A Couple of Callback Gotchas (and a Rails 5 Fix)

Rails callbacks can run code during different stages of a model’s lifecycle, but using after_save to enqueue background work can race with the database transaction. A job may try to load a record before the commit finishes, so another process cannot find it yet.

Reading notes

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• after_save runs before the surrounding transaction is committed, so Sidekiq may not be able to see the saved record yet.
• The example switches the indexing hook from after_save to after_commit so the job is queued only after the record becomes visible to other database connections.
• Rails test cases wrap each test in a transaction, which prevents after_commit from running in the usual way.
• The test_after_commit gem makes those callbacks run in tests after the relevant transaction boundary.
• The post says Rails 5 fixed this testing problem, so the extra gem would no longer be needed there.