Move migration compatibility behavior to per-adapter modules#57479
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Move migration compatibility behavior to per-adapter modules#57479yahonda wants to merge 1 commit into
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Adapter-specific migration compatibility logic was scattered across a single monolithic Compatibility class with adapter_name string comparisons. This made it hard to maintain and impossible for third-party adapters to extend without monkey-patching. Each built-in adapter now defines its own MigrationCompatibility module and returns it from the new `migration_compatibility_module_for` hook. Third-party adapters (e.g. cockroachdb) can override this hook to ship per-version legacy behavior without patching Rails internals. The hook is registered on Mysql2Adapter and TrilogyAdapter (not AbstractMysqlAdapter) so third-party adapters subclassing the abstract class are not implicitly opted in. The assembled module is included on the topmost user-defined class in the migration ancestry, preserving the pre-refactor lookup order where user overrides run ahead of adapter-specific code. Migrator#apply_adapter_compatibility_module covers migrations that override #migrate directly. Module caching uses ObjectSpace::WeakMap to avoid leaking anonymous/reloaded classes. Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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I like the idea but this removed all the simplicity of the superclass of the migration containing the version, now, if I get this correctly the code of that class changes the first time a migration is executed so it is hard to predict which behavior that class would have, it depends on modules included at runtime, that depends on which adapter is used. That is a lot of complexity to me.
A common design pattern to solve this problem is the strategy pattern, and we can avoid the inheritance complexity (module being included at runtime)
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Agreed. I've started reworking it around the strategy pattern on a separate branch, and I'll open it as a separate pull request once it's ready. |
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Motivation / Background
Adapter-specific migration compatibility logic was scattered across a single monolithic
Compatibilityclass withadapter_namestring comparisons. This made it hard to maintain and impossible for third-party adapters to extend without monkey-patching (e.g. cockroachdb adapter, oracle-enhanced #2596, oracle-enhanced #2710).Detail
Each built-in adapter now defines its own
MigrationCompatibilitymodule and returns it from the newmigration_compatibility_module_forhook. Third-party adapters can override this hook to ship per-version legacy behavior without patching Rails internals.The hook is registered on
Mysql2AdapterandTrilogyAdapter(notAbstractMysqlAdapter) so third-party adapters subclassing the abstract class are not implicitly opted in.Additional information
Verified that the CockroachDB adapter's monkey patch is no longer needed —
migration_compatibility_module_foris inherited fromPostgreSQLAdapter, and:datetime→:timestampconversion works correctly forMigration[6.1]on CockroachDB without any adapter-side patching.Checklist