Raible's Wiki: CreateDAO

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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|http://forum.java.sun.com/thread.jsp?forum=92&thread=425300&tstart=0&trange=15]). This object basically represents a database table. The ''other classes'' will be:

You will create an object and then some more classes to persist (save/retrieve/delete) that object from the database. In Java speak, this object is called a Plain Old Java Object (a.k.a. a [POJO|http://forum.java.sun.com/thread.jsp?forum=92&thread=425300&tstart=0&trange=15]). This object basically represents a database table. The ''other classes'' will be:

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* A [JUnit|http://www.junit.org] class to test our DAO is working

* A [JUnit|http://www.junit.org] class to test the DAO is working

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%%note __NOTE:__ If you're using MySQL and you want to use transactions (which you probably will) you have to use InnoDB tables. To do this, add the following to your mysql configuration file ({{/etc/my.cnf}} or {{c:\Windows\my.ini}}). The 2nd setting (for a UTF-8 character set) is needed for 4.1.7+.

{{{

[mysqld]

default-table-type=innodb

default-character-set=utf8

}}}

If you're using PostgreSQL and you get confusing errors about batch processing, try turning it off by adding {{<prop key="hibernate.jdbc.batch_size">0</prop>}} to your {{src/dao/**/hibernate/applicationContext-hibernate.xml}} file.

%%

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;:''You can also use [iBATIS|http://ibatis.com] as a persistence framework option. To install iBATIS in AppFuse, view the README.txt in {{extras/ibatis}}. If you're using iBATIS over Hibernate, I expect you have your reasons and are familiar with the framework. I also expect that you can figure out how to adapt this tutorial to work with iBATIS. ;-)''

;:''You can also use [iBATIS|http://ibatis.com] as a persistence framework option. To install iBATIS in AppFuse, view the README.txt in {{extras/ibatis}}. Then complete the [iBATIS version of this tutorial|CreateDAOiBATIS].''

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The first thing we need to do is create an object to persist. Let's create a simple "Person" object (in the {{src/dao/**/model}} directory) that has an id, a firstName and a lastName (as properties).

The first thing you need to do is create an object to persist. Create a simple "Person" object (in the {{src/dao/**/model}} directory) that has an id, a firstName and a lastName (as properties).

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This class should extend [BaseObject|http://raibledesigns.com/downloads/appfuse/api/org/appfuse/model/BaseObject.java.html], which has 3 abstract methods: (equals(), hashCode() and toString()) that you will need to implement in the Person class. The first two are required by Hibernate. The easiest way to do this is using [Commonclipse|http://commonclipse.sf.net]. More information on using this tool can be found on [Lee Grey's site|http://www.leegrey.com/hmm/2004/09/29/1096491256000.html]. Another Eclipse Plugin you can use is [Commons4E|http://commons4e.berlios.de/]. I haven't used it, so I can't comment on its functionality.

This class should extend [BaseObject|http://raibledesigns.com/downloads/appfuse/api/org/appfuse/model/BaseObject.java.html], which has 3 abstract methods: (equals(), hashCode() and toString()) that you will need to implement in the Person class. The first two are required by Hibernate. If you plan to put this object into the user's session, or expose it through a web service, you should implement {{java.io.Serializable}} as well.

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The easiest way to do this is using [Commonclipse|http://commonclipse.sf.net]. More information on using this tool can be found on [Lee Grey's site|http://www.leegrey.com/hmm/2004/09/29/1096491256000.html]. Another Eclipse Plugin you can use is [Commons4E|http://commons4e.berlios.de/]. I haven't used it, so I can't comment on its functionality.

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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.

Now that you have this POJO created, you 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.

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First of all, we add a [@hibernate.class|http://xdoclet.sourceforge.net/tags/hibernate-tags.html#@hibernate.class%20(0..1)] tag that tells Hibernate what table this object relates to:

First of all, add a [@hibernate.class|http://xdoclet.sourceforge.net/tags/hibernate-tags.html#@hibernate.class%20(0..1)] tag that tells Hibernate what table this object relates to:

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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.

You 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.

