model.update() should not update columns with a default value that hasn't changed
Description
If we try to instanciate a new model to update a single column, it will also update (and possibly override) all columns with a default value defined. (collections included)
The ValueManager should handle default values properly (previous_value should not be None I think).
Environment
Pull Requests
Activity
The PR looks good, but I tried to add a test for the issue described and could not reproduce it. could you have a look? It'd be good to have a test for the reported issue in addition to the underlying previous_value behavior, and I can't get one to work.
https://github.com/datastax/python-driver/compare/master...mambocab:attempt-657-repro
With some help from Alan, I've fixed the test. If the integration tests run clean, and if it looks good to you, feel free to merge.
Added some tests here.
