Note that Rails 7.1 changes `find_or_create_by!` so it calls
`create_or_find_by!` when no record is found, meaning we'll rarely get
`RecordNotUnique` exceptions when using this method during a race
condition.
Adding this index means we need to remove the uniqueness validation.
According to the `create_or_find_by` documentation [1]:
> Columns with unique database constraints should not have uniqueness
> validations defined, otherwise create will fail due to validation
> errors and find_by will never be called.
We're adding a test that checks what happens when using
`create_or_find_by!`.
Note that we're creating voters combining `create_with` with
`find_or_create_by!`. Using `find_or_create_by!(...)` with all
attributes (including non-key ones like `origin`) fails when a voter
already exists with different values, e.g. an existing `origin: "web"`
and an incoming `"booth"`. In this situation the existing record is not
matched and the unique index raises an exception.
`create_with(...).find_or_create_by!(user: ..., poll: ...)` searches by
the unique key only and applies the extra attributes only on creation.
Existing voters are returned unchanged, which is the intended behavior.
For the `take_votes_from` method, we're handling a (highly unlikely, but
theoretically possible) scenario where a user votes at the same time as
taking voters from another user. For that, we're doing something similar
to what `create_or_find_by!` does: we're updating the `user_id` column
inside a new transaction (using a new transactions avoids a
`PG::InFailedSqlTransaction` exception when there are duplicate
records), and deleting the existing voter when we get a
`RecordNotUnique` exception.
On `Poll::WebVote` we're simply raising an exception when there's
already a user who's voted via booth, because the `Poll::WebVote#update`
method should never be called in this case.
We still need to use `with_lock` in `Poll::WebVote`, but not due to
duplicate voters (`find_or_create_by!` method will now handle the unique
record scenario, even in the case of simultaneous transactions), but
because we use a uniqueness validation in `Poll::Answer`; this
validation would cause an error in simultaneous transactions.
[1] https://api.rubyonrails.org/v7.1/classes/ActiveRecord/Relation.html#method-i-create_or_find_by
This could be the case when JavaScript is disabled.
Note that, in `Poll/WebVote` we're calling `given_answers` inside a
transaction. Putting this code before the transaction resulted in a test
failing sometimes, probably because of a bug that might be possible to
reproduce by doing simultaneous requests.
With the old interface, there wasn't a clear way to send a blank ballot.
But now that we've got a form, there's an easy way: clicking on "Vote"
while leaving the form blank.
Our original interface to vote in a poll had a few issues:
* Since there was no button to send the form, it wasn't clear that
selecting an option would automatically store it in the database.
* The interface was almost identical for single-choice questions and
multiple-choice questions, which made it hard to know which type of
question we were answering.
* Adding other type of questions, like open answers, was hard since we
would have to add a different submit button for each answer.
So we're now using radio buttons for single-choice questions and
checkboxes for multiple-choice questions, which are the native controls
designed for these purposes, and a button to send the whole form.
Since we don't have a database table for poll ballots like we have for
budget ballots, we're adding a new `Poll::WebVote` model to manage poll
ballots. We're using WebVote instead of Ballot or Vote because they
could be mistaken with other vote classes.
Note that browsers don't allow removing answers with radio buttons, so
once somebody has voted in a single-choice question, they can't remove
the vote unless they manually edit their HTML. This is the same behavior
we had before commit 7df0e9a96.
As mentioned in c2010f975, we're now adding the `ChangeByZero` rubocop
rule, since we've removed the test that used `and change`.
