= 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-json-h2]]
=== JSON mapping changes on H2

On H2 1.4.200+, the type code `SqlTypes.JSON` now by default refers to the DDL type `json`, whereas before it was using `clob`.
Due to this change, schema validation errors could occur on existing databases.

The migration to `json` requires a migration expression like `cast(old as json)`.
Note that this change in behavior is backwards compatible and you do not need to change your schema,
unless you are running into schema validation errors and want to fix them.

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

This change was done because the native `json` type is 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

`hibernate.timezone.default_storage` now defaults to `DEFAULT`, meaning:

* if the database/dialect supports it, time zones of date/time values are stored by using the `timestamp with time zone` SQL column type;
* otherwise, time zones of date/time values are not stored, and date/time values are normalized to UTC.

In Hibernate ORM 5, time zones were not stored, but normalized to the time zone set in `hibernate.jdbc.time_zone`, the JVM time zone by default.

This discrepancy might lead to incorrect date/time being loaded from the database
for properties of type `OffsetDateTime` and `ZonedDateTime`
if your application was migrated from Hibernate ORM 5 and
was setting `hibernate.jdbc.time_zone` to a non-UTC timezone.

To revert to Hibernate ORM 5's behavior, set the configuration property `hibernate.timezone.default_storage` to `NORMALIZE`.

[[byte-and-character-array-mapping-changes]]
== Byte[]/Character[] mapping changes

The mappings for the wrapper array types `Byte[]` and `Character[]` have changed.

Prior to Hibernate 6.2, a `Byte[]` in the domain model was always just blindly converted to a `byte[]`,
possibly running into a `NullPointerException` if the `Byte[]` contains a `null` array element.
Similarly, `Character[]` was blindly converted to `char[]`, potentially running into the same `NullPointerException` problem.

Since disallowing `null` elements defeats the purpose of choosing the wrapper array type in the first place,
the Hibernate team concluded that changing the mapping for these types is fine,
because there can not be any reasonable real world uses of `Byte[]` and `Character[]`.

Another motivation for fixing this is that array handling code currently has to special case the element types
`Byte` and `Character`, and that binding SQL arrays of these types is not possible for native queries.

Starting with Hibernate 6.2, `Byte[]` and `Character[]` will be treated like other arrays.
See the link:{docsBase}/6.1/migration-guide/migration-guide.html#basic-arraycollection-mapping[6.1 Migration guide] for
details about the default DDL mapping.

A possible migration could involve the following steps in a migration script:

* Execute `alter table tbl rename column array_col to array_col_old` to have the old format available
* Execute `alter table tbl add column array_col DATATYPE array` to add the column like the new mapping expects it to be
* Run the query `select t.primary_key, t.array_col_old from table t` to extract `byte[]` or `String`
* For every result, load the Hibernate entity by primary key and set the field value to transformed result `Byte[]` or `Character[]`
* Finally, drop the old column `alter table tbl drop column array_col_old`

Alternatively, to revert to pre-6.2 behavior, annotate your array property with `@JavaType(ByteArrayJavaType.class)`
or `@JavaType(CharacterArrayJavaType.class)` or simply change the domain model type to `byte[]` and `char[]` respectively.

[[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, just under a different package,
namely `org.hibernate.community.dialect` instead of `org.hibernate.dialect`.
Note that this also includes version specific dialects like `PostgreSQL81Dialect`, `MariaDB102Dialect` etc.

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` if `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.

[[query-path-comparison]]
=== Query Path comparison

As of 6.2, comparisons of paths are type checked early. This means that a comparison predicate in HQL or JPA Criteria
might fail to construct if the types of the left and right hand side are not compatible.

In general, two types T1 and T2 are considered compatible if

* T1 == T2
* T1 instanceof T2 or T2 instanceof T1
* T1 is temporal and T2 is temporal
* T1 or T2 is unknown
* T1 can be widened/coerced to T2, or the other way around

Widening/Coercion usually refers to e.g. widening an integer to a long, but can also mean
that a string constant can be interpreted as enum when comparing against an enum attribute.

Note that a comparison of a temporal attribute against a string literal worked before

```sql
from MyEntity e where e.temporalAttribute > '2020-01-01'
```

but has to be changed to the proper temporal literal now

```sql
from MyEntity e where e.temporalAttribute > date 2020-01-01
```