Django Queryset - get related objects-CodePudding

I would like to get the related objects of each object in a queryset.

Example:

from django.contrib.contenttypes.fields import GenericRelation
from django.db import models


class Synonym:
    value = models.CharField(max_length=100)

class Name:
    synonyms = GenericRelation(Synonym)

names = Name.objects.all()
synonyms = names.values_list('synonyms', flat=True)  # <- returns the database id but not the object

But the value_list method returns only the id of the objects within the queryset.

I could flatten the output propably like this:

[synonym for name in list(names) for synonym in name.synonyms.all()]

But I wondered if there is a way to directly get the objects?

CodePudding user response：

What you already listed here is correct

qs = Name.objects.all()
[synonym for synonyms in list(qs) for synonym in synonyms]

But can be (Maybe) opitimized with (Need testing):

qs = Name.objects.all()
synonyms = []
for obj in qs:
    synonyms.extend(obj.synonyms.all())

CodePudding user response：

You can specify a value for the related_query_name=… parameter ^[Django-doc]:

from django.contrib.contenttypes.fields import GenericRelation


class Name(models.Model):
    synonyms = GenericRelation(Synonym, related_query_name='name')

You can then fetch items in reverse, for example with:

Synonym.objects.filter(name__isnull=False).distinct()

will fetch all Synonyms with a related Name object, whereas for example:

Synonym.objects.filter(name__value__startswith='a').distinct()

will retrieve all Synonyms for which there is a related Name object where the value starts with 'a'.