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Resourcen:

• Searchlogic (an alternative solution)
• Full episode source code

Quellcode:

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

# products_controller.rb
@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

# 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