Hibernate Orm Guide

Hibernate ORM is the de facto JPA implementation and offers you the full breath of an Object Relational Mapper. It works beautifully in Quarkus.

More often than not, you need one persistence unit with few configuration options. In Quarkus, you just need to:

  • add your settings in application.properties

  • annotate your entities with @Entity and friends

and we make some opinionated choices and educated guesses.

In your pom.xml, add the following dependencies:

  • the Hibernate ORM extension

  • your JDBC driver extension (quarkus-jdbc-postgresql, quarkus-jdbc-h2, quarkus-jdbc-mariadb, …​)

<dependencies>
    <!-- Hibernate ORM specific dependencies -->
    <dependency>
        <groupId>io.quarkus</groupId>
        <artifactId>quarkus-hibernate-orm</artifactId>
    </dependency>

    <!-- JDBC driver dependencies -->
    <dependency>
        <groupId>io.quarkus</groupId>
        <artifactId>quarkus-jdbc-postgresql</artifactId>
    </dependency>
</dependencies>

Annotate your persistent objects with @Entity, then add the relevant configuration properties in application.properties.

# configure your datasource
quarkus.datasource.url = jdbc:postgresql://localhost:5432/mydatabase
quarkus.datasource.driver = org.postgresql.Driver
quarkus.datasource.username = sarah
quarkus.datasource.password = connor

# drop and create the database at startup (use `update` to only update the schema)
quarkus.hibernate-orm.database.generation=drop-and-create

Note that these configuration properties are not the same ones as in your typical Hibernate ORM configuration file: they might differ in names, casing and don’t necessarily map 1:1 to each other. Please see below for the list of properties you can define.

An EntityManagerFactory will be created based on Quarkus datasource configuration as long as the Hibernate ORM extension is declared in your pom.xml. The dialect will be selected based on the JDBC driver.

You can then happily inject your EntityManager:

@ApplicationScoped
public class SantaClausService {
    @Inject
    EntityManager em; (1)

    @Transactional (2)
    public void createGift(String giftDescription) {
        Gift gift = new Gift();
        gift.setName(giftDescription);
        em.persist(gift);
    }
}

//and of course our entity
@Entity
public class Gift {
    private Long id;
    private String name;

    @Id @GeneratedValue(strategy = GenerationType.SEQUENCE, generator="giftSeq")
    public Long getId() {
        return id;
    }

    public void setId(Long id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }
}
  1. Inject your entity manager and have fun

  2. Mark your CDI bean method as @Transactional and the EntityManager will enlist and flush at commit.

To load some SQL statements when Hibernate ORM starts, add a import.sql in the root of your resources directory. It contains SQL DML statements (one by line). This is useful to have a data set ready for your tests or demos.

Properties to refine your Hibernate ORM configuration

There are optional properties useful to refine your EntityManagerFactory or guide guesses of Quarkus.

Dialect

quarkus.hibernate-orm.dialect

(e.g. org.hibernate.dialect.PostgreSQL95Dialect). Class name of the Hibernate ORM dialect. The complete list of bundled dialects is available in the Hibernate ORM JavaDoc.

Note

Not all the dialects are supported in GraalVM native executables: we currently provide driver extensions for PostgreSQL, MariaDB, Microsoft SQL Server and H2.

quarkus.hibernate-orm.dialect.storage-engine

(e.g. MyISAM or InnoDB). The storage engine to use when the dialect supports multiple storage engines.

Miscellaneous

quarkus.hibernate-orm.sql-load-script

(defaults to /import.sql) Name of the file containing the SQL statements to execute when Hibernate ORM starts. By default, simply add import.sql in the root of your resources directory and it will be picked up without having to set this property.

quarkus.hibernate-orm.batch-fetch-size

(defaults to -1 i.e. batch fetching is disabled). The size of the batches used when loading entities and collections.

Query

quarkus.hibernate-orm.query.query-plan-cache-max-size

The maximum size of the query plan cache.

quarkus.hibernate-orm.query.default-null-ordering

(defaults to none). Default precedence of null values in ORDER BY clauses. Options are none, first, last.

