Because I didn't found a simple solution for importing the database from Heroku (Postgresql) on my localhost (Mongoid). Import your database on localhost or online with this script (from Heroku)

import-pg-mongodb.rb

## Requirements:
##   - Ruby on Rails
##   - Existing Heroku Application
##   - HTTParty

# Get the json content of the
# backup and parse it
url = 'https://dataclips.heroku.com/xxx.json'
json = HTTParty.get(url)

# Cache the json result in the
# variables for them
fields = json['fields']
values = json['values']

# Initialize empty array for users
# and an empty hash for the puffer
users = []
puffer = {}

# Set the only arguments to be
# included in the User
allowed_arguments = ['email', 'encrypted_password', 'sign_in_count', 'name', 'username']

# For each value in the backup
# run the loop
values.each do |value|
  # For each data and the index
  # in the value var run the
  # loop
  value.each_with_index do |data, index|
    # Only run if the current field is
    # included in the allowed arguments
    # variable
    if allowed_arguments.include?(fields[index])
      # Include the hash into the puffer
      # variable
      puffer.merge!(:"#{fields[index]}" => data)
    end
  end

  # Merge the password wit the current
  # puffer variable
  puffer.merge!(:password => SecureRandom.hex(4))

  # Push the current user into the
  # users array
  users.push(puffer)

  # And empty the puffer variable
  puffer = {}
end

# # Render the json for the browser
# # output
# render json: users.to_json

# Or Put each user into the local
# database
users.each do |user|
  u = User.new user
  unless u.save
    raise "User #{u} could not be saved!"
  end
end