next exercise

Doc/course.xml

@@ -18136,7 +18136,101 @@ public class User {
         <section xml:id="sect_MappingComponents">
           <title>Mapping components</title>
-          <para/>
+          <para>We consider a simple example. We may add an email property to
+          <classname>session3.User</classname>:</para>
+
+          <programlisting>...
+public class User {
+  ...
+  private Email address; ...</programlisting>
+
+          <para>Why do we use a separate class Email rather than a simple
+          <emphasis role="bold"><code>private String email</code></emphasis>
+          declaration? The answer is quite simple: We want Email instances to
+          be extensible and allow for method definitions like
+          <code>sendEmail(...)</code>:</para>
+
+          <programlisting>public class Email {
+
+  private String emailAddress;
+  ...
+  void sendEmail(final String subject, final String content) {}
+}</programlisting>
+
+          <para>Our <code>Email</code> class may of course have more than just
+          one property. We don't want to email addresses to be database
+          entities themselves. Instead they are meant to be components of User
+          instances. This is achieved by:</para>
+
+          <glosslist>
+            <glossentry>
+              <glossterm>Annotate class Email to be embeddable:</glossterm>
+
+              <glossdef>
+                <programlisting>package component.email;
+
+<emphasis role="bold"> @Embeddable</emphasis> public class Email {
+
+  private String emailAddress;
+   ...
+}</programlisting>
+              </glossdef>
+            </glossentry>
+
+            <glossentry>
+              <glossterm>Annotate <code>emailAddress</code> to become an
+              embedded property:</glossterm>
+
+              <glossdef>
+                <programlisting>package component.email;
+...
+public class User {
+
+private Email address;
+  <emphasis role="bold">@Embedded</emphasis>
+  public Email getEmailAddress() { return address;}
+...</programlisting>
+              </glossdef>
+            </glossentry>
+          </glosslist>
+
+          <para>We may now persist <classname>component.email.User</classname>
+          instances:</para>
+
+          <programlisting>package component.email;
+...
+public class PersistUser {
+...
+      {
+        final Transaction transaction = session.beginTransaction();
+         final User u = new User(123, "goik", "Martin Goik");
+         u.setEmailAddress(<emphasis role="bold">new Email("goik@hdm-stuttgart.de")</emphasis>);
+         session.save(u);
+         transaction.commit();
+      } ...</programlisting>
+
+          <qandaset role="exercise">
+            <qandadiv>
+              <qandaentry>
+                <question>
+                  <para>Consider the following sketch of an address
+                  class:</para>
+
+                  <programlisting>public class Address {
+
+  private String street;
+  private String city;
+  private String zipcode;
+  ...
+}</programlisting>
+
+                  <para>Extend class <classname>session3.User</classname> to
+                  allow for two properties <code>homeAddress</code> and
+                  <code>workAddress</code> of type Address.</para>
+                </question>
+              </qandaentry>
+            </qandadiv>
+          </qandaset>
         </section>
       </section>