관련 필드에 잘못된 조회가 있습니다 : 존재

Question

내 데이터베이스에 다른 클래스의 외래 키로 사용하는 Photo 클래스가 있습니다. 이것들은 그 두 가지 예입니다.

class SubstancePointsLabel(ResultBase): 
    #: photo being labeled 
    photo = models.ForeignKey(Photo, related_name='substance_points_labels') 

class SubstancePoint(EmptyModelBase): 
    #: photo 
    photo = models.ForeignKey(Photo, related_name='substance_points') 

(나에게) 이러한 경우 보인다에서 ResultBase 및 EmptyModelBase하지만 아무것도의 유일한 차이점은 원인이 될 수 있습니다. 사진 예를 들어

class EmptyModelBase(models.Model): 
    """ Base class of all models, with no fields """ 

    def get_entry_dict(self): 
     return {'id': self.id} 

    def get_entry_attr(self): 
     ct = ContentType.objects.get_for_model(self) 
     return 'data-model="%s/%s" data-id="%s"' % (
      ct.app_label, ct.model, self.id) 

    def get_entry_id(self): 
     ct = ContentType.objects.get_for_model(self) 
     return '%s.%s.%s' % (ct.app_label, ct.model, self.id) 

    class Meta: 
     abstract = True 
     ordering = ['-id'] 

class ResultBase(UserBase): 
    """ Base class for objects created as a result of a submission """ 

    #: The MTurk Assignment that the user was in when this record was created 
    mturk_assignment = models.ForeignKey(
     'mturk.MtAssignment', null=True, blank=True, 
     related_name='+', on_delete=models.SET_NULL 
    ) 

    #: True if created in the mturk sandbox 
    sandbox = models.BooleanField(default=False) 

    #: This has been marked by an admin as invalid or incorrect AND will be 
    #: re-scheduled for new labeling. This can happen when an experiment is 
    #: changed and things need to be recomputed. 
    invalid = models.BooleanField(default=False) 

    #: The method by which the quality label was obtained 
    QUALITY_METHODS = (
     ('A', 'admin'), ('C', 'CUBAM'), 
     ('M', 'majority vote'), ('Q', 'qualification'), 
     ('S', 'seed point'), 
    ) 
    quality_method_to_str = dict((k, v) for (k, v) in QUALITY_METHODS) 
    #: The method by which the quality label was obtained 
    quality_method = models.CharField(
     max_length=1, choices=QUALITY_METHODS, blank=True, null=True) 

    #: time taken to specify this label in ms 
    time_ms = models.IntegerField(blank=True, null=True, db_index=True) 

    #: time taken to specify this label in ms, excluding time that the user was 
    #: in another window 
    time_active_ms = models.IntegerField(blank=True, null=True, db_index=True) 

    #: payment for this specific label 
    reward = models.DecimalField(
     decimal_places=4, max_digits=8, null=True, blank=True) 

    def save(self, *args, **kwargs): 
     if not self.id and self.mturk_assignment: 
      self.sandbox = self.mturk_assignment.hit.sandbox 
     if not self.reward: 
      from common.utils import compute_label_reward 
      self.reward = compute_label_reward(self) 
     super(ResultBase, self).save(*args, **kwargs) 

    def time_s(self): 
     """ Time pretty-printed in seconds (helper for templates) """ 
     if self.time_ms: 
      t = self.time_ms/1000.0 
      return round(t, 2 if t < 10 else 1) 
     else: 
      return None 

    def time_active_s(self): 
     """ Active pretty-printed time in seconds (helper for templates) """ 
     if self.time_active_ms: 
      t = self.time_active_ms/1000.0 
      return round(t, 2 if t < 10 else 1) 
     else: 
      return None 

    def mark_invalid(self, save=True): 
     dirty = (not self.invalid) 
     self.invalid = True 
     self.quality_method = 'A' 
     if save: 
      self.save() 
     if dirty: 
      marked_invalid.send(sender=self.__class__, instance=self) 

    def get_thumb_overlay(self): 
     return self.__unicode__() 

    class Meta: 
     abstract = True 
     ordering = ['-time_ms'] 

, 나는 관련 이름을 통해 SubstancePointsLabel 및 SubstancePoint에 액세스 할 수 있어요.

In : photo.substance_points_labels.count() 
Out: 3 

In : photo.substance_points.count() 
Out: 9 

다음과 같이 관련 클래스가 존재하는지 여부에 따라 사진 인스턴스를 필터링하고 싶습니다.

In : Photo.objects.filter(substance_exists_labels__exists=True).count() 
Out: 335932 

이제는 위와 같이 일부 작동합니다. 다른 몇 가지 경우 쿼리는 다음과 같은 오류를 반환합니다.

