What to do if the user wants to make a destructive change?

[vr2262]

At the moment, if a question is deleted from a survey, any answers to that question will be deleted as well. If a survey is deleted, all submissions to that survey will be deleted. Wacky things can happen if the user modifies a question.

What should we do in these scenarios? We could...

1. Do nothing. The user should be aware of potentially destructive actions.
2. Warn the user. Before the user makes any destructive change, display a warning and offer to export any data that would be affected.
3. Avoid deleting things. Instead of actually doing anything destructive, any modification results in an entirely new survey.

[csytan]

My vote is for number 3.

[csytan]

1. May be buggy and hard to handle having two submissions with different schemas.
2. Basically the same as number 3 (if we delete submissions that have the old schema)

Updating existing submissions with an older schema isn't an exact science and probably not worth the trouble.

[vr2262]

For what it's worth, here are the various scenarios and what the application does now (i.e., option 1).

Action	Consequence
Delete survey	All submissions to that survey get deleted as well
Delete a question	Answers to that question get deleted
Change the type_constraint_name of a question	Existing answers will still be there in the database, but the application won't display them (this could be changed, in principle)
Delete a choice from a multiple choice question	Any answers that selected that choice will be deleted
Add a new question, choice, or branch	Nothing bad happens
Rearrange existing questions, choices, or branches	Nothing bad happens

[dpapathanasiou]

I vote for 3 as well, largely b/c it's consistent with the idea of immutable data databases, e.g. Datomic

[vr2262]

I have made the proposed change (option 3) in the non_destructive_update branch. Here is the new consequence table:

Action	Consequence
Delete survey	All submissions to that survey get deleted as well.
Update survey	The existing survey will be renamed to end with "(new version created on <ISO time>)". A new survey will be created, and any submissions that can sensibly be copied over will be.
Delete a question in an update	Answers to that question will not appear in the updated version.
Change the type_constraint_name of a question	Existing answers will not be copied over to the new version, with the exception of multiple_choice ↔ multiple_choice_with_other, which will preserve answers corresponding to surviving choices.
Delete a choice from a multiple choice question	Any answers that selected that choice will not be copied over.
Add a new question, choice, or branch	Nothing bad happens. This counts as an update, so it creates a new survey with copied-over submissions.
Rearrange existing questions, choices, or branches	Nothing bad happens. This counts as an update, so it creates a new survey with copied-over submissions.