ActiveRecord Mysql2 SelectiveTruncation method is unreliable about database_cleaner-active_record HOT 6 OPEN

@graaff It's a good point.

We have a method to check for row count. If that doesn't work we use AUTO_INCREMENT. See: https://github.com/DatabaseCleaner/database_cleaner/blob/master/lib/database_cleaner/active_record/truncation.rb#L70

In the scenario that you're describing, row_count is returning 0?

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I see now that I forgot to mention that I am using the :deletion strategy. There the SelectiveTruncation method uses the information_schema to determine row_count. The row_count method in truncation.rb looks like it should work since it uses plain SQL, rather than internal MySQL information.

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Also, it should be noted that MySQL states that table_rows: "For InnoDB tables, the row count is only a rough estimate used in SQL optimization." [http://dev.mysql.com/doc/refman/5.5/en/tables-table.html]

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@graaff Would you mind submitting a PR for this? It'd be great if we can use the same way to calculate row_count for both deletion and truncation strategies. I don't understand why they're different right now.

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I've just experienced this issue while porting GitLab's spec suite from the truncation strategy to the deletion strategy: https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/16516#note_55605767

If there's still interest in a PR to fix this upstream, I'm happy to work on it so we can remove the above monkey-patch!

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@lupine awesome, yes, we're interested. Thanks!

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