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Refactoring Patterns: Method Object

Here’s how you can deal with huge and messy method.

  1. Take a huge method and extract it to it’s own class.
  2. Pass all dependencies as parameters
  3. Replace body of original method with Method Object call.

Before:

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def matches_conditions_hash?(subject, conditions = @conditions)
  if conditions.empty?
    true
  else
    if model_adapter(subject).override_conditions_hash_matching? subject, conditions
      model_adapter(subject).matches_conditions_hash? subject, conditions
    else
      conditions.all? do |name, value|
        if model_adapter(subject).override_condition_matching? subject, name, value
          model_adapter(subject).matches_condition? subject, name, value
        else
          attribute = subject.send(name)
          if value.kind_of?(Hash)
            if attribute.kind_of?(Array) || (defined?(ActiveRecord) && attribute.kind_of?(ActiveRecord::Relation))
              attribute.any? { |element| matches_conditions_hash? element, value }
            else
              !attribute.nil? && matches_conditions_hash?(attribute, value)
            end
          elsif !value.is_a?(String) && value.kind_of?(Enumerable)
            value.include? attribute
          else
            attribute == value
          end
        end
      end
    end
  end
end

After:

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def matches_conditions_hash?(subject, conditions = @conditions)
  IsMatchesConditionsHash.(model_adapter, subject, conditions)
end

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class IsMatchesConditionsHash < Struct.new(:model_adapter, :subject, :conditions)

  def self.call(*args)
    new(*args).call
  end

  def initialize(model_adapter, subject, conditions)
    self.model_adapter  = model_adapter
    self.subject    = subject
    self.conditions = conditions
  end

# ======== actual logic
  def call
    return true if conditions.empty?

    if model_adapter.override_conditions_hash_matching?(subject, conditions)
      return model_adapter.matches_conditions_hash?(subject, conditions)
    end

    conditions.all? do |name, value|
      if model_adapter.override_condition_matching?(subject, name, value)
        return model_adapter.matches_condition?(subject, name, value)
      end

      condition_match?(subject.send(name), value)
    end
  end
# ========

  private

  def condition_match?(attribute, value)
    case value
    when Hash       then match_hash_value(attribute, value)
    when Enumerable then (!value.is_a?(String) && value.include?(attribute))
    else attribute == value
    end
  end

  def match_hash_value(attribute, value)
    if attribute.kind_of?(Array) || (defined?(ActiveRecord) && attribute.kind_of?(ActiveRecord::Relation))
      attribute.any? { |element| self.class.(model_adapter, element, value) }
    else
      !attribute.nil? && self.class.(model_adapter, attribute, value)
    end
  end
end

We can go deeper of course. Shave the yak completely. But that’s a good start.

Actually, in this case, the implementation was moved back to the original class with a few private methods extracted. But nice thing about Method Object – it helps to understand all the dependencies this beast have, so you can deal with it.

References:

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