Verify and apply filters using a callback name

[davidstosik]

What?

At the moment, the only way to customise the process of verifying or applying a filter is to write a callable inline, in the filter declaration.
My suggestion is to accept, as apply: and verify: parameter values, either a callable, or a method name (string or symbol).

How?

Using the same apply: option as previously, we could also pass a callback name, that would need to be defined on the resource class.

filter :public, apply: :apply_public_filter

# (...)

def self.apply_public_filter(records, value, _options)
  records.where(public: (value == "public"))
end

Same goes with verify:

filter :user_id, verify: :verify_filter_user_id

# (...)

def self.verify_filter_user_id(values, _context)
  current_user = context ? context[:current_user] : nil
  values.map do |id|
    id == "me" ? current_user.try(:id) : id
  end
end

Why?

Although the existing solution is a progress from the previous suggestion to override the apply_filters and verify_filters methods, it does not allow code factorisation, and sometimes makes the code harder to read. I personally ended up with a lot of, in my opinion disgraceful declarations like the one below:

filter :custom, apply: ->(*args) { my_custom_filter_callback(*args) }

The solution above makes it easier to factorise, and follows a pattern that I think is quite common.

[lgebhardt]

@davidstosik Thanks, that's a nice addition. And thanks for the excellent write up on the problem and solution! I think this should be the model for how to submit a PR.

[davidstosik]

Thanks, but I merely copied what looked like a nice template from the original issue thread #526. :)
Thanks for the merge, this is going to help!

[lgebhardt]

I thought it look vaguely familiar. Glad you used it, and thanks to @iamvery for using it in #526

[iamvery]

❤️