Data Mapper vs Active Record

Features

Data Mapper

• Separates model classes from database operations.
• Database operations are managed by a mapper class.
• Objects are not aware of the existence of the database.

Data Mapper - Martin Fowler

Active Record

• Model classes themselves contain methods for database operations.
• Database rows are represented as instances of the model.

Active Record - Martin Fowler

Benefits

Data Mapper

• High flexibility and maintainability.
• Suitable for handling complex domain logic.

Active Record

• Low learning curve.
• Rapid development.

Suitable Use Cases

Data Mapper

• Cases with complex queries and transactions.

Active Record

• Small projects or cases with relatively simple queries and transactions.

Sample Code

Data Mapper

from sqlalchemy import create_engine, Column, Integer, String, ForeignKey
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.orm import sessionmaker, relationship

engine = create_engine('sqlite:///example.db')
Base = declarative_base()

class User(Base):
    __tablename__ = 'users'
    id = Column(Integer, primary_key=True)
    name = Column(String)
    orders = relationship("Order", back_populates="user")

class Order(Base):
    __tablename__ = 'orders'
    id = Column(Integer, primary_key=True)
    description = Column(String)
    user_id = Column(Integer, ForeignKey('users.id'))
    user = relationship("User", back_populates="orders")

Base.metadata.create_all(engine)
Session = sessionmaker(bind=engine)
session = Session()

Active Record

class User < ApplicationRecord
  has_many :orders
end

class Order < ApplicationRecord
  belongs_to :user
end

user = User.create(name: 'Alice')
order = user.orders.create(description: 'First Order')

Libraries

Data Mapper

• Python - SQLAlchemy
• Java - Hibernate
• .NET - Entity Framework
• JavaScript - TypeORM (Node.js)
• Go - GORM

Active Record

• Ruby on Rails - Active Record
• PHP - Eloquent (Laravel)
• Java - ActiveJDBC
• Python - peewee
• C# - ActiveRecord (Castle Project)
• JavaScript - Sequelize (Node.js)
• Swift - Core Data (Apple)

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