org.eclipse.persistence.annotations
Annotation Type ClassExtractor
@Target(value=TYPE)
@Retention(value=RUNTIME)
public @interface ClassExtractor
A ClassExtractor allows for a user defined class indicator in place of
providing a discriminator column. The class has the following restrictions:
- It must extend the org.eclipse.persistence.descriptors.ClassExtractor
class and implement the extractClassFromRow(Record, Session) method.
- That method must take a database row (a Record/Map) as an argument and
must return the class to use for that row.
This method will be used to decide which class to instantiate when reading
from the database. It is the application's responsibility to populate any
typing information in the database required to determine the class from the
row.
The ClassExtractor must only be set on the root of an entity class or
sub-hierarchy in which a different inheritance strategy is applied. The
ClassExtractor can only be used with the SINGLE_TABLE and JOINED inheritance
strategies.
If a ClassExtractor is used then a DiscriminatorColumn cannot be used. A
ClassExtractor also cannot be used on either the root or its subclasses.
In addition, for more complex configurations using a ClassExtractor and a
SINGLE_TABLE strategy, the descriptor's withAllSubclasses and onlyInstances
expressions should be set through the ClassExtractor's initialize method.
- See Also:
org.eclipse.persistence.descriptors.InheritancePolicy.setWithAllSubclassesExpression(Expression),
org.eclipse.persistence.descriptors.InheritancePolicy.setOnlyInstancesExpression(Expression)- Author:
- Guy Pelletier
- Since:
- EclipseLink 2.1
|
Required Element Summary |
java.lang.Class |
value
(Required) Defines the name of the class extractor that should be
applied to this entity's descriptor. |
value
public abstract java.lang.Class value
- (Required) Defines the name of the class extractor that should be
applied to this entity's descriptor.