has_many ：通过在连接表中创建重复项
我创建了 3 个模型：User、City、UserCity。
用户类：
class User < ActiveRecord::Base
has_many :user_cities, :dependent => :destroy, :uniq => true
has_many :cities, :through => :user_cities
end
城市类：
class City < ActiveRecord::Base
has_many :user_cities, :dependent => :destroy, :uniq => true
has_many :users, :through => :user_cities
end
UserCity 类：
class UserCity < ActiveRecord::Base
belongs_to :user
belongs_to :city
end
然后我尝试
u = User.new()
c = City.new()
u.cities << c
c.users << u
p UserCity.all.size # => 2
user_cities 表有重复项。然后，我编写了
UserCity 类：
class UserCity < ActiveRecord::Base
validates :user_id, :uniqueness => {:scope => :city_id}
belongs_to :user
belongs_to :city
end
并运行上面相同的 ruby 代码。但在 c.users << 之后失败了u 因为我禁止重复。
如何使 u.cities 具有 c 和 c.users 具有 u 而不复制连接表中的数据？
补充：
所以，如果我只选择 c.users << u，我只能对城市执行此操作吗？
cities = Array.new()
UserCity.where(:user_id => u.id).each do |uc|
cities << City.find(uc.city_id)
end
I created 3 models, User, City, UserCity.
User class:
class User < ActiveRecord::Base
has_many :user_cities, :dependent => :destroy, :uniq => true
has_many :cities, :through => :user_cities
end
City class:
class City < ActiveRecord::Base
has_many :user_cities, :dependent => :destroy, :uniq => true
has_many :users, :through => :user_cities
end
UserCity class:
class UserCity < ActiveRecord::Base
belongs_to :user
belongs_to :city
end
And then I tried
u = User.new()
c = City.new()
u.cities << c
c.users << u
p UserCity.all.size # => 2
user_cities table had duplicates. So then, I coded
UserCity class:
class UserCity < ActiveRecord::Base
validates :user_id, :uniqueness => {:scope => :city_id}
belongs_to :user
belongs_to :city
end
and run the same ruby code above. But it failed after c.users << u because I prohibited duplicate.
How can I make u.cities have c and c.users have u without duplicating data in join table?
Added:
So, if I choose only c.users << u, can I only do this for cities?
cities = Array.new()
UserCity.where(:user_id => u.id).each do |uc|
cities << City.find(uc.city_id)
end
如果你对这篇内容有疑问，欢迎到本站社区发帖提问 参与讨论，获取更多帮助，或者扫码二维码加入 Web 技术交流群。
绑定邮箱获取回复消息
由于您还没有绑定你的真实邮箱，如果其他用户或者作者回复了您的评论，将不能在第一时间通知您！
发布评论
评论（2）
选择
u.cities << c或c.users <<你。它们中的每一个都会导致将一行插入到连接表中。Choose either
u.cities << corc.users << u. Each of them cause a row inserted in to the join table.您可能还想通过在数据库中添加索引来防止数据库中出现重复项，如果您不小心尝试添加重复的联接条目，这会引发错误。在迁移中做这样的事情：
You might also want to prevent duplicates in the db by adding an index in the db which would raise an error if you accidentally try to add a duplicate join entry. Do something like this in a migration: