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Django Filter by latest related object

I've setup a system to track moderation tasks for various objects in the database. These are linked via a Generic Foreign Key relation. Given a ObjectModerationState Object I must determine its state from the most recent StateTransisition object.

The solution must lend it self to be used in a SimpleListFilter for sorting on list_display using list_filter.

e.g. Given States - Queued - Completed - Verify

I should be able to filter ObjectModerationState Objects, based on the latest state value in the StateTransisition object.

I've been leaning towards some sort of annotation on the ObjectModerationState.

Here's what I have that isn't working.


class ObjectModerationState(models.Model):
    job = models.ForeignKey(JobDescription)
    object_id = models.TextField(help_text="Primary key of the model under moderation.")
    content_type = models.ForeignKey(ContentType, help_text="Content type of the model under moderation.")
    object = generic.GenericForeignKey()

class StateTransisition(models.Model):
    state = models.ForeignKey(State)
    moderation_details = models.ForeignKey("ObjectModerationState", related_name='states')
    changed_by = models.ForeignKey("auth.User", related_name='+', null=False,
                                   help_text="If you create the task, then usually this will be you.")
    date_updated = models.DateTimeField(_("Date Set"))
    last_modified = models.DateTimeField(auto_now=True)

    def __unicode__(self):
        return "%s in state %s by %s" % (self.moderation_details.object, self.state, self.changed_by)

    class Meta:
        ordering = ['last_modified', ]
        get_latest_by = 'last_modified'

class State(Orderable):
    label = models.CharField(_("State Label"), max_length=100, unique=True)
    description = models.TextField(_("Description"), max_length=200, null=True, blank=True,
                                   help_text=_("Explination of this state in context"))
    valid_transitions = models.ManyToManyField("State", null=True, blank=True,
                                               help_text=_("You must add these mappings."))

    def __unicode__(self):
        return "%s" % (self.label)

    class Meta:
        abstract = False


class CurrentStateFilter(SimpleListFilter):
    title = 'current state'
    parameter_name = 'current state'

    def lookups(self, request, model_admin):
        states = State.objects.all()
        return  [(c.id, c) for c in states]

    def queryset(self, request, queryset):
        if self.value():
            queryset.filter(states__state__id=self.value()) <<< ????
            return queryset


  • I believe the problem is similar to this which it seems can't be done, if the solution is correct. complex annotate on django query set
like image 928
Nathan Keller Avatar asked Mar 25 '23 00:03

Nathan Keller

1 Answers

Caching is definitely a good way to go for this case. For the sake of completeness, however, I wanted to show that I've been able to do the same thing with the following Django ORM query:


So, for each EventGroup, latest_event_date is annotated to be the maximum value of timestamp for the events of that group. Furthermore, I filter to include only the EventGroups whose latest event has a state of EventState.STATE_PROCESSED.

I'm fairly certain something like this would work in your case.

like image 98
TGO Avatar answered Apr 06 '23 03:04