How to get the entity mapping to database table binding metadata from Hibernate
Imagine having a tool that can automatically detect if you are using JPA and Hibernate properly. Hypersistence Optimizer is that tool!
Introduction
Lukas Eder has posted a very interesting question on Stack Overflow, asking about a way of getting access to the binding metadata between entity mappings and database tables.
While I have previously answered a similar question using this article, I realized that particular use case was much simpler since it only extracted the database metadata. In this article, you are going to see how easily you can get the bridge information between your JPA entities and the underlying database schema.
How to get the entity mapping to database table binding metadata from Hibernate@vlad_mihalcea https://t.co/w972BC1ty0 pic.twitter.com/QXrrnYdOuK
— Java (@java) April 23, 2019
Integrator
Hibernate is very flexible, so it defines many SPI (Service Provider Interfaces) that you can register to customize Hibernate internals. One of these interfaces is org.hibernate.integrator.spi.Integrator which is used by many technologies that integrate with Hibernate ORM, like Bean Validation, Envers or JACC Security Provider.
Using the Hibernate Integrator API, we can write our own component that captures the SessionFactory build-time metadata which, otherwise, is only available during bootstrap.
public class MetadataExtractorIntegrator
implements org.hibernate.integrator.spi.Integrator {
public static final MetadataExtractorIntegrator INSTANCE =
new MetadataExtractorIntegrator();
private Database database;
private Metadata metadata;
public Database getDatabase() {
return database;
}
public Metadata getMetadata() {
return metadata;
}
@Override
public void integrate(
Metadata metadata,
SessionFactoryImplementor sessionFactory,
SessionFactoryServiceRegistry serviceRegistry) {
this.database = metadata.getDatabase();
this.metadata = metadata;
}
@Override
public void disintegrate(
SessionFactoryImplementor sessionFactory,
SessionFactoryServiceRegistry serviceRegistry) {
}
}
The org.hibernate.boot.Metadata is what we are interested in since it contains the PersistentClass entity bindings.
To register MetadataExtractorIntegrator with Hibernate we have two possibilities based on the underlying bootstrap method.
Hibernate-native boostrap
If you’re using the Hibernate-native bootstrap, then you can register the Integrator with the BootstrapServiceRegistryBuilder as follows:
final BootstrapServiceRegistry bootstrapServiceRegistry =
new BootstrapServiceRegistryBuilder()
.enableAutoClose()
.applyIntegrator( MetadataExtractorIntegrator.INSTANCE )
.build();
final StandardServiceRegistry serviceRegistry =
new StandardServiceRegistryBuilder(bootstrapServiceRegistry)
.applySettings(properties())
.build();
JPA boostrap
If you’re using the JPA bootstrap, then you can register the Integrator with the BootstrapServiceRegistryBuilder as follows:
Map<String, Object> configuration = new HashMap<>();
Integrator integrator = integrator();
if (integrator != null) {
configuration.put("hibernate.integrator_provider",
(IntegratorProvider) () -> Collections.singletonList(
MetadataExtractorIntegrator.INSTANCE
)
);
}
EntityManagerFactory entityManagerFactory = new EntityManagerFactoryBuilderImpl(
new PersistenceUnitInfoDescriptor(persistenceUnitInfo),
configuration
)
.build();
That’s for when you want to bootstrap JPA without any persistence.xml configuration file.
