error.txt

undefined property or relationship '<<' on Category

Same happens when doing rekenserviceinstance.categories.new(category: somecategory).

undefined property or relationship 'new' on Category

model.rb

class Rekenservice
  include DataMapper::Resource  
  
  property :id,               Serial
   
  has n, :categories, :through => Resource
  
  def self.new(hash)
    hash[:categoriesss].each do |category|
      categories << Category.get(category)
    end
    hash.delete :categoriesss

    super hash
  end
  
  def update(hash)
    #categories.clear
    #hash[:categories].each do |category|
    #  categories.new(category: Category.get(category))
    #end
    hash! :categories
  
    super hash
  end
end

class Category
  include DataMapper::Resource  
  
  property :id,       Serial
  property :name,     String,   :required => true

  has n, :rekenservices, :through => Resource
end