What is an ORM (Object-Relational Mapping)?
Definition
Technique that converts data between incompatible type systems in OOP languages, allowing manipulation of database records as objects.
How It Works
- Maps database tables → classes
- Table rows → objects
- Table columns → object attributes
Key Features
- Data Mapping: Automatic type conversion between SQL and language types
- CRUD Operations: Create, Read, Update, Delete methods
- Query Building: Object-based query construction (e.g., Django's
filter(), Hibernate's HQL) - Relationships: Handles 1:1, 1:many, many:many associations
- Transactions: ACID-compliant operations
Popular ORMs
| Language | ORM |
|---|---|
| Java | Hibernate |
| .NET | Entity Framework |
| Python | Django ORM, SQLAlchemy |
| Ruby | ActiveRecord |
| PHP | Eloquent |
Advantages
- Reduces SQL boilerplate
- Database-agnostic code
- Automatic schema migrations
- SQL injection protection
- Type safety
Disadvantages
- Performance overhead
- Learning curve
- Complex queries harder to optimize
- Potential N+1 query problem
Use Cases
✅ Rapid development
✅ Simple CRUD operations
✅ Multi-database support needs
When Not to Use
❌ Complex analytical queries
❌ High-performance requirements
❌ Existing optimized SQL codebase