Trying to prevent duplicate username creation in Sinatra app - ruby

Question

Hi I am trying to prevent duplicate user name creation, and my application keeps trying to redirect me to a hypothetical account page and keeps throwing username undefined error in my erb file, and I am actually trying to redirect back to signup page if the user name already exist.
Here is my model for User class:
class User <ActiveRecord::Base
include Slugifiable::InstanceMethods
extend Slugifiable::ClassMethods
validates_uniqueness_of :username, case_sensitive: false <---This should validate if username exist
has_many :players
has_secure_password
end
Here is my user controller post method where it should either create or redirect back to signup page and give a flash message that the user name exist already
post '/signup' do
if params[:username] == "" || params[:email] == "" || params[:password] == "" || params[:name] == ""
flash[:notice] = "<h3 class ='alert'>Please fill-in info!</h3>"
redirect to '/signup'
else
if #user
flash[:notice] = "<h3>Username already exist, try anoter one.</h3>"
redirect to '/signup'
else
#user = User.create(:username => params[:username], :email => params[:email], :password =>
params[:password], :name => params[:name])
session[:user_id] = #user.id
redirect to '/account'
end
end
end
When I try to create a duplicate username for testing purposes....it keeps redirecting me to an account page but throws an error that username is undefined from erb file. It works fine when creating a completely new username though. What am I doing wrong?

Answer 1

"throws an error ... from erb" sounds like there's an issue in an ERB file somewhere?
User.create probably silently fails when the uniqueness check triggers, i.e. it sounds like it sets #user.username to nil, or #user itself is nil.
You also never defined what it should do when the validation check fails.
You can:
use User.create! to raise an exception.
check #user.valid? and #user.errors for any errors, and report them to the user