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5.2 Migration Guide

Table of Contents

This guide discusses migration from Hibernate ORM version 5.1 to version 5.2. For migration from earlier versions, see any other pertinent migration guides as well.

Background

Lots of work has been done for 6.0. One of the things 6.0 will need is a unified view of "type systems" including its own type system (Type, EntityPersister, CollectionPersister, etc) and JPA’s type system - which would mean unifying all of this in hibernate-core. Because of this and the other large changes slated for 6.0 we decided to release a 5.2 that showed a clear migration path to the changes in 6.0 but that still supported the older calls and expectations as much as possible.

Move to Java 8 for baseline

Hibernate 5.2 is built using Java 8 JDK and will require Java 8 JRE at runtime (we are investigating whether Java 9 will also work). This has a number of implications:

  • The hibernate-java8 module has been merged into hibernate-core and the Java 8 date/time types are now natively supported.

  • (todo) support for Java 8 Optional

  • (todo) support for other Java 8 features?

hibernate-entitymanager merged into hibernate-core

The hibernate-entitymanager module has also been merged into hibernate-core.

  • org.hibernate.SessionFactory now extends javax.persistence.EntityManagerFactory - temporarily it technically extends org.hibernate.jpa.HibernateEntityManagerFactory (which in turn extends javax.persistence.EntityManagerFactory) for backwards compatibility. HibernateEntityManagerFactory is deprecated.

  • org.hibernate.Session now extends javax.persistence.EntityManager - temporarily it technically extends org.hibernate.jpa.HibernateEntityManager (which in turn extends javax.persistence.EntityManager) for backwards compatibility. HibernateEntityManager is deprecated.

  • org.hibernate.Query (deprecated in favor of new org.hibernate.query.Query) now extends the JPA contracts javax.persistence.Query and javax.persistence.TypedQuery. ProcedureCall and StoredProcedureQuery as well.

  • org.hibernate.HibernateException now extends javax.persistence.PersistenceExceptions. Hibernate methods that "override" methods from their JPA counterparts now will also throw various JDK defined RuntimeExceptions (such as IllegalArgumentException, IllegalStateException, etc) as required by the JPA contract.

  • Persister/type access is now exposed through org.hibernate.Metamodel, which extends javax.persistence.metamodel.Metamodel. MetamodelImpl now manages all aspects of type system (see below).

  • Cache management has also been consolidated. org.hibernate.Cache now extends javax.persistence.Cache. CacheImpl now manages all aspects of cache regions (see below).

SessionFactory hierarchy cleanup

As part of merging hibernate-entitymanager into hibernate-core, I also wanted to take a moment to clean up some of these very old contracts, In conjunction with the move to Java 8 (default methods) and needing to implement JPA methods now in core I decided to implement more of a composition approach here, thus:

  • SessionFactoryImplementor used to have a number of methods pertaining to managing and accessing entity and collection persisters. Since we need to deal with JPA Metamodel contract anyway, I went ahead and moved all of that code into our new org.hibernate.metamodel.spi.MetamodelImplementor

  • SessionFactory and SessionFactoryImplementor each had a number of methods dealing with cache regions. Many of these methods have been deprecated since 5.0 and those will be removed. However, the functionality has been moved into the org.hibernate.Cache and org.hibernate.engine.spi.CacheImplementor contracts helping implement JPA’s javax.persistence.Cache role.

LimitHandler changes

In Hibernate 4.3, dialect implementations that did not support a limit offset would fetch all rows for a query and perform pagination in-memory. This solution, while functional, could have severe performance penalties. In 5.x, we preferred to favor performance optimizations which meant dialect implementations would throw an exception if a limit offset was specified but the dialect didn’t support such syntax.

As of 5.2.5.Final, we have introduced a new setting, hibernate.legacy_limit_handler, that is designed to allow users to enable the legacy 4.3 limit handler behavior. By default, this setting is false.

The specific dialects impacted by this change are restricted to the following.

  • Cache71Dialect

  • DB2390Dialect

  • InformixDialect

  • IngresDialect

  • RDMSOS2200Dialect

  • SQLServerDialect

  • TimesTenDialect

Note
 If a dialect that extends any in the above list but overrides the limit handler implementation, then those dialects remain unchanged, e.g. SQLServer2005Dialect.