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Now we'll add additional [@hibernate.property|http://xdoclet.sourceforge.net/tags/hibernate-tags.html#@hibernate.property%20(0..1)] tags for our other columns (first_name, last_name):

Now you'll add additional [@hibernate.property|http://xdoclet.sourceforge.net/tags/hibernate-tags.html#@hibernate.property%20(0..1)] tags for the other columns (first_name, last_name):

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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|http://xdoclet.sourceforge.net/tags/hibernate-tags.html#@hibernate.property%20(0..1)] reference for other attributes you can specify for this tag.

In this example, the only reason for adding the ''column'' attribute is because the column name is different from the property name. If they're the same, you don't need to specify the ''column'' attribute. See the [@hibernate.property|http://xdoclet.sourceforge.net/tags/hibernate-tags.html#@hibernate.property%20(0..1)] reference for other attributes you can specify for this tag.

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Now we'll create a DaoTest to test that our DAO works. "Wait a minute," you say, "we haven't created a DAO!" You are correct. However, I've found that [Test-Driven Development|http://www.artima.com/intv/testdriven.html] breeds higher quality software. For years, I thought __write your test before your class__ was hogwash. It just seemed stupid. Then I tried it and I found that it works great. The only reason I do all this test-driven stuff now is because I've found it rapidly speeds up the process of software development.

Now you'll create a DaoTest to test that your DAO works. "Wait a minute," you say, "I haven't created a DAO!" You are correct. However, I've found that [Test-Driven Development|http://www.artima.com/intv/testdriven.html] breeds higher quality software. For years, I thought __write your test before your class__ was hogwash. It just seemed stupid. Then I tried it and I found that it works great. The only reason I do all this test-driven stuff now is because I've found it rapidly speeds up the process of software development.

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To start, create a {{PersonDaoTest.java}} class in the {{test/dao/**/dao}} directory. This class should extend [BaseDaoTestCase|http://raibledesigns.com/downloads/appfuse/api/org/appfuse/dao/BaseDaoTestCase.java.html], a subclass of Spring's [AbstractDependencyInjectionSpringContextTests|http://www.springframework.org/docs/api/org/springframework/test/AbstractDependencyInjectionSpringContextTests.html] which already exists in this package. This parent class is used to load [Spring's|http://www.springframework.org] ApplicationContext (since Spring binds the layers together), and for (optionally) 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 "rb" variable.

To start, create a {{PersonDaoTest.java}} class in the {{test/dao/**/dao}} directory. This class should extend [BaseDaoTestCase|http://raibledesigns.com/downloads/appfuse/api/org/appfuse/dao/BaseDaoTestCase.java.html], a subclass of Spring's [AbstractTransactionalDataSourceSpringContextTests|http://www.springframework.org/docs/api/org/springframework/test/AbstractTransactionalDataSourceSpringContextTests.html] which already exists in this package. This parent class is used to load [Spring's|http://www.springframework.org] ApplicationContext (since Spring binds the layers together), and for (optionally) 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 "rb" variable.

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;:%%(color: blue)''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.''%%

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The code you see above is what we need for a basic Spring integration test that initializes and destroys our PersonDao. Spring will use autowiring byType to call the ''setPersonDao()'' method and set the "personDao" bean as a dependency of this class.

The code you see above is what you need for a basic Spring integration test that initializes and configures an implementation of PersonDao. Spring will use autowiring byType to call the ''setPersonDao()'' method and set the "personDao" bean as a dependency of this class.

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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:

Now you need test that the CRUD (create, retrieve, update, delete) methods work in your DAO. To do this, create 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 the <junit> task in build.xml. Below are 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:

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;:%%(color: blue)''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|http://www.dbunit.org] is used to populate the 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:''%%

;:%%(color: blue)''In the testGetPerson method, you'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|http://www.dbunit.org] is used to populate the database with test data before the tests are run, you can simply add the new table/record to the metadata/sql/sample-data.xml file:''%%

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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 {{PersonDaoTest.java}} and define your property values inside it:

In the above example, you can see that person.set*(value) is being called to populate the Person object before saving it. This is easy in this example, but it could get quite cumbersome if you'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 {{PersonDaoTest.java}} and define your property values inside it:

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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.

