Annotates a class which serves as a static metamodel for an entity, enabling
type-safe access to entity attribute names and related objects such as instances
of Sort
s for an attribute. A metamodel class contains one or more
public static
fields corresponding to persistent fields of the entity class.
The type of each of these fields must be either String
, Attribute
,
or a subinterface of Attribute
defined in this package.
Jakarta Data defines the following conventions for static metamodel classes:
- The metamodel class can be an interface or concrete class.
- The name of the static metamodel class should consist of underscore (
_
) followed by the entity class name. - Fields of type
String
should be named with all upper case. - Fields of type
Attribute
should be named in lower case or mixed case.
For example, for the following entity,
@Entity public class Person { @Id public long ssn; @Embedded public Name name; public int yearOfBirth; } @Embeddable public class Name { public String first; public String last; }
An application programmer may define a static metamodel as follows,
@StaticMetamodel(Person.class) public interface _Person { String SSN = "ssn"; String NAME = "name"; String NAME_FIRST = "name.first"; String NAME_LAST = "name.last"; String YEAROFBIRTH = "yearOfBirth"; SortableAttribute<Person> ssn = new SortableAttributeRecord<>(SSN); Attribute<Person> name = new AttributeRecord<>(NAME); TextAttribute<Person> name_first = new TextAttributeRecord<>(NAME_FIRST); TextAttribute<Person> name_last = new TextAttributeRecord<>(NAME_LAST); SortableAttribute<Person> yearOfBirth = new SortableAttributeRecord<>(YEAROFBIRTH); }
And use it to refer to entity attributes in a type-safe manner,
Order<Person> order = Order.by(_Person.yearOfBirth.desc(), _Person.name_last.asc(), _Person.name_first.asc(), _Person.ssn.asc());
Alternatively, an annotation processor might generate static metamodel classes
for entities at compile time. The generated classes must be annotated with the
@Generated
annotation. The fields may be
statically initialized, or they may be initialized by the provider during system
initialization. In the first case, the fields are declared final
and the
metamodel class can be an interface. In the second case, the fields are declared
non-final
and volatile
and the metamodel class must be a concrete
class.
In cases where multiple Jakarta Data providers provide repositories for the same entity type, no guarantees are made of the order in which the Jakarta Data providers attempt to initialize the fields of the static metamodel class for that entity.
-
Required Element Summary
-
Element Details
-
value
Class<?> valueAn entity class.- Returns:
- the entity class.
-