How to Generate UUID in Ruby

Generate UUID with SecureRandom.uuid

Ruby's SecureRandom module provides built-in UUID generation with no external dependencies. Part of Ruby's standard library since version 1.9, SecureRandom.uuid creates cryptographically secure random UUIDs (version 4) perfect for session tokens, database primary keys, and unique identifiers.

require 'securerandom'

uuid = SecureRandom.uuid
puts uuid  # "550e8400-e29b-41d4-a716-446655440000"

Basic UUID Generation Examples

SecureRandom.uuid generates RFC 4122 compliant UUIDs with proper formatting including hyphens. Each call creates a unique, cryptographically random UUID suitable for production use in web applications, APIs, and database systems.

require 'securerandom'

# Generate single UUID v4
uuid = SecureRandom.uuid
puts uuid  # "550e8400-e29b-41d4-a716-446655440000"

# Generate multiple UUIDs
uuids = 5.times.map { SecureRandom.uuid }
uuids.each { |u| puts u }

# Store in variable
session_id = SecureRandom.uuid
user_token = SecureRandom.uuid

# Uppercase format
upper_uuid = SecureRandom.uuid.upcase

# Remove hyphens
compact_uuid = SecureRandom.uuid.delete('-')

UUID Validation with Regular Expression

Validate UUID strings from user input or external sources using Ruby's pattern matching. This regex pattern checks for proper UUID v4 format including correct hyphen placement and valid hexadecimal characters in each section.

UUID_REGEX = /\A[0-9a-f]{8}-[0-9a-f]{4}-[1-7][0-9a-f]{3}-[89ab][0-9a-f]{3}-[0-9a-f]{12}\z/i

def valid_uuid?(str)
  UUID_REGEX.match?(str)
end

# Test validation
puts valid_uuid?("550e8400-e29b-41d4-a716-446655440000")  # true
puts valid_uuid?("not-a-uuid")  # false
puts valid_uuid?("550E8400-E29B-41D4-A716-446655440000")  # true (case insensitive)

# Validate and sanitize
def parse_uuid(str)
  str = str.strip.downcase
  valid_uuid?(str) ? str : nil
end

# Usage in method
def create_resource(uuid_string)
  return { error: "Invalid UUID" } unless valid_uuid?(uuid_string)
  { id: uuid_string, created: true }
end

Rails Active Record UUID Primary Keys

Rails provides excellent support for UUID primary keys through migrations and model configurations. Using UUIDs instead of auto-incrementing integers offers better security, easier data merging across databases, and improved distributed system compatibility.

# db/migrate/20250101000000_create_users.rb
class CreateUsers < ActiveRecord::Migration[7.0]
  def change
    create_table :users, id: :uuid do |t|
      t.string :name
      t.string :email, null: false
      t.timestamps
    end
    
    add_index :users, :email, unique: true
  end
end

# app/models/user.rb
class User < ApplicationRecord
  # UUID is auto-generated for primary key
  validates :email, presence: true, uniqueness: true
  
  # Generate UUID before validation (if needed for custom logic)
  before_validation :generate_uuid, on: :create
  
  private
  
  def generate_uuid
    self.id ||= SecureRandom.uuid
  end
end

# Usage
user = User.create(name: "Alice", email: "alice@example.com")
puts user.id  # "550e8400-e29b-41d4-a716-446655440000"

# db/migrate/20250101000001_enable_pgcrypto.rb
class EnablePgcrypto < ActiveRecord::Migration[7.0]
  def change
    enable_extension 'pgcrypto'
  end
end

# Then use gen_random_uuid() in PostgreSQL
# config/database.yml should use postgresql adapter

UUID Gem for Advanced Features

For UUID v1, v3, and v5 support beyond the standard library's v4 implementation, install the uuid gem. This provides timestamp-based UUIDs (v1) and namespace-based hash UUIDs (v3, v5) for deterministic ID generation.

# Using uuid gem
require 'uuid'

generator = UUID.new

# UUID v1 (timestamp-based)
uuid_v1 = generator.generate

# UUID v4 (random) - still prefer SecureRandom.uuid
uuid_v4 = UUID.generate

# Display UUID
puts uuid_v1  # Includes timestamp and MAC address

API Response with UUID Generation

When building REST APIs with Ruby, generate UUIDs for new resources and include them in JSON responses. This pattern works with Sinatra, Rails API mode, or any Ruby web framework for creating resource identifiers.

require 'securerandom'
require 'json'

class ApiController
  def create_resource
    resource = {
      id: SecureRandom.uuid,
      name: params[:name],
      created_at: Time.now.iso8601
    }
    
    # Save to database...
    
    {
      status: 201,
      body: resource.to_json,
      headers: { 'Content-Type' => 'application/json' }
    }
  end
  
  def validate_and_fetch(uuid_string)
    unless valid_uuid?(uuid_string)
      return {
        status: 400,
        body: { error: 'Invalid UUID format' }.to_json
      }
    end
    
    # Fetch resource by UUID...
    resource = find_resource(uuid_string)
    
    {
      status: 200,
      body: resource.to_json
    }
  end
end

Related Programming Language UUID Guides