def has_one(association_id, options = {})
options.assert_valid_keys(:class_name, :foreign_key, :remote, :conditions, :order, :include, :dependent, :counter_cache, :extend)
association_name, association_class_name, association_class_primary_key_name =
associate_identification(association_id, options[:class_name], options[:foreign_key], false)
require_association_class(association_class_name)
module_eval do
after_save "association = instance_variable_get(\"@\#{association_name}\")\nunless association.nil?\nassociation[\"\#{association_class_primary_key_name}\"] = id\nassociation.save(true)\nassociation.send(:construct_sql)\nend\n"
end
association_accessor_methods(association_name, association_class_name, association_class_primary_key_name, options, HasOneAssociation)
association_constructor_method(:build, association_name, association_class_name, association_class_primary_key_name, options, HasOneAssociation)
association_constructor_method(:create, association_name, association_class_name, association_class_primary_key_name, options, HasOneAssociation)
case options[:dependent]
when :destroy, true
module_eval "before_destroy '#{association_name}.destroy unless #{association_name}.nil?'"
when :nullify
module_eval "before_destroy '#{association_name}.update_attribute(\"#{association_class_primary_key_name}\", nil)'"
when nil, false
else
raise ArgumentError, "The :dependent option expects either :destroy or :nullify."
end
deprecated_has_association_method(association_name)
deprecated_association_comparison_method(association_name, association_class_name)
end