@Target(value={METHOD,FIELD}) @Retention(value=RUNTIME) public @interface MapKey
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.
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<Integer, Employee> 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<String, Employee> getEmployees() {... } ... } @Entity public class Employee { @Id public Integer getEmpId() { ... } ... @ManyToOne @JoinColumn(name="dept_id") public Department getDepartment() { ... } ... }
public abstract String name
Default: If the
name
element is not specified, the primary key of the
associated entity is used as the map key. If the
primary key is a composite primary key and is mapped
as IdClass
, an instance of the primary key
class is used as the key.
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