JavaMuse

Unit-testing Hibernate with HsqlDB

The Motivation

I've used lots of methods to transform data between databases and object code. From hand-coded SQL to JDO to EJB. I've never found a method I liked particularly well. This distaste has become especially acute since adopting test-driven development (TDD) as a guiding philosophy.

Unit-testing should have as few barriers as possible. For relational databases those barriers range from external dependencies (is the database running?) to speed to keeping the relational schema synchronized with your object model. For these reasons it is vital to keep database access code away from the core object model and to test as much as possible without touching a real database.

This has often led me to one of two patterns. The first is externalizing all data access to domain objects and their relationships to separate classes or interfaces. These are typically data store objects that can retrieve, edit, delete and add domain entities. This is the easiest to mock-out for unit-testing, but tends to leave your domain model objects as data-only objects with little or no related behavior. Ideally access to child records would be directly from the parent object rather than handing the parent object to some third-party class to determine the children.

The other method has been to have the domain objects have access to an interface into the data-mapping layer a la Martin Fowler’s Data Mapper pattern. This has the advantage of pushing object relationships inside the domain model where the object-relational interface can be expressed once. Classes that use the domain model are unaware of the persistence mechanism because it is internalized into the domain model itself. This keeps your code focused on the business problem you are trying to solve and less about the object-relational mapping mechanism.

My current project involves crunching a number of baseball statistics and running simulations with the data. Since the data was already in a relational database it was a chance for me to explore the Hibernate object-relational mapping system. I have been very impressed with Hibernate, but I ran into the problem was trying to insert a layer of indirection while using Hibernate as my data mapper for unit-testing. The extra layer was so flimsy that it felt embarrassing to write it. The real deployed version was simply a pass-through to a Hibernate-specific implementation. Even worse, the mock versions had more complexity in them than the real "production" version simply because they didn't have some of the basic object storage and mapping that came with Hibernate.

I also had enough complex Hibernate query usage that I wanted to unit-test this significat portion of the application. However, testing against a ‘live’ database is a bad idea, because it almost invariably introduces a maintenance nightmare. In addition, since tests are best when they are independent from each other, using the same obvious primary keys in test fixture data means you have to create code to clean the database before each test case, which is a real problem when lots of relationships are involved

By using HSQLDB and Hibernate's powerful schema-generation tool I was able to unit-test the mapping layer of the application and find numerous bugs in my object queries I would not have found as easily by manual testing. With the techniques outlines below I was able unit-test my entire application during development with no compromises in test coverage.

Setting up HSQLDB

I used version 1.7.3.0 of HSQLDB. To use an in-memory version of the database you need to invoke the static loader for the org.hsqldb.jdbcDriver. Then when you get a JDBC connection you use JDBC url such as jdbc:hsqldb:mem:yourdb where 'yourdb' is the name of the in-memory database you want to use.

Since I'm using Hibernate (3.0 beta 4), I hardly ever need to touch real-live JDBC objects. Instead I can let Hibernate do the heavy lifting for me--including automatically creating the database schema from my Hibernate mapping files. Since Hibernate creates its own connection pool it will automatically load the HSQLDB JDBC driver based on the configuration code lives in a class called TestSchema. Below is the static initializer for the class.

Hibernate provides a number of different ways to configure the framework, including programmatic configuration. The code above sets up the connection pool. Note that the user name 'sa' is required to use HSQLDB's in-memory database. Also be sure to specify a blank as the password. To enable Hibernate's automatic schema generation set the hibernate.hbm2ddl.auto property to 'create-drop'.

Testing In Practice

My project is crunching a bunch of baseball statistics so I add the four classes that I'm mapping ( Player, PitchingStint, BattingStint and FieldingStint). Finally I create a Hibernate SessionFactory and insert it into the HibernateUtil class which simply provides a single access method for my entire application for Hibernate sessions. The code for the HibernateUtil is below:

Since all of my code (production code as well as unit-tests) get their Hibernate sessions from the HibernateUtil I can configure it in one place. For unit-tests the first bit of code to access the TestSchema class will invoke the static initializer which will setup Hibernate and inject the test SessionFactory into the HibernateUtil. For production code the SessionFactory will be initialized lazily using the standard hibernate.cfg.xml configuration mechanism.

So what does this look like in the unit-tests? Below is a snippet of a test that checks the the logic for determining what positions a player is eligible to play at for a fantasy baseball league:

One of the most important things in unit-testing is to keep your test-cases isolated. Since this method still involves a database, you need a way to clean your database prior to each test case. I have four tables in my schema so I wrote a reset() method on the TestSchema that removes all rows from the tables using JDBC. Note because HSQLDB knows about foreign keys, the order in which the tables are deleted is important. Here is the code:

When bulk deletes become finalized in Hibernate 3.0 we should able to remove this last bit of direct JDBC from our application. Until then we have to get a Connection and issue direct SQL to the database.

Be sure not to close your Connection, closing the Session is sufficient for resource cleanup. Out of habits developed from writing lots of hand-crafted JDBC code, the first version closed the JDBC Connection. Since I configured Hibernate to create a connection pool with only one Connection I completely torpedoed any tests after the first one.Be sure to watch out for this!

