Co-authored-by: NJonathan Hefner <jonathan@hefner.pro>

Co-authored-by: NJonathan Hefner <jonathan@hefner.pro>

If we defined a callback before an association that updates the object, then this may end up being
manipulated to being `false` when it should be `true`. We guard this be only defining it once.

The implication of it being false, in this case, is that the children aren't updated with the parent_id
and so they fail to associate to one another.

See https://github.com/rails/rails/issues/38120 for more details

Using words such as 'just', 'simply' and 'easy' implies to the reader
that the tasks they are trying to accomplish are tasks that anyone can
do, which might then frustrate them if they find it difficult to
complete.

This commit rephrases some usage of these words to aid understanding in
the readers without making them feel belittled.

[ci skip]

In #35861 documentation for `after_save_commit` was added, but also old
documentation was adapted. I think adapting the old documentation is not
necessary because there are already examples for `after_commit` on
`:destroy` above. On top of that the action invoked by the callback on
`:destroy` (`:log_user_saved_to_db`) talks about saving when the object
is destroyed, which can be misleading.

As I believe the documentation added by #35861 is already enough this
patch removes the modified part, which made sense before adding docs for
`after_save_commit` but is already covered by other parts of this guide.

This reverts commit 6b69ae51, reversing
changes made to 84bd9ada.

Reason: We already use "happen" a lots for callbacks and validations.

https://github.com/rails/rails/pull/35324#issuecomment-465096483

[ci skip]

Change 'happen' to a more technical term

http links will be redirected to the https version, but still better to
just directly link to the https version.

[ci skip] A regular expression was used to find a lot of missing Oxford
commas and add them.  The regular expression was as follows.

", ([a-zA-Z0-9.\`:'\"]+ ){1,6}(or|and) "

Closes #31998

Changed sentence to be more clear

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Users could have more than one `before_destroy` callback in their models.

[ci skip]

Updated text

Follow up to #27608

07d3d402 changed how exceptions are handled in after_commit
and after_destroy callbacks.  This commit updates the 5.0
release notes and the  ActiveRecord callback guide to reflect
the new behavior.

[ci skip]

The `increment!` and `decrement!` methods were recently reimplemented to
make them safe to call from multiple connections concurrently. This
changed their behaviour in a few ways.

Previously they used `update_attribute`, which calls the attribute
setter method, runs callbacks, and touches the record. Now they behave
more like `update_column`, writing the update to the database directly
and bypassing all of those steps.

The beginning of the note on the :on option is not capitalised correctly.
The :destroy symbol in the after_commit example is unnecessarily wrapped in an array.

Mention that halting chain does not re-raise  `ActiveRecord::RecordInvalid` exception as well, similar to `ActiveRecord::Rollback`

Fixes #22297

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It's pretty common for folks to monkey patch `ActiveRecord::Base` to
work around an issue or introduce extra functionality. Instead of
shoving even more stuff in `ActiveRecord::Base`, `ApplicationRecord` can
hold all those custom work the apps may need.

Now, we don't wanna encourage all of the application models to inherit
from `ActiveRecord::Base`, but we can encourage all the models that do,
to inherit from `ApplicationRecord`.

Newly generated applications have `app/models/application_record.rb`
present by default. The model generators are smart enough to recognize
that newly generated models have to inherit from `ApplicationRecord`,
but only if it's present.

Those are actually shortcuts for `after_commit`.

Before:

    after_commit :add_to_index_later, on: :create
    after_commit :update_in_index_later, on: :update
    after_commit :remove_from_index_later, on: :destroy

After:

    after_create_commit  :add_to_index_later
    after_update_commit  :update_in_index_later
    after_destroy_commit :remove_from_index_later

I deleted self from the callbacks guides code example because it's unnecessary and this way it's more like the other examples where self was not used.

- Changed `IN` to `ON` in all note sentences in guides.

References #18148.

Adding after_commit/after_rollback to list of callbacks in order helps
explain the callback order as well as making it consistent with the API
docs at http://api.rubyonrails.org/classes/ActiveRecord/Callbacks.html