How to validate emails with error messages - ruby-on-rails

Question

[Update] I still dont know what to put in my else of my create conroller to put and error message.
I am trying to validate the format of users email.
This is the html the error is coming from
<% if #user.errors.any? %>
<div id="error_explanation">
<h2><%= pluralize(#user.errors.count, "error") %> prohibited this article
from being saved:</h2>
<ul>
<% #user.errors.full_messages.each do |msg| %>
<li><%= msg %></li>
<% end %>
</ul>
</div>
<% end %>
I experimented with this from an old ruby video but it didn't seen to pan out.
This is my user.rb model
class User < ApplicationRecord
has_secure_password
validates :email, presence: true, uniqueness: true
validates :password, length: { minimum: 4 }
validates :email, format: { with: /(\A([a-z]*\s*)*\<*([^#\s]+)#((?:[-a-z0-9]+\.)+[a-z]{2,})\>*\Z)/i }
end
I get these errors currently
No route matches {:action=>"show", :controller=>"users", :id=>nil},
missing required keys: [:id]
and
undefined method `errors' for nil:NilClass
whenever the password or email makes an error from the requirements.
my create action in my sessions controller:
class UsersController < ApplicationController
def new
#user = User.new
end
def create
#user = User.create(password: params[:password], email: params[:email], firstname: params[:firstname], lastname: params[:lastname])
if #user.save
redirect_to user_path(#user)
else
format.xml { render :xml => #user.errors, :status => :unprocessable_entity }
end
end
def show
#user = User.find(params[:id])
end
end

Answer 1

When there is no user with the requested email address, your #user variable will be nil in the controller (since this is the returned value of the find_by_email method if nothing is found)
In that case, you are explicitly rendering your new view which then attempts to render errors on the #user object. However, since the variable is nil instead of the User object you are apparently expecting there, nil.errors fails with the error you are seeing there.
To solve this, you should either check in your view if you have an actual #user object, or render a more suitable view from your controller.

Answer 2

3 issues here
def create
#user = User.create(password: params[:password], email: params[:email], firstname: params[:firstname], lastname: params[:lastname])
redirect_to user_path(#user)
end
That function tries to create a user and regardless of success it then goes on to redirect to the show action
1) You need to check if the User.create actually succeeds then take appropriate action
2) You have no route for the show action so you need to fix that but
3) None of your actions are specifying the format. What happens if someone is using an XML feed Are you sure you want to show the user, Just show a list of users, there won't be anything much to see
Several people including asked for the full stack trace which you seem to have ignored. This would be so much easier to track down the origination of your error had you done so, including the params sent to the create action
def create
if #user = User.create(password: params[:password], email: params[:email], firstname: params[:firstname], lastname: params[:lastname])
redirect_to user_path(#user)
else
format.html { render :action => "new" }
end
end
Now you have to track down why the create failed
You should also show the errors to the user by using a flash message