Querying multiple linked classes in Rails - ruby-on-rails

Question

I want to query multiple tables. For example in posts table there is a user_id linked to users id. While showing every post, I also want to display the picture of the user. My approach is this, but there is a problem. #user.picture method is undefined.
<% #programs.each do |post| %>
<%= #user = User.where("id = post.user_id") %>
<li class="one-third column">
<div class="wrapper">
<div class="postThumb"><img src="<%= #user.picture %>" /></div>
<div class="postDetails">
<%= link_to "#{ post.title.upcase! }".html_safe, all_posts_path, :class => "postTitle" %>
<p><%= truncate post.details, :length => 90 %></p>
</div>
</div>
</li>
<% end %>
Program Controller:
class ProgramController < ApplicationController
def index
#programs = Program.all
end
User model:
class User < ActiveRecord::Base
attr_accessible :password, :username, :oauth_token, :provider, :uid, :oauth_expires_at, :picture, :email, :name, :location, :gender, :updated_at, :is_admin
has_many :posts
has_one :program
has_many :programdetails, :through => :program
end
Program model:
class Program < ActiveRecord::Base
attr_accessible :details, :title, :user_id
belongs_to :user
has_many :programdetails
end

Answer 1

Try this instead, in the controller:
#programs = Program.includes(:user) # this will return all programs and related users in
# 2 database queries rather than N+1 queries
Then in the view:
<div class="postThumb"><img src="<%= post.user.picture %>" /></div>
Also, you can use image_tag instead.
Finally, you can probably change your post title link to:
<%= link_to post.title.upcase, all_posts_path, :class => "postTitle" %>

Answer 2

#user = post.user. Rails association will give back the associated user by itself.
And to correct above, syntactically, #user = User.find(post.user_id)

Answer 3

try changing this: #user = User.where("id = post.user_id")
into this: #user = User.where(id: post.user_id).first
or even better: #user = post.user as suggested by kiddorails

Answer 4

There is a much easier way to do this using the relations you have already defined:
Programs Controller
def index
#programs = Program.
includes(:user). # eager load user relation to avoid n+1
all
end
View
<% #programs.each do |post| %>
<li class="one-third column">
<div class="wrapper">
<div class="postThumb"><img src="<%= post.user.picture %>" /></div>
<div class="postDetails">
<%= link_to "#{ post.title.upcase! }".html_safe, all_posts_path, :class => "postTitle" %>
<p><%= truncate post.details, :length => 90 %></p>
</div>
</div>
</li>
<% end %>