Association between Post and Location - ruby-on-rails

Question

This my first ruby on rails application.
Model Location and Post, Location has many post.I create location as tree structure with ancestry gem.
class Post < ActiveRecord::Base
belongs_to :location, :counter_cache => true
end
class Location < ActiveRecord::Base
include Tree
has_ancestry :cache_depth => true
has_many :posts
end
This my Post Controller
class PostsController < ApplicationController
before_action :set_post, only: [:show, :edit, :update, :destroy]
def index
#posts = Post.all
end
def show
end
def new
#post = Post.new
end
def edit
end
def create
#post = Post.new(post_params)
respond_to do |format|
if #post.save
format.html { redirect_to #post, notice: 'Post was successfully created.' }
format.json { render action: 'show', status: :created, location: #post }
else
format.html { render action: 'new' }
format.json { render json: #post.errors, status: :unprocessable_entity }
end
end
end
def update
respond_to do |format|
if #post.update(post_params)
format.html { redirect_to #post, notice: 'Post was successfully updated.' }
format.json { head :no_content }
else
format.html { render action: 'edit' }
format.json { render json: #post.errors, status: :unprocessable_entity }
end
end
end
def destroy
#post.destroy
respond_to do |format|
format.html { redirect_to posts_url }
format.json { head :no_content }
end
end
private
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(:name, :location_id)
end
end
Creating Post with location in Post _form.html.erb
<%= simple_form_for #post do |f| %>
<% if #post.errors.any? %>
<div id="error_explanation">
<h2><%= pluralize(#post.errors.count, "error") %> prohibited this post from being saved: </h2>
<ul>
<% #post.errors.full_messages.each do |msg| %>
<li><%= msg %></li>
<% end %>
</ul>
</div>
<% end %>
<%= f.input :name %>
<%= f.select :location_id, Location.all.at_depth(4) { |l| [ l.name, l.id ] } %>
<div class="actions">
<%= f.submit %>
</div>
<% end %>
My question are
First question- f.select :location_id , how display location name, not location id, i am using with simple form
Second question- Post index got error in <%= post.location.name %>
<% #posts.each do |post| %>
<tr>
<td><%= post.name %></td>
<td><%= post.location.name %></td>
<td><%= link_to 'Show', post %></td>
<td><%= link_to 'Edit', edit_post_path(post) %></td>
<td><%= link_to 'Destroy', post, method: :delete, data: { confirm: 'Are you sure?' } %> </td>
</tr>
<% end %>

Answer 1

First question:
Check the simple_form syntax for a dropdown. It is mentioned in the docs and you should be able to get this working by yourself.
Second question:
Does the offending post really have a related location? If it does not have one, it can not display the name of course. To counter these nil errors, use try:
<%= post.location.try(:name) %>
try will call the method name on location only if location is not nil.

Answer 2

For your first question :
Maybe you should read about "options_for_select"
http://guides.rubyonrails.org/form_helpers.html#option-tags-from-a-collection-of-arbitrary-objects
<% cities_array = City.all.map { |city| [city.name, city.id] } %>
<%= options_for_select(cities_array) %>
For your second question:
What is your error ?
Maybe one of your "post.location" is nil.
If so, try:
post.location.name unless post.location.nil?
Hope this can help