问题
I'm new in using GenericForeignKey, and I couldn't make it to work in a query statement. The tables are roughly like the following:
class Ticket(models.Model):
issue_ct = models.ForeignKey(ContentType, related_name='issue_content_type')
issue_id = models.PositiveIntegerField(null=True, blank=True)
issue = generic.GenericForeignKey('issue_ct', 'issue_id')
class Issue(models.Model):
scan = models.ForeignKey(Scan)
A scan creates one issue, an issue generates some tickets, and I made Issue as a foreign key to Ticket table. Now I have a Scan object, and I want to query for all the tickets that related to this scan. I tried this first:
tickets = Tickets.objects.filter(issue__scan=scan_obj)
which doesn't work. Then I tried this:
issue = Issue.objects.get(scan=scan_obj)
content_type = ContentType.objects.get_for_model(Issue)
tickets = Tickets.objects.filter(content_type=content_type, issue=issue)
Still doesn't work. I need to know how to do these kind of queries in django? Thanks.
回答1:
The Ticket.issue
field you've defined will help you go from a Ticket
instance to the Issue
it's attached to, but it won't let you go backwards. You're close with your second example, but you need to use the issue_id
field - you can't query on the GenericForeignKey
(it just helps you retrieve the object when you have a Ticket
instance). Try this:
from django.contrib.contenttypes.models import ContentType
issue = Issue.objects.get(scan=scan_obj)
tickets = Ticket.objects.filter(issue_id=issue.id, issue_ct=ContentType.objects.get_for_model(issue))
回答2:
Filtering across a GenericForeignKey
can by creating a second model that shares the db_table
with Ticket
. First split up Ticket into an abstract model and concrete model.
class TicketBase(models.Model):
issue_ct = models.ForeignKey(ContentType, related_name='issue_content_type')
issue_id = models.PositiveIntegerField(null=True, blank=True)
class Meta:
abstract = True
class Ticket(models.Model):
issue = generic.GenericForeignKey('issue_ct', 'issue_id')
Then create a model that also subclasses TicketBase
. This subclass will have all the same fields except issue
which is instead defined as a ForeignKey
. Adding a custom Manager
allows it to be filtered to just a single ContentType
.
Since this subclass does not need to be synced or migrated it can be created dynamically using type()
.
def subclass_for_content_type(content_type):
class Meta:
db_table = Ticket._meta.db_table
class Manager(models.Manager):
""" constrain queries to a single content type """
def get_query_set(self):
return super(Manager, self).get_query_set().filter(issue_ct=content_type)
attrs = {
'related_to': models.ForeignKey(content_type.model_class()),
'__module__': 'myapp.models',
'Meta': Meta,
'objects': Manager()
}
return type("Ticket_%s" % content_type.name, (TicketBase,), attrs)
来源:https://stackoverflow.com/questions/11960422/django-how-do-i-query-based-on-genericforeignkeys-fields