Rails concerns note

[hungle00]

A Rails Concern is a module that extends the ActiveSupport::Concern module. Concerns allow us to include modules with methods (both instance and class) and constants into a class so that the including class can use them.

A concern provides two blocks:

1. included

• The code inside the included block is evaluated in the context of the including class.
• You can write class macros (validations, associations, scopes, etc.) here, and any methods become instance methods of the including class.

2. class_methods

• The methods added inside this block become the class methods on the including class.
• Instead of the class_methods block, you can create a nested module named ClassMethods.

For example, a concern named Taggable

module Taggable
  extend ActiveSupport::Concern

  included do

  end

  class_methods do

  end
end

To use this concern, you include the module as usual. For example, if the Post model wanted the visibility functionality, it would include the Taggable concern.

Justin Weiss has a great article that describes just how you can use Rails concern to refactor feature filter Product by attribute.

module Filterable
  extend ActiveSupport::Concern

  module ClassMethods
    def filter(filtering_params)
      results = self.where(nil)
      filtering_params.each do |key, value|
        results = results.public_send("filter_by_#{key}", value) if value.present?
      end
      results
    end
  end
end

In Product model:

class Product
  include Filterable
end

In controller that filter products by each attributes:

def index
  @products = Product.filter(params.slice(:status, :location, :starts_with))
end

• https://ifiwere.me/technology/2020/10/09/clean_index_filtering_rails.html
• https://www.justinweiss.com/articles/search-and-filter-rails-models-without-bloating-your-controller/