Mastering Many-to-One Relationships in Spring Boot: A Complete Guide with Examples

 

Many-to-One Relationship

Explanation of Many-to-One Relationship in Spring Boot

In a many-to-one relationship, multiple entities from one table (child) are related to a single entity in another table (parent). This is common in real-world scenarios, like multiple employees belonging to a single department.

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Example: Employees and Departments in Spring Boot

Here’s how you can implement a many-to-one relationship in Spring Boot:

Step 1: Define the Entity Classes

1. Department Entity:

   @Entity
   public class Department {
       @Id
       @GeneratedValue(strategy = GenerationType.IDENTITY)
       private Long id;
   
       private String name;
   
       // Getters and Setters
   }
   

2. Employee Entity:

   @Entity
   public class Employee {
       @Id
       @GeneratedValue(strategy = GenerationType.IDENTITY)
       private Long id;
   
       private String name;
   
       @ManyToOne
       @JoinColumn(name = "department_id")
       private Department department;
   
       // Getters and Setters
   }
   

Step 2: Create Repositories

• Define repositories for both entities:

  public interface EmployeeRepository extends JpaRepository<Employee, Long> {}
  public interface DepartmentRepository extends JpaRepository<Department, Long> {}
  

Step 3: Save Data

• Save departments and assign them to employees.

  @RestController
  @RequestMapping("/api")
  public class EmployeeController {
  
      @Autowired
      private EmployeeRepository employeeRepository;
  
      @Autowired
      private DepartmentRepository departmentRepository;
  
      @PostMapping("/addEmployee")
      public Employee addEmployee(@RequestBody Employee employee) {
          return employeeRepository.save(employee);
      }
  
      @PostMapping("/addDepartment")
      public Department addDepartment(@RequestBody Department department) {
          return departmentRepository.save(department);
      }
  }
  

Step 4: Test the Relationship

1. Save a few departments, e.g., "IT" and "HR."
2. Create employees and associate them with their respective departments by setting the department field.

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Key Benefits of Many-to-One Relationships in Spring Boot

• Streamlined database design with reduced redundancy.
• Easy navigation of relationships (e.g., fetch all employees of a department).
• Simplified data management using JPA's cascading operations.

This approach ensures scalability and clarity, especially for applications with complex data relationships!