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Note that the < character must be escaped as < in XML. With annotations, you need to add a Hibernate extension annotation to declare check constraints:

While we have typically refrained from long, boring code listings in this book, it is important to show a complete example of how all the pieces fit together to build an EJB JAR by using most of the techniques and tasks discussed in this chapter. Listing 14.4 demonstrates using Ant to build a database from SQL, reverse engineering it into entity beans by using Middlegen, generating many EJB artifacts from the Middlegen-generated entity beans and manually built source code, compiling it all, and then bundling it all into an EJB JAR. Figure 14.4 shows this graphically.

@Entity @org.hibernate.annotations.Check( constraints = "START_DATE < END_DATE" ) public class Item { ... }

< xml version="1.0" encoding="UTF-8" > <!DOCTYPE project [ <!ENTITY properties SYSTEM "file:../../../app/properties.xml"> ]> <project name="EJB Examples" default="main" basedir="."> &properties; <property <property <property <property name="name" value="ejbexample"/> name="build.dir" location="build"/> name="src.dir" location="src"/> name="gen.src.dir" location="${build.dir}/src/java"/> <property name="java.classes.dir"

Multirow table constraints can be implemented with more complex expressions. You may need a subselect in the expression to do this, which may not be supported in your DBMS check your product documentation first. However, there are common multirow table constraints you can add directly as attributes in Hibernate mappings. For example, you identify the login name of a User as unique in the system:

<property name="username" type="string"> <column name="USERNAME" length="16" not-null="true" check="regexp_like(USERNAME,'^[[:alpha:]]+$')" unique="true"/> </property>

location="${build.dir}/classes"/> <property name="ejb.dd.dir" location="${java.classes.dir}/META-INF"/> <property name="standard-ejb.dir" location="${build.dir}/standard-ejb"/> <property name="ejb.jar.file" location="${standard-ejb.dir}/${name}-ejb.jar"/> <property name="sql.dir" location="sql"/> <property name="sql.create.file" location="${sql.dir}/create.sql"/> <property name="application.xml" location="metadata/application.xml"/> <property <property <property <property <property <property name="db.dir" location="${build.dir}/db"/> name="db.name" value="example"/> name="db.url" value="jdbc:hsqldb:${db.dir}/${db.name}"/> name="db.driver" value="org.hsqldb.jdbcDriver"/> name="db.username" value="sa"/> name="db.password" value=""/>

Unique constraint declaration is also possible in annotation metadata:

<path id="compile.classpath"> <pathelement location="${j2ee.jar}"/> <pathelement location="${struts.jar}"/> </path> <path id="xdoclet.classpath"> <pathelement location="${log4j.jar}"/> <pathelement location="${xdoclet.jar}"/> <pathelement location="${j2ee.jar}"/> <!-- javadoc is needed --> <pathelement path="${java.class.path}"/> </path> <!-- ======================================================== --> <!-- Default starting point --> <!-- ======================================================== --> <target name="main" depends="ear"/> <!-- ======================================================== --> <!-- Clean everything --> <!-- ======================================================== --> <target name="clean" description="Clean all generated stuff"> <delete dir="${build.dir}"/> <delete dir="${db.dir}"/> </target> <!-- ======================================================== --> <!-- Create sample DB --> <!-- ======================================================== --> <target name="build-db" description="Build sample database">

@Column(name = "USERNAME", length = 16, nullable = false, unique = true) @org.hibernate.annotations.Check( constraints = "regexp_like(USERNAME,'^[[:alpha:]]+$')" ) private String username;

