A Ruby on Rails controller concern which adds basic CRUD operations for any model.

crud.rb

# frozen_string_literal: true

# Controller concern for basic crud. 
# Can be added to any controller like so
# include Crud
# Assumptions: 
#  1. Model class defines a constant called WHITELIST_FIELDS 
#     as an array of symbols for attributed that are allowed for creating a record. 
#  2. Model is serialized elsewhwere. This can be done either by overwriting as_json
#     method in the model class, or by using separate serializers. By default as_json 
#     will render all the model attributes. 
module Crud
  extend ActiveSupport::Concern

  included do
    # guess the model name from the controller name
    # eg. if the controller is users_controller, modelname will be User
    def model_class_const
      controller_name.singularize.capitalize.constantize
    end

    # create a sumbol for the model name 
    def model_class_symbol
      model_class_const.to_s.downcase.to_sym
    end
    
    # List records
    def index
      render_records
    end
  
    # Create record
    def create
      @record = model_class_const.create! record_params
      render_record message: "#{model_class_const.to_s} created"
    end
  
    # Delete record
    def delete
      record.destroy
      render_record message: "#{model_class_const.to_s} deleted"
    end
  
    private
    
    # Find record using params[:id]
    def record
      @record ||= model_class_const.find(params[:id])
    end
  
    # Find all records. You can also paginate them here if you like. 
    def records
      @records ||= model_class_const.order(created_at: :desc, updated_at: :desc)
    end
  
    # Render one record
    def render_record(**opts)
      render json: {
        record: record.as_json
      }.merge(opts)
    end
  
    # Render array of records
    def render_records(**opts)
      render json: { 
        records: records.as_json
    }.merge(opts)
    end
  
    # Strong params.
    # Note: this assumes that the WHITELIST_FIELDS is an array of symbols defined
    #       in the model class. eg. User model may have 
    #       WHITELIST_FIELDS = %i[name email]
    def record_params
      params.require(model_class_symbol).permit(model_class_const::WHITELIST_FIELDS)
    end
  
  end

end

Pretty cool stuff!