= 6.2 Migration Guide
:toc:
:toclevels: 4
:docsBase: https://docs.jboss.org/hibernate/orm
:versionDocBase: {docsBase}/6.2
:userGuideBase: {versionDocBase}/userguide/html_single/Hibernate_User_Guide.html
:javadocsBase: {versionDocBase}/javadocs
:fn-logical-1-1: footnote:[A "true" one-to-one mapping is one in which both sides use the same primary-key value and the foreign-key is defined on the primary-key column to the other primary-key column.  A "logical" one-to-one is really a many-to-one with a UNIQUE contraint on the key-side of the foreign-key.  See link:{docsBase}/6.2/userguide/html_single/Hibernate_User_Guide.html#associations for more information]


This guide discusses migration to Hibernate ORM version 6.2. For migration from
earlier versions, see any other pertinent migration guides as well.

* link:{docsBase}/6.1/migration-guide/migration-guide.html[6.1 Migration guide]
* link:{docsBase}/6.0/migration-guide/migration-guide.html[6.0 Migration guide]


[[ddl-changes]]
== DDL type changes

[[ddl-uuid-mariadv]]
=== UUID mapping changes on MariaDB

On MariaDB, the type code `SqlTypes.UUID` now by default refers to the DDL type `uuid`, whereas before it was using `binary(16)`.
Due to this change, schema validation errors could occur on existing databases.

The migration to `uuid` requires a migration expression like `cast(old as uuid)`.

To retain backwards compatibility, configure the setting `hibernate.type.preferred_uuid_jdbc_type` to `BINARY`.

[[ddl-uuid-sqlserver]]
=== UUID mapping changes on SQL Server

On SQL Server, the type code `SqlTypes.UUID` now by default refers to the DDL type `uniqueidentifier`, whereas before it was using `binary(16)`.
Due to this change, schema validation errors could occur on existing databases.

The migration to `uuid` requires a migration expression like `cast(old as uuid)`.

To retain backwards compatibility, configure the setting `hibernate.type.preferred_uuid_jdbc_type` to `BINARY`.

[[ddl-json-oracle]]
=== JSON mapping changes on Oracle

On Oracle 12.1+, the type code `SqlTypes.JSON` now by default refers to the DDL type `blob` and on 21+ to `json`, whereas before it was using `clob`.
Due to this change, schema validation errors could occur on existing databases.

The migration to `blob` and `json` requires a migration expression like `cast(old as blob)` and `cast(old as json)` respectively.

To get the old behavior, annotate the column with `@Column(definition = "clob")`.

This change was done because `blob` and `json` are way more efficient and because we don't expect wide usage of `SqlTypes.JSON` yet.

[[ddl-implicit-datatype-enum]]
=== Datatype for enums

Hibernate 6.1 changed the implicit SQL datatype for mapping enums from `TINYINT` to `SMALLINT` to account for
Java supporting up to 32K enum entries which would overflow a `TINYINT`.  However, almost no one is developing
enums with that many entries.  Starting in 6.2, the choice of implicit SQL datatype for storing enums is sensitive
to the number of entries defined on the enum class.  Enums with more than 128 entries are stored as `SMALLINT` implicitly,
otherwise `TINYINT` is used.

NOTE:: On MySQL, enums are now stored using the `ENUM` datatype by default


[[ddl-timezones]]
=== Timezone and offset storage

`OffsetDateTime` and `ZonedDateTime` now always map to `TIMESTAMP WITH TIME ZONE` by default


[[ddl-check]]
=== Check constraints for boolean and enum mappings
Check constraints now correctly generated for boolean and enum mappings


[[logical-1-1-unique]]
== UNIQUE constraint for optional one-to-one mappings

Previous versions of Hibernate did not create a UNIQUE constraint on the database for
logical{fn-logical-1-1} one-to-one associations marked as optional.  That is not correct
from a modeling perspective as the foreign-key should be constrained as unique.  Starting in
6.2, those UNIQUE constraints are now created.

If this causes problems for an application, creation of the UNIQUE constraint can be skipped
using `@jakarta.persistence.ForeignKey(NO_CONSTRAINT)`.

Often the association can also be remapped using `@ManyToOne` + `@UniqueConstraint` instead.

[[oracle-number]]
== Column type inference for `number(n,0)` in native SQL queries on Oracle

Since Hibernate 6.0, columns of type `number` with scale 0 on Oracle were interpreted as `boolean`, `tinyint`, `smallint`, `int`, or `bigint`,
depending on the precision.

Now, columns of type `number` with scale 0 are interpreted as `int` or `bigint` depending on the precision.

[[database-versions]]
== Removal of support for legacy database versions

This version introduces the concept of minimum supported database version for most of the database dialects that Hibernate supports. This implies that the legacy code for versions that are no longer supported by their vendors, has been removed from the hibernate-core module. It is, however, still available in the hibernate-community-dialects module.

