Deep transform_keys for inline associations

[trevorturk]

Is your feature request related to a problem? Please describe.

I'd like to have an option for transform_keys to work down through inline associations. Currently, you need to repeat transform_keys within each association block.

Additional context

Here's a code example based on the README which demonstrates the issue:

class User
  attr_reader :created_at
  attr_accessor :articles

  def initialize
    @created_at = Time.now
    @articles = []
  end
end

class Article
  attr_accessor :user_id

  def initialize(user_id)
    @user_id = user_id
  end
end

class AnotherUserResource
  include Alba::Resource

  transform_keys :lower_camel

  attributes :created_at

  many :articles do
    # transform_keys :lower_camel
    
    attributes :user_id
  end
end

user = User.new
article = Article.new(1)
user.articles << article

AnotherUserResource.new(user).to_h

Note the commented-out transform_keys macro, which, when un-commented, results in the desired output. Here's an example from the console showing the difference:

# articles.user_id, not transformed into lower_camel
{:createdAt=>2022-07-26 21:18:29.721693 -0500, :articles=>[{:user_id=>1}]}
# articles.userId, transformed if you repeat the `transform_keys` within the inline association
{:createdAt=>2022-07-26 21:18:29.721693 -0500, :articles=>[{:userId=>1}]}

Ideally, I'd like to avoid repeating transform_keys for inline associations, but things do work as expected currently, so this is only a nice-to-have. I'm not sure if it would be convenient in Alba's code to make this possible, but I thought I'd mention it.

Thank you!

[okuramasafumi]

@trevorturk I came up with the following code:

class AnotherUserResource
  include Alba::Resource

  transform_keys :lower_camel, cascade: true # <- `cascade` option

  attributes :created_at

  many :articles do
    # transform_keys :lower_camel # This line is not required but works as if this line exists
    
    attributes :user_id
  end
end

Here, cascade: true option has an effect to enable the same key transformation in inline associations.
I also thought true is unclear about what it actually does, so maybe cascade: :inline is better so that in the future we can add cascade: :all to override existing key transformation settings.

[trevorturk]

That makes sense to me. I was thinking perhaps deep_transform_keys as an option, but I like your idea of cascade: :inline. Perhaps if we see transform_keys in an inline associations, we accept that as an override, so then cascade: true would be fine, knowing it could be overridden.

Thank you for your consideration to this!

[trevorturk]

Today I was wondering if it would be worth making cascade the default behavior, so we wouldn't need any options. Although that may be considered a breaking change. I was surprised it didn't cascade, so arguably we could call it a bug fix?

In any case, I don't mind whatever the solution is, and frankly the current functionality is fine, just some minor cruft when defining a resource.

Anyway, thanks again!

[okuramasafumi]

Making cascade default seems reasonable to me. Yes, it's a breaking change, so we need to offer a cascade: false option for old behavior.
Unfortunately it's hard to produce deprecation warnings in this case, so we need to mention it in the document (CHANGELOG.md).