Django的通用外鍵和select_related

Question

我正在嘗試使用與通用外鍵的關係來選擇模型，但它不像預期的那樣工作。

我認爲這是更好地說明和理解的代碼

class ModelA(models.Model): 
created = models.DateTimeField(auto_now_add=True) 

class ModelB(models.Model): 
instanceA = models.ForeignKey(ModelA) 

content_type = models.ForeignKey(ContentType) 
object_id = models.PositiveIntegerField() 
content_object = generic.GenericForeignKey() 

class ModelC(models.Model): 
number = models.PositiveIntegerField() 
bInstances = generic.GenericRelation(ModelB) 

# Creating an instance of A and C 
aInstance=ModelA.objects.create() 
cInstance=ModelC.objects.create(number=3) 

# Adding instance of C to the B_set of instance A 
aInstance.modelb_set.add(content_object=cInstance) 

# Select all ModelA instances that have C as content object? Does not work 
whatIWant = ModelA.objects.filter(modelb__content_object=modelCInstance) 

# Pseudo-solution, requires calling whatIWant.modelA 
whatIWant = cInstance.bInstances.select_related("modelA") 

只是要清楚，我想這條線的工作：ModelA.objects.filter(modelb__content_object=modelCInstance)，顯然使用Django的過濾器上的關係content_object不支持。

在此先感謝！

Answer 1

看一看http://www.djangoproject.com/documentation/models/generic_relations/。 並嘗試：

ctype = ContentType.objects.get_for_model(modelCInstance) 
what_you_want = ModelA.objects.filter(modelb__content_type__pk=ctype.id, 
             modelb__object_id=modelCInstance.pk) 

請看看一些Django的coding/naming conventions，使你的代碼更容易閱讀和理解！