Variant requires Dict to have both key and value.

[jamadden]

Raise an error at construction time instead of waiting until when the field is validating.

Fixes #59

[cutz]

This looks reasonable to me. I did a quick audit looking for where we may see errors. There's the location that led to me opening the linked issue. How about something like Variant((Object(IDict)) is that going to require we add a key_type and value_type or other wise convert Object(IDict) to something else?

https://github.com/NextThought/nti.dataserver/blob/c2dbc10a922e4ebc62cfc08a29ead6ddb4a60ced/src/nti/contentsearch/interfaces.py#L163

[jamadden]

How about something like Variant((Object(IDict))

If it's caught by this test/change, it definitely wouldn't have worked before — it would have been raising AttributeError. If it's not caught by this test, it may or may not have worked, and it still may or may not. Either way, I don't see a compatibility issue.

Does that check out?

ETA: Yeah, it works:

>>> from nti.schema.field import Object
>>> from nti.schema.field import Variant
>>> from zope.interface.common.collections import IMapping
>>>
>>> v = Variant([Object(IMapping)])
>>> v.fromObject({'a': 'b'})
{'a': 'b'}