At this point, the PersonDaoTest class won't compile yet because there is no PersonDao.class in your classpath, you need to create it. PersonDao.java is an interface, and PersonDaoHibernate.java is the Hibernate implementation of that interface.

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First off, create a PersonDao.java interface in the {{src/dao/**/dao}} directory and specify the basic CRUD methods for any implementation classes. ''I've eliminated the JavaDocs in the class below for display purposes.''

First off, create a PersonDao.java interface in the {{src/dao/**/dao}} directory and specify the basic CRUD methods for any implementation classes.

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Notice in the class above there are no exceptions on the method signatures. This is due to the power of [Spring|http://www.springframework.org] and how it wraps Exceptions with RuntimeExceptions. At this point, you should be able to compile all the source in {{src/dao}} and {{test/dao}} using __ant compile-dao__. However, if you try to run __ant test-dao -Dtestcase=PersonDao__, you will get an error: <span style="color: red">No bean named 'personDao' is defined</span>. This is an error message from Spring - indicating that we need to specify a bean named ''personDAO'' in {{applicationContext-hibernate.xml}}. Before we do that, we need to create the PersonDao implementation class.

Notice in the class above there are no exceptions on the method signatures. This is due to the power of [Spring|http://www.springframework.org] and how it wraps Exceptions with RuntimeExceptions. At this point, you should be able to compile all the source in {{src/dao}} and {{test/dao}} using __ant compile-dao__. However, if you try to run __ant test-dao -Dtestcase=PersonDao__, you will get an error: <span style="color: red">No bean named 'personDao' is defined</span>. This is an error message from Spring - indicating that you need to specify a bean named ''personDao'' in {{applicationContext-hibernate.xml}}. Before you do that, you need to create the PersonDao implementation class.

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Let's start by creating 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/dao/**/dao/hibernate}} and name it {{PersonDaoHibernate.java}}. It should extend [BaseDaoHibernate|http://raibledesigns.com/downloads/appfuse/api/org/appfuse/dao/BaseDAOHibernate.java.html] and implement PersonDao. ''Javadocs eliminated for brevity.''

Let's start by creating 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/dao/**/dao/hibernate}} and name it {{PersonDaoHibernate.java}}. It should extend [BaseDaoHibernate|http://raibledesigns.com/downloads/appfuse/api/org/appfuse/dao/hibernate/BaseDaoHibernate.java.html] and implement PersonDao. ''Javadocs eliminated for brevity.''

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throw new ObjectRetrievalFailureException(Person.class, id);

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Now, if you try to run __ant test-dao -Dtestcase=PersonDao__, you will get the same error. We need to configure Spring so it knows that PersonDaoHibernate is the implementation of PersonDao, and we also need to tell it about the Person object.

Now, if you try to run __ant test-dao -Dtestcase=PersonDao__, you will get the same error. We need to configure Spring so it knows that PersonDaoHibernate is the implementation of PersonDao, and you also need to tell it about the Person object.

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First, we need to tell Spring where the Hibernate mapping file is located. To do this, open {{src/dao/**/dao/hibernate/applicationContext-hibernate.xml}} and add {{"Person.hbm.xml"}} to the following code block.

First, you need to tell Spring where the Hibernate mapping file is located. To do this, open {{src/dao/**/dao/hibernate/applicationContext-hibernate.xml}} and add {{"Person.hbm.xml"}} to the following code block.

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Now we need to add some XML to this file to bind PersonDaoHibernate to PersonDao. To do this, add the following at the bottom of the file:

Now you need to add some XML to this file to bind PersonDaoHibernate to PersonDao. To do this, add the following at the bottom of the file:

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;:''You could also use __autowire="byName"__ to the <bean> and get rid of the "sessionFactory" property''. %%(color: blue)''Personally, I like having the dependencies of my objects documented (in XML).''%%

%%note __NOTE:__ Don't forget to correct the package name in the "class" attribute above if you specified a package other then org.appfuse when you created your project.%%

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