Question

我有一个ModelBase和ModelA，ModelB。

我想将ModelA实例更改为ModelB实例。（我可以处理他们所拥有的属性的差异）

我看过相关的问题，但对我来说并不适用。

How can I create an inherited django model instance from an existing base model instance?
Change class of child on django models

EDIT

当你有Place - 餐厅/酒吧关系时，
我认为将餐厅换成酒吧是很合理的。

Answer 1

我将使用相同的共享属性值创建第二个模型的全新实例，然后删除旧的实例。对我来说似乎是最干净的方式。

如果ModelBase是抽象的：

instance = ModelA.objects.get(pk=1) #arbitrary        

# find parent class fields:
fields = [f.name for f in ModelBase._meta.fields]

# get the values from the modelA instance
values = dict( [(x, getattr(instance, x)) for x in fields] )

#assign same values to new instance of second model
new_instance = ModelB(**values) 

#add any additional information to new instance here

new_instance.save() #save new one
instance.delete() # remove the old one

但是，如果ModelBase不是抽象，那么你将不得不做一个额外的解决方法：

fields = [f.name for f in ModelBase._meta.fields if f.name != 'id']
#... other parts are the same...

new_instance.modelbase_ptr = instance.modelbase_ptr #re-assign related parent
instance.delete() #delete this first!
new_instance.save()

Answer 2

在yuvi的回答中，手动分配modelbase_ptr并保存失败，因为在保存之前删除了instance.modelbase_ptr。

建立在yuvi的答案这里是一个更明确的例子，并且通常用于抽象和非抽象的转换：

ModelBase - ＆gt; ModelChild
ModelChild - ＆gt;模型库
ModelChild - ＆gt; ModelChild

可选择保留原始ID，这遵循django docs推荐的方法。

ex_model = ModelA
new_model = ModelB

ex_instance = ex_model.objects.get(pk=1) #arbitrary

# find fields required for new_model:
new_fields = [f.name for f in new_model._meta.fields]

# make new dict of existing field : value
new_fields_dict = dict( [(x, getattr(ex_instance, x, None)) for x in new_fields] )

# Save temp copy as new_model with new id
# modelbase_ptr will be created automatically as required
new_fields_dict.pop('project_ptr', None)
temp_instance = new_model(**new_fields_dict) 
temp_instance.pk = None
temp_instance.id = None
temp_instance.save()
# you must set all your related fields here
temp_instance.copy_related(ex_instance)

ex_instance.delete() 

# (optional) Save final copy as new_model with original id
final_instance = new_model(**new_fields_dict)
final_instance.save()
final_instance.copy_related(temp_instance)
temp_instance.delete()

# here are the removed fields, handle as required
removed_fields = [f.name for f in ex_model._meta.fields if f.name not in new_fields_dict.keys()]
removed_fields_dict = dict( [(x, getattr(ex_instance, x, None)) for x in removed_fields] )

在Class ModelBase中：

def copy_related(self, from):
    # include all your related fields here
    self.related_field = from.related_field.all()
    self.related_field_a = from.related_field_a.all()

Answer 3

我不得不处理相同的问题，yuvi和arctelix的答案都对我不起作用。 yuvi解决方案出现错误，arctelix解决方案使用新的pk创建新对象。

这里的目标是更改子类模型，同时保持原始超类与旧pk相同。

首先：删除 old 子类并保留超类。选中Django documents。

第二：添加新的子类及其字段，并将超类传递给它。选中this q

示例：一个地点可能是餐馆或咖啡馆，而您想将餐馆地点改为咖啡馆。如下：

class Place(models.Model):
            name = models.CharField(max_length=50)
            address = models.CharField(max_length=80)

class Caffe(Place):
    serves_hot_dogs = models.BooleanField(default=False)
    serves_pizza = models.BooleanField(default=False)

class Restaurant(Place):
    serves_tea = models.BooleanField(default=False)
    serves_coffee = models.BooleanField(default=False)

# get the objecte to be changed
rest = Restaurant.objects.get(pk=1) #arbitrary number
#delete the subclass while keeping the parent
rest.delete(keep_parents=True)

place = Place.objects.get(pk=1) # the primary key must be the same as the deleted restaurant

# Create a caffe and pass the original place
caffee = Caffe(place_ptr_id=place.pk) #this will empty the parent field

#update parent fields
caffee.__dict__.update(place.__dict__)

#add other field
........

#save the caffe
caffee.save()

将子类模型实例转换为django中的另一个子类模型实例？

3 个答案: