#212 Refactoring & Dynamic Delegator

May 03, 2010 | 7 minutes | Refactoring, Active Record, Rails 3.0

Learn how to refactor a set of conditional Active Record queries using a Dynamic Delegator.

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Searchlogic (an alternative solution)
Full episode source code

          rails console
                
        Product.search({}).class
Object.instance_methods
BasicObject.instance_methods
        
Product.search({}).class
Object.instance_methods
BasicObject.instance_methods

          products_controller.rb
                
        @products = Product.search(params)
        
@products = Product.search(params)

          models/product.rb
                
        def self.search(params)
  products = scope_builder
  products.where("name like ?", "%" + params[:name] + "%") if params[:name]
  products.where("price >= ?", params[:price_gt]) if params[:price_gt]
  products.where("price <= ?", params[:price_lt]) if params[:price_lt]
  products
end

def self.scope_builder
  DynamicDelegator.new(scoped)
end
        
        
        
        
        
        
        
        
        
      
def self.search(params)
  products = scope_builder
  products.where("name like ?", "%" + params[:name] + "%") if params[:name]
  products.where("price >= ?", params[:price_gt]) if params[:price_gt]
  products.where("price <= ?", params[:price_lt]) if params[:price_lt]
  products
end

def self.scope_builder
  DynamicDelegator.new(scoped)
end

          lib/dynamic_delegator.rb
                
        class DynamicDelegator < BasicObject
  def initialize(target)
    @target = target
  end
  
  def method_missing(*args, &block)
    result = @target.send(*args, &block)
    @target = result if result.kind_of? @target.class
    result
  end
end
        
        
        
        
        
        
        
        
        
      
class DynamicDelegator < BasicObject
  def initialize(target)
    @target = target
  end
  
  def method_missing(*args, &block)
    result = @target.send(*args, &block)
    @target = result if result.kind_of? @target.class
    result
  end
end