Where:

class Teacher < ActiveRecord::Base
  has_and_belongs_to_many :students
end

and

class Student < ActiveRecord::Base
  has_and_belongs_to_many :teachers
end

for rails 4:

rails generate migration CreateJoinTableStudentTeacher student teacher

for rails 3:

rails generate migration students_teachers student_id:integer teacher_id:integer

for rails < 3

script/generate migration students_teachers student_id:integer teacher_id:integer

(note the table name lists both join tables in alphabetical order)

and then for rails 3 and below only, you need to edit your generated migration so an id field is not created:

create_table :students_teachers, :id => false do |t| 

转自：http://stackoverflow.com/questions/4381154/rails-migration-for-has-and-belongs-to-many-join-table