Configuring Middlgen to generate Hibernate files from MySQL

Following on from my earlier post , I'll now show you how to configure Middlegen and talk to your MySQL database. You will need to have ANT installed in order to run the ANT tasks that I customized to build the hbms and the Java objects.

I performed the Middlegen connection tasks using ANT version 1.7, MySQL version 5.0.24-community-nt and MySQL client version 5.1.11 and Middlegen 2.1

In your build.xml, set the following Middlegen property
<property name="Middlegen.home" value="${lib}/Middlegen"/>

The lib directory has 2 main jars, Middlegen-2.1.jar and Middlegen-hibernate-plugin-2.1.jar.

Both these jars are required to
(1) Run Middlegen and connect to MySQL
(2) Create Hbm mappings from the database and convert the hbm mappings into Java objects.

Firstly create a directory where you are going to store your generated files using the Middlegen-init ANT task.

<target name="Middlegen-init"
description="Initializes everything, creates directories, etc.">
<mkdir dir="${gen.java}" />
</target>


The next task is Middlegen which talks to the database but inorder to do so, it needs to know where the database is located, what driver file to use and what connection properties to use, so make the task know all this by defining the following properties in the build.xml

<property name="database.initialise.script" value="${main.resources}/database/ddl/FULL_DROP_INITIALISE.sql"/>
<property name="database.driver.file" value="${lib}/mysql-connector-java-3.0.14-production-bin.jar"/>
<property name="database.driver.classpath" value="${database.driver.file}"/>
<property name="database.driver" value="org.gjt.mm.mysql.Driver"/>
<property name="database.url" value="jdbc:mysql://localhost/testdatabase"/>
<property name="database.userid" value="root"/>
<property name="database.password" value="root"/>
<property name="database.schema" value="testdatabase"/>
<property name="database.catalog" value=""/>

You'll notice that the properties talk about a 'database.driver' which should be on the 'database.driver.classpath'.
This driver can be found within the mysql-connector-java-3.0.14-production-bin.jar so it should be downloaded and made available to the application.

Now, write the following ANT tasks in your build.xml

<!-- Middlegen related Tasks --->
<!-- =================================================================== -->
<!-- Run Middlegen -->
<!-- =================================================================== -->
<target
name="Middlegen"
description="Run Middlegen"
unless="Middlegen.skip"
depends="Middlegen-init"
>

<taskdef
name="Middlegen"
classname="Middlegen.MiddlegenTask"
classpathref="lib.class.path"
/>

<Middlegen
appname="${name}"
prefsdir="${Middlegen.prefs}"
gui="${gui}"
databaseurl="${database.url}"
initialContextFactory="${java.naming.factory.initial}"
providerURL="${java.naming.provider.url}"
datasourceJNDIName="${datasource.jndi.name}"
driver="${database.driver}"
username="${database.userid}"
password="${database.password}"
schema="${database.schema}"
catalog="${database.catalog}"
includeViews="false"
>

<!-- Sets up the hibernate plug-in for Middlegen -->

<hibernate
destination="${gen.java}"
package="${name}.persistence"
genXDocletTags="true"
javaTypeMapper="Middlegen.plugins.hibernate.HibernateJavaTypeMapper"
/>
</Middlegen>

</target>

<!-- =================================================================== -->
<!-- Run hbm2java -->
<!-- =================================================================== -->
<target name="hbm2java" description="Generate .hbm and then .java from .hbm files.">
<taskdef
name="hbm2java"
classname="net.sf.hibernate.tool.hbm2java.Hbm2JavaTask"
classpathref="lib.class.path"
/>
<hbm2java output="${gen.java}">
<fileset dir="${gen.java}">
<include name="**/*.hbm.xml"/>
</fileset>
</hbm2java>
</target>
<!-- End of Middlegen related Tasks --->

To create the HBM mappings for ALL tables in your 'testdatabase' schema:
Run the 'Middlegen' task which will
(1) create a directory to store the generated files
(2) connect to your MySQL database based on the params supplied and generate the hbm mapping files.

You can customize the hbm files according to your requirements, now run the hbm2java mapper task on these files by invoking the target 'hbm2java'. The java files will be generated and stored in the same directory alongside their respective hbms.

Well, that's all there is to it.

Middlegen is a very useful tool as it takes away the pain of manually creating these files and helps you setup your Hibernate environment within a couple of hours.

For more info on the subject refer to the Middlegen homepage.

MiddleGen and Hibernate: Making life easy in the middle

If you have been working in the Hibernate or in the EJB space, chances are high that you have had to write intermediate files such as hbms, in the case of Hibernate, that bridge the gap between the database tables and the Java objects (read POJOs) that exist within the application and are responsible for transporting data around.

While writing the hbm files manually, is a good idea if you really want to learn about how they are structured and the different types of relationships that they can be define within the data model, it becomes a tedious task if your data architect is not sure of what he or she is doing and/or keeps changing the DDL regularly.

In an AGILE project scenario, where requirements are welcomed at late stages of the build process, having a tool that can generate the hbm files and the related Java files (which are essentially POJOs) can be a boon. This is where MiddleGen comes in.

While MiddleGen is basically (an open source) database driven tool for generating code from the database to the presentation layer (Struts), I found its confluence with Hibernate to be really useful. It took me basically half-an-hour to set up MiddleGen and configure the Ant Tasks that came with the sample set of examples (in the MiddleGen download), to connect to my MYSQL database and generate a set of hbm files and their corresponding Java counterparts. In my next post, I'll explain the sequence of steps that I followed in setting up MiddleGen to talk to my database and generating the hbms and the Java files.