Database

quarkus.hibernate-orm.database.generation

(e.g. drop-and-create which is awesome in development mode). Select whether the database schema is generated or not. Options are none, create, drop-and-create, drop, update. The default is none.

quarkus.hibernate-orm.database.generation.halt-on-error

(defaults to false) Whether we should stop on the first error when applying the schema.

quarkus.hibernate-orm.database.default-catalog

The default catalog to use for the database objects.

quarkus.hibernate-orm.database.default-schema

The default schema to use for the database objects.

quarkus.hibernate-orm.database.charset

The charset of the database.

JDBC

quarkus.hibernate-orm.jdbc.timezone

The time zone pushed to the JDBC driver.

quarkus.hibernate-orm.jdbc.statement-fetch-size

How many rows are fetched at a time by the JDBC driver.

quarkus.hibernate-orm.jdbc.statement-batch-size

The number of updates (inserts, updates and deletes) that are sent by the JDBC driver at one time for execution.

Logging

quarkus.hibernate-orm.log.sql

(defaults to false). Show SQL logs and format them nicely.

quarkus.hibernate-orm.log.jdbc-warnings

(defaults to false). Whether JDBC warnings should be collected and logged.

Statistics

quarkus.hibernate-orm.statistics

(defaults to false) Whether statistics collection is enabled.

Note

Do not mix persistence.xml and quarkus.hibernate-orm.* properties in application.properties. Quarkus will raise an exception. Make up your mind on which approach you want to use.

Tip

Want to start a PostgreSQL server on the side with Docker?

docker run --ulimit memlock=-1:-1 -it --rm=true --memory-swappiness=0 --name postgres-quarkus-hibernate -e POSTGRES_USER=hibernate -e POSTGRES_PASSWORD=hibernate -e POSTGRES_DB=hibernate_db -p 5432:5432 postgres:10.5

Setting up and configuring Hibernate ORM with a persistence.xml

Alternatively, you can set a META-INF/persistence.xml to setup Hibernate ORM. This is useful for:

  • migrating existing code

  • when you have relatively complex settings requiring the full flexibility of the configuration

  • or if you like it the good old way

Note

If you have a persistence.xml, then you cannot use the quarkus.hibernate-orm.* properties and only persistence units defined in persistence.xml will be taken into account.

Your pom.xml dependencies as well as your Java code would be identical to the precedent example. The only difference is that you would specify your Hibernate ORM configuration in META-INF/persistence.xml:

<persistence xmlns="http://xmlns.jcp.org/xml/ns/persistence"
             xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
             xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/persistence
             http://xmlns.jcp.org/xml/ns/persistence/persistence_2_1.xsd"
             version="2.1">

    <persistence-unit name="CustomerPU" transaction-type="JTA">

        <description>My customer entities</description>

        <properties>
            <!-- Connection specific -->
            <property name="hibernate.dialect" value="org.hibernate.dialect.PostgreSQL95Dialect"/>

            <property name="hibernate.show_sql" value="true"/>
            <property name="hibernate.format_sql" value="true"/>

            <!--
                Optimistically create the tables;
                will cause background errors being logged if they already exist,
                but is practical to retain existing data across runs (or create as needed) -->
            <property name="javax.persistence.schema-generation.database.action" value="drop-and-create"/>

            <property name="javax.persistence.validation.mode" value="NONE"/>
        </properties>

    </persistence-unit>
</persistence>

Caching

Applications that frequently read the same entities can see their performance improved when the Hibernate ORM second-level cache is enabled.

Caching of entities

To enable second-level cache, mark the entities that you want cached with @javax.persistence.Cacheable:

@Entity
@Cacheable
public class Country {
    int dialInCode;
    // ...
}

When an entity is annotated with @Cacheable, all its field values are cached except for collections and relations to other entities.

This means the entity can be loaded without querying the database, but be careful as it implies the loaded entity might not reflect recent changes in the database.

