HABTM should fall back to using the normal CollectionAssociation's size calculation if the collection is not cached or loaded.

This addresses both #14913 and #14914 for master.

Rewrite to avoid 'we'/'you', add missing period, and keep lines at 80 chars. Cheers :)

Improve readability with help from @senny

[ci skip]

`before_add` callbacks are fired before the record is saved on
`has_and_belongs_to_many` assocations *and* on `has_many :through`
associations.  Before this change, `before_add` callbacks would be fired
before the record was saved on `has_and_belongs_to_many` associations, but
*not* on `has_many :through` associations.

Fixes #14144

when destroying a record on a has_many :through association.
:destroy method has own counter_cache callbacks.

This commit fixes reported issue #7630 in which counter
caches were not being updated properly when replacing
has_many_through relationships

If assigning to a has_many :through collection against an unsaved
object using the collection=[<array_of_items>] syntax, the join models
were not properly created, previously.

It has been moved to active_record_deprecated_finders.

Use #to_a instead.

Bug #6289

If a record is removed from a has_many :through, all of the join records
relating to that record should also be removed from the through
association's target.

(Previously the records were removed in the database, but only one was
removed from the in-memory target array.)

Fixes #3425.

added an alias for new to build to the AR collection proxy, this corrects an issue where the collection proxies were not consistent

singular and collection relations in AR can now specify mass-assignment security options (:as and :without_protection) in build, create and create! methods.

Associations - where possible, call attributes methods rather than directly accessing the instance variables

Split AssociationProxy into an Association class (and subclasses) which manages the association, and a CollectionProxy class which is *only* a proxy. Singular associations no longer have a proxy. See CHANGELOG for more.

Allow building and then later saving has_many :through records, such that the join record is automatically saved too. This requires the :inverse_of option to be set on the source association in the join model. See the CHANGELOG for details. [#4329 state:resolved]

Refactor the implementations of AssociatioCollection#delete and #destroy to be more consistent with each other, and to stop passing blocks around, thus making the execution easier to follow.

Correctly update counter caches on deletion for has_many :through [#2824 state:resolved]. Also fixed a bunch of other counter cache bugs in the process, as once I fixed this one others started appearing like nobody's business.

Support the :dependent option on has_many :through associations. For historical and practical reasons, :delete_all is the default deletion strategy employed by association.delete(*records), despite the fact that the default strategy is :nullify for regular has_many. Also, this only works at all if the source reflection is a belongs_to. For other situations, you should directly modify the through association.

Make record.association.destroy(*records) on habtm and hm:t only delete records in the join table. This is to make the destroy method more consistent across the different types of associations. For more details see the CHANGELOG entry.