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由 David Stosik 提交于
When dumping the database schema, Rails will dump foreign key names only if those names were not generate by Rails. Currently this is determined by checking if the foreign key name is `fk_rails_` followed by a 10-character hash. At [Cookpad](https://github.com/cookpad), we use [Departure](https://github.com/departurerb/departure) (Percona's pt-online-schema-change runner for ActiveRecord migrations) to run migrations. Often, `pt-osc` will make a copy of a table in order to run a long migration without blocking it. In this copy process, foreign keys are copied too, but [their name is prefixed with an underscore to prevent name collision ](https://www.percona.com/doc/percona-toolkit/LATEST/pt-online-schema-change.html#cmdoption-pt-online-schema-change-alter-foreign-keys-method). In the process described above, we often end up with a development database that contains foreign keys which name starts with `_fk_rails_`. That name does not match the ignore pattern, so next time Rails dumps the database schema (eg. when running `rake db:migrate`), our `db/schema.rb` file ends up containing those unwanted foreign key names. This also produces an unwanted git diff that we'd prefer not to commit. In this PR, I'd like to suggest a way to expose the foreign key name ignore pattern to the Rails configuration, so that individual projects can decide on a different pattern of foreign keys that will not get their names dumped in `schema.rb`.
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