Hibernate 6.1 - What's new.pdf

What’s new in Hibernate 6.1?
by Christian Beikov

Who am I?
Christian Beikov
Long time Hibernate community contributor
Full time Hibernate developer at Red Hat since 2020
Founder of Blazebit and creator of Blaze-Persistence
Living in Vienna/AT and Bonn/DE
Like to play tennis and go running

Previously on “What’s next?”...
Subqueries in the from clause
Common table expressions
Lateral joins
Insert-or-Update a.k.a. Upsert
Table functions
SQL structs
SQL arrays

Subqueries in the from clause (6.1)
Common table expressions
Lateral joins (6.1)
Insert-or-Update a.k.a. Upsert
Table functions
SQL structs
SQL arrays (6.1)

Subqueries in the from clause (6.1)
Common table expressions (planned for 6.2)
Lateral joins (6.1)
Insert-or-Update a.k.a. Upsert (planned for 6.2)
Table functions
SQL structs
SQL arrays (6.1)

Demo time
https://github.com/beikov/presentation-hibernate-6

What’s next?
Common table expressions (planned for 6.2)
Insert-or-Update a.k.a. Upsert (planned for 6.2)
Table functions
SQL structs
SQL enums
JSON, XML and array functions
Joins in DML (update, delete)

Motivation for Hibernate 6.0
Performance improvements
● Read by name is slow in JDBC ResultSet
● JPA Criteria implementation required string building and parsing
Design improvements
● Query AST was Antlr2 based and hard to maintain/extend
● Dialect speciﬁc SQL translation was hard
● Runtime model was centered around Type
● Cleanup of deprecated APIs and SPIs
● More type safety and generics improvements

Read by name
Changing to position based ResultSetreading has big impact
● Throughput testing showed it is faster
● Many APIs and SPIs needed to adapt e.g. Type
● Allows omitting select aliases and produce smaller SQL
Took the opportunity to implement select item deduplication
● Occasionally requested enhancement
● Reduce amount of fetched data

Read by name
Hibernate 5.x
select
entity0_.id as id1_1_0_,
entity0_.name as name2_1_0_,
entity0_.id as onetoone3_1_0_
from
Entity entity0_
where
entity0_.id=?
Hibernate 6.0
select
e1_0.id,
e1_0.name
from
Entity e1_0
where
e1_0.id=?

JPA Criteria
5.x handles JPA Criteria on top of HQL
● CriteriaQueryis translated to HQL and then parsed
● But uses a special CriteriaLoaderwith custom fetch handling
6.0 introduces the semantic query model (SQM) as AST model
● SQM AST implements JPA Criteria API
● HQL is also parsed to SQM AST
● Further boost with hibernate.criteria.copy_treedisabled
● Smart handling of plain values parameter vs. literal

Query improvements
Semantic query model (SQM) as uniﬁed AST for JPA Criteria and HQL
Easier maintenance/extensibility thanks to update to ANTLR4
Functions received lots of new features
● FunctionReturnTypeResolverwith full AST access e.g. extract(second)
● FunctionArgumentTypeResolverinference through context e.g. coalesce(..)
● ArgumentsValidatorfor early type validation
● Can generate special SQM- and SQL-AST for e.g. emulations

Query improvements
Set operation support (from ANSI SQL-92)
select e from Entity e where e.type = 1
union
intersect
except
select e from Entity e where e.deleted

Query improvements
Set operation support in JPA Criteria
HibernateCriteriaBuilder cb = session.getCriteriaBuilder();
var q1 = cb.createQuery( Entity.class );
var q2 = cb.createQuery( Entity.class );
// Apply restrictions to q1 and q2 ...
TypedQuery<Entity> q = session.createQuery( cb.union( q1, q2 ) );

Query improvements
LIMIT, OFFSETand FETCHclause support (ANSI SQL 2003)
select p.name, p.score
from Player p
order by p.score desc
fetch first 3 rows with ties
name score
Thor 10
Hulk 10
Tony 7
Vision 7

Query improvements
LIMIT, OFFSETand FETCHclause support
HibernateCriteriaBuilder cb = session.getCriteriaBuilder();
JpaCriteriaQuery<Entity> q1 = cb.createQuery( Entity.class );
JpaRoot<Entity> root = q1.from( Entity.class );
q1.fetch( 3, FetchClauseType.ROWS_WITH_TIES );
TypedQuery<Entity> q = session.createQuery( q1 );

