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
For reasons that might or might not affect production installations, the
test checking simultaneous requests to create poll voters in the
officing voters controller wasn't behaving as expected.
The expected behavior, since commit 9a8bfac5b, is that the second
request reaching the `with_lock` part of the code waits for the first
request to finish and so this second request raises an
`ActiveRecord::RecordInvalid` exception when trying to save a voter with
the same poll and the same user as the first one.
However, 95% of the time that wasn't the case. Instead, when entering
the `@user.with_lock` block, the second request would replace its
`@voter` object with the `@voter` object saved in the same request, so
the second call to `save!` would succeed as it would simply update the
existing record.
This is a behavior that we could accept if it were consistent and
happened 100% of the time, but that isn't the case. 5% of the time, we
do get the `ActiveRecord::RecordInvalid` exception. So 5% of the time we
got a failure in the test:
```
1) Officing::VotersController POST create does not create two records
with two simultaneous requests
Failure/Error: @user.with_lock { @voter.save! }
ActiveRecord::RecordInvalid:
Validation failed: User User has already voted
# ./app/controllers/officing/voters_controller.rb:25:in `block in create'
# ./app/controllers/officing/voters_controller.rb:25:in `create'
# ./app/controllers/application_controller.rb:50:in `switch_locale'
# ./spec/controllers/officing/voters_controller_spec.rb:15:in `block (5 levels) in <top (required)>'
```
So we're changing the `with_lock` block so it includes the
initialization of the object. This way, we get the
`ActiveRecord::RecordInvalid` exception 100% of the time.
Note that in commit 9a8bfac5b we also rescued the
`ActionDispatch::IllegalStateError` exceptions. I'm not why we were
getting those exceptions when running the tests, and I'm not sure
whether we keep getting after these changes, but it doesn't really
matter. The reason is that in Consul Democracy 2.3.0 we're going to add
a unique index to the `poll_voters` table, which (according to the tests
done in the past) will make both the `@user.lock` block and rescuing the
`ActionDispatch::IllegalStateError` unnecessary.
So, in other words, these changes will never make it to production
because this part of the code will be changed again before releasing
version 2.3.0.
Note that, when taking votes from an erased user, since poll answers
don't belong to poll voters, we were not migrating them in the
`take_votes_from` method (and we aren't migrating them now either).
For the HashAlignment rule, we're using the default `key` style (keys
are aligned and values aren't) instead of the `table` style (both keys
and values are aligned) because, even if we used both in the
application, we used the `key` style a lot more. Furthermore, the
`table` style looks strange in places where there are both very long and
very short keys and sometimes we weren't even consistent with the
`table` style, aligning some keys without aligning other keys.
Ideally we could align hashes to "either key or table", so developers
can decide whether keeping the symmetry of the code is worth it in a
case-per-case basis, but Rubocop doesn't allow this option.
We were very inconsistent regarding these rules.
Personally I prefer no empty lines around blocks, clases, etc... as
recommended by the Ruby style guide [1], and they're the default values
in rubocop, so those are the settings I'm applying.
The exception is the `private` access modifier, since we were leaving
empty lines around it most of the time. That's the default rubocop rule
as well. Personally I don't have a strong preference about this one.
[1] https://rubystyle.guide/#empty-lines-around-bodies
Polls that were not votable by a user were not being displayed in the officing interface. Creating a confusing situation for officers.
With this commit polls that are not votable by a user will be displayed, with the corresponding message explaining that that poll can only be voted by residents of a certain geozone.
