Hyperlink Class Cannot Be Pickled

[mlavin]

Related to #3350, the rest_framework.relations.Hyperlink instances cannot be pickled as demonstrated with this sample:

>>> import pickle
>>> from rest_framework.relations import Hyperlink
>>> link = Hyperlink('http://example.com', 'test')
>>> pickle.loads(pickle.dumps(link))
Traceback (most recent call last):
  File "<console>", line 1, in <module>
TypeError: __new__() missing 1 required positional argument: 'name'

For serializers which use the hyperlink relations, this breaks the caching of the response objects since most of the cache backends rely on pickle by default.

[xordoquy]

Thanks a lot @mlavin. I think this can be linked to another issue where cache was failing with a similar message though we were not able to identify where it did come from.

[lsanpablo]

Hi @xordoquy, I would like to start contributing. Can I try this issue? I have solved @mlavin 's specific case by implementing the getnewargs() method https://docs.python.org/3.1/library/pickle.html#pickle.object.__getnewargs__ in lsanpablo@44a3d41 , but I've yet to write a test case.

[xordoquy]

Hi @Cheglader, thanks for working at it. Looking forward to your pull request :)

[glynjackson]

Same issue using HyperlinkedIdentityField +1

[jpadilla]

I'd be great if anyone having this issue could give @Cheglader's PR #3701 a try.

[glynjackson]

This is my example code that fails.

class TestSerializer(serializers.HyperlinkedModelSerializer):
    url = serializers.HyperlinkedIdentityField(view_name='detail')

Error:

TypeError at /v1/test
__new__() takes exactly 3 arguments (2 given)
Request Method: GET
Request URL:    http://127.0.0.1:8000/v1/vendor
Django Version: 1.8.4
Exception Type: TypeError
Exception Value:    
__new__() takes exactly 3 arguments (2 given)
Exception Location: /Users/glyn/Documents/workspace/shortbite/django-env/lib/python2.7/site-packages/django/core/cache/backends/locmem.py in get, line 54
Python Executable:  /Users/glyn/Documents/workspace/shortbite/django-env/bin/python
Python Version: 2.7.8

Adding the following fixes the issue for me:

def __getnewargs__(self):
        return(str(self), self.name,)

[glynjackson]

@jpadilla yep @Cheglader's PR #3701 works for me! I'm using memcache and this has been a real pain. Any idea if/when the PR will be accepted?