Introduction

When developing modern applications that interact with relational databases, handling relationships between entities is a key challenge. Java Persistence API (JPA) provides a standardized way to define and manage relationships, ensuring data integrity and optimized queries.

This document outlines a Spring Boot project demonstrating how to implement One-to-One, One-to-Many, Many-to-One, and Many-to-Many relationships using JPA and Hibernate ORM.

Problem Definition

In a real-world organization, different entities interact with one another in various ways. Managing these relationships efficiently in a database is essential for maintaining data consistency, query performance, and application logic.

Consider a scenario where we need to model the following relationships:

1. Employee & Address (One-to-One): Each employee has a single address.
2. Department & Employees (One-to-Many): A department can have multiple employees, but each employee belongs to only one department.
3. Employee & Mission (Many-to-Many): Employees can be assigned to multiple missions, and each mission can involve multiple employees.

Without proper relationship mapping, developers may face issues like:

• Data inconsistency due to incorrect cascade settings.
• Inefficient queries leading to poor performance.
• Complicated joins in SQL that could be simplified with ORM techniques.

To solve these challenges, we use JPA annotations to define and manage entity relationships in Spring Boot applications.

Solution

We will build a Spring Boot application that models real-world relationships between employees, departments, addresses, and missions. The project will: