What should i do after i generated a model in ruby on rails

I created a Model in a ruby on rails app rails g model subject_structure name:string abbreviation:string

I created the relations

class SubjectStructure < ActiveRecord::Base
  has_many :subjects
end

class Subject< ActiveRecord::Base
  belongs_to:subject_structure
end

When i run the app i get the error undefined method subject_structure for #<Subject:0x9d3aa78>