EE 5.19

The Java EE Platform requires that a Java EE Product Provider provide a database 
in the operational environment (see Section EE.2.6, “Database”). The Java EE 
Product Provider must also provide a preconfigured, default data source for use by 
the application in accessing this database.
The Java EE Product Provider must make the default data source accessible to 
the application under the JNDI name java:comp/DefaultDataSource.
The Application Component Provider or Deployer may explicitly bind a 
DataSource resource reference to the default data source using the lookup element 
of the Resource annotation or the lookup-name element of the resource-ref
deployment descriptor element. For example,
@Resource(lookup="java:comp/DefaultDataSource")
DataSource myDS;
In the absence of such a binding, the mapping of the reference will default to 
the product's default data source.
For example, the following will map to a preconfigured data source for the 
product's default database:
@Resource
DataSource myDS;

<persistence version="2.1" 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://www.oracle.com/webfolder/technetwork/jsc/xml/ns/persistence/persistence_2_1.xsd">

   <persistence-unit name="default" transaction-type="JTA">
   </persistence-unit>

</persistence>

10:41:31,002 ERROR [org.jboss.msc.service.fail] (ServerService Thread Pool -- 50) MSC000001: Failed to start service jboss.persistenceunit."jpa-standard.war#default": org.jboss.msc.service.StartException in service jboss.persistenceunit."jpa-standard.war#default": org.hibernate.HibernateException: Connection cannot be null when 'hibernate.dialect' not set
	at org.jboss.as.jpa.service.PersistenceUnitServiceImpl$1.run(PersistenceUnitServiceImpl.java:134) [wildfly-jpa-8.0.0.Alpha4.jar:8.0.0.Alpha4]
	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145) [rt.jar:1.7.0_21]
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615) [rt.jar:1.7.0_21]
	at java.lang.Thread.run(Thread.java:722) [rt.jar:1.7.0_21]
	at org.jboss.threads.JBossThread.run(JBossThread.java:122) [jboss-threads-2.1.0.Final.jar:2.1.0.Final]
Caused by: org.hibernate.HibernateException: Connection cannot be null when 'hibernate.dialect' not set
	at org.hibernate.engine.jdbc.dialect.internal.DialectFactoryImpl.determineDialect(DialectFactoryImpl.java:98)
	at org.hibernate.engine.jdbc.dialect.internal.DialectFactoryImpl.buildDialect(DialectFactoryImpl.java:66)
	at org.hibernate.engine.jdbc.internal.JdbcServicesImpl.configure(JdbcServicesImpl.java:193)
	at org.hibernate.boot.registry.internal.StandardServiceRegistryImpl.configureService(StandardServiceRegistryImpl.java:88)
	at org.hibernate.service.internal.AbstractServiceRegistryImpl.initializeService(AbstractServiceRegistryImpl.java:159)
	at org.hibernate.service.internal.AbstractServiceRegistryImpl.getService(AbstractServiceRegistryImpl.java:131)
	at org.hibernate.cfg.Configuration.buildTypeRegistrations(Configuration.java:1844)
	at org.hibernate.cfg.Configuration.buildSessionFactory(Configuration.java:1802)
	at org.hibernate.jpa.boot.internal.EntityManagerFactoryBuilderImpl$4.perform(EntityManagerFactoryBuilderImpl.java:844)
	at org.hibernate.jpa.boot.internal.EntityManagerFactoryBuilderImpl$4.perform(EntityManagerFactoryBuilderImpl.java:836)
	at org.hibernate.boot.registry.classloading.internal.ClassLoaderServiceImpl.withTccl(ClassLoaderServiceImpl.java:368)
	at org.hibernate.jpa.boot.internal.EntityManagerFactoryBuilderImpl.build(EntityManagerFactoryBuilderImpl.java:835)
	at org.jboss.as.jpa.hibernate4.management.TwoPhaseBootstrapImpl.build(TwoPhaseBootstrapImpl.java:44)
	at org.jboss.as.jpa.service.PersistenceUnitServiceImpl$1.run(PersistenceUnitServiceImpl.java:115) [wildfly-jpa-8.0.0.Alpha4.jar:8.0.0.Alpha4]
	... 4 more

10:41:31,010 ERROR [org.jboss.as.controller.management-operation] (DeploymentScanner-threads - 1) JBAS014613: Operation ("full-replace-deployment") failed - address: ([]) - failure description: {"JBAS014671: Failed services" => {"jboss.persistenceunit.\"jpa-standard.war#default\"" => "org.jboss.msc.service.StartException in service jboss.persistenceunit.\"jpa-standard.war#default\": org.hibernate.HibernateException: Connection cannot be null when 'hibernate.dialect' not set
    Caused by: org.hibernate.HibernateException: Connection cannot be null when 'hibernate.dialect' not set"}}

   <persistence-unit name="default" transaction-type="JTA">
      <jta-data-source>java:comp/DefaultDataSource</jta-data-source>
      <exclude-unlisted-classes>false</exclude-unlisted-classes>
   </persistence-unit>

JBAS014775:    New missing/unsatisfied dependencies:
      service jboss.naming.context.java.module.jpa-standard.jpa-standard.DefaultDataSource (missing) dependents: [service jboss.persistenceunit."jpa-standard.war#default".__FIRST_PHASE__] 
      service jboss.persistenceunit."jpa-standard.war#default".__FIRST_PHASE__ (missing) dependents: [service jboss.deployment.unit."jpa-standard.war".POST_MODULE]