Since you can never be sure what state the database may be in when your test class is running (imagine running all of your test cases), you should include database cleanup in your setUp() methods like so:

Conclusion

Being able to test against a real-live RDBMS without all of the hassles of trying to run tests against your deployed database is essential, even when working with sophisticated O/R mappers like Hibernate. The example I showed here is not exclusive to Hibernate and could probably be made to work with JDO or TopLink, though Hibernate makes this kind of testing particularly easy since it has a built-in schema generation tool. With a setup like the one described above you don't ever have to leave the comfort of your IDE and still have extensive test coverage over your code.

posted @ 2007-03-13 14:05 满山红叶 阅读(417) | 评论 (0) | 编辑 收藏

HSQLDB文档

				jdbc:hsqldb:c:\db\test 
		

				jdbc:hsqldb:http://websrv
		

				jdbc:hsqldb:. 
		

				c1=DriverManager.getConnection("jdbc:hsqldb:.","sa",""); 
		

				c2=DriverManager.getConnection("jdbc:hsqldb:test","sa","");
		

				c3=DriverManager.getConnection("jdbc:hsqldb:http://dbserver","sa",""); 
		

				c4=DriverManager.getConnection("jdbc:hsqldb:hsql://dbserver","sa","");
		

posted @ 2007-03-13 14:01 满山红叶 阅读(334) | 评论 (0) | 编辑 收藏

vimtutor 乱码

posted @ 2007-02-28 19:06 满山红叶 阅读(251) | 评论 (0) | 编辑 收藏

ubuntu 6.10 edgy 安装与配置

posted @ 2007-02-17 14:34 满山红叶 阅读(707) | 评论 (16) | 编辑 收藏

Hello,World in Hibernate 入门

本文介绍如何用hibernate写一个hello world 程序，以及说明Hibernate下的对象的识别。
1、配置文件hibernate.cfg.xml：

<? xml version = ' 1.0 '  encoding = ' utf-8 ' ?>
<! DOCTYPE hibernate - configuration PUBLIC
         " -//Hibernate/Hibernate Configuration DTD 3.0//EN "
         " http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd " >

< hibernate - configuration >

     < session - factory >

         <!--  Database connection settings  -->
         < property name = " connection.driver_class " > com.mysql.jdbc.Driver </ property >
         < property name = " connection.url " > jdbc:mysql: // localhost:3306/eg</property>
         < property name = " connection.username " > root </ property >
         < property name = " connection.password " > 4864452 </ property >

         <!--  JDBC connection pool (use the built - in)  -->
         < property name = " connection.pool_size " > 1 </ property >

         <!--  SQL dialect  -->
         < property name = " dialect " > org.hibernate.dialect.MySQLInnoDBDialect </ property >

         <!--  Enable Hibernate ' s automatic session context management -->
         < property name = " current_session_context_class " > thread </ property >

         <!--  Disable the second - level cache   -->
         < property name = " cache.provider_class " > org.hibernate.cache.NoCacheProvider </ property >

         <!--  Echo all executed SQL to stdout  -->
         < property name = " show_sql " > true </ property >

         <!--  Drop and re - create the database schema on startup 
         < property name = " hbm2ddl.auto " > create </ property >
          -->
    
         < mapping resource = " eg/Message.hbm.xml " />
        
        
     </ session - factory >

</ hibernate - configuration >

2、源文件：

package  eg;

public   class  Message  {
     private  Long id;
     private  String text;
             
     private  Message nextMessage;

     public  Message()  {}
     public  Message(String text) {
         this .text = text;
    }
    
     public   void  setId(Long id)  {
         this .id  =  id; 
    }

     public   void  setText(String text)  {
         this .text  =  text; 
    }

     public   void  setNextMessage(Message nextMessage)  {
         this .nextMessage  =  nextMessage; 
    }
        public  Long getId()  {
         return  ( this .id); 
    }
        public  String getText()  {
         return  ( this .text); 
    }
        public  Message getNextMessage()  {
         return  ( this .nextMessage); 
    }  
}

3、配置文件：Messsage.hbm.xml

<? xml version = " 1.0 "  encoding = " utf-8 " ?>

<! DOCTYPE hibernate - mapping PUBLIC
     " -//Hibernate/Hibernate Mapping DTD 3.0//EN "  
     " http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd " >

< hibernate - mapping >
     < class
        name =" eg.Message "
        table = " MESSAGE "
     >

         < id
            name = " id "
            column = " MESSAGE_ID "
            type = " java.lang.Long "
         >
             < generator  class = " native " />
                         
         </ id >
         < property
            name = " text "
            type = " java.lang.String "
            update = " true "
            insert = " true "
            column = " MESSAGE_TEXT "
         />

         < many - to - one
            name = " nextMessage "
             class = " jmuse.eg.Message "
            cascade = " all "
            outer - join = " auto "
            update = " true "
            insert = " true "
            column = " NEXT_MESSAGE_ID "
         />

