I have two models with a 1-to-Many relationship - parent and child. I want to query all parents with no children. In SQL I would do something like this:
SELECT p.*
FROM parent p
LEFT JOIN children c on (p.id=c.parent_id)
WHERE c.id IS NULL
How can I do the same with a single Django query?
The relevant parts of the model are:
class Parent(model):
...
class Child(model):
parent = ForeignKey(Parent, related_name='children')
Use the isnull
field lookup, which:
Takes either True or False , which correspond to SQL queries of IS NULL and IS NOT NULL , respectively.
Thus, the queryset will look like the following:
Parent.objects.filter(children__isnull=True)
menus = Menu.objects.filter(parent__name__isnull=True)
{% for menu in menus %}
{% if menu.childs.count > 0 %} ...
{% endif %}
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