Ok here we go again. Now I am struggling get Hibernate working with the persistence unit declaration.
The reason I am writing this is more a pointer to myself should I ever have to do this again. Oh, check out my project on github. It is an implementation of a repository pattern using hibernate. It is extendable if you download the source and implement other providers. It is defined for standalone instances, not the full Java 5 EE stack although I am pretty sure with a bit of tweeking it can be used in that instance.
First I was getting the dreaded "javax.persistence.PersistenceException: No Persistence provider for EntityManager named”. After a little testing I figured out that the properties file contained an inverted commas wrapped persistence unit name where it should not have been wrapped
datastore.database.persistanceunit = "PU1" -> wrong!
datastore.database.persistanceunit = PU1 -> resolved correctly.
Ok so yeah I am rusty but bare with me. After getting that right I started running into Unable to build EntityManagerFactory. Drilling down a bit further it came down to not having an initial context. So I went and manipulated the persistence.xml file to no avail. Then I started digging deeper and found a ClassNotDefined exception (doh!). Seems I had forgotten to include the Postgres driver jar file (this is one feature I really like in C#, if you reference an assembly that references another assembly you get a warning if you haven’t referenced the dependency. Although I can see how this falls through using an XML configuration when there is no type checking happening. So the driver is obviously being created using some sort of reflection. Note to the Hibernate and JPA developers – please provide more verbose or smarter messages. Perhaps I just need to wake up!
Ok well, now the persistence.xml looks like this:
<?xml version="1.0" encoding="UTF-8"?>
<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="CommunityPlatformPU" transaction-type="RESOURCE_LOCAL">
<provider>org.hibernate.ejb.HibernatePersistence</provider>
<properties>
<property name="hibernate.dialect" value="org.hibernate.dialect.PostgreSQLDialect"/>
<property name="hibernate.connection.username" value="xxx"/>
<property name="hibernate.connection.driver_class" value="org.postgresql.Driver"/>
<property name="hibernate.connection.password" value="xxx"/>
<property name="hibernate.connection.url" value="jdbc:postgresql://localhost:5432/database"/>
<property name="hibernate.cache.provider_class" value="org.hibernate.cache.NoCacheProvider"/>
<property name="hibernate.hbm2ddl.auto" value="update"/>
</properties>
</persistence-unit>
</persistence>
Right, new exception to deal with. For primary keys I prefer using UUIDs or GUIDs as they are always unique. Yes I know indexing issues blah blah blah speed related issues blah blah blah. I use it for a reason. When I transform the data into XML I want globally unique Ids so I can link via Ids. Now I usually got round this with the @PrePersist annotation (because the implementations only supported the integer values) but wanted to see if there had been any improvements since my last run in with JPA. Turns out there has been.
This is the way you use UUIDs as PrimaryKeys
@Id
@GeneratedValue(generator="system-uuid")
@GenericGenerator(name = "system-uuid", strategy = "uuid2")
@Type(type = "pg-uuid")
private UUID id;
public UUID getId() {
return id;
}
public void setId(UUID id) {
this.id = id;
}
Cool! Next …
This little rig didn’t seem to like the jdbc3 drivers so switching to the jdbc4 drivers seemed to resolve that.
So that is that! Finally my test is passing and I am able to go to bed 
Well almost. Next it is time to configure the caching for the database and the connection pooling. Seems most of the libraries are included in the hibernate distribution. So the final persistence.xml file looks like this:
<?xml version="1.0" encoding="UTF-8"?>
<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="CommunityPlatformPU" transaction-type="RESOURCE_LOCAL">
<provider>org.hibernate.ejb.HibernatePersistence</provider>
<properties>
<property name="hibernate.dialect" value="org.hibernate.dialect.PostgreSQLDialect"/>
<property name="hibernate.connection.username" value="dev"/>
<property name="hibernate.connection.driver_class" value="org.postgresql.Driver"/>
<property name="hibernate.connection.password" value="dev"/>
<property name="hibernate.connection.url" value="jdbc:postgresql://localhost:5432/communityplatform"/>
<property name="hibernate.hbm2ddl.auto" value="update"/>
<property name="hibernate.cache.provider_class" value="org.hibernate.cache.EhCacheProvider" />
<property name="hibernate.cache.use_second_level_cache" value="true" />
<property name="c3p0.min_size" value="5" />
<property name="c3p0.max_size" value="20" />
<property name="c3p0.timeout" value="300" />
<property name="c3p0.max_statements" value="50" />
<property name="c3p0.idle_test_period" value="3000" />
<property name="current_session_context_class" value="thread" />
</properties>
</persistence-unit>
</persistence>
Green light on the tests, creating the database structure and persisting the information. Cool, now it is definitely time for bed, big day tomorrow, Skye turns 6
References:
http://docs.jboss.org/hibernate/core/3.6/reference/en-US/html/mapping.html#d0e5294
http://docs.jboss.org/hibernate/core/3.3/reference/en/html/performance.html#performance-cache
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