[Erp5-dev] past values of a property

[bartek]

Hello,

A couple of would-be users of ERP5 asked me about possibility to
store/retrieve past values of an object property, to be able to find out
who changed it and when, and if necessary to rollback or use a past
value "as of a given date". There is a number of common use cases for
that, which I'll describe elsewhere.

Currently, the only way to retrieve a past value is the Zope's in-build
mechanism, which is difficult to use and can serve only emergency
purposes, and all the history is irrecoverably lost when database is
packed. But I think it can be easily implemented using accessor
generation and property sheets. What I mean is this: an application
developer defines in a property sheet which properties should be
"tracked", like this:

_trackable = ('title', 'vat_code')

This would modify behaviour of respective setters so that when a value
changes, the change is stored in contained object similar to
workflow_history (sthg like "property_history"). Then getters could
accept an argument "at_date" - et ceatera.

What do you think?

Bartek

-- 
"feelings affect productivity. (...) unhappy people write worse
software, and less of it."
Karl Fogel, "Producing Open Source Software"