Explanation/Reference:
Annotation Type MapKey specifies the map key for associations of type java.util.Map when the map key is itself the primary key or a persistent field or property of the entity that is the value of the map.
Example:
@ Entity
public class Department {
. ..
@ OneToMany(mappedBy="department")
@ MapKey(name="name")
public Map<String, Employee> getEmployees() {... }
. ..
}
@Entity
public class Employee {
@ Id public Integer getEmpId() { ... }
. ..
@ ManyToOne
@ JoinColumn(name="dept_id")
public Department getDepartment() { ... }
...
}
Reference: javax.persistence, Annotation Type MapKey