       </ class >

</ hibernate - mapping >

4、最后的包结构：

+ lib 
     antlr.jar 
     cglib.jar 
     asm.jar 
     asm - attrs.jars 
     commons - collections.jar 
     commons - logging.jar 
     hibernate3.jar 
     jta.jar 
     dom4j.jar 
     log4j.jar 
＋src 
     + eg
       Message.java
       Message.hbm.xml
       TestMessage.java
     hibernate.cfg.ml
     log4j.properties

5、测试：

 session.beginTransaction();
        Message m = new  Message( " hello,world " );
        session.save(m);
        session.getTransaction().commit();
        session.close();

 你会发现在数据库中有一条信息了，id=1
Hibernate的对象识别是通过对象的Id 来识别的：
如：

我们刚才在数据库中保存了一个Id为1的Message对象。
如果：
session.beginTraction();
Message m = new  Message();
m.setId( new  Long( 1 ));
m.setText( " This is another greeting " );
session.saveOrUpdate(m);
sesion.getTraction.commit();

posted @ 2007-02-10 17:42 满山红叶 阅读(559) | 评论 (0) | 编辑 收藏

对象的存储和关系型数据库

ORM 的原则是将一个类映射到一张表上，然而对象和关系型数据库之间有一点的差异。
对象和对象之间的关系有一对一，一对多，多对多。这三个关系的关系的存储是有差异的。
1、一对一：我们可以用两张表分别表示两个类。他们之间的关系我们可以用主关键字或者外关键字来表示。然而这里有一个粒度的问题(The problem of granularity )。关于粒度问题见第4点。
2、一对多：我们也可以用两张表来表示两个类。他们的关系我们可以用外键来关联。
3、多对多：我们可以用两张表来表示这两个类。用第三张表来表示他们之间的关系。
4、关于问题的粒度：
      如：一个用户和一个地址之间的关系。当然我们可以用一对一的方法来解决。
然而这样是否合理？也许最好的方法是在数据库中增加一个新的数据类型Address(country state city zipcode etc.)。这样我们就很容易把这个粒度问题解决了。不幸的是，数据库是不允许自定义类型的（也许现在的数据库可以，鄙人不太清楚，呵呵）。Hibernate 对这个问题有了很好的解决。见以后的文章。
5、对象之间可以有继承的关系，这是数据库望洋兴叹的。Hibernate 对这个问题有了很好的解决。见以后的文章。
6、对象的身份识别问题。
    大家都知道，java中的对象识别是用equals()和haseCode()来实现。
   举例：

package  jmuse.eg;
/** */ /**
 *@hibernate.class table="MESSAGE"
 *
  */

public   class  Message  {
     private  Long id;
     private  String text;
     private  String string;
     public   void  setString(String s) {
        string = s;
    }
     /** */ /**
     *@hibernate.property 
     *
      */
      public  String getString() {
         return   this .string;
    }
    
     private  Message nextMessage;
     public  Message()  {}
     public  Message(String text) {
         this .text = text;
    }
    
     public   void  setId(Long id)  {
         this .id  =  id; 
    }

     public   void  setText(String text)  {
         this .text  =  text; 
    }

     public   void  setNextMessage(Message nextMessage)  {
         this .nextMessage  =  nextMessage; 
    }
     /** */ /**
     *@hibernate.id column="MESSAGE_ID" generator-class="native"
     *
      */
     public  Long getId()  {
         return  ( this .id); 
    }
     /** */ /**
     *@hibernate.property column="MESSAGE_TEXT"
     *
      */
     public  String getText()  {
         return  ( this .text); 
    }
     /** */ /**
     *@hibernate.many-to-one column="NEXT_MESSAGE_ID" cascade="all"
     *
      */
     public  Message getNextMessage()  {
         return  ( this .nextMessage); 
    }
}

这样的类由于没有实现equals()和haseCode()，所以如果用下面的代码我们可以看到如下输出：

Message m1 = new  Message("Hello");
Message m2 = new  Message("Hello");
if (!(m2.equals(m1)) )log.info( " m1 and m2 are not idential " );
else  log.info( " m1 and m2 are identical " );

////////////// /out put //////////////
m1 and m2 are not idential

但是我们加上如下代码：

  public   boolean  equals(Object o) {
         if ( this == o)  return   true ;
         if ( ! (o  instanceof  Message)) 
                 return   false ;
         final  Message m = (Message)o;
         return   this .getText().equals(m.getText());
    }
     public   int  hashCode() {
         // return text==null?System.identityHashCode(this):text.hashCode();
         int  hase = 20 ;
        
         return   20 * hase + getText().hashCode();
    }

//////////// out put //////////// /
m1 and m2 are identical

这就是java的对象识别。如果你将修改后的Message对象加入到java.util.Set中，不管你加多少，最后size()仍然为1。
 那么hibernate中的对象识别如何呢？见以后文章。呵呵。

 

posted @ 2007-02-10 14:44 满山红叶 阅读(594) | 评论 (0) | 编辑 收藏