javax.persistence
Annotation Type MapKeyClass

@Target(value={METHOD,FIELD})
@Retention(value=RUNTIME)
public @interface MapKeyClass

Is used to specify the type of the map key for associations of type java.util.Map. The map key can be a basic type, an embeddable class, or an entity. If the map is specified using Java generics, the MapKeyClass annotation and associated type need not be specified; otherwise they must be specified.

The MapKeyClass annotation is used in conjunction with ElementCollection or one of the collection-valued relationship annotations (OneToMany or ManyToMany). The MapKey annotation is not used when MapKeyClass is specified and vice versa.

    Example 1:

    @Entity
    public class Item {
       @Id int id;
       ...
       @ElementCollection(targetClass=String.class)
       @MapKeyClass(String.class)
       Map images;  // map from image name to image filename
       ...
    }

    Example 2:

    // MapKeyClass and target type of relationship can be defaulted

    @Entity
    public class Item {
       @Id int id;
       ...
       @ElementCollection
       Map<String, String> images; 
        ...
     }

     Example 3:

     @Entity
     public class Company {
        @Id int id;
        ...
        @OneToMany(targetEntity=com.example.VicePresident.class)
        @MapKeyClass(com.example.Division.class)
        Map organization;
     }

     Example 4:

     // MapKeyClass and target type of relationship are defaulted

     @Entity
     public class Company {
        @Id int id;
        ...
        @OneToMany
        Map<Division, VicePresident> organization;
     }

 

See Also:

ElementCollection, OneToMany, ManyToMany

Since:

Java Persistence 2.0

Required Element Summary

java.lang.Class

value (Required) The type of the map key.

Element Detail

value

public abstract java.lang.Class value

(Required) The type of the map key.