CreateDAO

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About this Tutorial

We will create an object and then some more classes to persist (save/retrieve/delete) that object from the database. In Java speak, we call the object a Plain Old Java Object (a.k.a. a POJO). This object basically represents a database table. The other classes will be:

• A Data Access Object (a.k.a. a DAO), an Interface and a Hibernate Implementation
• A JUnit class to test our DAO is working

AppFuse uses Hibernate for it's persistence layer. Hibernate is an Object/Relational (O/R) Framework that allows you to relate your Java Objects to database tables. It allows you to very easily perform CRUD (Create, Retrieve, Update, Delete) on your objects.

I will tell you how I do stuff in the Real World in text like this.

Let's get started on creating a new Object, DAO and Test in AppFuse's architecture.

Table of Contents

• [1] Create a new Object and add XDoclet tags
• [2] Create a new database table from the object using Ant
• [3] Create a new DaoTest to run JUnit tests on the DAO
• [4] Create a new DAO to perform CRUD on the object
• [5] Notify Hibernate that this object exists in ServiceLocator (for tests) and in hibernate.cfg.xml (for webapp)
• [6] Run the DaoTest

Create a new Object and add XDoclet tags [#1]

I usually open an existing object (i.e. User.java or Resume.java) and save it as a new file. Then I delete all the methods and properties. This gives me the basic JavaDoc header. I'm sure I could edit Eclipse templates to do this, but since I develop on 3 different machines, this is just easier.

In the code snippet above, we're extending BaseObject because it has the following useful methods: toString(), equals(), hashCode() - the latter two are required by Hibernate.

Now that we have this POJO created, we need to add XDoclet tags to generate the Hibernate mapping file. This mapping file is used by Hibernate to map objects → tables and properties (variables) → columns.

First of all, we add a @hibernate.class tag that tells Hibernate what table this object relates to:

We also have to add a primary key mapping or XDoclet will puke when generating the mapping file. Note that all @hibernate.* tags should be placed in the getters' Javadocs of your POJOs.

I try to remember to add the Person object to ServiceLocator.java and hibernate.cfg.xml at this point. This is covered in [step 5].

Create a new database table from the object using Ant [#2]

[schemaexport] create table person (
[schemaexport]    id BIGINT NOT NULL AUTO_INCREMENT,
[schemaexport]    primary key (id)
[schemaexport] )

If you want to look at the Person.hbm.xml file that Hibernate generates for you, look in the build/ejb/gen/**/persistence directory. Here's the contents of Person.hbm.xml (so far):

Now we'll add additional @hibernate.property tags for our other columns (firstName, lastName):

In this example, the only reason for adding the column attribute is because the column name is different from our property name. If they're the same, you don't need to specify the column attribute. See the @hibernate.property reference for other attributes you can specify for this tag.

Run "ant setup-db" again to get the additional columns added to your table.

[schemaexport] create table person (
[schemaexport]    id BIGINT NOT NULL AUTO_INCREMENT,
[schemaexport]    first_name VARCHAR(255),
[schemaexport]    last_name VARCHAR(255),
[schemaexport]    primary key (id)
[schemaexport] )

Create a new DaoTest to run JUnit tests on your DAO [#3]

To start, create a PersonDaoTest.java class in the test/ejb/**/persistence directory. This class should extend BaseDaoTestCase, which already exists in this package. This parent class is mainly used for automatically loading a .properties file (ResourceBundle) that has the same name as your *Test.class. In this example, if you put a PersonDaoTest.properties file in the same directory as PersonDaoTest.java, this file's properties will be available via an "rd" variable.

I usually copy (open → save as) an existing test (i.e. UserDaoTest.java) and find/replace [Uu]ser with [Pp]erson, or whatever the name of my object is.

The code you see above is what we need for a basic JUnit test that initializes and destroys our PersonDao. The "conn" object is initialized (and obtains a connection) in the BaseDaoTestCase class.

Now we need to actually test that the CRUD (create, retrieve, update, delete) methods work in our DAO. To do this we created methods that begin with "test" (all lower case). As long as these methods are public, have a void return type and take no arguments, they will be called by our <junit> task in our Ant build.xml file. Here's some simple tests for testing CRUD. An important thing to remember is that each method (also known as a test), should be autonomous. Add the following methods to your PersonDaoTest.java file:

In the testGetPerson method, we're creating a person and then calling a get. I usually enter a record in the database that I can always rely on. Since DBUnit is used to populate our database with test data before our tests are run, you can simply add the new table/record to the metadata/sql/sample-data.xml file:

<table name='person'>
    <column>id</column>
    <column>firstName</column>
    <column>lastName</column>
    <row>
      <value>1</value>
      <value>Matt</value>
      <value>Raible</value>
    </row>
</table>

This way, you can eliminate the "create new" functionality in the testGetPerson method. If you'd rather add this record directly into the database (via SQL or a GUI), you can rebuild your sample-data.xml file using "ant db-export" and then "cp db-export.xml metadata/sql/sample-data.xml".

In the above example, you can see that we're calling person.set*(value) to populate our object before saving it. This is easy in this example, but it could get quite cumbersome if we're persisting an object with 10 required fields (not-null="true"). This is why I created the ResourceBundle in the BaseDaoTestCase. Simply create a PersonDaoTest.properties file in the same directory as the PersonDaoTest.java file and define your property values inside it:

firstName=Matt
lastName=Raible

At this point, the PersonDaoTest class won't compile yet because there is no PersonDao.class in our classpath, we need to create it. PersonDAO.java is an interface, and PersonDAOHibernate.java is the Hibernate implementation of that interface. Let's go ahead and create those.

Create a new DAO to perform CRUD on the object [#4]

At this point, you should be able to compile all the source in src/ejb and test/ejb using "ant compile-ejb". However, if you try to run "ant test-ejb -Dtestcase=PersonDao", you will get an error: DAOException: no DAOHibernate class.

The ant task for running tests is called "test-module." If you pass in a testcase parameter (using -Dtestcase=name), it will look for **/*${testcase}* - allowing us to pass in Person, PersonDao, or PersonDaoTest - all of which will execute the PersonDaoTest class.

Let's squash that bug and create a PersonDaoHibernate class that implements the methods in PersonDao and uses Hibernate to get/save/delete the Person object. To do this, create a new class in src/ejb/**/persistence and name it PersonDAOHibernate.java. It should extend BaseDaoHibernate and implement PersonDAO.

Now, if you try to run "ant test-ejb -Dtestcase=PersonDao", you will get an error that no Persister was found for the Person object, which brings us to the final step.

Notify Hibernate that this object exists [#5]

The JUnit tests use the database.properties file to initialize a Hibernate database connection, whereas Tomcat uses JNDI. Therefore, we must edit a different file for Tomcat: web/WEB-INF/classes/hibernate.cfg.xml. Add a new line for the Person.hbm.xml file in the following XML fragment:

Run the DaoTest [#6]

Yeah Baby, Yeah: BUILD SUCCESSFUL
Total time: 26 seconds

Next Up: Part II: Creating new Managers - A HowTo for creating Business Delegates that talk to the database tier (DAOs) and the web tier (Struts Actions).