Rails dependent: :destroy causes ArgumentError

Question

I have a User model in my rails app as follows

class User < ActiveRecord::Base
  has_many :parts, dependent: :destroy
  has_many :assemblies, dependent: :destroy
  has_many :packages, dependent: :destroy
  has_many :manufacturers, dependent: :destroy
  //more code here
end

I also have dependent: :restrict in some other models.

When I run the following in rails console, I get an ArgumentError:

u = User.first
u.parts

The call to u.parts gives the following error message:

ArgumentError: Unknown key: dependent
    from /home/david/.rvm/gems/ruby-1.9.3-p0/gems/activesupport-3.2.1/lib/active_support/core_ext/hash/keys.rb:44:in `block in assert_valid_keys'
    from /home/david/.rvm/gems/ruby-1.9.3-p0/gems/activesupport-3.2.1/lib/active_support/core_ext/hash/keys.rb:43:in `each_key'
    from /home/david/.rvm/gems/ruby-1.9.3-p0/gems/activesupport-3.2.1/lib/active_support/core_ext/hash/keys.rb:43:in `assert_valid_keys'
    from /home/david/.rvm/gems/ruby-1.9.3-p0/gems/activerecord-3.2.1/lib/active_record/associations/builder/association.rb:33:in `validate_options'
    from /home/david/.rvm/gems/ruby-1.9.3-p0/gems/activerecord-3.2.1/lib/active_record/associations/builder/association.rb:24:in `build'
    from /home/david/.rvm/gems/ruby-1.9.3-p0/gems/activerecord-3.2.1/lib/active_record/associations/builder/collection_association.rb:23:in `build'
    from /home/david/.rvm/gems/ruby-1.9.3-p0/gems/activerecord-3.2.1/lib/active_record/autosave_association.rb:139:in `build'
    from /home/david/.rvm/gems/ruby-1.9.3-p0/gems/activerecord-3.2.1/lib/active_record/associations/builder/has_and_belongs_to_many.rb:8:in `build'
    from /home/david/.rvm/gems/ruby-1.9.3-p0/gems/activerecord-3.2.1/lib/active_record/associations/builder/collection_association.rb:13:in `build'
    from /home/david/.rvm/gems/ruby-1.9.3-p0/gems/activerecord-3.2.1/lib/active_record/associations.rb:1600:in `has_and_belongs_to_many'
    from /home/david/code/PartSorter/app/models/part.rb:5:in `<class:Part>'
    from /home/david/code/PartSorter/app/models/part.rb:1:in `<top (required)>'
    from /home/david/.rvm/gems/ruby-1.9.3-p0/gems/activesupport-3.2.1/lib/active_support/dependencies.rb:469:in `load'
    from /home/david/.rvm/gems/ruby-1.9.3-p0/gems/activesupport-3.2.1/lib/active_support/dependencies.rb:469:in `block in load_file'
    from /home/david/.rvm/gems/ruby-1.9.3-p0/gems/activesupport-3.2.1/lib/active_support/dependencies.rb:639:in `new_constants_in'
    from /home/david/.rvm/gems/ruby-1.9.3-p0/gems/activesupport-3.2.1/lib/active_support/dependencies.rb:468:in `load_file'
... 12 levels...
    from /home/david/.rvm/gems/ruby-1.9.3-p0/gems/activesupport-3.2.1/lib/active_support/dependencies.rb:554:in `get'
    from /home/david/.rvm/gems/ruby-1.9.3-p0/gems/activesupport-3.2.1/lib/active_support/dependencies.rb:588:in `constantize'
    from /home/david/.rvm/gems/ruby-1.9.3-p0/gems/activerecord-3.2.1/lib/active_record/inheritance.rb:111:in `block in compute_type'
    from /home/david/.rvm/gems/ruby-1.9.3-p0/gems/activerecord-3.2.1/lib/active_record/inheritance.rb:109:in `each'
    from /home/david/.rvm/gems/ruby-1.9.3-p0/gems/activerecord-3.2.1/lib/active_record/inheritance.rb:109:in `compute_type'
    from /home/david/.rvm/gems/ruby-1.9.3-p0/gems/activerecord-3.2.1/lib/active_record/reflection.rb:172:in `klass'
    from /home/david/.rvm/gems/ruby-1.9.3-p0/gems/activerecord-3.2.1/lib/active_record/associations/association.rb:117:in `klass'
    from /home/david/.rvm/gems/ruby-1.9.3-p0/gems/activerecord-3.2.1/lib/active_record/associations/association.rb:165:in `find_target?'
    from /home/david/.rvm/gems/ruby-1.9.3-p0/gems/activerecord-3.2.1/lib/active_record/associations/collection_association.rb:332:in `load_target'
    from /home/david/.rvm/gems/ruby-1.9.3-p0/gems/activerecord-3.2.1/lib/active_record/associations/collection_proxy.rb:44:in `load_target'
    from /home/david/.rvm/gems/ruby-1.9.3-p0/gems/activerecord-3.2.1/lib/active_record/associations/collection_proxy.rb:88:in `method_missing'
    from /home/david/.rvm/gems/ruby-1.9.3-p0/gems/railties-3.2.1/lib/rails/commands/console.rb:47:in `start'
    from /home/david/.rvm/gems/ruby-1.9.3-p0/gems/railties-3.2.1/lib/rails/commands/console.rb:8:in `start'
    from /home/david/.rvm/gems/ruby-1.9.3-p0/gems/railties-3.2.1/lib/rails/commands.rb:41:in `<top (required)>'
    from script/rails:6:in `require'
    from script/rails:6:in `<main>'

I'm not sure why this isn't working - I followed the guide here to add the dependent part but it isn't working. Any ideas?

edit: the contents of part.rb are as follows:

class Part < ActiveRecord::Base
  has_many :part_packages
  has_many :packages, through: :part_packages
  belongs_to :manufacturer
  has_and_belongs_to_many :assemblies, :dependent => :restrict
  belongs_to :user


  validates :name, :user_id, :presence => true

  def quantity
    @quantity = 0
    self.part_packages.each do |pp|
      @quantity += pp.quantity
    end
    @quantity
  end
end

Answer 1

:dependent is not a valid option for has_and_belongs_to_many, so you need to get rid of it and write your own solution that does what you want.

Alternatively, you may wish to have an explicit join model instead of using has_and_belongs_to_many. That way you could use :dependent for the relationship with the join model.