Require admins to apply exactly one theme to Guidance

[stephaniesimms]

as part of bug issue #1183 we accidentally enabled admins to remove all themes from Guidance. reinstate the requirement to apply at least one theme for each piece of Guidance - it doesn't make sense to create un-themed Guidance because this will never display on templates.

[vyruss]

While we're fixing this, I think we should change this to be "exactly one Theme to Guidance". After discussion with @sjDCC we came to the conclusion that it makes no sense to apply multiple Themes to one piece of Guidance.

This requires:

• Changing the data model Themes <-> Guidance relationship from HABTM to FK
• Changing the guidance tickboxes so that only one can be selected
• Changing the controller so that it only accepts exactly one theme per guidance
  • Updating the controller with the appropriate warning messages

[briri]

fixed as part of #1326. It made sense to address it at the same time as adding in the validations

[stephaniesimms]

after testing I am able to create and publish guidance with no themes (screenshot 1). once i apply a theme and save it, then uncheck the box and save, my changes are not applied so it appears to be requiring at least one theme at that point. i can still apply multiple themes.

• desired behavior is to mark the field "Themes" with a red asterisk and require users to apply one theme only before allowing them to save guidance.
• also need to revise the tooltip (screenshot 2) with the following proposed text (@sjDCC can confirm): "Select one theme that is relevant to this guidance. This will display your generic organization-level guidance, or any Schools/Departments for which you create guidance groups, across all templates that have questions with the corresponding theme tags."

[stephaniesimms]

radio buttons are definitely the answer here @briri . please revise the tooltip and then this will be good to go:

• "Select one theme that is relevant to this guidance. This will display your generic organization-level guidance, or any Schools/Departments for which you create guidance groups, across all templates that have questions with the corresponding theme tags."

[stephaniesimms]

tooltip looks good. but when I create a new piece of guidance the Text area doesn't recognize that I've input text and won't allow me to save. I get the field validation message (screenshot below) the first time I click Save. I have to click Save a second time and then it allows me to proceed. Please amend so it saves after the first click.