I have 2 models connected via M2M relation
class Paper(models.Model):
title = models.CharField(max_length=70)
authors = models.ManyToManyField(B, related_name='papers')
class Author():
name = models.CharField(max_length=70)
Is there a way to include authors
as all related authors' IDs (and maybe name somehow)?
Is there a way to include papers
IDs as reverse relation (and maybe title as well)?
Author.objects.all().annotate(related_papers=F('papers'))
this only adds id of one paper, first one it finds I think.
Furthermore, changing related_papers
to papers
gives an error:
ValueError: The annotation ‘papers’ conflicts with a field on the model.
From what I understand in your comments, you're using DRF. I will give you 2 answers.
1) If you're talking about model serializer, you can use PrimaryKeyRelatedField :
class AuthorSerializer(serializers.ModelSerializer):
papers=serializers.PrimaryKeyRelatedField(many=True, read_only=True)
class Meta:
model = Author
fields = ['name', 'papers']
class PaperSerializer(serializers.ModelSerializer):
class Meta:
model = Paper
fields = '__all__'
This will return the IDs for the other side of the relationship whether you're on Paper or Author side. That will return the primary keys, not a representation of the object itself.
2) Now you're also talking about performance (e.g. database hit at each iteration).
Django (not DRF-specific) has a queryset method to handle preloading related objects. It's called prefetch_related.
For example, if you know you're going to need the relation object attributes and want to avoid re-querying the database, do as follow:
Author.objects.all().prefetch_related('papers')
# papers will be already loaded, thus won't need another database hit if you iterate over them.