SQLite3::ConstraintException: column email is not unique - ruby-on-rails

Question

I'm absolutely new to Rails, I nearly do not know what I am doing. But. The problem is: signing up new user with Devise results in:
SQLite3::ConstraintException: column email is not unique:
INSERT INTO "users" ("created_at","encrypted_password", "name", "updated_at")
VALUES (?, ?, ?, ?)
And the request parameters:
{"utf8"=>"✓",
"authenticity_token"=>"1bgk4ovS3JitphVkIvcCZi3ex8QsBq4eEf6ZihQLiHg=",
"user"=>{"name"=>"Someone",
"email"=>"8#prosto.me",
"password"=>"[FILTERED]"},
"commit"=>"Sign up"}
User model:
class User < ActiveRecord::Base
# Include default devise modules. Others available are:
# :token_authenticatable, :confirmable,
# :lockable, :timeoutable and :omniauthable
devise :database_authenticatable, :registerable,
:recoverable, :rememberable, :trackable;
end
DB migration:
class DeviseCreateUsers < ActiveRecord::Migration
def self.up
change_table(:users) do |t|
## Database authenticatable
t.string :email, :null => false, :default => ""
t.string :name, :null => false, :default => ""
t.string :encrypted_password, :null => false, :default => ""
## Recoverable
t.string :reset_password_token
t.datetime :reset_password_sent_at
## Rememberable
t.datetime :remember_created_at
## Trackable
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
## Confirmable
# t.string :confirmation_token
# t.datetime :confirmed_at
# t.datetime :confirmation_sent_at
# t.string :unconfirmed_email # Only if using reconfirmable
## Lockable
# t.integer :failed_attempts, :default => 0 # Only if lock strategy is :failed_attempts
# t.string :unlock_token # Only if unlock strategy is :email or :both
# t.datetime :locked_at
## Token authenticatable
# t.string :authentication_token
# Uncomment below if timestamps were not included in your original model.
# t.timestamps
end
add_index :users, :email, :unique => true
add_index :users, :name, :unique => true
add_index :users, :reset_password_token, :unique => true
# add_index :users, :confirmation_token, :unique => true
# add_index :users, :unlock_token, :unique => true
# add_index :users, :authentication_token, :unique => true
end
def self.down
# By default, we don't want to make any assumption about how to roll back a migration when your
# model already existed. Please edit below which fields you would like to remove in this migration.
end
end
Please tell me if I need to provide any other code.
And thank you for all your help in advance.
Update with DB schema:
ActiveRecord::Schema.define(version: 20131012114812) do
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, null: false
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.string "name"
end
add_index "users", ["email"], name: "index_users_on_email", unique: true
add_index "users", ["reset_password_token"], name: "index_users_on_reset_password_token", unique: true
end
Update 2: And there is also a problem with authentication. Devise tells 'Invalid email or password' for any previously successfully signed up user in attempt to login.

Answer 1

SQLite is telling you that it's trying to create a new record, where one of the values will be an email, but there is already an existing record with that email.
An easy way to read your database records is query the DB in a terminal window:
$ rails console
$ User.all
If you want to see your test DB, which will be loaded with your fixtures:
$ rails console -e=test
$ User.all
Look for records that have the same email of the one you're trying to create.
If this is your first time using Devise, you should check your fixtures. Devise currently defaults to two fixtures that have no attributes. If you're running in a test environment then those fixtures will be loaded into the test DB as a two records with nil values for email, which are duplicate email values. Fixtures like the ones below will get you passed your error message.
file: app/test/fixtures/users.yml
one:
email: user#example.com
encrypted_password: password1
two:
email: user2#example.com
encrypted_password: password2

Answer 2

Do you have any other "email" columns in that database?
Perhaps you already had a "users" table, where the email column has been replicated with Devise. It would be helpful if you could show us which columns your table has :)

Answer 3

Try adding a uniqueness validation to your User model:
validates_uniqueness_of :email, :allow_blank => true
This will re-render your user creation form instead of causing an error.