Django queryset filter for backwards related fields

Question

How can you filter a model based on a model that relates to it? Example below...this works, but I think this hits the DB twice and is pretty inelegant. Is there a way to do it directly with querysets? Maybe somehow with select_related(), but haven't been able to figure that one out. I want to return a QuerySet of Project.

from django.db import models

class Person(models.Model):
    pass

class Project(models.Model):
    pass

class Action(models.Model):
    person = models.ForeignKey(Person)
    project = models.ForeignKey(Project)

# Better way to do this?
def projects_by_person(person):
    actions = Action.objects.filter(person=person)
    project_ids = actions.values_list('project')
    return Project.objects.filter(id__in=project_ids)

Answer 1

Try this. I haven't tested it let me know if you have any issues

#Untested Code
Project.objects.filter(action__person = person)