ActiveRecord - undefined method 'match'

Question

I'm trying to encode a simple hierarchy in my records, but I'm running into a weird error.

require 'rubygems'
require 'active_record'

ActiveRecord::Base.establish_connection(
  :adapter => "sqlite3",
  :database => ":memory:"
)
ActiveRecord::Schema.define do
  create_table :foos do |t|
    t.string :name, :null => false
    t.integer :parent_id, :default => nil
  end
end

class Foo < ActiveRecord::Base
  belongs_to :parent, :class_name => Foo
end

bar = Foo.create( :name => 'Bar' )
p [ :bar, bar ]

baz = Foo.create( :name => 'Baz', :parent_id => bar.id )
p [ :baz, baz ]

quux = Foo.create( :name => 'Quux', :parent => bar )
p [ :quux, quux ]

When I run it, I get:

% ruby temp.rb
-- create_table(:foos)
   -> 0.0269s
[:bar, #<Foo id: 1, name: "Bar", parent_id: nil>]
[:baz, #<Foo id: 2, name: "Baz", parent_id: 1>]
/path/to/activerecord-3.0.9/lib/active_record/base.rb:1014:in `method_missing': undefined method `match' for Foo(id: integer, name: string, parent_id: integer):Class (NoMethodError)
        from /path/to/activerecord-3.0.9/lib/active_record/base.rb:1184:in `compute_type'
        from /path/to/activerecord-3.0.9/lib/active_record/reflection.rb:162:in `send'
        from /path/to/activerecord-3.0.9/lib/active_record/reflection.rb:162:in `klass'
        from /path/to/activerecord-3.0.9/lib/active_record/associations/association_proxy.rb:262:in `raise_on_type_mismatch'
        from /path/to/activerecord-3.0.9/lib/active_record/associations/belongs_to_association.rb:23:in `replace'
        from /path/to/activerecord-3.0.9/lib/active_record/associations.rb:1465:in `parent='
        from /path/to/activerecord-3.0.9/lib/active_record/base.rb:1564:in `send'
        from /path/to/activerecord-3.0.9/lib/active_record/base.rb:1564:in `attributes='
        from /path/to/activerecord-3.0.9/lib/active_record/base.rb:1560:in `each'
        from /path/to/activerecord-3.0.9/lib/active_record/base.rb:1560:in `attributes='
        from /path/to/activerecord-3.0.9/lib/active_record/base.rb:1412:in `initialize'
        from /path/to/activerecord-3.0.9/lib/active_record/base.rb:502:in `new'
        from /path/to/activerecord-3.0.9/lib/active_record/base.rb:502:in `create'
        from temp.rb:25

If I add has_many :children, :class_name => Foo, :as => :parent to the definition of Foo, and instead do quux = bar.children.create(name => 'Quux') I get a similar error.

What am I doing wrong?

Answer 1

The :class_name option to belongs_to expects a string, rather than a class.

class Foo < ActiveRecord::Base
  belongs_to :parent, :class_name => "Foo"
end

You might also want to consider using acts_as_tree or some other plugin (there are many; I don't recall what is currently favoured) designed for dealing with this sort of hierarchy; it might make your life easier down the road.