MONGOID-5751 avoid unnecessary autosaves of unchanged subtrees#6134
Merged
jamis merged 2 commits intomongodb:9.0-stablefrom Apr 20, 2026
Merged
MONGOID-5751 avoid unnecessary autosaves of unchanged subtrees#6134jamis merged 2 commits intomongodb:9.0-stablefrom
jamis merged 2 commits intomongodb:9.0-stablefrom
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…db#6133) * MONGOID-5751 avoid unnecessary autosaves of unchanged subtrees * avoid loading HasMany proxies into memory, just to check if they're dirty * account for belongs_to sometimes storing a literal object instead of a proxy * Add Mongoid.autosave_saves_unchanged_documents feature flag to preserve legacy behavior
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Pull request overview
Adds a feature flag to avoid autosaving unchanged referenced-association subtrees (preventing unnecessary after_save callbacks), while preserving legacy behavior behind a configurable option and warning.
Changes:
- Introduces
Mongoid.autosave_saves_unchanged_documentsconfiguration option plus a deprecation-style warning when legacy behavior is in effect. - Updates referenced autosave to skip saving unchanged documents unless they (or in-memory autosaved descendants) are new/changed/marked for destruction.
- Adds a regression spec for MONGOID-5751 verifying
after_savecallbacks do not fire for pre-existing unchanged children when the flag is disabled.
Reviewed changes
Copilot reviewed 4 out of 4 changed files in this pull request and generated 2 comments.
| File | Description |
|---|---|
| spec/mongoid/association/auto_save_spec.rb | Adds regression coverage for autosave callback behavior across a parent/child/grandchild referenced tree. |
| lib/mongoid/warnings.rb | Adds a one-time warning for the legacy “save unchanged autosave docs” behavior. |
| lib/mongoid/config.rb | Adds the autosave_saves_unchanged_documents configuration option and documents its intended lifecycle. |
| lib/mongoid/association/referenced/auto_save.rb | Implements recursive “changed in subtree” detection (cycle-guarded) and skips autosaving unchanged docs when configured. |
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Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>
comandeo-mongo
approved these changes
Apr 20, 2026
jamis
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feature
This was referenced Apr 23, 2026
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(Backport of #6133)
This PR fixes a bug with
autosave: trueassociations, that causedafter_savecallbacks to be invoked on children even if they hadn't changed. It recursively checks the entire subtree and skips saving it if nothing in it has changed.Summary
The legacy behavior of associations with
autosave: trueresulted in all#savebeing invoked on all children of those associations, whether those children actually needed it or not. All correspondingafter_savehooks were invoked as well, recursively, clear to the bottom of the autosave tree.This PR adds an option to change this behavior, ensuring that subtrees are only autosaved if there are any changed documents in the subtree.
The default is
true, allowing the legacy behavior to prevail. If your program depends on this legacy behavior, you are encouraged to rewrite the affected code and set the value tofalse. The default value of this option will befalsein Mongoid 9.1, and will go away in Mongoid 10. At that point the legacy autosave behavior will be removed.