Support for DurationField in schema mode

[vmspike]

For now Django doesn't support str(timedelta) representation, so this patch provide correct conversion from timedelta to string.

[landscape-bot]

Code quality remained the same when pulling f1d9bba on vmspike:feature into 3b235cb on djangonauts:master.

[vmspike]

Also can you please provide short guide or key points of other fields support? Or is it too complex and there is no even rough instructions? I'm interested in FileField and ImageField, ForeignKey and ManyToMany (like ReferencesField, but in schema mode)?

[nemesifier]

Hi @vmspike, thank you for contributing.

Have you noticed the build is failing?
The VirtualField implementation is quite an experimental feature, although version after version is improving a lot, but there's till some work to do in order to establish best practices and clean up the implementation.
Having some django core dev helping out would probably clarify many doubts I have and I hope in the near future I'll be able to separate the VirtualField implementation in a generic django package that can be used with other databases too (namely: mysql and sqlite).

Short answer: no instructions yet.

Regarding this feature, if you manage to add a proper failing unit test and fix the build for other django versions we can include this in the next release.
Please read:
http://djangonauts.github.io/django-hstore/#_developers_guide

[vmspike]

Thanks for reply, got it.
Sorry for any inaccuracies, I'm newbie in python/django and it's my first pull request.
I'll try to find time to prepare the code in compliance with your rules.
But Django < 1.8 doesn't have DurationField in stock. What to do in this case? Add support only for django >= 1.8?

[nemesifier]

Yes, the best thing would be to do conditional support. Take a look at other parts of the code where this is done.