Caching of collections and relations

Collections and relations need to be individually annotated to be cached; in this case the Hibernate specific @org.hibernate.annotations.Cache should be used, which requires also to specify the CacheConcurrencyStrategy:

package org.acme;

@Entity
@Cacheable
public class Country {
    // ...

    @OneToMany
    @Cache(CacheConcurrencyStrategy.READ_ONLY)
    List<City> cities;

    // ...
}

Caching of queries

Queries can also benefit from second-level caching. Cached query results can be returned immediately to the caller, avoiding to run the query on the database.

Be careful as this implies the results might not reflect recent changes.

To cache a query, mark it as cacheable on the Query instance:

Query query = ...
query.setHint("org.hibernate.cacheable", Boolean.TRUE);

If you have a NamedQuery then you can enable caching directly on its definition, which will usually be on an entity:

@Entity
@NamedQuery(name = "Fruits.findAll",
      query = "SELECT f FROM Fruit f ORDER BY f.name",
      hints = @QueryHint(name = "org.hibernate.cacheable", value = "true") )
public class Fruit {
   ...

That’s all! Caching technology is already integrated and enabled by default in Quarkus, so it’s enough to set which ones are safe to be cached.

Tuning of Cache Regions

Caches store the data in separate regions to isolate different portions of data; such regions are assigned a name, which is useful for configuring each region independently, or to monitor their statistics.

By default entities are cached in regions named after their fully qualified name, e.g. org.acme.Country.

Collections are cached in regions named after the fully qualified name of their owner entity and collection field name, separated by # character, e.g. org.acme.Country#cities.

All cached queries are by default kept in a single region dedicated to them called default-query-results-region.

All regions are bounded by size and time by default. The defaults are 10000 max entries, and 100 seconds as maximum idle time.

The size of each region can be customized via the quarkus.hibernate-orm.cache."<region_name>".memory.object-count property (Replace <region_name> with the actual region name).

To set the maximum idle time, provide the number of seconds via the quarkus.hibernate-orm.cache."<region_name>".expiration.max-idle property (Replace <region_name> with the actual region name).

Note

The double quotes are mandatory if your region name contains a dot. For instance:

quarkus.hibernate-orm.cache."org.acme.MyEntity".memory.object-count=1000

Limitations of Caching

The caching technology provided within Quarkus is currently quite rudimentary and limited.

The team thought it was better to have some caching capability to start with, than having nothing; you can expect better caching solution to be integrated in future releases, and any help and feedback in this area is very welcome.

Note

These caches are kept locally, so they are not invalidated or updated when changes are made to the persistent store by other applications.

Also, when running multiple copies of the same application (in a cluster, for example on Kubernetes/OpenShift), caches in separate copies of the application aren’t synchronized.

For these reasons, enabling caching is only suitable when certain assumptions can be made: we strongly recommend that only entities, collections and queries which never change are cached. Or at most, that when indeed such an entity is mutated and allowed to be read out of date (stale) this has no impact on the expectations of the application.

Following this advice guarantees applications get the best performance out of the second-level cache and yet avoid unexpected behaviour.

On top of immutable data, in certain contexts it might be acceptable to enable caching also on mutable data; this could be a necessary tradeoff on selected entities which are read frequently and for which some degree of staleness is acceptable; this " acceptable degree of staleness" can be tuned by setting eviction properties. This is however not recommended and should be done with extreme care, as it might produce unexpected and unforeseen effects on the data.

Rather than enabling caching on mutable data, ideally a better solution would be to use a clustered cache; however at this time Quarkus doesn’t provide any such implementation: feel free to get in touch and let this need known so that the team can take this into account.

Finally, the second-level cache can be disabled globally by setting hibernate.cache.use_second_level_cache to false; this is a setting that needs to be specified in the persistence.xml configuration file.

When second-level cache is disabled, all cache annotations are ignored and all queries are run ignoring caches; this is generally useful only to diagnose issues.