Rails displaying tables of a has_one relationship - ruby-on-rails-3

Question

I'm trying to wrap my head around Rails and have come into some difficulty trying to understand why somethings work and others do not
For example, having 2 tables:
Class User
table users
email:string
password:string
class Profile
table profiles
firstname:string
lastname:string
city:string
user_id:integer
Now each user should have 1 profile.
so in the module user.rb I have
has_one :profile
and in profile.rb
belongs_to :user
now all I want to do is show both tables in a table
<table>
<tr>
<th>User_ID</th>
<th>Email</th>
<th>Password digest</th>
<th>First Name</th>
<th>Last Name</th>
<th>City</th>
</tr>
<% #users.each do |user| %>
<tr>
<td><%= user.id %></td>
<td><%= user.email %></td>
<td><%= user.password %></td>
<td><%= user.profile.firstname %></td>%></td>
<td><%= user.profile.lastname %></td>%></td>
<td><%= user.profile.city %></td>%></td>
</tr>
<% end %>
</table>
I have a controller Show with an index page
def index
#this works
#users = User.all(:include => :profile)
end
This snippet of code I have found works, it displays the table properly.
But I have a list of other code that I've gathered/cobbled by trying to get this to work, that do not work.
So this list of codes would have been inside the def index individually tring to connect the two tables
#users = #users.build_profile()
Throws error: undefined method `build_profile' for nil:NilClass
#users = #users.profile
Throws error: undefined method `profile' for nil:NilClass
#users = #user.collect { |user| user.profile }
Throws error: undefined method `collect' for nil:NilClass
#users = Profile.find(:all)
Throws error: undefined method `email' for #Profile:0x46da5a0
<% #users.each do |user| %>
<tr>
<td><%= user.id %></td>
<td><%= user.email %></td>
<td><%= user.password %></td>
<td><%= user.proflie.firstname %></td>
#users = #profile.create_user()
Throws error: undefined method `create_user' for nil:NilClass
#users = #users.profiles
Throws error: undefined method `profiles' for nil:NilClass
#users = #user.each { |user| user.profiles }
Throws error: undefined method `each' for nil:NilClass
Why are all of these other ones failing, they seemed to work for other users that had similar problems (connecting two tables with a 1 to zero relationship)

Answer 1

The majority of the problems you are experiencing are caused just by the fact that you are calling methods on nil. You need to initialize the #users collection before you can call methods on it. Also make sure that you actually have some users in the database.
Getting all of the users:
#users = User.all(:include => :profile)
#users = User.includes(:profile) # I prefer this syntax
Building a profile. Note that you need to call this on one particular User, not on the collection given by the all method:
#profile = #users.first.build_profile # This won't actually save the profile
Getting the first user's profile
#profile = #users.first.profile
Getting all profiles:
#profiles = #users.collect { |user| user.profile }
Getting the first user's email:
#email = #users.first.profile.email
The rest is just a slightly modified version of the above.