_set in Django for a queryset

django django-queryset
user7517947 picture user7517947 · Feb 7, 2017 · Viewed 25.8k times · Source

I'm a bit confused how to use _set in a QuerySet in Django. For example, an object Blog b, and the object Entry related by the attribute entry_set. What is the meaning of b.entry_set.all()?

I would appreciate if someone could use this example to display the possible output.

Answer

karthikr picture karthikr · Feb 7, 2017

What you are seeing is a reverse related object lookup.

In your example:

class Blog(models.Model):
    pass

class Entry(..):
    blog = Blog(..)

Now, given object e of type Entry, you would do e.blog to access the related object Blog - which is a forward relation. The _set is a reverse lookup class variable django puts in for you.

So, given object b - you would do:

entries = b.entry_set.all()

The reason the reverse is a queryset is, ForeignKey is 1-to-many relationship. Hence, the reverse is a queryset.

The _set object is made available when related_name is not specified.

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