Develop Reference

How to create Objects in database if does not exists with JPA?

I have a web application that I use JPA / Hibernate I want to know how to hibernate can generate the non-existent tables from entities.
the persistence file is as follows:
What I can add as property ?
<persistence xmlns="http://java.sun.com/xml/ns/persistence"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://java.sun.com/xml/ns/persistence
http://java.sun.com/xml/ns/persistence/persistence_1_0.xsd"
version="1.0">
<persistence-unit name="BankingApp">
<provider> org.hibernate.ejb.HibernatePersistence</provider>
<properties>
<property name="hibernate.connection.driver_class" value="oracle.jdbc.driver.OracleDriver"/>
<property name="hibernate.connection.url" value="jdbc:oracle:thin:#localhost:1521:XE"/>
<property name="hibernate.connection.username" value="user"/>
<property name="hibernate.connection.password" value="password"/>
<property name="hibernate.dialect" value="org.hibernate.dialect.Oracle10gDialect"/>
</properties>
</persistence-unit>
</persistence>

You can add this property
<property name="hibernate.hbm2ddl.auto" value="update"/>
The possible values for this property are:
validate: Only validates the schema
update: Update the schema
create: Create the schema, override previous data
create-drop: Create the schema and drop the schema at the end of the session

I found the solution, simply add the following property:
<property name="hibernate.hbm2ddl.auto" value="create"/>

Exclude one class from creating a Table in hibernate

I have a persistence unit like this:
<persistence-unit name="persistence Unit"
transaction-type="JTA">
<provider>org.hibernate.ejb.HibernatePersistence</provider>
<class>com.example.User</class>
<class>com.example.Team</class>
<exclude-unlisted-classes />
<properties>
<property name="hibernate.hbm2ddl.auto" value="update" />
<property name="hibernate.ejb.naming_strategy" value="org.hibernate.cfg.ImprovedNamingStrategy" />
<property name="hibernate.connection.charSet" value="UTF-8" />
<!-- JTA stuff -->
<property name="hibernate.transaction.manager_lookup_class"
value="org.hibernate.transaction.BTMTransactionManagerLookup" />
</properties>
</persistence-unit>
When the server loads first time, this creates table for User and Team, but i dont want to create a table for Team. Is it possible?
Some settings in the persistence table maybe?

If table Team isn't changed (INSERT or UPDATE) by your application in any way, you could remove write permissions for it in your database system.

Exclude Team class from your persistance.xml Remove following line.
<class>com.example.Team</class>

Hsqldb driver being randomly null

I am involved in writing a project which requires servlet->database connection. I am collaborating with another person who have designed a database using HyperSQL (hsqldb), I am now trying to merge my project with his by adding his code to mine.
Further to my issue though. When I copy the code, it works, usually. I have few methods that use the data from the database and compare them with user input.
When attempting to connect to the database, I would randomly succeed or fail, getting the following error ;
Unable to acquire a connection from driver [null]
I of course initialise a driver ;
Class.forName("org.hsqldb.jdbcDriver").newInstance();
Now, when running my method, it sometimes succeeds, and sometimes fails, here is the XML file for the DB;
<?xml version="1.0" encoding="UTF-8"?>
<!--
Creates both the HyperSQL databases using hibernate. No password or username is set.
-->
<persistence version="1.0" xmlns="http://java.sun.com/xml/ns/persistence" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://java.sun.com/xml/ns/persistence http://java.sun.com/xml/ns/persistence/persistence_1_0.xsd">
<persistence-unit name="monsters" transaction-type="RESOURCE_LOCAL">
<class>databaseManagement.Monster</class>
<exclude-unlisted-classes>true</exclude-unlisted-classes>
<properties>
<property name="hibernate.connection.driver_class" value="org.hsqldb.jdbcDriver"/>
<property name="hibernate.connection.username" value=""/>
<property name="hibernate.connection.password" value=""/>
<property name="hibernate.connection.url" value="jdbc:hsqldb:monsters"/>
<property name="hibernate.dialect" value="org.hibernate.dialect.HSQLDialect"/>
<property name="hibernate.hbm2ddl.auto" value="update"/>
</properties>
</persistence-unit>
<persistence-unit name="users" transaction-type="RESOURCE_LOCAL">
<class>databaseManagement.User</class>
<exclude-unlisted-classes>true</exclude-unlisted-classes>
<properties>
<property name="hibernate.connection.driver_class" value="org.hsqldb.jdbcDriver"/>
<property name="hibernate.connection.username" value=""/>
<property name="hibernate.connection.password" value=""/>
<property name="hibernate.connection.url" value="jdbc:hsqldb:users"/>
<property name="hibernate.dialect" value="org.hibernate.dialect.HSQLDialect"/>
<property name="hibernate.hbm2ddl.auto" value="update"/>
</properties>
</persistence-unit>
</persistence>

Probably an attempt is made to open the database in a readonly directory.
You need to specify a username for both persistence units. The default username is "SA".
The file path of the database that you specify in the URL is relative. It resolves to the execution directory. As you are developing a web application, you need to specify a directory that can be written to.
One way of doing this is by including a variable in the path, such as "jdbc:hsqldb:file:{$directorypath}/monsters" where the directorypath is the name of the web application's data dirctory, as specified in your web.xml file.