The minimum supported dialect versions are as follows:

|===
|Dialect |Minimum supported version

|MySQL
|5.7

|SQL Server 2008
|10.0

|DB2
|10.5

|DB2i
|7.1

|DB2z
|12.1

|MariaDB
|10.3

|H2
|1.4.197

|Derby
|10.14.2

|Sybase
|16.0

|CockroachDB
|21.1

|PostgreSQL
|10.0

|Oracle
|11.2

|HSQLDB
|2.6.1
|===


[[cdi]]
== Changes to CDI handling

When CDI is available and configured, Hibernate can use the CDI `BeanManager` to resolve various
bean references.  JPA explicitly defines support for this for both attribute-converters and
entity-listeners.

Hibernate also has the ability to resolve some of its extension points using the CDI `BeanManager`.
Version 6.2 adds a new boolean `hibernate.cdi.extensions` setting to control this:

true:: indicates to use the CDI `BeanManager` to resolve these extensions
false:: (the default) indicates to not use the CDI `BeanManager` to resolve these extensions

The previous behavior was to always load the extensions from CDI if it was available.  However,
this can sometimes lead to timing issues with the `BeanManager` not being ready for use when we need
those extension beans.  Starting with 6.2, these extensions will only be resolved from the CDI
`BeanManager` is `hibernate.cdi.extensions` is set to true.


[[enhancement]]
== Change enhancement defaults and deprecation

The `enableLazyInitialization` and `enableDirtyTracking` enhancement tooling options in the ANT task, Maven Plugin and Gradle Plugin,
as well as the respective `hibernate.enhancer.enableLazyInitialization` and `hibernate.enhancer.enableDirtyTracking` configuration settings,
switched their default values to `true` and the settings are now deprecated for removal without replacement.
See link:https://hibernate.atlassian.net/browse/HHH-15641[HHH-15641] for details.

The global property `hibernate.bytecode.use_reflection_optimizer` switched the default value to `true`
and the setting is now deprecated for removal without replacement. See link:https://hibernate.atlassian.net/browse/HHH-15631[HHH-15631] for details.

// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
// API / internal
[[api-internal]]
== API / SPI / Internal distinction

Dating back to Hibernate 5.x, we have been cleaning up packages to make the distinction between contracts
which are considered an API, SPI and internal.  We've done some more work on that in 6.2 as well.

[[api-internal-cfg]]
=== org.hibernate.cfg package

The `org.hibernate.cfg` package has been especially egregious in mixing APIs and internals historically.  The only
true API contracts in this package include `org.hibernate.cfg.AvailableSettings` and `org.hibernate.cfg.Configuration`
which have been left in place.

Additionally, while it is considered an internal detail, `org.hibernate.cfg.Environment` has also been left in place
as many applications have historically used it rather than `org.hibernate.cfg.AvailableSettings`.

A number of contracts are considered deprecated and have been left in place.

The rest have been moved under the `org.hibernate.boot` package where they more properly belong.


[[api-internal-loader]]
=== org.hibernate.loader package

Most of the `org.hibernate.loader` package is really an SPI centered around `org.hibernate.loader.ast`
which supports loading entities and collections by various types of keys - primary-key, unique-key,
foreign-key and natural-key.  `org.hibernate.loader.ast` has already been previously well-defined
in terms of SPI / internal split.


// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
// SPI

[[spi]]
== Changes in integration contracts (SPIs)

SPI is a category of interfaces that we strive to maintain with more stability than internal APIs, but which might change from minor to minor
upgrades as the project needs a bit of flexibility.

These are not considered public API so should not affect end-user (application developer's) code but such changes might break integration
with other libraries which integrate with Hibernate ORM.

During the development of Hibernate ORM 6.2 the following SPIs have seen some modifications:

[[spi-lock]]
=== EntityPersister#lock

Changed from `EntityPersister#lock(Object, Object, Object, LockMode, SharedSessionContractImplementor)` to `EntityPersister#lock(Object, Object, Object, LockMode, EventSource)`.
This should be trivial to fix as `EventSource` and `SharedSessionContractImplementor` are both contracts of the `SessionImpl`; to help transition we recommend using
the methods `isEventSource` and `asEventSource`, available on the `SharedSessionContractImplementor`contract.

N.B. method `asEventSource` will throw an exception for non-compatible type; but because of previous restrictions all invocations to `lock` actually had to be compatible:
this is now made cleared with the signature change.

[[spi-multiLoad]]
=== EntityPersister#multiLoad

The same change was applieed to `multiLoad(Object[] ids, SharedSessionContractImplementor session, MultiIdLoadOptions loadOptions)`,
now migrated to `multiLoad(Object[] ids, EventSource session, MultiIdLoadOptions loadOptions)`

The same conversion can be safely applied.

[[spi-afterDeserialize]]
=== Executable#afterDeserialize

As in the previous two cases, the parameter now accepts `EventSource` instead of `SharedSessionContractImplementor`.

The same conversion can be safely applied.

[[spi-JdbcType]]
=== JdbcType#getJdbcRecommendedJavaTypeMapping()

The return type of `JdbcType#getJdbcRecommendedJavaTypeMapping()` was changed from `BasicJavaType` to `JavaType`.
Even though this is a source compatible change, it breaks binary backwards compatibility.
We decided that it is fine to do this though, as this is a new minor version.