Measurable Ratings: change log improvements

[rovats]

There is a client requirement to create a report for any changes made to ratings under a measurable category.

Current sample entries in the change_log table:

Added: Q2 2019 with a rating of: G Updated: Q3 2019 with a rating of: Z Removed: Q2 2019

Suggested improvements to help with this requirement:

• Modify the Update log message to include the previous rating
• Modify the Remove log message to include the previous rating
• Include rating name along with code, eg: ..with a rating of: Z (Unknown)
• Add a child_id field on change_log to store the measurable_id (this will help narrow down measurables by category, in case there are multiple measurables with the same name in different categories)

Any suggestions/objections?

@davidwatkins73 @kamransaleem

[kamransaleem]

Sounds like a good idea to include the old value. Wonder if this should be formalised in a separate column since being a change log it makes sense.

[rovats]

We could add nullable old_value and new_value fields, but in cases where multiple fields updated together, populating these might not make sense.