rb:sequel-patterns

Sequel Patterns

Sequel is a flexible, high-performance ORM for Ruby.

When to Choose Sequel

Factor	ActiveRecord	Sequel
Performance	Good	6-7x faster simple queries
Memory	~100MB	~35MB for same dataset
Flexibility	Convention-based	Explicit control
Learning Curve	Gentle	Moderate
Rails Integration	Native	Via sequel-rails gem
Complex SQL	Limited	Excellent

Use Sequel when:

• High-throughput read operations
• Memory-constrained environments
• Complex SQL requirements
• Non-Rails applications
• Data processing pipelines

Use ActiveRecord when:

• Standard Rails application
• Team familiar with Rails conventions
• Rapid prototyping
• Heavy use of Rails generators

Installation

Standalone

# Gemfile
gem 'sequel'
gem 'pg'  # or 'mysql2', 'sqlite3'

# Connect
DB = Sequel.connect('postgres://user:pass@localhost/mydb')

With Rails

# Gemfile
gem 'sequel'
gem 'sequel-rails'

# Initialize
# config/initializers/sequel.rb
DB = Sequel.connect(Rails.configuration.database_configuration[Rails.env])

Models

Defining Models

class User < Sequel::Model
  # Table name inferred: :users
  
  # Explicit table name
  set_dataset :my_users
end

# Alternative: dataset block
class User < Sequel::Model
  dataset do
    where(active: true)
  end
end

Schema Definition

# migrations/001_create_users.rb
Sequel.migration do
  change do
    create_table :users do
      primary_key :id
      String :name, null: false
      String :email, null: false, unique: true
      DateTime :created_at, null: false, default: Sequel::CURRENT_TIMESTAMP
      
      index :email
    end
  end
end

Datasets

The core of Sequel's power is the Dataset abstraction.

Basic Queries

# Retrieving
users = User.all                          # Array of User objects
user = User.first                         # First user
user = User[id: 1]                        # By primary key
user = User.find(name: 'John')            # By conditions

# Filtering
active_users = User.where(active: true)
recent = User.where(created_at: > 1.week.ago)

# Chaining
dataset = User.where(active: true)
              .where(created_at: > 1.month.ago)
              .order(:created_at)
              .limit(10)