JPA, externalizing column, table or schema names? - spring

Question

I adapt Spring+Hibernate+Tomcat+Oracle application to distributed form and need to make schema names customizable in JPA annotations, something like with Spring EL:
#Entity
#Table(name = "LOSS", schema="${app.dataSchema}")
public class Loss { ... }
I look for support of placeholders in annotation like ${app.dataSchema} in above example. Or any other possibility...
Idea - to have application that can be deployed on another site without recompilation, where preserved DB relations/hierarchy, but some names are changed and can be configured by system properties, JNDI or deploy context descriptor.
One solution that I see - to create view in selected schema - to provide bridge between actual schema/table/column and application hard-coded names.
But I hope that JPA/Hibernate/Spring have some instruments for such configuration...

Answer 1

Use orm.xml. That is what JPA provides it for. Putting deployment info in annotations is a bad idea if you ever need to change deployment, so just having a different orm.xml file means you can easily achieve that. Note that you can set a default schema in the persistence-unit-defaults part of orm.xml too

Answer 2

Externalize Schema
By EntityManagerFactory
<bean id="domainEntityManagerFactory" class="org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean">
<property name="persistenceUnitName" value="pun"/>
<property name="dataSource" ref="domainDataSource"/>
<property name="jpaVendorAdapter">
<bean class="org.springframework.orm.jpa.vendor.HibernateJpaVendorAdapter">
<property name="generateDdl" value="false"/>
<property name="showSql" value="false"/>
<property name="databasePlatform" value="${hibernate.dialect}"/>
</bean>
</property>
<property name="jpaProperties">
<props>
<prop key="hibernate.hbm2ddl.auto">create-update</prop>
<prop key="hibernate.default_schema">${yourSchema}</prop>
</props>
</property>
</bean>
By orm.xml
...
<persistence-unit name="MySchemaPU" transaction-type="JTA">
<provider>
<mapping-file>META-INF/orm.xml</mapping-file>
...
orm.xml below:
<?xml version="1.0" encoding="UTF-8"?>
<entity-mappings xmlns="http://java.sun.com/xml/ns/persistence/orm"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://java.sun.com/xml/ns/persistence/orm http://java.sun.com/xml/ns/persistence/orm_1_0.xsd"
version="1.0">
<persistence-unit-metadata>
<persistence-unit-defaults>
<schema>myschema</schema>
</persistence-unit-defaults>
</persistence-unit-metadata>
</entity-mappings>
By persistence.xml
<persistence-unit name="myPersistenceUnit" transaction-type="RESOURCE_LOCAL">
<provider>org.hibernate.ejb.HibernatePersistence</provider>
<jta-data-source>myDatasource</jta-data-source>
<properties>
.....
<property name="hibernate.default_schema" value="MYSCHEMA"/>
</properties>
</persistence-unit>
For Columns and Tables the deployment must be changed. You cannot replace placeholders at runtime in compiled classes.

Answer 3

Hibernate has org.hibernate.cfg.Configuration which is a point where packages are scanned and config files are read.
It uses org.hibernate.cfg.AnnotationBinder.bindClass(...) which read annotations on classes.
These classes (8 kLOC) and methods so long that I can't read them easy so I have no hope to subclass Configuration...
Ever if note that all classes and initialisation code binded to concrete classes without possibility to inject own, seems my task can't be solved easy with current Hibernate 4.x architecture.
I start looking for alternatives and ask about externaliztion of config in EBean mailing list and got answer:
public class MySchemaNamingConvention
extends com.avaje.ebean.config.UnderscoreNamingConvention {
#Override
protected TableName getTableNameFromAnnotation(Class<?> beanClass) {
final Table t = findTableAnnotation(beanClass);
if (t != null && !isEmpty(t.name())) {
String catalog = t.catalog();
String schema = t.schema();
////// CUSTOM schema processing code HERE.
////// CUSTOM schema processing code HERE.
////// CUSTOM schema processing code HERE.
return new TableName(quoteIdentifiers(catalog),
quoteIdentifiers(schema),
quoteIdentifiers(t.name()));
}
return null;
}
So damn easy that I say good bye to Hibernate!
UPDATE #Xstian. Before I migrate to Ebean I set default schema through hibernate.default_schema and extensively use views and synonyms to control which table will be accessible (Oracle):
grant select on ANOTHER_SCHEMA.TBL to MY_SCHEMA;
create or replace view MY_SCHEMA.TBL as select * from ANOTHER_SCHEMA.TBL;
create or replace synonym MY_SCHEMA.TBL for ANOTHER_SCHEMA.TBL;
During migration to views/synonyms I have issue only with DB constraints.
In case if you use Oracle - FK constraint on view not work unless you add constraint with disable novalidate keyword and same to referenced PK:
alter view MY_SCHEMA.XXX add constraint PK_XXX primary key(ID) disable novalidate;
alter table/view MY_SCHEMA.TBL add constraint FK_XXX foreign key (XXX_ID)
references MY_SCHEMA.XXX (ID) disable novalidate;
And synonyms don't allow FK constraint at all for Oracle!
Seems that Hibernate dictate of data layout and I think to switch to more flexible framework - Ebean, but I also evaluate sql2o and jOOQ.