克隆继承的Django模型实例 [英] Clone an inherited django model instance

问题描述

当我克隆Django模型实例时，我曾经清理过 pk字段。
这似乎不适用于继承的模型：

When I clone a django model instance I used to clean the 'pk' field. This seems not to work with an inherited model :

执行以下操作：

class ModelA(models.Model):
    info1 = models.CharField(max_length=64)

class ModelB(ModelA):
    info2 = models.CharField(max_length=64)

class ModelC(ModelB):
    info3 = models.CharField(max_length=64)

现在让我们创建一个实例并通过常规方式克隆它（我使用的是django shell）：

Now let's create an instance and clone it by the 'usual' way ( I am using a django shell ):

In [1]: c=ModelC(info1="aaa",info2="bbb",info3="ccc")

In [2]: c.save()

In [3]: c.pk
Out[3]: 1L

In [4]: c.pk=None  <------ to clone

In [5]: c.save()   <------ should generate a new instance with a new index key

In [6]: c.pk       
Out[6]: 1L         <------ but don't

In [7]: ModelC.objects.all()
Out[7]: [<ModelC: ModelC object>]   (only one instance !)

唯一的wa y我发现是这样做的：

The only way I found was to do :

In [16]: c.pk =None

In [17]: c.id=None

In [21]: c.modela_ptr_id=None

In [22]: c.modelb_ptr_id=None

In [23]: c.save()

In [24]: c.pk
Out[24]: 2L    <---- successful clone containing info1,info2,info3 from original instance

In [25]: ModelC.objects.all()
Out[25]: [<ModelC: ModelC object>, <ModelC: ModelC object>]

我发现这很丑陋，有没有更好的方法可以从继承的对象中克隆实例模型？

I find that very ugly, is there a more nice way to clone an instance from an inherited model ?

推荐答案

c=ModelC(info1="aaa",info2="bbb",info3="ccc")
# creates an instance

c.save()
# writes instance to db

c.pk=None
# I doubt u can nullify the auto-generated pk of an existing object, because a pk is not nullable
c.save()
# if I'm right nothing will happen here.

所以c始终是同一对象。如果要克隆它，则需要生成一个新对象。在ModelC中使用构造函数：

So c will always be the same object. If you want to clone it you need to generate a new object. Either with a constructor within ModelC:

def __init__(another_modelC_obj=null, self):
   if another_modelC_obj:
      # for every field in another_modelC_obj: do self.field = another_modelC_obj.field
   super().__init__()

所以你可以去

c2=ModelC(c)

或直接通过以下方式调用它：

Or call it directly with:

c2=ModelC(c.info1, c.info2, c.info3)

然后c2和c将尽管他们的pk是一样的

Then c2 and c will be identical despite of their pk

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