rails用generate为两个模型创建has_and_belongs_to_many中间表

假设

teachers和students具备many-to-many的关系，那么需要一个Join 表，has_and_belongs_to_many默认该表名字为teachers_students，这样建立好关联之后可以直接通过teachers.students来获取。

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|