If you want to use the persistence.xml configuration file, then you just need to provide a new property to declare the custom Integrator:
<property
name="hibernate.integrator_provider"
value="com.vladmihalcea.book.hpjp.hibernate.metadata.MetadataExtractorIntegrator"
/>
Domain Model
Assuming we have the following database tables mapped by our JPA application:
When running the following test case:
Metadata metadata = MetadataExtractorIntegrator.INSTANCE.getMetadata();
for ( PersistentClass persistentClass : metadata.getEntityBindings()) {
Table table = persistentClass.getTable();
LOGGER.info( "Entity: {} is mapped to table: {}",
persistentClass.getClassName(),
table.getName()
);
for(Iterator propertyIterator = persistentClass.getPropertyIterator();
propertyIterator.hasNext(); ) {
Property property = (Property) propertyIterator.next();
for(Iterator columnIterator = property.getColumnIterator();
columnIterator.hasNext(); ) {
Column column = (Column) columnIterator.next();
LOGGER.info( "Property: {} is mapped on table column: {} of type: {}",
property.getName(),
column.getName(),
column.getSqlType()
);
}
}
}
Hibernate generates the following output:
Entity: com.vladmihalcea.book.hpjp.util.providers.entity.BlogEntityProvider$Tag is mapped to table: tag Property: name is mapped on table column: name of type: varchar(255) Property: version is mapped on table column: version of type: integer Entity: com.vladmihalcea.book.hpjp.util.providers.entity.BlogEntityProvider$PostComment is mapped to table: post_comment Property: post is mapped on table column: post_id of type: bigint Property: review is mapped on table column: review of type: varchar(255) Property: version is mapped on table column: version of type: integer Entity: com.vladmihalcea.book.hpjp.util.providers.entity.BlogEntityProvider$Post is mapped to table: post Property: title is mapped on table column: title of type: varchar(255) Property: version is mapped on table column: version of type: integer Entity: com.vladmihalcea.book.hpjp.util.providers.entity.BlogEntityProvider$PostDetails is mapped to table: post_details Property: createdBy is mapped on table column: created_by of type: varchar(255) Property: createdOn is mapped on table column: created_on of type: datetime(6) Property: version is mapped on table column: version of type: integer
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Conclusion
Hibernate is highly customizable, and the Integrator SPI allows you to get access to the Hibernate Metadata which you can later inspect from your enterprise application.
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Hey Vlad, thank you very much for this blog, very helpful!
I have a little problem, I also need to retrieve the size of the varchars from the database, but for some reason they always return varchar(255), even if the size is smaller.
Do you have any clue on how I could achieve this??
Thanks!
You can query the
INFORMATION_SCHEMA.COLUMNStable to get the column length.As always, one more informative blog by you.
I tried it, but i am unable to get my code working
1. How to have more than one Integrators say MetadataExtractorIntegrator and EventListenerIntegrator.
2. How to configure incase of CustomLocalSessionFactoryBean (extends LocalSessionFactoryBean).
3. How to get/modify getCollectionMappings from configuration ?
4. Can i do it without overriding LocalSessionFactoryBean ?
My need is, based on the system property, i need to use different schema i,e. either schema or mock_schema, along with EventListenerIntegrator.
Here is my old code which i am trying to replace
@Override
protected void postProcessConfiguration(Configuration config) {
super.postProcessConfiguration(config);
}
private void replaceSchemaName(Table table) {
if (DatabasePlatform.DEFAULT_INVENTORY_SCHEMA.equals(table.getSchema())) {
table.setSchema(DatabasePlatform.INVENTORY_SCHEMA);
}
if (table.getName().startsWith(DatabasePlatform.DEFAULT_INVENTORY_SCHEMA + “.”)) {
table.setName(table.getName().replaceFirst(DatabasePlatform.DEFAULT_INVENTORY_SCHEMA, DatabasePlatform.INVENTORY_SCHEMA));
}
}
I am replacing Earlier
public class CustomHibernateSessionFactoryBean extends org.springframework.orm.hibernate3.annotation.AnnotationSessionFactoryBean {
with
public class CustomHibernateSessionFactoryBean extends org.springframework.orm.hibernate5.LocalSessionFactoryBean {
Your question is more about Spring than Hibernate so you are better off addressing it on the Spring forum.
I followed these steps but it looks like getSqlType() method always returns null. What can be the cause of this ?
You can find the test case in my High-Performance Java Persistence GitHub repository. Run my test in debug and compare with yours and see where they differ.