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Boost Spring Boot Performance with FetchType.LAZY in Hibernate
Improve your Spring Boot application’s performance by using FetchType.LAZY in Hibernate. Learn how lazy loading prevents unnecessary database queries and speeds up your API with a complete example.
When working with Spring Boot and Hibernate, one of the biggest performance mistakes is using EAGER fetching for entity relationships.
❌ Problem:
- Fetching unnecessary data from the database
- Increasing response time due to large joins
- N+1 query problem (multiple queries slowing down performance)
💡 Solution: Use FetchType.LAZY to load only the necessary data when it's actually needed.
In this article, we’ll explore:
✅ What is FetchType.LAZY?
✅ Why EAGER fetching is bad for performance
✅ A complete example with one-to-many relationship
✅ How FetchType.LAZY reduces database queries
⚡ What is FetchType.LAZY in Hibernate?
In Hibernate, lazy loading (FetchType.LAZY) means that related entities are not fetched from the database until you explicitly access them.
📌 Example: Using FetchType.LAZY in One-to-Many Relationship
Let’s assume we have a Department and Employee relationship where a department has multiple employees.
1️⃣ Define Department Entity (One-to-Many Relationship)
@Entity
@Table(name = "departments")
public class Department {
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
private Long id;
private String name;
@OneToMany(mappedBy = "department", fetch = FetchType.LAZY) // Lazy Loading
private List<Employee> employees;
// Constructors, Getters, and Setters
}✅ FetchType.LAZY ensures that employees are not loaded until explicitly needed.
2️⃣ Define Employee Entity (Many-to-One Relationship)
@Entity
@Table(name = "employees")
public class Employee {
@Id
@GeneratedValue(strategy =…
