虽然在has_many中强制执行模型的唯一性

Question

I have a User model, which has_many Dish through Recommendation . I would like to enforce uniqueness of Dish , as well as uniqueness of Recommendation .

How should I go about this in ActiveRecord ?

In my dish.rb :

validate_uniqueness_of :dish_name

What I would like to have is: when an user recommends a dish, create a new dish if it does not exist, then create recommendation. If the dish already exists, then just create recommendation and point to existing dish.

Do I need to handle these situations manually (ie, checking existence of dish in controller), or ActiveRecord has a way to handle it internally?

Update: validate_uniqueness_of :dish_name only checks and return error message if the dish was created there. It probably won't create new recommendation that points to existing dish .

Answer 1

您总是可以.find_or_create_by_<attribute>找到开始的菜

Answer 2

As I see, more than one user can recommend the same dish.

Your models should look like:

Class User < ActiveRecord::Base
has_many :recommendations
has_many :dishes, :through => :recommendations
end

Class Dish < ActiveRecord::Base
has_many :recommendations
has_many :users, :through => :recommendations
end

So your Recommendations table in database should have two columns (beside it's id and timestamps) called user_id and dish_id . To validate that a user doesn't recommend the same dish twice, do:

Class Recommendations < ActiveRecord::Base
belongs_to :dish
belongs_to :user
validates_uniqueness_of :dish_id, :scope => :user_id
end

And i didn't know about the .find_or_create_by method that Dan recommended, so definetly try to use something like that.

Hope i helped :)