One-to-One Association:
*一个person只对应一个personal_info
*一个personal_info只属于一个person
*belongs to用foreign key来链接
rails g model personal_info height:float weight:float person:references
此外你同时也有2个method
build_personal_info(hash)
#=> 在数据库中创建record
create_personal_info(hash)
#=> 在memory中创建record #=> Both remove the previous reference in the DB
用于person的实例
你需要用 has_one/belongs_to 去建立1对1association
One-to-Many Assoication:
*一个Person可能有1个或多个jobs
*但一个jobs只属于一个Person
belongs to的关系用foreign key来建立
rails g model job title company position_id person:references
#in model class Person < ActiveRecord::Base
has_one :personal_info
has_many :jobs
end class Job < ActiveRecord::Base
belongs_to :person
end
person.jobs = jobs
# 用新的array替换现有的jobs person.jobs << job(s)
# 添加新的jobs person.jobs.clear
# 将foreign key 设置为NULL， 解除这个person和jobs之间的关系 create! where!
#加了！才会提醒是否成功
# :dependent class Person < ActiveRecord::Base
has_one :personal_info, dependent: :destroy
end # 这样删除person的时候同时会删除跟person相关的personal_info
Many-to-Many association:
*一个person可以有很多hobbies
*一个hobbies可以被很多person共享
has_many&belongs_to_many
#join table rails g model hobby name rails g migration create_hobbies_people person:references hobby:references #生成Migration
class CreateHobbiesPeople < ActiveRecord::Migration
def change
create_table :hobbies_people, id: false do |t|
t.references :person, index: true, foreign_key: true
t.references :hobby, index:true, foreign_key: true
end
end
end #model
class Person < ActiveRecord::Base
has_and_belongs_to_many :hobbies
end class Hobby < ActiveRecord::Base
has_and_belongs_to_many :people
end
Many-to-Many 包含了2个model和3个migration
Join table只存在数据库中，不在ruby代码里面
Rich Many-to-Many assoiciation:
#SalaryRange Model and Migration rails g model salary_range min_salary:float max_salary:float job:references class CreateSalaryRanges < ActiveRecord::Migration
def change
create_table :salary_ranges do |t|
t.float :min_salary
t.float :max_salary
t.references :job, index: true, foreign_key: true t.timestamps null: false
end
end
end #model class Person < ActiveRecord::Base
has_many :jobs
has_many :approx_salaries, through: :jobs, source: :salary_range def max_salary
approx_salaries.maximum(:max_salary)
end
end class Job < ActiveRecord::Base
belongs_to :person
has_one :salary_range
end class SalaryRange < ActiveRecord::Base
belongs_to :job
end