issues with installing devise - ruby-on-rails

Question

here's my current user schema:
# == Schema Information
#
# Table name: users
#
# id :integer not null, primary key
# first_name :string
# last_name :string
# created_at :datetime not null
# updated_at :datetime not null
#
require 'elasticsearch/model'
class User < ActiveRecord::Base
searchkick word_start: [:user]
has_many :posts
validates :first_name, :last_name, presence: true
end
these are the steps I'm able to go through before the problem rears its head:
rails generate devise:install
rails generate devise user
rake db:migrate
once i try to migrate it, this is what comes up:
== 20160707230510 AddDeviseToUsers: migrating =================================
-- change_table(:users)
rake aborted!
StandardError: An error has occurred, this and all later migrations canceled:
PG::DuplicateColumn: ERROR: column "email" of relation "users" already exists
: ALTER TABLE "users" ADD "email" character varying DEFAULT '' NOT NULL
/Users/aa/Documents/railsy/basicProject/db/migrate/20160707230510_add_devise_to_users.rb:5:in `block in up'
/Users/aa/Documents/railsy/basicProject/db/migrate/20160707230510_add_devise_to_users.rb:3:in `up'
ActiveRecord::StatementInvalid: PG::DuplicateColumn: ERROR: column "email" of relation "users" already exists
: ALTER TABLE "users" ADD "email" character varying DEFAULT '' NOT NULL
/Users/aa/Documents/railsy/basicProject/db/migrate/20160707230510_add_devise_to_users.rb:5:in `block in up'
/Users/aa/Documents/railsy/basicProject/db/migrate/20160707230510_add_devise_to_users.rb:3:in `up'
PG::DuplicateColumn: ERROR: column "email" of relation "users" already exists
/Users/aa/Documents/railsy/basicProject/db/migrate/20160707230510_add_devise_to_users.rb:5:in `block in up'
/Users/aa/Documents/railsy/basicProject/db/migrate/20160707230510_add_devise_to_users.rb:3:in `up'
Tasks: TOP => db:migrate
(See full trace by running task with --trace)
as you can tell from my earlier user schema, there is no email column there. so ... why does this error come up?
**EDIT - should have posted devise migration file - the one that doesn't work **
class AddDeviseToUsers < ActiveRecord::Migration
def self.up
change_table :users do |t|
## Database authenticatable
t.string :email, 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, null: false
t.datetime :current_sign_in_at
t.datetime :last_sign_in_at
t.inet :current_sign_in_ip
t.inet :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, null: false # Only if lock strategy is :failed_attempts
# t.string :unlock_token # Only if unlock strategy is :email or :both
# t.datetime :locked_at
# Uncomment below if timestamps were not included in your original model.
# t.timestamps null: false
end
add_index :users, :email, unique: true
add_index :users, :reset_password_token, unique: true
# add_index :users, :confirmation_token, unique: true
# add_index :users, :unlock_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.
raise ActiveRecord::IrreversibleMigration
end
end
EDIT AGAIN
when i run rails g devise user ... this is what comes up:
Running via Spring preloader in process 72318
invoke active_record
create db/migrate/20160707230510_add_devise_to_users.rb
insert app/models/user.rb
route devise_for :users

Answer 1

Turns out all I had to do was to do rake db:setup which recreates the db. Then I ran rake db:migrate, and no issues came up this time.
FYI. Hope this helps someone out there.

Answer 2

To eliminate migration errors on duplicate fields, use t.change as shown below.
t.change :email, :string, :null => false, :default => ""
Notice that for t.change to work, you have to specify the type for the field being changed. In the case of the email migration above, the email field was of type string.
You can refer at: devise wiki