In : Photo.objects.filter(substance_points__exists=True).count() 
--------------------------------------------------------------------------- 
TypeError         Traceback (most recent call last) 
/data_nfs/opensurfaces2/server/matclass/tasks.pyc in <module>() 
----> 1 Photo.objects.filter(substance_points__exists=True).count() 

/data_nfs/opensurfaces2/venv/local/lib/python2.7/site-packages/django/db/models/manager.pyc in manager_method(self, *args, **kwargs) 
    90   def create_method(name, method): 
    91    def manager_method(self, *args, **kwargs): 
---> 92     return getattr(self.get_queryset(), name)(*args, **kwargs) 
    93    manager_method.__name__ = method.__name__ 
    94    manager_method.__doc__ = method.__doc__ 

/data_nfs/opensurfaces2/venv/local/lib/python2.7/site-packages/django/db/models/query.pyc in filter(self, *args, **kwargs) 
    689   set. 
    690   """ 
--> 691   return self._filter_or_exclude(False, *args, **kwargs) 
    692 
    693  def exclude(self, *args, **kwargs): 

/data_nfs/opensurfaces2/venv/local/lib/python2.7/site-packages/django/db/models/query.pyc in _filter_or_exclude(self, negate, *args, **kwargs) 
    707    clone.query.add_q(~Q(*args, **kwargs)) 
    708   else: 
--> 709    clone.query.add_q(Q(*args, **kwargs)) 
    710   return clone 
    711 

/data_nfs/opensurfaces2/venv/local/lib/python2.7/site-packages/django/db/models/sql/query.pyc in add_q(self, q_object) 
    1329   existing_inner = set(
    1330    (a for a in self.alias_map if self.alias_map[a].join_type == self.INNER)) 
-> 1331   clause, require_inner = self._add_q(where_part, self.used_aliases) 
    1332   self.where.add(clause, AND) 
    1333   for hp in having_parts: 

/data_nfs/opensurfaces2/venv/local/lib/python2.7/site-packages/django/db/models/sql/query.pyc in _add_q(self, q_object, used_aliases, branch_negated, current_negated) 
    1356     child_clause, needed_inner = self.build_filter(
    1357      child, can_reuse=used_aliases, branch_negated=branch_negated, 
-> 1358      current_negated=current_negated, connector=connector) 
    1359     joinpromoter.add_votes(needed_inner) 
    1360    target_clause.add(child_clause, connector) 

/data_nfs/opensurfaces2/venv/local/lib/python2.7/site-packages/django/db/models/sql/query.pyc in build_filter(self, filter_expr, branch_negated, current_negated, can_reuse, connector) 
    1223    # refactored when composite fields lands. 
    1224    condition = field.get_lookup_constraint(self.where_class, alias, targets, sources, 
-> 1225              lookups, value) 
    1226    lookup_type = lookups[-1] 
    1227   else: 

/data_nfs/opensurfaces2/venv/local/lib/python2.7/site-packages/django/db/models/fields/related.pyc in get_lookup_constraint(self, constraint_class, alias, targets, sources, lookups, raw_value) 
    1575     root_constraint.add(value_constraint, OR) 
    1576   else: 
-> 1577    raise TypeError('Related Field got invalid lookup: %s' % lookup_type) 
    1578   return root_constraint 
    1579 

TypeError: Related Field got invalid lookup: exists 

클래스는 같은 방식으로 생성되며 같은 방식으로 쿼리됩니다. 어떤 이유로 인스턴스에 오류가 발생하고 다른 사람들에게는 오류가 발생할 수 있습니까?

Answer 1

당신은 exclude 방법 __isnull 조회를 사용하여 작업을 수행 할 수 있습니다.

Photo.objects.exclude(substance_points__isnull=True).count() 

---

또는 당신은 사용할 수 있습니다 conditional expression

from django.db.models import When, Case, IntegerField 

Photo.objects.annotate(
    has_substance_points=Case(
     When(
      substance_points__isnull=True, then=0 
     ), 
     default=1, 
     output_field=IntegerField() 
    ) 
).filter(has_substance_points=1).count() 

Above query will return count of photos that has substance_points

---

UPDATE

아니면, 단지 substance_points의 사진 수를 원한다면 아래 접근법을 생각할 수도 있습니다.

SubstancePoint.objects.all().order_by('photo_id').distinct('photo_id').count() 
# Query will return count of photos that has substance_points 

Answer 2

Django의 필드 조회에는 "__exists"와 같은 것이 있습니까 ?? "__isnull"을 사용하여 동일한 작업을 수행하는 쉬운 방법이 있습니다. 대신에 :

당신이 할 수

Photo.objects.filter(substance_points__exists=True).count() 

:

Photo.objects.filter(substance_points__isnull=False).count()