Question

I have three models:

category.rb

class Category
  include Mongoid::Document

  # Relationships
  has_many :posts, :autosave => true
  has_many :boards, :autosave => true
  accepts_nested_attributes_for :boards
  accepts_nested_attributes_for :posts


  #fields
  field :name

  #attr
  attr_accessible :name
end

My model board.rb

class Board
 include Mongoid::Document

 # Relationships
  has_many :posts, :dependent => :destroy , :autosave => true
  accepts_nested_attributes_for :posts
  belongs_to :category

  #fields
  field :name
  field :description

  #attr
  attr_accessible :name, :posts_attributes, :description, :category_id

end

My post.rb

class Post
 include Mongoid::Document

 # Relationships
 belongs_to :board
 belongs_to :category
 belongs_to :user

 #fields  
 field :content

 #attr
 attr_accessible :content :board_id, :category_id

end

In my posts_controller

def create

   @post = current_user.posts.new(params[:post])
   @board = @post.board
   @board.user = current_user

 if @board.category_id? 
  @post.category_id = @board.category_id
 end

  respond_to do |format|
   if @post.save
     format.html { redirect_to root_url, notice: 'Post was successfully created.' }
     format.json { render json: root_url, status: :created, location: @post }
   else
     format.html { render action: "new" }
     format.json { render json: @post.errors, status: :unprocessable_entity }
   end
 end

end

In my view new action:

<%= form_for(@post) do |f| %>
 <%= f.text_area :content %>
 <%= f.collection_select :board_id, Board.where(:user_id => current_user.id), :id, :name%>
 <%= f.submit :id => "button_submit_pin_edit" %>
<% end %>

The boards in select field, may or may not have a parent category already assigned.

I want get the attributes from category (the name of the category for this event) in my post view without using a select field, or an input field.

with this code in posts.controller.rb

if @board.category_id? 
  @post.category_id = @board.category_id
 end

I see in my console for Post.first e.j.:

<Post _id: 4f1d96241d41c8280800007c, _type: nil, created_at: 2012-01-23 17:17:24 UTC, user_id: BSON::ObjectId('4f0b19691d41c80d08002b20'), board_id: BSON::ObjectId('4f1455fa1d41c83988000510'), category_id: BSON::ObjectId('4f1c2d811d41c8548e000008'), content: "nuevo post"> 

If I write:

post = Post.first

and

post.board

I get the object board fine. This does works fine.

but If I write:

post.category

I get:

=> nil

I have try in view new post add hidden field:

hidden_field(:category, :name)

How can I get the params of object category?
Thanks

Answer 1

Don’t set it using the ID fields. Instead of this in your PostsController:

if @board.category_id? 
  @post.category_id = @board.category_id
end

Try this line:

@post.category = @board.category

Which will set the @post.category belongs_to relationship to point to @board.category assuming it exists (is not nil). Mongoid will handle the setting of the category_id field for you. Read the mongoid documentation about relationships for a more detailed explanation.