Rails 4, not saving #user.save when registering new user - ruby-on-rails-4

Question

When I try to register an user, it does not give me any error but just cannot save the user.
I don't have attr_accessible. I'm not sure what I am missing. Please help me.
user.rb
class User < ActiveRecord::Base
has_secure_password
validates :email, presence: true,
uniqueness: true,
format: { with: /\A([^#\s]+)#((?:[-a-z0-9]+\.)+[a-z]{2,})\Z/i }
validates :password, presence: true, length: {minimum: 6}
validates :nickname, presence: true, uniqueness: true
end
users_controller.rb
class UsersController < ApplicationController
def new
#user = User.new
end
def create
#user = User.new(user_params) # Not saving #user ...
if #user.save
flash[:success] = "Successfully registered"
redirect_to videos_path
else
flash[:error] = "Cannot create an user, check the input and try again"
render :new
end
end
private
def user_params
params.require(:user).permit(:email, :password, :nickname)
end
end
Log:
Processing by UsersController#create as HTML
Parameters: {"utf8"=>"✓", "authenticity_token"=>"x5OqMgarqMFj17dVSuA8tVueg1dncS3YtkCfMzMpOUE=", "user"=>{"email"=>"example#example.com", "password"=>"[FILTERED]", "nickname"=>"example"}, "commit"=>"Register"}
(0.1ms) begin transaction
User Exists (0.2ms) SELECT 1 AS one FROM "users" WHERE "users"."email" = 'example#example.com' LIMIT 1
User Exists (0.1ms) SELECT 1 AS one FROM "users" WHERE "users"."nickname" = 'example' LIMIT 1
(0.1ms) rollback transaction

Answer 1

Regarding our short discussion in the comments, it appears that one or two things are happening to cause #user.save to return false:
One of the validation rules are failing
A callback within your model is returning false, thus halting processing and rolling back the transaction
There are a few quick ways to debug the validations. I figured I could describe them so you could learn a few options.
A. Change the call within the if statement to instead use the bang method of save:
if #user.save!
This will cause the app to raise an exception if validation fails, displaying the validation errors within the browser on your screen. In this particular scenario, you'd want to remember to remove the ! after you're done debugging because you probably don't want the final version of your app doing that.
Or...
B. Within the else statement, add this line:
raise #user.errors.to_yaml
This will display the validation errors within the browser on the screen. Of course, remember to remove this line after you're done debugging.
Or...
C. Within the else statement, add this line and then run the form post:
puts #user.errors.to_yaml
This will display the validation errors within your console. You'll want to remember to remove this line after you're done debugging, but it's "less worse" if you happen to forget because at least the extra info is only output to STDOUT.
You may want to try each of these just to get a little practice and to see what your options are in simple debugging scenarios like this.

Answer 2

High chances that error is in password confirmation. You use has_secure_password from Rails, which automagically handles password confirmation for you. And here is the problem - you don't have it before user creation. Thus just add. For details check out similar question on has_secure_password
And check, that you have password_digest:string in users table :)