使用jsonpickle进行类型演变(python) [英] type evolution with jsonpickle (python)

问题描述

jsonpickle中对此有任何支持吗?

Is there any support of this in jsonpickle?

例如我存储并反对，他们修改了其架构，然后尝试将其加载回去.

E.g. I store and object, them modify its schema, then try to load it back.

例如，以下更改(属性添加)

The following change, for instance, (attribute addition)

import jsonpickle

class Stam(object):

   def __init__(self, a):
     self.a = a

   def __str__(self):
     return '%s with a=%s' % (self.__class__.__name__, str(self.a))


js = jsonpickle.encode(Stam(123))
print 'encoded:', js

class Stam(object):

   def __init__(self, a, b):
     self.a = a
     self.b = b

   def __str__(self):
     return '%s with a=%s, b=%s' % (self.__class__.__name__, str(self.a), str(self.b))

s=jsonpickle.decode(js)
print 'decoded:', s

产生错误:

encoded: {"py/object": "__main__.Stam", "a": 123}
decoded: Traceback (most recent call last):
  File "C:\gae\google\appengine\ext\admin\__init__.py", line 317, in post
    exec(compiled_code, globals())
  File "<string>", line 25, in <module>
  File "<string>", line 22, in __str__
AttributeError: 'Stam' object has no attribute 'b'

推荐答案

jsonpickle中不支持类型演变或类型迁移.

There is no support for type evolution or type migrations within jsonpickle.

您最好的做法是将数据的JSON表示(通过json.loads加载)到列表/字典/字符串/数字的基本Python结构中.遍历此Python表示形式，添加空/默认b键.然后通过json.dumps重新保存JSON.

Your best course of action would be to load (via json.loads) the JSON representation of your data into a basic Python structure of lists / dicts / strings / numbers. Traverse this Python representation, adding in empty/default b keys. Then re-save the JSON via json.dumps.

然后您可以使用jsonpickle加载数据的修改版本.

You can then use jsonpickle to load the modified version of the data.

temp = json.loads(js)
temp['b'] = None
js = json.dumps(temp)
jsonpickle.decode(js)

如果您的对象模型更复杂，这显然会变得更加复杂，但是您可以检查py/object键以查看是否需要修改对象.

This obviously gets more complicated if your object model is more complex, but you can check the py/object key to see if you need to modify the object.

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