How can i use accepts nested attributes with the HABTM?

问题

I have two models User and Category.

    class User < ActiveRecord::Base
        has_and_belongs_to_many :categories
        accepts_nested_attributes_for :categories
    end

similarly

    class Category < ActiveRecord::Base
        has_and_belongs_to_many :users
    end

i have a requirement where i have to add the categories to the categories table and add the reference so that i can get the categories related to user but if another user enters the same category then i have to make use of the id instead of creating new one. How can i do it?

And one more thing is i have to add an attribute type which refers that category type. for example

user1 ----> category1, category2
user2 ----> category2

here user1 and user2 has category2 but the type in category2 may differ.So how can i maintain this? please help me. I am ready to answer your question.

回答1:

You must use has_many :through instead of HABTM to add the field type to the relationship:

class User < ActiveRecord::Base
  has_many :lines
  accepts_nested_attributes_for :lines
  has_many :categories, through: :lines
end

class Line < ActiveRecord::Base
  belongs_to :users
  belongs_to :category
end

class Category < ActiveRecord::Base
  has_many :lines
  has_many :users, through: :lines
end

Add the type attribute to the class Line.

ref: http://guides.rubyonrails.org/association_basics.html#the-has-many-through-association

You will need two controllers with the restful actions: users and categories

Then, in your user form, something like:

<%= nested_form_for @user do |f| %>
...#user attributes
<%= f.fields_for :lines do |line| %>
<%= line.label :category %>
<%= line.collection_select(:category_id, Category.all, :id, :name , {include_blank: 'Select Category'} ) %>
<%= line.label :type %>
<%= line.text_field :type %>
...#the form continues

EDIT -

The category is independent of user, as well as user is independent of category.

The association class Line will join users and categories through the category_id and user_id:

________          _______________
| user |          |     line    |          ____________
|----- |          |-------------|          | category |
| id   |----------| user_id     |          |----------|
| name |1        *| category_id |----------| id       |
| email|          | type        |*        1| name     | 
|______|          |_____________|          |__________|

example:

git hub: https://github.com/gabrielhilal/nested_form

heroku: http://nestedform.herokuapp.com/

来源：https://stackoverflow.com/questions/18575039/how-can-i-use-accepts-nested-attributes-with-the-habtm

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ruby-on-rails