csvから読んだり呼んだりdbに書いたりする

base_csv_loader.rb

class BaseCsvLoader
  class_attribute :file_path

  class << self
    def file_path(path)
      self.file_path = path
    end

  def load
    CSV.read(file_path, headers: false, row_sep: "\n")
  end
end

base_item.rb

class BaseItem
  class_attribute :attributes, default: {}

  class << self
    def attribute(attr, options = {})
      key = options.fetch(:key, attr)
      attributes[key] = attr
    end

    def inherited(subclass)
      subclass.attributes = {}
    end
  end

  def initialize(item)
    @item = item
    klass = self.class
    attributes.each do |key, _attr|
      next if klass.method_defined?(key)

      const_name = key.upcase
      klass.define_method(key) { @item[klass.const_get(const_name)] } if klass.const_defined?(const_name)
    end
  end

  def to_hash
    attributes.each_with_object({}) do |(key, _attr), hash|
      raise(NotImplementedError, "You must implement #{self.class}##{key}") unless respond_to?(key)

      hash[key] = public_send(key)
    end
  end

  alias to_h to_hash

  def create?
    raise(NotImplementedError, "You must implement #{self.class}##{__method__}")
  end

  def update?
    raise(NotImplementedError, "You must implement #{self.class}##{__method__}")
  end

  def destroy?
    raise(NotImplementedError, "You must implement #{self.class}##{__method__}")
  end
end

base_record_operator.rb

class BaseRecordOperator
  class_attribute :model
  class_attribute :find_key

  class << self
    def model(model)
      self.model = model
    end

    def find_key(find_key)
      self.find_key = find_key
    end
  end

  def initialize(item:)
    @item = item
    @item_hash = item.to_h
  end

  def operate
    if @item.create?
      create
    elsif @item.update?
      update
    elsif @item.destroy?
      destroy
    end
  end

  private

  def create
    record = model.new(@item_hash)
    record.save
  end

  def update
    record = model.find_by(find_key => @item_hash[find_key])
    record.assign_attributes(@item_hash)
    record.save
  end

  def destroy
    record = model.find_by(find_key => @item_hash[find_key])
    record.destroy if record.present?
  end
end

example.rb

class Example
  def modify_books
    BookCsvLoader.new.load.each do |row|
      item = Book.new(row)
      BookDBOperator.new(item).operate
    end
  end
end

class BookCsvLoader < BaseCsvLoader
  file_path 'hoge.csv'
end

module Constants
  ID = 1
  TITLE = 2
  AUTHOR = 3
end

class Book < BaseItem
  include Constants
  
  attribute :id
  attribute :title
  attribute :author
  
  def author
    @item[AUTHOR] || 'unknown'
  end
  
  def create?
    !update?
  end
  
  def update?
    Book.exists?(id: id)
  end
  
  def destroy?
    false
  end
end

class BookRecordOperator < BaseRecordOperator
  model Book
  find_key :id
end