jakarta.persistence.MapKey

Specifies the map key for associations of type Map<K,V> 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.

If a persistent field or property other than the primary key is used as a map key then it is expected to have a uniqueness constraint associated with it.

The MapKeyClass annotation is not used when MapKey is specified and vice versa.

Example 1:

 @Entity
 public class Department {
     ...
     @OneToMany(mappedBy = "department")
     @MapKey  // map key is primary key
     public Map getEmployees() {... }
     ...
 }

 @Entity
 public class Employee {
     ...
     @Id
     Integer getEmpId() { ... }
     @ManyToOne
     @JoinColumn(name = "dept_id")
     public Department getDepartment() { ... }
     ...
 }

Example 2:

 @Entity
 public class Department {
     ...
     @OneToMany(mappedBy = "department")
     @MapKey(name = "name")
     public Map getEmployees() {... }
     ...
 }

 @Entity
 public class Employee {
     @Id
     public Integer getEmpId() { ... }
     ...
     @ManyToOne
     @JoinColumn(name = "dept_id")
     public Department getDepartment() { ... }
     ...
 }

Since:

Jakarta Persistence (JPA) 1.0