= Hibernate 6.6.0.Final
Steve Ebersole
:awestruct-tags: ["Hibernate ORM", "Releases"]
:awestruct-layout: blog-post

:family: 6.6

:docs-url: https://docs.jboss.org/hibernate/orm/{family}
:javadocs-url: {docs-url}/javadocs
:migration-guide-url: {docs-url}/migration-guide/migration-guide.html
:intro-guide-url: {docs-url}/introduction/html_single/Hibernate_Introduction.html
:user-guide-url: {docs-url}/userguide/html_single/Hibernate_User_Guide.html
:ql-guide-url: {docs-url}/querylanguage/html_single/Hibernate_Query_Language.html

[[jakarta-data]]
== Jakarta Data

Hibernate 6.6 includes a complete implementation of the Jakarta Data 1.0 Release. As https://in.relation.to/2024/04/18/jakarta-data-1/[discussed here], our implementation:

- is based on compile-time code generation via an annotation processor, enabling unprecedented compile-time type safety, and
- is backed by Hibernate's `StatelessSession`, which has been enhanced especially to meet the needs of Jakarta Data.

This implementation already passes the Jakarta Data TCK, and we have a request for certification pending.

To make use of _Hibernate Data Repositories_, you'll need to depend on:

- our annotation processor, `hibernate-jpamodelgen`, and
- the Jakarta Data API, `jakarta.data-api.

For example, in Gradle:

[source,groovy]
----
implementation 'jakarta.data:jakarta.data-api:1.0.0'
implementation 'org.hibernate.orm:hibernate-core:6.6.0.Final'

annotationProcessor 'org.hibernate.orm:hibernate-jpamodelgen:6.6.0.Final'
----

For more information, please see the brand-new _Hibernate Data Repositories_ link:{docs-url}/repositories/html_single/Hibernate_Data_Repositories.html[documentation].


[[concrete-proxy]]
== @ConcreteProxy

6.6 also provides a new `@ConcreteProxy` annotation intended as an improved replacement for the deprecated `@Proxy` and `@LazyToOne` annotations.  Indicates that lazy references should be instantiated as the concrete type rather than the referenced type.

Consider the following model and data

[source,java]
----
@ConcreteProxy
@Entity
@Inheritance
class Payment { ... }

@Entity
class CardPayment extends Payment { ... }

session1.persist( new CardPayment( 1, ... ) );
----


As a simple example -

[source,java]
----
Payment loaded = session2.getReference( Payment.class, 1 );
----

Historically, Hibernate would create a lazy proxy for `loaded` of type `Payment`.  Attempts to cast that reference to `CardPayment` would result in a casting error.  `@ConcreteProxy` forces Hibernate to resolve the actual, concrete type and create a proxy of that type instead -

[source,java]
----
CardPayment loaded = (CardPayment) session2.getReference( Payment.class, 1 );
----

IMPORTANT: Hibernate will try a number of different ways to determine the concrete type, but may ultimately have to fall back to hitting the database which might have an effect on performance.

This feature works with both Hibernate's legacy proxy-based laziness and the newer bytecode enhancement laziness.


[[extended-array]]
== Extended Array support

ORM 6.6 adds support for mapping arrays of embeddable aggregate types e.g.

[source,java]
----
@Entity
class MyEntity {
	List<MyEmbeddable> embeddableAggregateList;
}

@Struct
@Embeddable
class MyEmbeddable { ... }

----

[[array-syntax-sugar]]
== Syntax sugar for array functions

Plenty of syntax sugar for array operations was added:


|===
|Function |Syntax sugar |

|`array(1, 2)`
|`[1, 2]`
|Shorthand bracket syntax for array construction

|`array_slice(array, 1, 2)`
|`array[1:2]`
|Shorthand bracket syntax for array slicing

|`array_length(array)`
|`length(array)`
|Overload length function with array_length semantics on array input

|`array_position(array, element)`
|`position(element in array)`
|Overload position function with array_position semantics on array input

|`array_to_string(array, ',', 'null')`
|`cast(array as String)`
|Support casting array to string

|`array_contains(array, element)`
|`array contains element` or `element in array`
|Contains predicate for containment check

|`array_includes(array, array)`
|`array includes subArray`
|Predicate to for subset checking

|`array_intersects(array, array(1, 2))`
|`array intersects [1, 2]`
|Overlaps predicate for overlaps check
|===

[[string-syntax-sugar]]
== Syntax sugar for string functions

The bracket syntax can now also be used for string typed expressions to select a single character by index,
or obtain a substring by start and end index.

`stringPath[2]` is syntax sugar for `substring(stringPath, 2, 1)` and returns a `Character`.
`stringPath[2:3]` is syntax sugar for `substring(stringPath, 2, 3-2+1)`,
where `3-2+1` is the expression to determine the desired string length.


[[embeddable-inheritance]]
== Embeddable Inheritance

Another new feature of this version is discriminator-based inheritance for `@Embeddable` types. An `@Embeddable` class
may be extended by other `@Embeddable` classes, in which case the `@Embedded` properties using that type will
rely on an additional discriminator column to store information about the composite value's subtype.

When retrieving the inherited embedded property, Hibernate will read the discriminator value and instantiate the
correct `@Embeddable` subtype with its corresponding properties.

For example, a mapping like this:
[source,java]
----
@Embeddable
@DiscriminatorValue( "parent" )
@DiscriminatorColumn( name = "embeddable_type" )
class ParentEmbeddable implements Serializable {
	private String parentProp;
	// ...
}

@Embeddable
@DiscriminatorValue( "child_one" )
class ChildOneEmbeddable extends ParentEmbeddable {
	private Integer childOneProp;
	// ...
}

@Entity
class TestEntity {
	@Embedded
	private ParentEmbeddable embeddable;
	// ...
}
----

Will result in the following table structure:
[source,sql]
----
create table TestEntity (
    -- ...
    embeddable_type varchar(31) not null,
    parentProp varchar(255),
    childOneProp integer,
    -- ...
)
----

You can choose to customize the discriminator column properties using the `@DiscriminatorColumn` annotation on the root embeddable type, and you can pick the discriminator values to use for each subtype with the `@DiscriminatorValue` annotation, just like with entities.

For more detailed information please refer to the link:{user-guide-url}#embeddable-inheritance[Embeddable inheritance] user guide chapter.

[[oracle-vector]]
== Oracle Vector support

Oracle engineers contributed the support for vector data types and functions to the `hibernate-vector` module
to use with Oracle database version 23.4 and newer.

For further information about vectors, consult the link:https://docs.oracle.com/en/database/oracle/oracle-database/23/vecse/overview-node.html[Oracle documentation].

[[one-to-many-mapped-by-any]]
== `@OneToMany(mappedBy)` support for `@Any`

So far, the target of `@OneToMany` had to be a `@ManyToOne`. To map a `@OneToMany` based on an any association,
it was necessary to spell out a custom `@SQLRestriction` and specify the join columns.

Targeting an `@Any` association is now supported and will default to the appropriate join columns,
as well as add a `@SQLRestriction` to the `@OneToMany` automatically.

[[apply-filter-to-load-by-key]]
== `@Filter` support for load by key

Filters can opt in to be applicable also to find by key operations
like `Session.find()`, lazy initialization and to-one association fetching,
by setting `@FilterDef(applyToLoadByKey = true)`.

If the target row of an association is filtered by such a load by key enabled filter,
Hibernate ORM will throw a `EntityFilterException` to prevent potential data loss
that can happen when flushing an entity that owns such an association.

Also, the `@TenantId` filter was changed to apply to load by key operations by default.