Refactoring Ruby on Rails

Ruby on Rails / Refactoring – parameter object pattern

Ruby on Rails / Refactoring – parameter object pattern February 1, 20183 Comments

Sometimes is hard no to pass many parameters to a single method and this is the moment when parameter object comes in. The parameter object is a primitive Ruby object where parameters are attributes so you can pass one argument which is an object instance instead of multiple parameters. Let’s jump to a sample class to better demonstrate it:

class Notificator
  def push_update(title, content, category)
    some_api_class.push(title: title, content: content, category: category)

We have some sample class responsible for pushing an update to the API. As we can see our parameters are related to the API message. Let’s create a simple class which will be our parameter object in this case:

class ApiMessage
  attr_reader :title, :content, :category
  def initialize(title:, content:, category:)
    @title = title
    @content = content
    @category = category

Now we can update our Notificator class to require only one method argument:

class Notificator
  def push_update(api_message)
    some_api_class.push(title: api_message.title, content: api_message.content, category: api_message.category)

Our code is more readable now and it will be easier to test it. It’s important to treat parameter object as a very simple object otherwise we would miss the idea behind this refactoring pattern and we would end up with a normal class including some extra functionality and a lot of code.

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  1. Hi, thanks for the article.

    Do you think this is really worth it in this case?

    The code becomes a lot more “noisy” after your refactoring with “api_message” repeated 3 times. How about using a hash instead?

    1. I think we can also use key arguments, it will be more readable than a hash. However, this is a very simple case so it may be not worth to do this but I wanted to just present the idea behind this pattern

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