Add option to defer persisting additions/removals on collection associations. Add marked_for_deletion.

[WelpThatWorked]

Motivation / Background

Presently, any additions or removals of existing records to a collection association are persisted to the database immediately, rather than waiting for save to be called manually. This can be unexpected or undesirable in cases such as generating a preview or looking back at what changes just occurred. While there exist some workarounds, they seem a bit cumbersome, and there have occasionally been requests for it to not be persisted immediately, so I thought having a toggle on that behavior might be more convenient.

Detail

• Add the :defer option for collection associations with autosave enabled. Setting this to true will defer the persisting of additions/removals until the parent (or child, in the case of has_many) is saved.
  • Applies to methods using concat() or replace(). Using collection.destroy(record) or collection.delete(record) still persists immediately, since mark_for_deletion/destruction is simultaneously available.
  • Removals are flagged for deletion, while additions are autosaved due to changes in the record (has_many) or changes in the through record (habtm, has_many :through)
  • Reloading a habtm or has_many :through association now resets the internal through association to keep the records listed on both targets in sync.
• Add marked_for_deletion to Autosave Associations, a mirror of marked_for_destruction that calls delete instead of destroy.
  • Add marked_for_removal? which checks if either flag is set.
  • If both flags are set, destruction takes precedence.
  • I'm concerned the wording of some of the documentation in autosave_association.rb might be a bit messy where the two overlap, but I'm unsure.
• Add change-tracking methods <association>_added_records and <association>_previously_added_records
  • I'm not sure this is worthwhile, as it might be more flexibly accomplished by the use of added/removed callback, and implementing similar methods for removals seems it would require keeping a copy of deleted/destroyed records in memory regardless of if the function would be used.
  • Not sure about the name.

Additional information

Other previous related discussion:
#17368
#42097
#46685
Rails Forum