How can I do to access to a foreign key in the other side?

Question

I am working a on projects using Django. Here is my models.py :

class Owner(models.Model):
    name = models.CharField(max_length=200)

class Cat(models.Model):
    owner = models.ForeignKey(Owner, on_delete=models.CASCADE)
    pseudo = models.CharField(max_length=200)

I did that :

first_owner = Owner.objects.get(id=1)

And I would like to do something like that

first_owner.Cat

to get all the cats from an owner

I know I can do something like that :

first_cat = Owner.objects.get(id=1)

owner = first_cat.owner

But I would like the reverse operation without using ManyToMany field because every cats has an only owner in my case.

My aim is to do that using only one query.

Asked By: Peter

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Source

Answer 1

To get all Cat instances from Owner instance in the view you can do:

first_owner = get_object_or_404(Owner,id=1)

all_instances = first_owner.cat_set.all()

In the template you can do it as:

{% for owner in first_owner.cat_set.all %}
   {{owner.psuedo}}

{% endfor %}

Answered By: Sunderam Dubey

Answer 2

You can add related_name in your model and use it for get all objects referenced as ForeignKey from the given field like below:

class Cat(models.Model):
    owner = models.ForeignKey(Owner, on_delete=models.CASCADE, 
             related_name='cats') #---> you can put whatever related_name you want 
    pseudo = models.CharField(max_length=200)

and query it like this:

first_owner = Owner.objects.get(id=1)
all_instances = first_owner.cats.all()

You will get all objects referenced as ForeignKey in your Cats model.

Answered By: Divya Prakash

How can I do to access to a foreign key in the other side?

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