Django多个外键，相同的相关名称

Question

I would like to create a model(1) with multiple foreign keys to the same other model(2). I want these foreign keys to have the same related_name because each foreign key will point to difference instances of model(2), because I need one reversed relation for all foreign keys.

Maybe an example will be more explicit :

class Parent(Model):
    name = models.CharField(max_length=100)

class Child(Model):
    name = models.CharField(max_length=100)
    father = models.ForeignKey(Parent, related_name='children')
    mother = models.ForeignKey(Parent, related_name='children')

How can I do that ?

I already know an ugly way to do so :

class Parent(Model):
    name = models.CharField(max_length=100)

    @property
    def children(self):
         # Pick the existing one in fields 'children_1' or 'children_2'

class Child(Model):
    name = models.CharField(max_length=100)
    father = models.ForeignKey(Parent, related_name='children_1')
    mother = models.ForeignKey(Parent, related_name='children_2')

Answer 1

The related_names can not be the same, since this would introduce confusion: an object that is related through the mother is not (exactly) the same as an object related through the father .

You can alter your modeling (for example by introducing a ManyToManyField with the Parent , and for example add extra data in the relation about the sex of the parent). But a disavantage of this approach is that now, you no longer set the cardinality of the relation to 2: it means a Child can (by desing) have zero parents, one parent, two parents, three parents, or more. Furthermore it could be possible that a child has two mothers, or two fathers, or two mothers and three fathers. So it can result in a lot of extra logic to prevent certain cases. Note that in some countries that is possible: in some countries extra people can be listed as "parents", and they have the same legal rights and duties as a parent.

You can however define such property to obtain the children , by making a query to fetch all Child objects where the mother , or the father is self :

from django.db.models import 

class Parent(Model):
    name = models.CharField(max_length=100)

    @property
    def children(self):
         return Child.objects.filter()

You could for example name the related names 'father_of' and 'mother_of' such that you can query some_parent.mother_of to obtain children where the some_parent is the mother_of . This could be useful if you for example would want to list a table with mothers and their children, or if you would make an application where it is possible that Parent s change gender.

If you however want to have strict Father s and Mother s, then it might be beneficial to define two separate models. The advantage is that you can both name the related_name s 'children' then, and furthermore by design you check that the father of a Child is a male (and similar for a mother being female).