Type System Customizations

customizations.adoc

Type System Customization

Hibernate’s "type system" can be customized in a number of ways depending on the nature of the type (basic, entity, etc).

Note	Customization of the Hibernate type system is considered an integration activity, as opposed to an application activity. As of 6.0, all of Hibernate’s type system is considered "incubating"

JavaTypeDescriptorRegistry

A Java type in the type system is modeled as org.hibernate.type.descriptor.java.spi.JavaTypeDescriptor. Hibernate always deals with a JavaTypeDescriptor rather than simply a java.lang.Class because the descriptor gives Hibernate additional information about the Java type.

org.hibernate.type.descriptor.java.spi.JavaTypeDescriptorRegistry is a registry of JavaTypeDescriptor by name. Generally the name is simply the name of the described Java type. Descriptors can be added to the registry or overridden, although generally this would only happen for basic types.

SqlTypeDescriptorRegistry

A SQL type is modeled as org.hibernate.type.descriptor.sql.SqlTypeDescriptor. Again, the descriptor tells Hibernate additional information about the type.

org.hibernate.type.descriptor.sql.spi.SqlTypeDescriptorRegistry is a registry of SqlTypeDescriptor by an integer code. Generally this code maps to one of the java.sql.Types codes, however Hibernate supports "extended" codes.

MutabilityPlan

Yadda yadda yadda…​

Basic Type Customization

A basic type in Hibernate boils down to the mapping between a Java type and a SQL type via JDBC.

BasicJavaDescriptor

org.hibernate.type.descriptor.java.spi.BasicJavaDescriptor is a specialization of JavaTypeDescriptor that describes Java types that are basic values (as opposed to an entity or an embeddable). Hibernate requires that all basic types be represented by a real Java Class : no non-POJO representations (MAP) are supported for basic types. The values in the JavaTypeDescriptorRegistry for basic types are always keyed by the name of corresponding Java class.

BasicJavaDescriptor is further specialized into:

• org.hibernate.type.descriptor.java.spi.EnumJavaDescriptor

• org.hibernate.type.descriptor.java.spi.TemporalJavaDescriptor

• org.hibernate.type.descriptor.java.spi.Primitive

• org.hibernate.type.descriptor.java.spi.NumericJavaDescriptor

Generally the BasicJavaDescriptor for a particular Java type is resolved from the JavaTypeDescriptorRegistry. There area number of ways to influence picking which BasicJavaDescriptor is used:

1. Register a corresponding descriptor with the registry.

2. Specify a particular descriptor to use

3. Implicitly via SqlTypeDescriptor#getJdbcRecommendedJavaTypeMapping (custom SqlTypeDescriptor)

todo Examples…​

SqlTypeDescriptor

Determining the SqlTypeDescriptor to use for a basic mapping is determined in a number of ways:

1. Register a corresponding descriptor with the registry.

2. Specify a particular descriptor to use

3. Implicitly via BasicJavaDescriptor#getJdbcRecommendedSqlType (custom BasicJavaDescriptor)

todo Examples…​

Hibernate’s Legacy Type

UserType and BasicType.

Changes due to reading from JDBC by position rather than by name

CDI integration for resolving named type classes

todo Examples…​

BasicValueConverter

Yadda yadda yadda…​

todo Examples…​

@JavaType

Non-basic Type Customization

org.hibernate.metamodel.model.creation.spi.RuntimeModelDescriptorClassResolver

org.hibernate.metamodel.model.creation.spi.RuntimeModelDescriptorFactory

EntityTypeDescriptor

Yadda yadda yadda…​

MappedSuperclassTypeDescriptor

Yadda yadda yadda…​

EmbeddedTypeDescriptor

Yadda yadda yadda…​

PersistentCollectionDescriptor

org.hibernate.metamodel.model.domain.spi.PersistentCollectionDescriptor org.hibernate.collection.spi.CollectionSemantics

Support for collection types other than those from the Java Collection Framework