How to query nested relations

Using Django
1

Below are my django models

class Member(models.Model):
     first_name = models.CharField(_("First name"), max_length=256)

class Community(models.Model):
    member = models.ForeignKey(
        Member,
        verbose_name=_("Member"),
        on_delete=models.CASCADE,
    )
    name = models.ForeignKey(
        CommunityName,
        null=True,
        blank=True,
        on_delete=models.SET_NULL,
        related_name="community",
        verbose_name=_("Name"),
    )

class CommunityName(models.Model):
    name = models.CharField(_("name of community"), max_length=256)

how to query communities a member has been to without repeating community names a member has been to more than ones

A member can leave in a community or different communities at different point in time. To get all communities a member have stayed in.

m = Member.objects.get(id=1) [http://m.community](https://t.co/6j6ECyK83l?amp=1)_set.all()

This gives me all communities a member belong to but I want to find all CommunityNames a member belong to. E.g A member have stayed in CommunityA, CommunityB and CommunityA at different point in time but CommunityNames a member belongs to are CommunityA and CommunityB. Any help finding CommunityName a member belongs to.

2

Hi Kofi.

I think there’s improvement to be made on how your data is modeled, but correct me if I’m wrong.

  • A Community may have 1 name
  • A Community may have 1 or more Members

Based on that assumptions CommunityName should be a Community own field, not a ForeignKey to another model.

class Member(models.Model):
     first_name = models.CharField(_("First name"), max_length=256)

class Community(models.Model):
    name = models.CharField(_("name of community"), max_length=256)
    member = models.ForeignKey(
        Member,
        verbose_name=_("Member"),
        on_delete=models.CASCADE,
    )

Regarding your question:

member = Member.objects.get(id=1)
member.community_set.all()
# Should return a queryset containing all communities a Member belongs to

Where does this _set field comes from? Spoiler: it’s automatically created by Django

If you don’t like the autogenerated field, you define your own with related_name on the ForeignKey field. Example

1 Like
3

Thanks a lot it was helpful