Omniauth error -- PG::Error: ERROR: duplicate key value violates - ruby-on-rails

Question

So, I've helped a friend add Omniauth to his app, and for some reason omniauth only worked the first time.
But now, it's returning:
PG::Error: ERROR: duplicate key value violates
unique constraint "index_users_on_email"
DETAIL: Key (email)=() already exists. : INSERT INTO "users"
("created_at", "provider", "uid", "updated_at", "username")
VALUES ($1, $2, $3, $4, $5) RETURNING "id"
It's like it only accepts one, and then says "already exists". How can we get this workin'?
user.rb
class User < ActiveRecord::Base
# Include default devise modules. Others available are:
# :token_authenticatable, :confirmable,
# :lockable, :timeoutable and :omniauthable
devise :database_authenticatable, :registerable, :omniauthable,
:recoverable, :rememberable, :trackable, :validatable
has_many :songs
has_many :comments
acts_as_voter
def self.from_omniauth(auth)
where(auth.slice(:provider, :uid)).first_or_create do |user|
user.provider = auth.provider
user.uid = auth.uid
user.username = auth.info.nickname
end
end
def self.new_with_session(params, session)
if session["devise.user_attributes"]
new session["devise.user_attributes"] do |user|
user.attributes = params
user.valid?
end
else
super
end
end
def password_required?
super && provider.blank?
end
def update_with_password(params, *options)
if encrypted_password.blank?
update_attributes(params, *options)
else
super
end
end
def email_required?
super && provider.blank?
end
end
schema snippit
create_table "users", force: true do |t|
t.string "email", default: "", null: false
t.string "encrypted_password", default: "", null: false
t.string "reset_password_token"
t.datetime "reset_password_sent_at"
t.datetime "remember_created_at"
t.integer "sign_in_count", default: 0
t.datetime "current_sign_in_at"
t.datetime "last_sign_in_at"
t.string "current_sign_in_ip"
t.string "last_sign_in_ip"
t.datetime "created_at"
t.datetime "updated_at"
t.boolean "admin"
t.string "provider"
t.string "uid"
t.string "username"
end
omni controller
class OmniauthCallbacksController < Devise::OmniauthCallbacksController
def all
user = User.from_omniauth(request.env["omniauth.auth"])
if user.persisted?
flash.notice = "Signed in!"
sign_in_and_redirect user
else
session["devise.user_attributes"] = user.attributes
redirect_to new_user_registration_url
end
end
alias_method :twitter, :all
end
All access keys are setup appropriately following railscasts latest ep on it.

Answer 1

You have a unique constraint on the email field. Because this field is defined as not nullable and has a default value of "" (empty string). This means if you don't specify the email, your DBMS will set this field to "". Of course, because it has a unique constraint, you'll only be able to add two users without email, because only one can have the empty string email.
If you didn't create the constraint manually, then I assume rails has created it for you (because there's an index on the email field too apparently) by assuming the first field is the table primary key, since you didn't specify any. This made it create both an index and a unique constraint on it.

Answer 2

A more simple explanation could be that this is caused due to your test data being generated without a unique email. Try looking in /test/fixtures/users.yml, if you see something like:
one: {
}
two: {
}
then change it to
one: {
email: tester1#stack.com
}
one: {
email: tester2#stack.com
}
Or you can delete the contents of the file.

Answer 3

You can remove the index from the email since devise sets it as unique. You can't have duplicate blank email addresses according to how devise sets up things by default. Here is a migration example.
class ChangeEmail < ActiveRecord::Migration
def change
remove_index :users, :email
end
end