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“Hibernate – A Developers Notebook” – migrating to Hibernate 3.0, Chapter 2
2 Comments · Posted by Administrator in Java
This is chapter 2 of rewriting the examples of O'Reillys book "Hibernate - A Developers Notebook" for using Hibernate 3.0 instead of Hibernate 2.x . To get the context, read chapter 1.
The goal of chapter 2 is to write a hbm file for a single table, generating the corresponding java file and compile it.
A main difference when using Hibernate 3.0 is the ant task definition for hbm2java. It now looks like this:
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<taskdef name="hibernatetool"
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classname="org.hibernate.tool.ant.HibernateToolTask"
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classpathref="project.class.path"/>
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<target name="codegen" depends="prepare"
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description="Generate Java source from the O/R mapping files">
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<hibernatetool destdir="${source.root}">
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<configuration propertyFile="${source.root}/hibernate.properties">
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<fileset dir="${source.root}">
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<include name="**/*.hbm.xml"/>
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</fileset>
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</configuration>
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<hbm2java />
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</hibernatetool>
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</target>
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Also, the package-name of the schemaexport-task has changed:
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<taskdef name="schemaexport"
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classname="org.hibernate.tool.hbm2ddl.SchemaExportTask"
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classpathref="project.class.path"/>
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Another difference is the jdbc-url for HSQLDB 1.8. You have to insert "file" as in:
jdbc:hsqldb:file:${data.dir}/music
(in ant task "db") or
jdbc:hsqldb:file:data/music
in hibernate.properties
I developed offline so I ran into the problem that the XML parser wants to download the mapping-dtd as advertised in the DOCTYPE-section of the hbm.xml file. I stripped off the http://www.hibernate.org part of the url, downloaded the dtd and placed it in the root-directory.
After using Ant 1.6, everything worked fine. (Otherwise I got:
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java.lang.NoSuchMethodError: org.apache.tools.ant.Project.createClassLoader
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(Lorg/apache/tools/ant/types/Path;)Lorg/apache/tools/ant/AntClassLoader;
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at org.hibernate.tool.ant.HibernateToolTask.execute(HibernateToolTask.java:113)
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)...
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The generated code reveals some differences:
- The type of the volume attribute is java.lang.Short, not short "as advertised". This is because of the xml-attribute "not-null" set to null. However if you ommit this xml-attribute, java.lang.Short is used again.
- There is no all-attributes-as-parameters-constructor.
- There is no equals and no hash-code implementation.
I have not yet any idea about why's that. Comments are welcome. Point 2 + 3 might be because different code templates.
2 comments
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<< “Hibernate – A Developers Notebook” – migrating to Hibernate 3.0, Chapter 3
chl · September 30, 2005 at 23:49
Thanks for posting about your experiences and tips. They are very helpful.
Kieran · January 22, 2006 at 21:50
Thanks for this. I just started Hibernate and have not been able to figure out what I have been doing wrong, but I will try it with 3.0 and see if I can get it to work.