Django left outer join with filter

Django 2.0 introduced FilteredRelation objects, which can produce pretty much exactly the LEFT OUTER JOIN query you mentioned with code similar to:

User.objects.annotate(
    filtered_foo=FilteredRelation('foo', condition=Q(foo_<criteria>))
).values(...) # e.g. 'user__id', 'filtered_foo__id'

However, it looks like you need to explicitly ask for the fields of filtered_foo that you want to use, either by specifying in values or with additional annotations. Alternatively, you can also aggregate over fields of filtered_foo grouped by the User.

To get a LEFT OUTER JOIN you can go:

User.objects.select_related('foo').filter(Q(foo__isnull=True) | Q(<other criteria here>))

Django uses the foo__isnull=True to direct it to generate a LEFT OUTER JOIN. Giving foo__isnull=False to generates an INNER JOIN as it would without the filter parameter.