Environment specific Persistence xml in java standalone application

I have a standalone java application, which uses JPA for its persistence.
Right now I have a persistence.xml in META-INF.My application is currently in development.
My question is that if I move from development to the next envirnoment, say QA. I have to modify the persistence.xml and rebuild the jar. Is this the right way to go about it ?
If not,if I move the connection properties to a different file, where should this file be placed?
<persistence xmlns="http://java.sun.com/xml/ns/persistence"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://java.sun.com/xml/ns/persistence
http://java.sun.com/xml/ns/persistence/persistence_2_0.xsd" version="2.0">
<persistence-unit name="pu1" transaction-type="RESOURCE_LOCAL">
<provider>org.hibernate.ejb.HibernatePersistence</provider>
<class>ClassA</class>
<class>ClassB</class>
<class>ClassC</class>
<class>ClassD</class>
<properties>
<property name="hibernate.dialect" value="org.hibernate.dialect.Oracle9Dialect" />
<property name="hibernate.connection.driver_class" value="oracle.jdbc.OracleDriver" />
<property name="hibernate.show_sql" value="true" />
<property name="hibernate.connection.username" value="username" />
<property name="hibernate.connection.password" value="password" />
<property name="hibernate.connection.url"
value="url" />
<property name="hibernate.max_fetch_depth" value="3" />
<property name="hibernate.archive.autodetection" value="class" />
</properties>
</persistence-unit>
</persistence>
Thanks in advance !

That's a good question. Normally, you put all these environment settings in an external file, say application.properties, and pass the location to it to the JVM when you start your application (e.g. -Dconfig.location=/conf/)
Then you should find a way to get the externalized properties into your EntityManagerFactory. You can't do that in persistence.xml, you can only hard-code things there. But you can do it when creating the entity manager factory by passing vendor properties.
If using a framework like spring, for example, this is easier to do, as spring provides a factory bean for the entity manager. Otherwise you should handle it yourself. Here's the relevant bit from spring:
provider.createEntityManagerFactory(persistenceUnitInfo, getJpaPropertyMap())

Hibernate/JPA: Mapping entities to different databases

I have an application which manages 3 databases. I use hibernate with JPA on seam framework.
So I have a persitence.xml file with three persitence-unit like this (I remove properties for db2 and db3):
<persistence-unit name="db1" transaction-type="JTA" >
<provider>org.hibernate.ejb.HibernatePersistence</provider>
<jta-data-source>db1source</jta-data-source>
<properties>
<property name="hibernate.dialect"
value="org.hibernate.dialect.Oracle10gDialect" />
<property name="hibernate.connection.driver_class"
value="oracle.jdbc.driver.OracleDriver" />
<property name="hibernate.hbm2ddl.auto" value="validate" />
<property name="hibernate.show_sql" value="false" />
<property name="hibernate.format_sql" value="true" />
<property name="hibernate.default_schema" value="SI_TEC" />
<property name="hibernate.validator.apply_to_ddl" value="false" />
<property name="hibernate.transaction.manager_lookup_class"
value="org.hibernate.transaction.WeblogicTransactionManagerLookup" />
</properties>
</persistence-unit>
<persistence-unit name="db2" transaction-type="JTA">
<provider>org.hibernate.ejb.HibernatePersistence</provider>
<jta-data-source>d2source</jta-data-source>
</persistence-unit>
<persistence-unit name="db3" transaction-type="JTA">
<provider>org.hibernate.ejb.HibernatePersistence</provider>
<jta-data-source>d3source</jta-data-source>
</persistence-unit>
In my seam components.xml file, I create 3 managed-persistence-context to map seam with my hibernate configuration.
Finally, I have several entities and my problem is here. I need to persist some entities in db2 and other in db3. So database schema are different and when I deploy my application, I get this error:
org.hibernate.HibernateException: Missing table: PORTAILPERMISSION
at org.hibernate.cfg.Configuration.validateSchema(Configuration.java:1113)
at org.hibernate.tool.hbm2ddl.SchemaValidator.validate(SchemaValidator.java:139)
at org.hibernate.impl.SessionFactoryImpl.<init>(SessionFactoryImpl.java:349)
at org.hibernate.cfg.Configuration.buildSessionFactory(Configuration.java:1327)
at org.hibernate.cfg.AnnotationConfiguration.buildSessionFactory(AnnotationConfiguration.java:867)
Truncated. see log file for complete stacktrace
Because, the table PORTAILPERMISSION doesn't exist in db2.
My question is:
How to specify in entity class what database (or persitence-unit) must be used to validate entity in startup ?
Thanks for your help.

You try to explicitly list classes (<class>..</class>) in each persistence unit. And use
<exclude-unlisted-classes>true</exclude-unlisted-classes>