CreateDAO

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Sobre este 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.

You can also use iBATIS 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. ;-)

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] Configure Spring for the Person object and PersonDao
• [6] Run the DaoTest

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

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).

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'm using generator-class="increment" instead of generate-class="native" because I found some issues when using "native" on other databases. If you only plan on using MySQL, I recommend you use the "native" value.

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/dao/gen/**/hibernate directory. Here's the contents of Person.hbm.xml (so far):

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

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,
[schemaexport]    first_name VARCHAR(255),
[schemaexport]    last_name VARCHAR(255),
[schemaexport]    primary key (id)
[schemaexport] )

If you want to change the size of your columns, specify a length=size attribute in your @hibernate.property tag. If you want to make it a required field (NOT NULL), add not-null="true".

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

Now we'll create a DaoTest to test 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 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.

To start, create a PersonDaoTest.java class in the test/dao/**/dao directory. This class should extend BaseDaoTestCase, which already exists in this package. This parent class is used to load Spring's ApplicationContext (since Spring binds the layers together), and 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 "rb" 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 "ctx" object is a reference to Spring's ApplicationContext, which is initialized in a static block of the BaseDaoTestCase's 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>first_name</column>
    <column>last_name</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:

I tend to just hard-code test values into Java code - but the .properties file is an option.

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]

Notice in the class above there are no exceptions on the method signatures. This is due to the power of Spring 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: No bean named 'personDao' is defined. 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.

The ant task for running dao tests is called "test-dao". 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 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 and implement PersonDAO. Javadocs eliminated for brevity.

You'll notice here that we're doing nothing with the person parameter. This is just a placeholder for now - in the future you may want to filter on it's properties using Hibernate's Query Language (HQL) or using Criteria Queries.

An example using a Criteria Query:

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.

Configure Spring for the Person object and PersonDao [#5]

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.

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:

You could also use autowire="byName" to the <bean> and get rid of the "sessionFactory" property. Personally, I like having the dependencies of my objects documented (in XML).

Run the DaoTest [#6]

Yeah Baby, Yeah: BUILD SUCCESSFUL
Total time: 14 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).