115 lines
6.7 KiB
Plaintext
115 lines
6.7 KiB
Plaintext
= 5.2 Migration Guide
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:toc:
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This guide discusses migration from Hibernate ORM version 5.1 to version 5.2. For migration from
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earlier versions, see any other pertinent migration guides as well.
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== Background
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Lots of work has been done for 6.0. One of the things 6.0 will need is a unified view of "type systems"
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including its own type system (Type, EntityPersister, CollectionPersister, etc) and JPA's type system - which
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would mean unifying all of this in hibernate-core. Because of this and the other large changes slated for 6.0
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we decided to release a 5.2 that showed a clear migration path to the changes in 6.0 but that still supported the
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older calls and expectations as much as possible.
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== Move to Java 8 for baseline
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Hibernate 5.2 is built using Java 8 JDK and will require Java 8 JRE at runtime (we are investigating whether
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Java 9 will also work). This has a number of implications:
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* The hibernate-java8 module has been merged into hibernate-core and the Java 8 date/time types are now natively
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supported.
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* (todo) support for Java 8 Optional
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* (todo) support for other Java 8 features?
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== hibernate-entitymanager merged into hibernate-core
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The hibernate-entitymanager module has also been merged into hibernate-core.
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* `org.hibernate.SessionFactory` now extends `javax.persistence.EntityManagerFactory` - temporarily it
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technically extends `org.hibernate.jpa.HibernateEntityManagerFactory` (which in turn extends
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`javax.persistence.EntityManagerFactory`) for backwards compatibility. `HibernateEntityManagerFactory`
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is deprecated.
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* `org.hibernate.Session` now extends `javax.persistence.EntityManager` - temporarily it
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technically extends `org.hibernate.jpa.HibernateEntityManager` (which in turn extends
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`javax.persistence.EntityManager`) for backwards compatibility. `HibernateEntityManager` is deprecated.
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* `org.hibernate.Query` (deprecated in favor of new `org.hibernate.query.Query`) now extends the JPA contracts
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`javax.persistence.Query` and `javax.persistence.TypedQuery`. `ProcedureCall` and `StoredProcedureQuery` as well.
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* `org.hibernate.HibernateException` now extends `javax.persistence.PersistenceExceptions`. Hibernate methods
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that "override" methods from their JPA counterparts now will also throw various JDK defined RuntimeExceptions
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(such as `IllegalArgumentException`, `IllegalStateException`, etc) as required by the JPA contract.
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* Persister/type access is now exposed through `org.hibernate.Metamodel`, which extends
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`javax.persistence.metamodel.Metamodel`. MetamodelImpl now manages all aspects of type system (see below).
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* Cache management has also been consolidated. `org.hibernate.Cache` now extends `javax.persistence.Cache`. CacheImpl
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now manages all aspects of cache regions (see below).
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== SessionFactory hierarchy cleanup
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As part of merging hibernate-entitymanager into hibernate-core, I also wanted to take a moment to clean up
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some of these very old contracts, In conjunction with the move to Java 8 (default methods) and needing to
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implement JPA methods now in core I decided to implement more of a composition approach here, thus:
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* SessionFactoryImplementor used to have a number of methods pertaining to managing and accessing entity and collection persisters.
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Since we need to deal with JPA Metamodel contract anyway, I went ahead and moved all of that code into our new
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`org.hibernate.metamodel.spi.MetamodelImplementor`
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* SessionFactory and SessionFactoryImplementor each had a number of methods dealing with cache regions.
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Many of these methods have been deprecated since 5.0 and those will be removed. However, the functionality
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has been moved into the `org.hibernate.Cache` and `org.hibernate.engine.spi.CacheImplementor` contracts
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helping implement JPA's `javax.persistence.Cache` role.
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== LimitHandler changes
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In Hibernate 4.3, dialect implementations that did not support a limit offset would fetch all rows for a query and
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perform pagination in-memory. This solution, while functional, could have severe performance penalties. In 5.x,
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we preferred to favor performance optimizations which meant dialect implementations would throw an exception if a
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limit offset was specified but the dialect didn't support such syntax.
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As of 5.2.5.Final, we have introduced a new setting, `hibernate.legacy_limit_handler`, that is designed to allow
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users to enable the legacy 4.3 limit handler behavior. By default, this setting is _false_.
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The specific dialects impacted by this change are restricted to the following.
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* Cache71Dialect
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* DB2390Dialect
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* InformixDialect
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* IngresDialect
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* RDMSOS2200Dialect
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* SQLServerDialect
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* TimesTenDialect
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NOTE: If a dialect that extends any in the above list but overrides the limit handler implementation, then those
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dialects remain unchanged, e.g. SQLServer2005Dialect.
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== Changes to schema management tooling
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In 5.2.3, a new strategy for retrieving database tables was introduced that improves SchemaMigrator and SchemaValidator
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performance. This strategy executes a single `java.sql.DatabaseMetaData#getTables(String, String, String, String[])`
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call to determine if each `javax.persistence.Entity` has a mapped database table.
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This strategy is the default, and uses the property setting `hibernate.hbm2ddl.jdbc_metadata_extraction_strategy=grouped`.
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This strategy may require `hibernate.default_schema` and/or `hibernate.default_catalog` to be provided.
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To use the old strategy, which executes a `java.sql.DatabaseMetaData#getTables(String, String, String, String[])` call for
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each javax.persistence.Entity, use the property setting `hibernate.hbm2ddl.jdbc_metadata_extraction_strategy=individually`.
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== Misc
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* QueryCacheFactory contract changed
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* RegionFactory contract changes
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* todo : merge AvailableSettings together
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* org.hibernate.Transaction now extends JPA's EntityTransaction and follows its pre- and post- assertions.
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e.g. begin() now throws an exception if transaction is already active.
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* (todo) following the above one, JPA also says that only PersistenceUnitTransactionType#JTA EntityManagers
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are allowed to access EntityTransactions. Need a strategy to handle this
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* Session#getFlushMode and Query#getFlushMode clash in terms of Hibernate (FlushMode) and JPA (FlushModeType)
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returns. #getFlushMode has been altered to return JPA's FlushModeType. The Hibernate FlushMode
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is still available via #getHibernateFlushMode and #setHibernateFlushMode. Same for Session#getFlushMode
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and EntityManager#getFlushMode.
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* Setting `hibernate.listeners.envers.autoRegister` has been deprecated in favor of
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`hibernate.envers.autoRegisterListeners`.
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* AuditReader#getCurrentRevision has been deprecated in favor of `org.hibernate.envers.RevisionListener`.
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* 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.
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