30 - Handle API response with value objects

本篇將介紹撰寫 Rails 的過程中整個重構的過程，比較偏向一個方向，以一個簡單的例子為例，假設我們請求 API 獲取 Active 的 User 列表：

以下的程式是一個很常見的方法，但這段程式碼中，不只打 Api + parser + 過濾 active user，這樣的方式並沒有辦法讓程式碼只負責一件事情。

response = Request.call('some_url')
parsed_response = JSON.parse(response)

eligible_users = []

parsed_response['people'].each do |person|
  if person['active'] == true
    eligible_users << {
      name: "#{person['firstName']} #{person['lastName']}",
      email: person['emailAddress']
    }
  end
end

eligible_users

The parser for the people

Parser 的責任在負責接收並提供方法來 return User

response = Request.call('some_url')
parser = PeopleParser.new(response)

eligible_users = []

parser.people.each do |person|
  if person['active'] == true
    eligible_users << {
      name: "#{person['firstName']} #{person['lastName']}",
      email: person['emailAddress']
    }
  end
end

eligible_users

Value object for a person

我們需要一個 pure ruby object 來處理 person

class Person
  def initialize(attributes)
    @attributes = attributes
  end

  def active?
    @attributes['active']
  end

  def email
    @attributes['emailAddress']
  end

  def name
    "#{@attributes['firstName']} #{@attributes['lastName']}"
  end
end

有了上述的 Person Object 我們的 Parser 可以再來進行修改

class PeopleParser
  def initialize(raw_response)
    @raw_response = raw_response
  end

  def people
    @parsed_json['people'].map { |attributes| Person.new(attributes) }
  end

  private

  def parsed_json
    @parsed_json ||= JSON.parse(@raw_response)
  end
end

response = Request.call('some_url')
parser = PeopleParser.new(response)

eligible_users = []

parser.people.each do |person|
  if person.active?
    eligible_users << {
      name: person.name,
      email: person.email
    }
  end
end

eligible_users

再來繼續重構：

Let person behave like a hash

接下來我們要命名一個 to_h 來組成 name + email 的 hash

class Person
  def initialize(attributes)
    @attributes = attributes
  end

  def to_h
    {
      name: name,
      email: email
    }
  end

  def active?
    @attributes['active']
  end

  def email
    @attributes['emailAddress']
  end

  def name
    "#{@attributes['firstName']} #{@attributes['lastName']}"
  end
end

程式碼也變得更直觀跟可讀性了

response = Request.call('some_url')
parser = PeopleParser.new(response)

eligible_users = parser.people.select(&:active?).map(&:to_h)

參考資料

• Handle API response with value objects