Changes to schema management tooling

In 5.2.3, a new strategy for retrieving database tables was introduced that improves SchemaMigrator and SchemaValidator performance. This strategy executes a single java.sql.DatabaseMetaData#getTables(String, String, String, String[]) call to determine if each javax.persistence.Entity has a mapped database table. This strategy is the default, and uses the property setting hibernate.hbm2ddl.jdbc_metadata_extraction_strategy=grouped. This strategy may require hibernate.default_schema and/or hibernate.default_catalog to be provided.

To use the old strategy, which executes a java.sql.DatabaseMetaData#getTables(String, String, String, String[]) call for each javax.persistence.Entity, use the property setting hibernate.hbm2ddl.jdbc_metadata_extraction_strategy=individually.

Changes to how Clob values are processed using PostgreSQL81Dialect and its subclasses

Up to and including 5.2.8, Clob values and values for String, character[], and Character[] attributes that are annotated with @Lob were:

  • bound using Clob representations of the data (using PreparedStatement#setClob or CallableStatement#setClob);

  • retrieved as Clob values (using ResultSet#getClob or CallableStatement#getClob), which were converted to the appropriate Java type;

  • stored as PostgreSQL Large Objects; i.e., an OID for the value is stored in a text column, which refers to the actual data stored in a different (PostgreSQL-specific) table.

In 5.2.9 and 5.2.10, due to the fix for HHH-11477, Clob values and values for String, character[], and Character[] attributes that are annotated with @Lob were:

  • bound using String representations of the data (using PreparedStatement#setString or CallableStatement#setString);

  • retrieved as String values (using ResultSet#getString or CallableStatement#getString), which were converted to the appropriate Java type;

  • stored as variable-length character strings.

In 5.2.11, the fix for HHH-11477 was reverted (HHH-11614) to restore the 5.2.8 behavior.

As a consequence of these changes, data persisted using a version of Hibernate prior to 5.2.9 cannot be read using 5.2.9 or 5.2.10. Data persisted using Hibernate 5.2.9 or 5.2.10 can no longer be read using 5.2.11 or later.

A workaround that can be used in 5.2.9 and 5.2.10 that will restore the 5.2.8/5.2.11 behavior is to override the PostgreSQL dialect with:

public SqlTypeDescriptor getSqlTypeDescriptorOverride(int sqlCode) {
	if( sqlCode == Types.CLOB ){
		return ClobTypeDescriptor.CLOB_BINDING;
	}
	return super.getSqlTypeDescriptorOverride( sqlCode );
}

In addition, any Clob values and values for String, character[], Character[] attributes that are annotated with @Lob that were stored as variable-length character strings using 5.2.9 or 5.2.10 should be updated to store the values as PostgreSQL Large Objects before migrating to 5.2.11.

For example, if variable-length character strings were stored by 5.2.9 or 5.2.10 for the following mapping:

@Entity(name = "TestEntity")
@Table(name = "TEST_ENTITY")
public static class TestEntity {
	@Id
	@GeneratedValue
	private long id;

	@Lob
	String firstLobField;

	@Lob
	String secondLobField;

	@Lob
	Clob clobField;

	...
}

the variable-length character strings can be converted to PostgreSQL Large Objects by executing the following SQL:

update test_entity
set clobfield = lo_from_bytea( 0, cast( clobfield as bytea ) ),
    firstlobfield = lo_from_bytea( 0, cast( firstlobfield as bytea ) ),
    secondlobfield = lo_from_bytea( 0, cast( secondlobfield as bytea ) )

Misc

  • QueryCacheFactory contract changed

  • RegionFactory contract changes

  • todo : merge AvailableSettings together

  • org.hibernate.Transaction now extends JPA’s EntityTransaction and follows its pre- and post- assertions. e.g. begin() now throws an exception if transaction is already active.

  • (todo) following the above one, JPA also says that only PersistenceUnitTransactionType#JTA EntityManagers are allowed to access EntityTransactions. Need a strategy to handle this

  • Session#getFlushMode and Query#getFlushMode clash in terms of Hibernate (FlushMode) and JPA (FlushModeType) returns. #getFlushMode has been altered to return JPA’s FlushModeType. The Hibernate FlushMode is still available via #getHibernateFlushMode and #setHibernateFlushMode. Same for Session#getFlushMode and EntityManager#getFlushMode.

  • Setting hibernate.listeners.envers.autoRegister has been deprecated in favor of hibernate.envers.autoRegisterListeners.

  • AuditReader#getCurrentRevision has been deprecated in favor of org.hibernate.envers.RevisionListener.

  • As of 5.2.11, NoopOptimizer#generate will no longer skip negative values and 0 when it has a positive increment size; instead it will return the value obtained from the database.