) 
WHERE (`dealer_contact`.`active` = True 
   AND `dealer_contact`.`activity` = 'gardening'  
   AND `contact`.`date_data_collected` >= '2012-10-01'  
   AND `contact`.`date_data_collected` < '2013-10-01'
   AND `dealer_contact`.`id_dealer` IN (265)) 
GROUP BY `contact`.`id_contact`
ORDER BY NULL;

I would get exactly what I need with this HAVING constraint:

HAVING SUM(IF(`dealer_contact`.`type`='customer', 1, 0)) = 0 

How can I get this fixed with a Django Queryset? I need a queryset in this instance.

Here I am using annotate only in order to get the GROUP BY on contact.id_contact.

Edit: My goal is to get the Contacts who have no "customer" relation in dealercontact but have "ref" relation(s) (according to the WHERE clause of course).

Models

class Contact(models.Model):
    id_contact = models.AutoField(primary_key=True)
    title = models.CharField(max_length=255L, blank=True, choices=choices_custom_sort(TITLE_CHOICES))
    last_name = models.CharField(max_length=255L, blank=True)
    first_name = models.CharField(max_length=255L, blank=True)
    [...]
    date_data_collected = models.DateField(null=True, db_index=True)

class Dealer(models.Model):
    id_dealer = models.AutoField(primary_key=True)
    address1 = models.CharField(max_length=45L, blank=True)
    [...]

class DealerContact(Auditable):
    id_dealer_contact = models.AutoField(primary_key=True)
    contact = models.ForeignKey(Contact, db_column='id_contact')
    dealer = models.ForeignKey(Dealer, db_column='id_dealer')
    activity = models.CharField(max_length=32, choices=choices_custom_sort(ACTIVITIES), db_index=True)
    type = models.CharField(max_length=32, choices=choices_custom_sort(DEALER_CONTACT_TYPE), db_index=True)

Answer 1

I figured this out by adding two binary fields in DealerContact: is_ref and is_customer.

If type='ref' then is_ref=1 and is_customer=0. Else if type='customer' then is_ref=0 and is_customer=1.

Thus, I am now able to use annotate(nb_customers=Sum('is_customer')) and then use filter(nb_customers=0).

The final queryset consists in:

Contact.objects.filter(dealercontact__dealer__pk__in=(265,),  
                       dealercontact__activity='gardening', 
                       date_data_collected__gte=datetime.date(2012,10,1),
                       date_data_collected__lt=datetime.date(2013,10,1))\
               .annotate(nb_customers=Sum('dealercontact__is_customer'))\
               .filter(nb_customers=0)