Update joined table

Rails
1

=#select * from hosts;
id | hostname |
----±---------+
1 | foo |
2 | bar |
3 | hoge |

=# select * from ipaddresses;
id | host_id | address |
----±--------±------------+
1 | 1 | 192.168.1.1 |
2 | 2 | 192.168.1.2 |
3 | 3 | 192.168.1.3 |

Model
host.rb
class Host < ActiveRecord::Base
has_one :ipaddress
end

ipaddress.rb
class Ipaddress < ActiveRecord::Base
belongs_to :host
end

View index.html.erb

Listing hosts

<% @hosts.each do |host| %>

<% end %> ------------------------------------------------------ I can see host.hostname and host.ipaddress.address.

I have a problem for updating ipaddress.address.
hosts_controller.rb

def edit
@host = Host.find(params[:id], :joins => “LEFT JOIN ipaddresses on
hosts.id=ipaddresses.host_id”, :select => “hosts.*,
ipaddresses.address”)
end

def update
@host = Host.find(params[:id], :joins => “LEFT JOIN ipaddresses on
hosts.id=ipaddresses.host_id”, :select => “hosts.*,
ipaddresses.address”)
@host.ipaddress.address = params[:address]
@host.ipaddress.save

respond_to do |format|
  if @host.update_attributes(params[:host])
    flash[:notice] = 'Host was successfully updated.'
    format.html { redirect_to(@host) }
    format.xml  { head :ok }
  else
    format.html { render :action => "edit" }
    format.xml  { render :xml => @host.errors, :status =>

:unprocessable_entity }
end
end
end

View edit.html.erb

Editing host

<% form_for(@host) do |f|%>
<%= f.error_messages %>

<%= f.label :host_id %>
<%= f.text_field :host_id %>

<%= f.label :hostname %>
<%= f.text_field :hostname %>

<%= f.label :IP %>
<%= f.text_field :address %>

<%= f.submit 'Update' %>

<% end %>

<%= link_to ‘Show’, @host %> |
<%= link_to ‘Back’, hosts_path %>

If I use @host.ipaddress.address = ‘192.168.1.10’, ipaddress.address is
updated,
but params[:address] is used, nil is updated to ipaddress.address,
and rails shows ‘Host was successfully updated.’.
Why?

Host Hostname IP
<%=h host.host_id %> <%=h host.hostname %> <%=h host.ipaddress.address %> <%= link_to 'Show', host %> <%= link_to 'Edit', edit_host_path(host) %> <%= link_to 'Destroy', host, :confirm => 'Are you sure?', :method => :delete %>