Ruby on Rails: How would i stay on the same page if the post is not saved?

Question

def create
    @addpost = Post.new params[:data]
    if @addpost.save
        flash[:notice] = "Post has been saved successfully."
        redirect_to posts_path
    else
        flash[:notice] = "Post can not be saved, please enter information."
    end
end

If the post is not saved then it redirects to http://0.0.0.0:3000/posts , but i need to stay on the page, with text input fields so that user can input data.

post model

class Post < ActiveRecord::Base

    has_many :comments
    validates :title, :presence => true
    validates :content, :presence => true
    validates :category_id, :presence => true
    validates :tags, :presence => true
end

new method

def new
    @arr_select = { 1=>"One",2=>"Two" ,3=>"Three" }
    @categories_select = Category.all.collect {|c| [ c.category_name, c.id ] }
end

new.html.erb

<h3>Add post</h3>

<%= form_tag :controller=>'posts', :action=>'create' do %>
    <%= label :q, :Title %>
    <%= text_field :data, :title, :class => :addtextsize %><br/>
    <%= label :q, :Content %>
    <%= text_area  :data, :content, :rows=>10 , :class => :addtextarea %><br/>
    <%= label :q, :Category %>
    <%= select :data, :category_id, @categories_select %><br/>
    <%= label :q, :Tags %>
    <%= text_field :data, :tags, :class => :addtextsize %><br/>
    <%= label :q, :Submit %>
    <%= submit_tag "Add Post" %>
<% end %>

What should i do ?

Answer 1

flash.now with render is what you're looking for.

flash.now[:notice] = "Post can not be saved, please enter information."
render :new

Also instead of

flash[:notice] = "Post has been saved successfully."
redirect_to posts_path

you can just write

redirect_to posts_path, :notice => "Post has been saved successfully."

and it will do the same thing. It works only with redirect_to though, not with render!

Answer 2

Something like this should do what you want:

flash[:notice] = "Post can not be saved, please enter information."
render :new

UPDATE: You updated your question so I have to update my answer. Render is the right way to do this. However, it looks like you load some categories and some other collection of stuff in your new method. Those same instance variables should be available to your create method. The cleanest way to do this is put them into another method and have that method used as a before_filter applied to both create and new. Something like this:

before_filter :load_stuff, :only => [:create, :new]

def load_stuff
  @arr_select = { 1=>"One",2=>"Two" ,3=>"Three" }
  @categories_select = Category.all.collect {|c| [ c.category_name, c.id ] }
end

Then your new method is pretty much blank and calling render :new in your create method should work.