Allow prefix/suffix options for store accessors

[untidy-hair]

Summary

####Background:

class SampleModel < ApplicationRecord
  store :settings, accessors: [:color, :dependencies], coder: JSON
  has_many :dependencies
end

There was a situation where association has_many :dependencies existed
whereas we needed the same key "dependencies" (the value is array of dependency's names) as a part of "settings" JSON, too, so that the JSON can be consumed as it is from some other stuff.

We needed SampleModel#dependencies to return the association dependencies (and thus we wanted to add a method like setting_dependencies for JSON dependencies),
but the default behavior of SampleModel#dependencies above is to return JSON dependencies.

####Workarounds:

1. remove_method, undef or alias, etc, to override
   => Didn't quite work well.
2. has_many :my_dependencies, class: Dependency and have def dependencies; my_dependencies; end to override
   => Too much carefulness is necessary to cover other methods that has_many generates so I avoided this.
3. Do not apply store (or store_accessor) for JSON dependencies, and add def setting_dependencies; settings[:dependencies]; end (and setter also).
   => This was the most viable option. But dependencies does not show up in SampleModel.stored_attributes (however you can add it).

But in the end, among stored accessors, only dependencies had setting_ prefix.
To be consistent and clearer, I ended up with adding setting_ for other stored accessors, too, in the similar way as No3 above. (setting_color/setting_dependencies for SampleModel above.)

This PR allows this prefix as an option out of the box.
The above was just one case but I think there will be some other cases, too, where prefix/suffix option is convenient and useful.
(Btw I referenced enum prefix for the implementation.)

store :settings, accessors: [ :two_factor_auth ], coder: JSON, _prefix: true
# => accessor will be model.settings_two_factor_auth
store_accessor :settings, :secret_question, _prefix: 'config'
# => accessor will be model.config_secret_question
store :settings, accessors: [ :login_retry ], _suffix: 'setting'
# => accessor will be model.login_retry_setting

Lastly, thank you for the great work, Rails team!

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[gmcgibbon]

Still relevant in 6.0.0.alpha. I think this is a good idea! See comments for some suggestions 👍

[gmcgibbon]

I think you can do extract_options! here instead.

[gmcgibbon]

Should it be _prefix or prefix like in active support's delegate? I guess enum have underscored options but I'm not sure which is preferred.

[rafaelfranca]

Without underscore, is the preffered way.

[gmcgibbon]

Should the examples be using symbols instead of strings for _prefix and _suffix values?

[untidy-hair]

Thanks for the comments @gmcgibbon. Looks like another similar PR #32306 was created and merged before they had noticed this PR... @rafaelfranca (or someone), if you think it's worth adding suffix option or this PR can improve something related, I would be happy to contribute!

[gmcgibbon]

Ah, thanks for pointing that out @untidy-hair. I'd say you're good to rebase and add the suffix option but if you want to wait for a core member's approval that's cool too 👍

[untidy-hair]

well, i'm not waiting for an approval but i just want to make sure they recognize this PR this time haha :P

[untidy-hair]

I'm going to work on this this weekend :)

[untidy-hair]

Rebased and updated per comments :) @gmcgibbon, @rafaelfranca please review again. Thanks!

[gmcgibbon]

👍

[untidy-hair]

Thanks for the review @gmcgibbon! @rafaelfranca, can we merge this?

[kamipo]

Why do we define the helper method in each _store_accessors_modules?

[untidy-hair]

@kamipo, thanks for the review! The definition is there so that we can call the chunk of code in _store_accessors_module context, but it's true that each model that calls store/store_accessor defines the helper method inside the _store_accessors_module. Maybe I should just move that part of code directly into inside the module_eval block, unless you have any better suggestion. If you do, let me know :)

[untidy-hair]

@kamipo updated. please review again. Thanks!

[kamipo]

Looks like that isn't correct appeared a subclass' accessor :secret_question.

[kamipo]

store_accessor(store_attribute, options[:accessors], options.slice(:prefix, :suffix)) if options.has_key? :accessors`

[kamipo]

def store_accessor(store_attribute, *keys, prefix: nil, suffix: nil)

[kamipo]

The prefix/suffix is just enough calculated once, there is no reason to do for each keys.

[untidy-hair]

@kamipo thanks for the comments. updated.

[kamipo]

Thanks!