How to get name of model linked from another model in Rails? - ruby-on-rails

Question

I have set up 2 models in Rails:
class Category < ActiveRecord::Base
attr_accessible :name
has_many :platforms
end
and
class Platform < ActiveRecord::Base
attr_accessible :name, :url, :country
validates :name, :presence => true, :length => { :minimum => 5 }
validates :url, :presence => true, :length => { :minimum => 5 }
belongs_to :categories
end
This is my platform controller :
class PlatformsController < ApplicationController
# GET /platforms
# GET /platforms.json
def index
#platforms = Platform.all
#categories = Category.all
respond_to do |format|
format.html # index.html.erb
format.json { render json: #platforms }
end
end
# GET /platforms/1
# GET /platforms/1.json
def show
#platform = Platform.find(params[:id])
#categories = Platform.categories
respond_to do |format|
format.html # show.html.erb
format.json { render json: #platform }
end
end
# GET /platforms/new
# GET /platforms/new.json
def new
#platform = Platform.new
#categories = Category.all
respond_to do |format|
format.html # new.html.erb
format.json { render json: #platform }
end
end
# GET /platforms/1/edit
def edit
#platform = Platform.find(params[:id])
#categories = Category.find(:all)
end
# POST /platforms
# POST /platforms.json
def create
#platform = Platform.new(params[:platform])
##categories = Category.new(params[:name])
#categories = #platform.categories.create(params[:categories])
respond_to do |format|
if #platform.save
format.html { redirect_to #platform, notice: 'Platform was successfully created.' }
format.json { render json: #platform, status: :created, location: #platform }
else
format.html { render action: "new" }
format.json { render json: #platform.errors, status: :unprocessable_entity }
end
end
end
# PUT /platforms/1
# PUT /platforms/1.json
def update
#platform = Platform.find(params[:id])
#categories = Category.find(:all)
respond_to do |format|
if #platform.update_attributes(params[:platform])
format.html { redirect_to #platform, notice: 'Platform was successfully updated.' }
format.json { head :no_content }
else
format.html { render action: "edit" }
format.json { render json: #platform.errors, status: :unprocessable_entity }
end
end
end
# DELETE /platforms/1
# DELETE /platforms/1.json
def destroy
#platform = Platform.find(params[:id])
#platform.destroy
respond_to do |format|
format.html { redirect_to platforms_url }
format.json { head :no_content }
end
end
end
I do not understand what I do wrong, but it doesnt correctly assign categories to platforms, and also in the platforms index view, when I try to use :
<%= platform.categories %>
it gives me error cannot find Category with id= "and here the respective id"
I am really confused since I followed tutorial for this one.
I use Rails 3.2.8

Answer 1

Without your view, I can't say for sure what it is you're trying to do exactly. Most importantly, what is in your params[:categories] hash? Given the name, it sounds like you intended for it to be multiple categories. However, your code is written as if you intended it to be a single set of attributes which describe one Category.
Since I can't say for sure what you want to do, I'll answer your question by explaining what you are doing. Maybe that will help you figure out how to fix it.
Your create code currently looks like this:
# POST /platforms
# POST /platforms.json
def create
#platform = Platform.new(params[:platform])
##categories = Category.new(params[:name])
#categories = #platform.categories.create(params[:categories])
The first line creates the new Platform and is easy. Skipping over the comment to the third line. This is probably what's tripping you up.
You are selecting the associations for your newly created Platform and trying to create a new category with attributes as stored in the params[:categories] hash. I'm afraid this is not allowed. (I think it throws an ActiveRecord::RecordNotSaved exception, but I could be wrong.) You can not create on a #platform which hasn't been persisted yet. Instead, I think you want build.
Here is the relevant documentation:
http://api.rubyonrails.org/classes/ActiveRecord/Associations/ClassMethods.html
The difference between create and build is that build just sets up the association without actually saving it to the database yet. create saves it immediately. The nice thing about build is that you don't actually have to save it yourself. It tags along for free when you call #platform.save or #platform.update_attributes. Also, save is automatically wrapped in a transaction, so it won't create the new Category if it fails to create the new Platform for whatever reason.
The next interesting thing is that you are assigning the result of your create to #categories. I don't think this is what you want either. You don't need to save the new Category because it tags along with your #platform. However, if the save of the platform fails, then you are going to re-render your new view with this value of #categories whereas in new you set #categories = Category.all. This could certainly cause some confusion on the new view after a failed create.
In summary, I think your create code should look something like the following.
# POST /platforms
# POST /platforms.json
def create
#platform = Platform.new(params[:platform])
#platform.categories.build(params[:categories])
respond_to do |format|
if #platform.save
format.html { redirect_to #platform, notice: 'Platform was successfully created.' }
format.json { render json: #platform, status: :created, location: #platform }
else
#categories = Category.all
format.html { render action: "new" }
format.json { render json: #platform.errors, status: :unprocessable_entity }
end
end
end
If you're params[:categories] is not a hash of category attributes and is actually a comma delimited string of category names, then you would want to do something like the following instead of my second line above:
params[:categories].split(",").each do |category|
#project.categories.build(name: category)
end
You may also want to check out accepts_nested_attributes_for which can DRY out your controller even more.
http://api.rubyonrails.org/classes/ActiveRecord/NestedAttributes/ClassMethods.html
I hope that helps.