One to Many relationship

Parameters#

Annotation	Purpose
@TableGenerator	Specifies generator name and table name where generator can be found
@GeneratedValue	Specifies generation strategy and refers to name of generator
@ManyToOne	Specifies many to one relationship between Employee and Department
@OneToMany(mappedBy=“department”)	creates bi-directional relationship between Employee and Department by simply referring to @ManyToOne annotation in Employee entity
## One To Many relationship
One to Many mapping is generally simply a bidirectional relationship of Many to One mapping. We will take same example that we took for Many to one mapping.

Employee.java

@Entity
public class Employee {

    @TableGenerator(name = "employee_gen", table = "id_gen", pkColumnName = "gen_name", valueColumnName = "gen_val", allocationSize = 100)
    @Id
    @GeneratedValue(strategy = GenerationType.TABLE, generator = "employee_gen")
    private int idemployee;
    private String firstname;
    private String lastname;
    private String email;

    @ManyToOne
    @JoinColumn(name = "iddepartment")
    private Department department;

    // getters and setters    
}

Department.java

@Entity
public class Department {

    @TableGenerator(table = "id_gen", pkColumnName = "gen_name", valueColumnName = "gen_val", name = "department_gen", allocationSize = 1)
    @Id
    @GeneratedValue(strategy = GenerationType.TABLE, generator = "department_gen")
    private int iddepartment;
    private String name;

    @OneToMany(mappedBy = "department")
    private List<Employee> employees;

    // getters and setters    
}

This relationship is represented in database as below.

There are two points to remember about jpa one to many mapping:

The many to one side is the owning side of relationship. The column is defined on that side.
The one to many mapping is the inverse side side so the mappedBy element must be used on the inverse side.

Complete example can be referred here