Django order by foreignkey - django

Question

models.py:
class Address(models.Model):
text = models.TextField(max_length=2060, null=True, blank=True, default=None, unique=True)
class Tag(models.Model):
text = models.CharField(max_length=255, null=True, blank=True, default=None, unique=True)
class AddressTagJoin(models.Model):
address = models.ForeignKey(Address, on_delete=models.CASCADE, null=True, blank=True, related_name='address_tag_join')
tag = models.ForeignKey(Tag, on_delete=models.CASCADE, null=True, blank=True, related_name='address_tag_join')
In above, Address and Tag objects are only used as AddressTagJoin's foreignkey target.
What I want to do is two kind of queryset..
When I got address "https://www.google.com", I want to get Tag queryset ordered by most used for Address (text = "www.google.com")
Tag.objects.order_by(count_of_AddressTagJoin_and_It's_address_foreignkey_is_for_"www.google.com")
In reverse, I got tag "google", I want to get Address queryset ordered by most how many used for Tag (text="google")
Address.objects.order_by(count_of_AddressTagJoin_and_It's_tag_foreignkey_is_for_"google")
How can I do that?

Answer 1

from what I understood, you require:
"For the address "google.com" most used tags in order"
By taking an example I'll reach to the query.
There is this table AddressTagJoin:
address__text | tag__id
"google.com" | 1
"google.com" | 2
"google.com" | 1
"yahoo.com" | 2
"google.com" | 3
"google.com" | 3
"google.com" | 3
If we filter AddressTagJoin based on address "google.com" and then group this based on tag__id to get the tag counts(for the address most used tags), ordering it we get:
tag__id | tag_count
3 | 3
1 | 2
2 | 1
The desired result which you want is:
tags --> 3, 1, 2
Query for this will be:
from django.db.models import Count
tags_list = list(
AddressTagJoin.objects.filter(address__text__icontains="www.google.com")
.values('tag__id')
.annotate(tag_count=Count('tag__id'))
.order_by('-tag_count')
.values_list('tag__id', flag=True)
)
tags = Tag.objects.filter(id__in=tags_list)
Note
Please check the query there might be little adjustments required. This will give you an idea for the second query, both are almost same.
Also, If you want to optimize this query you can use select_related in the tag_list query. You can refer to the docs here
PS: I haven't implemented the models to check the query because of time constraints.