"form_with cannot find the Post model" - ruby-on-rails

Question

I am trying to create the form on my "new" page. I am using form_with. I have already checked my routes, controllers and views, but I have not yet identified the problem.
The error that is returning is:
NameError in Pages # new
undefined local variable or method `post 'for # <# <Class: 0x00007f5640e1f440>: 0x00007f5640e1c060>
Did you mean? #post
Extracted source (around line # 5):
<% = form_with (model: post, location: true) do | form | %>
<div class = "form-group">
<% = form.label: title%>
Below is my form using form_with:
<h1> CREATE NEW ARTICLE </h1>
<% = form_with (model: post, location: true) do | form | %>
<div class = "form-group">
<% = form.label: title%>
<% = form.text_field: title, class: 'form-control'%>
</div>
<div class = "form-group">
<% = form.label: author%>
<% = form.text_field: author, class: 'form-control'%>
</div>
<div class = "form-group">
<% = form.label: body%>
<% = form.text_area: body, class: 'form-control', rows: 10%>
</div>
<% = form.submit class: 'btn btn-primary', data: {disable_with: 'Creating ..'}%>
<% end%>
this is my controller:
class PagesController <ApplicationController
def articles
#posts = Post.all
end
def new
#post = Post.new
end
def show
#post = Post.find (params [: id])
end
def create
#post = # Post.new (post_params)
# post.save
redirect_to article_path (#post)
end
private
def post_params
params.require (: post) .permit (: title,: author,: body)
end
end
Now here are my routes:
Rails.application.routes.draw do
root 'pages # index'
get 'articles', to: 'pages # articles'
get 'articles / new', to: 'pages # new'
get 'articles /: id', to: 'pages # show', as: 'article'
post 'articles', to: 'pages # create'
end

Answer 1

Replace
<% = form_with(model: post, location: true) do | form | %>
.....
<% end %>
with
<% = form_with(model: post, local: true) do | form | %>
....
<% end %>
and new.html.erb should contains
<%= render 'form', post: #post` %>
And update your controller with posts_controller.rb
class PostsController < ApplicationController
before_action :find_post, only: [:show]
def index
#posts = Post.all
end
def new
#post = Post.new
end
def show
end
def create
#post = Post.new(post_params)
#post.save
redirect_to #post
end
private
def find_post
#post = Post.find(params[:id])
end
def post_params
params.require(:post).permit(:title, :author, :body)
end
end
Routes should be as
get 'posts', to: 'posts#index'
get 'posts/new', to: 'posts#new'
get 'posts/:id', to: 'posts#show'
post 'posts', to: 'posts#create'
or simply as
resources :posts, only: [:index, :new, :show, :create]

Answer 2

There's quite a lot of whitespace issues going on in your code snippets, but I think that might be a side effect of however you've copied the code rather than any deliberate cause.
The error you're seeing is because the form_with method doesn't know what post is. In your controller, you set up #post in your new method, which means that new.html.erb will be able to see the instance variable #post, but it won't know what post (without the #) is.
So if the form is in new.html.erb, you'd need to use #post in place of post here.
That said, common Rails behaviour is to have the form in its own partial _form.html.erb. That might be the case here (you don't specify the file names of your views). In that case, you can tell the partial to use local variables rather than the instance variable that the main template file uses.
To do that, you need to map an instance variable to a local one in the render call to your form, for example:
# in new.html.erb
<%= render 'form', post: #post` %>
This is saying 'take the object that I can see as #post, and make it available as the post local variable within the form template'.