<mkdir dir="${db.dir}"/> <sql driver="${db.driver}" url="${db.url}" userid="${db.username}" Creates the password="${db.password}" database from print="true" SQL CREATE autocommit="true" TABLE script src="${sql.create.file}" onerror="continue"> <classpath> <pathelement location="${hsqldb.jar}"/> </classpath> </sql> </target> <!-- ======================================================== --> <!-- Run Middlegen --> <!-- ======================================================== --> <target name="middlegen" depends="build-db" description="Run Middlegen"> <mkdir dir="${gen.src.dir}"/> <taskdef name="middlegen" classname="middlegen.MiddlegenTask" classpath="${middlegen.jar};${xdoclet.jar};${hsqldb.jar}" /> <middlegen gui="${gui}" Middlegen produces destination="${gen.src.dir}" XDoclet-configured driver="${db.driver}" entity bean classes databaseurl="${db.url}" for each table username="${db.username}" password="${db.password}" package="org.example.antbook.ejb" interfacepackage="org.example.antbook.interfaces" /> </target> <!-- ======================================================== --> <!-- Run XDoclet --> <!-- ======================================================== --> <target name="xdoclet" depends="middlegen" description="Generate artifacts from EJBs"> <mkdir dir="${ejb.dd.dir}"/> <taskdef name="ejbdoclet" classname="xdoclet.ejb.EjbDocletTask" classpath="${xdoclet.jar}" /> <property name="struts.base.class" value="org.apache.struts.action.ActionForm"/>

And, of course, you can do this in JPA XML descriptors (there is no check constraint, however):

<entity class="auction.model.User" access="FIELD"> <attributes> ... <basic name="username"> <column name="USERNAME" length="16" nullable="false" unique="true"/> </basic> </attributes> </entity>

<ejbdoclet sourcepath="${gen.src.dir};${src.dir}" destdir="${gen.src.dir}" excludedtags="@version,@author" ejbspec="2.0" classpathref="xdoclet.classpath"> <packageSubstitution packages="ejb" substituteWith="interfaces"/> <fileset dir="${gen.src.dir}"> <include name="**/*Bean.java" /> </fileset> <fileset dir="${src.dir}" includes="**/*Bean.java"/> <dataobject/> <valueobject/> <localinterface/> <utilobject/> XDoclet generates <localhomeinterface/> EJB artifacts from <entitypk/> Middlegen and our own code <entitycmp/> <homeinterface/> <remoteinterface/> <entitypk/> <strutsform> <packageSubstitution packages="ejb" substituteWith="struts"/> </strutsform> <deploymentdescriptor destdir="${ejb.dd.dir}" validatexml="true" /> <jboss version="2.4" xmlencoding="UTF-8" destdir="${ejb.dd.dir}" /> </ejbdoclet> </target> <!-- ======================================================== --> <!-- Compile everything --> <!-- ======================================================== --> <target name="compile" depends="xdoclet" description="Compile source code"> <javac destdir="${java.classes.dir}" classpathref="compile.classpath"> Compiles both generated <src path="${gen.src.dir};${src.dir}"/> and maintained code </javac> </target> <!-- ======================================================== --> <!-- Build EJB JARs --> <!-- ======================================================== --> <target name="ejb-jar" depends="compile" description="Make EJB JAR files"> <mkdir dir="${standard-ejb.dir}"/>

The exported DDL includes the unique constraint:

<ejbjar srcdir="${java.classes.dir}" descriptordir="${ejb.dd.dir}" destdir="${standard-ejb.dir}" naming="ejb-name" genericjarsuffix="-ejb.jar"> <include name="ejb-jar.xml"/> <dtd publicId="-//Sun Microsystems, Inc.// DTD Enterprise JavaBeans 1.1//EN location="${j2ee.dir}/${j2ee.subdir}/ejb-jar_1_1.dtd"/> </ejbjar> </target>

create table USERS ( ... USERNAME varchar(16) not null unique check(regexp_like(USERNAME,'^[[:alpha:]]+$')), ... );

<!-- ======================================================== --> <!-- Build EAR --> <!-- ======================================================== --> <target name="ear" depends="ejb-jar" description="Build EAR file"> <mkdir dir="${dist.dir}"/> <ear destfile="${dist.dir}/${name}.ear" appxml="${application.xml}"> Packages EJB JAR <fileset dir="${standard-ejb.dir}"/> file into EAR </ear> </target> </project>

A unique constraint can also span several columns. For example, CaveatEmptor supports a tree of nested Category objects. One of the business rules says that a particular category can t have the same name as any of its siblings. Hence, you need a multicolumn multirow constraint that guarantees this uniqueness: