Rails association new_path error - ruby-on-rails

Question

I have two models post and topic in my rails app
class Post < ActiveRecord::Base
#relation between topics and post
belongs_to :topic
#post is valid only if it's associated with a topic:
validates :topic_id, :presence => true
#can also require that the referenced topic itself be valid
#in order for the post to be valid:
validates_associated :topic
end
And
class Topic < ActiveRecord::Base
#relation between topics and post
has_many :posts
end
I am trying to create association between both of them.
I want multiple post corresponding to each topic
I have used nested routes
Rails.application.routes.draw do
# nested routes
resources :topics do
resources :posts
end
resources :userdetails
devise_for :users, :controllers => { :registrations => "registrations" }
My Post controller looks like
class PostsController < ApplicationController
# before_action :set_post, only: [:show, :edit, :update, :destroy]
before_filter :has_userdetail_and_topic, :only =>[:new, :create]
# GET /posts
# GET /posts.json
#for new association SAAS book
protected
def has_userdetail_and_topic
unless(#topic =Topic.find_by_id(params[:topic_id]))
flash[:warning] = 'post must be for an existing topic'
end
end
public
def new
#post = #topic.posts.build
###topic = Topic.find(params[:topic_id1])
end
def index
#posts = Post.all
end
# GET /posts/1
# GET /posts/1.json
def show
end
# GET /posts/new
# GET /posts/1/edit
def edit
end
# POST /posts
# POST /posts.json
def create
##topic.posts << #post
##current_user = current_user.id
#current_user.posts << #topic.posts.build(params[:post])
##post = Post.new(post_params )
##post.userdetail_id = current_user.id
#Association functional between topic and post
#Class variable used
###topic.posts << #post
respond_to do |format|
if #post.save
format.html { redirect_to #post, notice: 'Post was successfully created.' }
format.json { render :show, status: :created, location: #post }
else
format.html { render :new }
format.json { render json: #post.errors, status: :unprocessable_entity }
end
end
end
# PATCH/PUT /posts/1
# PATCH/PUT /posts/1.json
def update
respond_to do |format|
if #post.update(post_params)
format.html { redirect_to #post, notice: 'Post was successfully updated.' }
format.json { render :show, status: :ok, location: #post }
else
format.html { render :edit }
format.json { render json: #post.errors, status: :unprocessable_entity }
end
end
end
# DELETE /posts/1
# DELETE /posts/1.json
def destroy
#post.destroy
respond_to do |format|
format.html { redirect_to posts_url, notice: 'Post was successfully destroyed.' }
format.json { head :no_content }
end
end
private
# Use callbacks to share common setup or constraints between actions.
def set_post
#post = Post.find(params[:id])
end
# Never trust parameters from the scary internet, only allow the white list through.
def post_params
params.require(:post).permit(:topic_id,:issue, :description, :rating, :userdetail_id)
end
end
I am trying to navigate from topics/index via code <td><%= link_to 'Write', new_topic_post_path(#topic) %> </td>
but when i try to go at localhost:3000/topics]
I am getting error
No route matches {:action=>"new", :controller=>"posts", :topic_id=>nil} missing required keys: [:topic_id]
Can any body tell me about this error, as i am new to rails please clearly specify answer.
And I have one more doubt, please tell me if i am doing association between topic and post incorrectly.I have confusion about this line of code -
#topic.posts << #post

Answer 1

What the error missing required keys: [:topic_id] is telling you is that you need to provide a hash with the key topic_id:
<%= link_to 'Write', new_topic_post_path(topic_id: #topic) %>
Passing a resource as to a route helper only works for the id param:
<%= link_to #topic, topic_path(#topic) %>
Is a kind of shorthand for:
<%= link_to #topic, topic_path(id: #topic.to_param) %>
Addition:
#prcu is also correct. The #topic record needs to be saved to the database. Records which are not saved do not have an id since the database assigns the id column when the record is inserted.
You also need to set the #topic instance variable in PostsController:
#topic = Topic.find(params[:id])
This is commonly done with a before filter:
before_filter :set_topic, only: [:new]
def set_topic
#topic = Topic.find(params[:id])
end
The same also need to be done in TopicsController#index.

Answer 2

#topic is not set or it's not persisted. You can not use topic not saved to db in this helper.