JSON serialisation fails if models have timestamp objects as values.

[smn]

We should probably change the field type to just work with iso-strings (so we can json encode easily) but provide helpers for getting the actual datetime object.

>>> page = PageModel(modified_at='2014-09-19T00:00:00.000+00:00')
>>> print page.modified_at
'2014-09-19T00:00:00.000+00:00'
>>> print page.modified_at.datetime()
datetime.datetime(2014, 9, 19, 00, 00, 00, 000, tzinfo=tzoffset(None, 0))
>>>

Not having this caused major issues in Vumi.

@hodgestar & @jerith any suggestions from you guys considering the Vumi trouble?

[hodgestar]

My vote would be to serialize (and store) timestamps as UNIX timestamps in milliseconds. This is perhaps a topic better discussed over lunch, but in short:

• timestamps are simple and easily parsed
• there is any easy mapping to and from UTC
• milliseconds feel like a good level of granularity (too much happens in 1s and nanoseconds take one into regimes where defining what "current time" means becomes tricky)

[miltontony]

@smn didn't you resolve this?

[smn]

Nope, it's still an issue.