cards_count used as sequence breaks card creation after deletions

[Moreiq]

Summary
When cards are deleted, fizzy decrements cards_count on the account. Since assign_number uses cards_count as a sequence (account.increment!(:cards_count).cards_count), subsequent card creation attempts collide with existing card numbers, producing a UNIQUE constraint failed: cards.account_id, cards.number error and a 500 for all users on that account.
Steps to reproduce

Create ~150 cards on an account
Delete several cards (we deleted enough to bring cards_count back to 11)
Attempt to create a new card via the UI
500 Internal Server Error

Root cause
In app/models/card.rb:
rubydef assign_number
self.number ||= account.increment!(:cards_count).cards_count
end
cards_count is a standard Rails counter cache, which decrements on deletion. But here it's being used as a monotonically increasing sequence. These two roles are incompatible — a counter cache reflects the current count, not the highest number ever assigned.
Fix applied in production
rubyaccount.update_columns(cards_count: account.cards.maximum(:number))
Suggested fix
Either use a separate cards_sequence column that only ever increments and is never decremented on deletion, or use MAX(number) + 1 at assignment time:
rubydef assign_number
self.number ||= (account.cards.maximum(:number) || 0) + 1
end
The MAX approach is slightly less efficient but correct. A dedicated sequence column would be both correct and performant.
Environment

Self-hosted via Docker on Hetzner
SQLite backend
fizzy version: fork "sha256:90f1a0a1fe73200fe7c90ea94f49596759d2031eadbcc58e2760ee3f7e6ecda9

[flavorjones]

In upstream Fizzy, cards_count is not a Rails counter cache — there's no counter_cache: true on the belongs_to :account association in Card. It's a dedicated sequence column that is only ever incremented, in assign_number:

  self.number ||= account.increment!(:cards_count).cards_count

There is no code anywhere in the codebase that decrements cards_count when cards are deleted. So in upstream Fizzy, deleting cards should not affect the sequence.

When reporting issues that generate a 500 response, in the future please provide the exception stack trace so we can diagose the issue.

[Moreiq]

So far the matter has been resolved by generating gap cards via Console, and I have not tried to delete the cards since then to avoid getting into the same issue.

[flavorjones]

If you imported cards, that might have been the cause -- recently fixed by @monorkin in #2597

[Moreiq]

I was trying to update the latest Github commits and built a docker:latest from source that overwrote the data. Then I restored the data that was backed up using the built-in tool.