Want to form a "email id" with editable text field for "username" and a constant "domain name"

I am creating an application having domains and users. Admin can select any domain and create user inside that domain. In the new user creation view i have a email field. Currently i am creating new user by entering the full email id like "sam@exmple.com".I would like to divide the email id so that only the "username(sam)" part is need to be inserted using the text field. The "@domain" part is appended with the username while the form is being submitted.I wish to have a view in which there will be a email section with a text field f开发者_如何学编程or username followed by @domain name(populated from database,population is happening). Here is my current view.

<%= form_for @user do |f| %>
  <%= f.hidden_field :domain_id %>  

  <%= f.label :email %>
  <%= f.text_field(:email, :size => 20) %>

  <%= f.submit "Create" %>

<% end %>

I am not being able to figure out how to do this. Can somebody help, please.

At present i am only having a text_field for my email section.So i need to write the full email id.But i wish to have something like this.

[.............]@example.com

In the text_field(i mean the square braces) only username need to be inserted.The domain part is populated from domain table as per selection of domain.How can i prepare the email section of my view so that all the 3 items(username,@,domain name) are concatenated to form a complete email id at the time of submission.

{update} Since i didn't want to add one more field to the table "users", i have not added "user_name" and trying to do with "email" only. Here is my view(question related portions only).

<%= form_for @user do |f| %>
 <%= f.label :email %>
 <%= f.text_field(:email, :size => 20) %>

 <%= f.submit "Create" %>
<% end %>

Controller(question related portions only)

class UsersController < ApplicationController
  def new       
    @domain = Domain.find(params[:id])
    @user = @domain.users.build
    @title = "Add User"
  end

 def create
   @user = User.new(params[:user])
   if @user.save
    flash[:success] = "Welcome!"
    redirect_to manageDomain2_path(:id => @user.domain_id)
   else
    @title = "Sign up"
    redirect_to addNewUser_path(:id => @user.domain_id)
   end
 end

end

Model(question related portion only)

class User < ActiveRecord::Base
  attr_accessor :email

  before_create :compose_email
    def compose_email
      domain = @domain.domain_name
      self.email = "#{email}@#{domain}"
    end
end

When i am trying with something like (for checking only)

domain = "example.com"

Then the email id is getting saved properly.(like sam@example.com) As i have many domains, i want to build this domain part dynamically.so when i am using

domain = @domain.domain_name

Im getting error as "undefined method domain_name". I guess this is due to unavailability of the instance domain in my user model. Can you please suggest,where am i doing wrong. Is there any alternative way for this?

I don't understand this part of your post: "I wish to have a view in which there will be a email section with a text field for username followed by @domain name(populated from database,population is happening). Here is my current view".

Can you elaborate/reword this? :)

Aside from that here is an idea. Define:

attr_accessor :user_name

in your User model. Then you can write somethign like this in your form:

<%= f.text_field(:username, :size => 20) %>

And finally, define a callback in your model:

before_create :compose_email

def compose_email
domain = ... #prepare domain here 
self.email = "#{user_name}#{domain}"
end

EDIT:

Ok, first, you do not have access to @domain in your model. It's defined in controller and available there and in the view.

Second, I see that you're using @domain.users.build so I guess that Domain has_many :users and User belongs_to :domain, right?

If so, you can write your compose_email method like this:

def compose_email
      domain = domain.domain_name  #we are using AR association here and we are calling domain on self, which is instance of user here, by default
      self.email = "#{email}@#{domain}"
end