Classification) @Column(name="PHONE_NUM") deepest Map phoneNumbers; // ... The @MapKeyClass annotation can be used each time the most important category can't be deduced from the characteristic definition or the opposite mapping metadata. principles for Maps studying in regards to the a number of Map editions can get type of complicated provided that we will decide on anyone of 3 other forms of key varieties and 3 other kinds of price kinds. lower than are a few of the easy ideas of utilizing a Map. • Use the @MapKeyClass and targetEntity/targetClass parts of the connection and point assortment mappings to specify the periods while an untyped Map is used. • Use @MapKey with one-to-many or many-to-many dating Map that's keyed on an characteristic of the objective entity. • Use @MapKeyJoinColumn to override the subscribe to column of the entity key. • Use @Column to override the column storing the values of a component selection of easy varieties. • Use @MapKeyColumn to override the column storing the keys whilst keyed by way of a easy kind. • Use @MapKeyTemporal and @MapKeyEnumerated if you would like to additional qualify a easy key that could be a temporal or enumerated sort. • Use @AttributeOverride with a “key. ” or “value. ” prefix to override the column of an embeddable characteristic variety that may be a Map key or a price, respectively. desk 5-1 summarizes the various various facets of utilizing a Map. a hundred twenty five CHAPTER five ■ assortment MAPPING desk 5-1. precis of Mapping a Map Map Mapping Key Annotation price Annotation Map @ElementCollection @MapKeyColumn, @Column @MayKeyEnumerated, @MapKeyTemporal Map @ElementCollection @MapKeyColumn, @MayKeyEnumerated, @MapKeyTemporal Map @OneToMany, @ManyToMany @MapKey, Mapped by means of embeddable, @AttributeOverride, @AssociationOverride Mapped via entity @MapKeyColumn, @MayKeyEnumerated, @MapKeyTemporal Map @ElementCollection Mapped through embeddable, @Column @AttributeOverride Map @ElementCollection Mapped via embeddable, @AttributeOverride Mapped via embeddable, @AttributeOverride, @AssociationOverride Map @OneToMany, @ManyToMany Mapped by means of embeddable Mapped by way of entity Map @ElementCollection @MapKeyJoinColumn @Column Map @ElementCollection @MapKeyJoinColumn Mapped through embeddable, @AttributeOverride, @AssociationOverride Map @OneToMany, @ManyToMany @MapKeyJoinColumn Mapped by way of entity Duplicates once we have been discussing the Set interface we pointed out that it used to be perfect for fighting duplicates. What we intended was once that the Set datatype in Java doesn't enable them. We didn’t fairly say something 126 CHAPTER five ■ assortment MAPPING approximately duplicates within the database. in truth, the JPA specification doesn't say whatever approximately no matter if duplicates are allowed in collections, both within the database or in reminiscence, and generally they won't be supported. To get a sense for why aiding duplicates is tough, we have to visit the knowledge version and discover the various gory information.