Many-to-Many relationship的实际应用(1)

需求：场景如下，user可以是多个group的会员，管理者和创建者。group有1个创建者，多个管理者和多个会员。

解决方案：

建立数据库：

sql 代码

CREATE TABLE `groups` (
  `id` int(11) NOT NULL auto_increment,
  `name` varchar(32) NOT NULL,
  `url` varchar(250) NOT NULL,
  `description` varchar(100) default NULL,
  `logo` int(11) NOT NULL,
  `created_time` datetime NOT NULL,
  PRIMARY KEY  (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

CREATE TABLE `users` (
  `id` int(11) NOT NULL auto_increment,
  `logo` int(11) NOT NULL,
  `name` varchar(25) NOT NULL,
  `sex` int(11) NOT NULL,
  `birthday` datetime NOT NULL,
  `location` varchar(100) NOT NULL,
  `hashed_password` varchar(40) NOT NULL,
  PRIMARY KEY  (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

CREATE TABLE `members` (
  `id` int(11) NOT NULL,
  `user_id` int(11) NOT NULL,
  `group_id` int(11) NOT NULL,
  `priviledge` varchar(10) default NULL,
  PRIMARY KEY  (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

 注意members这个表中的priviledge属性，priviledge属性有3个选择(creator, admin, leaguer)，分别代表user在group中的3种身份权限。

model代码：

ruby 代码

class Member < ActiveRecord::Base
  belongs_to :group
  belongs_to :user
end

class User < ActiveRecord::Base
  has_many :members
  has_many :groups,
    :through => :members,
    :order => "priviledge desc"
end

class Group < ActiveRecord::Base
  has_many :members
  has_many :users,
    :through => :members
  has_many :creators,
    :through => :members,
    :source => :user,
    :conditions => ["priviledge = 'creator'"]
  has_many :admins,
    :through => :members,
    :source => :user,
    :conditions => ["priviledge = 'admin'"]
  has_many :leaguers,
    :through => :members,
    :source => :user,
    :conditions => ["priviledge = 'leaguer'"]
end

 这里注意的是

ruby 代码

has_many :creators,
    :through => :members,
    :source => :user,
    :conditions => ["priviledge = 'creator'"]

 

不能用has_one来替代，所以替代的方法就是在Group里面加上如下代码：

ruby 代码

def creator
    creators[0]
end

这样可以使用Group#creator来得到管理员。

如下代码为测试代码：

ruby 代码

group = Group.find(2)
user = User.find(1)
member = Member.create(:group_id => group, :user_id => user, :priviledge => "admin")