Query improvements
Support for OVERclause a.k.a. window functions (ANSI SQL 2003)
select
format(c.ts as ‘yyyy’’Q’’Q’),
sum(c.amount),
sum(c.amount) - lag(sum(c.amount))
over (order by format(c.ts as ‘yyyy’’Q’’Q’)) as delta
from Costs c
group by format(c.ts as ‘yyyy’’Q’’Q’)
period amount delta
2021Q4 100 NULL
2022Q1 120 20

Query improvements
Ordered set-aggregate functions i.e. LISTAGG(ANSI SQL 2016)
select pr.id, listagg(p.name, ‘, ’) within group (order by p.name)
from Project pr join pr.participants p
group by pr.id
order by pr.id
id participants
1 Bruce Banner, Natasha Romanoff, Tony Stark
.. ..

Query improvements
Summarization support i.e. ROLLUP(ANSI SQL-99)
select
s.state,
s.city,
sum(s.price * s.quantity)
from Sales s
group by rollup (s.state, s.city)
order by s.state, s.city nulls last
state city amount
CA SF 100
CA SJ 120
CA NULL 220

Query improvements
FILTER clause support (ANSI SQL 2016)
select
count(*) filter (where s.price * s.quantity < 10) as small_sales,
count(*) filter (where s.price * s.quantity >= 10) as big_sales
from Sales s
small_sales big_sales
10 20

Query improvements
ILIKEpredicate support
select e
from Entity e
where e.name ilike ‘%tony%’
Fallback to lower(e.name) like lower(‘%tony’)

Query improvements
Tuple syntax support with great emulation
Align expressions/predicates i.e. ... where my_function(value > 1) and ...
Temporal arithmetic support i.e. ts1 - ts2returns Duration
Duration extraction support with BY operator i.e. (ts1 - ts2) by hour
Duration literal support i.e. ts1 + 1 day
Support for DISTINCT FROMpredicate
etc.

Query improvements
Session#createSelectionQueryfor select only queries
● No executeUpdatemethod
Session#createMutationQueryfor mutation only queries
● No getResultList/getSingleResultetc. methods
Early validations and communication of intent

Dialect speciﬁc SQL
SQL-AST as intermediate representation of (modern) SQL as tree
5.x has a single HQL to SQL string translator with lots of if-branches per dialect-support
Dialects in 6.0 provide custom translators for handling emulations
SQL-AST enables sophisticated transformations/emulations efﬁciently
● Introduction of dummy FROMelements (Sybase)
● Emulate aggregate functions through window functions (MySQL, SQL Server, …)

Runtime model
Model in 5.x was centered around org.hibernate.type.Type
Created OO runtime model since switch to read by position required changes anyway
Moved logic to runtime model deﬁned through capabilities i.e. Fetchable
Removed multi-column basic mappings in favor of custom embeddable mappings
Split logic from BasicTypeinto JdbcType/JavaTypeand removed most implementations
Introduce BasicTypeReferencein StandardBasicTypesfor late resolving

Support for new SQL types through Dialect contribution
● JSONtype for storing any type as JSONB/JSON/CLOB/VARCHAR
● UUIDtype for java.util.UUID
● INTERVAL_SECONDtype for java.time.Duration
● INETtype for java.net.InetAddress
Replace @TypeDefwith type safe variants i.e. @JavaTypeRegistration
Replace @Typewith type safe variants i.e. @JavaType
Mapping improvements

Mapping improvements
CompositeUserTypebridges gap between custom types and embeddables
Embeddable mapper class for deﬁning mapping structure
Full control on construction and deconstruction of custom type
● Support for library types i.e. MonetaryAmount
● Repurpose existing types i.e. OffsetDateTime
Out of the box support for Java records in discussion

Other changes
Switch to Jakarta Persistence
Remove deprecated stuff i.e. legacy Criteria API
Add type variables to APIs/SPIs where possible
Dialectwas majorly updated
Renaming of JavaTypeDescriptorand SqlTypeDescriptor
See https://github.com/hibernate/hibernate-orm/blob/6.0/migration-guide.adoc

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