如何在Django或SQL中查询非唯一在一起的值？

Question

Let's say I have this model:

class Contact(BaseModel):
    order = models.ForeignKey(Order, related_name='contacts', blank=True, null=True)
    type = models.CharField(max_length=15, choices=TYPES, blank=True))

I want to find all orders where order and type are not unique together.

For example, there is order A and there are related contacts:

Contact(order=orderA, type='broker')
Contact(order=orderA, type='broker')
Contact(order=orderA, type='delivery')

I want to find this orderA because this order and type='broker' are not unique together in Contact model.

And then there is orderB and these related contacts:

Contact(order=orderB, type='broker')
Contact(order=orderB, type='delivery')

I don't want this orderB because it and the field type are unique in Contact model.

I tried using annonate() of Django but failed to relate these two fields.

Is it possible to do this with Django queries?

If not, a slight hint of how I could do it in SQL would be greatly appreciated.

Thank you very much.

Answer 1

You could use a SQL query like:

select distinct order_id
from (
    select order_id, type
    from Contact
    group by order_id, type
    having count(*) > 1);

The "order" column is shown as "order_id" because that's the way Django names columns.

Answer 2

You could write a couple methods to solve this problem. I might have gone over board writing these methods for you but regardless heres an explaination. def equal_to takes self and some other contact, returns true if that contact is the same order and type else false. def all_not_unique returns a list of all not unique contact objects with no duplicates. And should be called like, not_unique = Contact.all_not_unique() .

def equal_to(self, other):
    assert(self.id != other.id)
    if self.order.id == other.order.id:
        if self.type == other.type:
            return True
    return false

@classmethod
def all_not_unique(cls):
    query_set = cls.objects.all()
    not_unique_query_set = []
    for contact_one in query_set:
        found = False
        for contact_two in query_set:
            if not found:
                if contact_one.id != contact_two.id:
                    if contact_one.equal_to(contact_two):
                        not_unique_query_set.append(contact_one)
                        found = True

Answer 3

This should do the trick

qs = (Contact.objects.values('order','type')
         .annotate(cnt=models.Count('pk'))
         .filter(cnt__gt=1))