Simple key example

Doc/Persist/topics.xml

@@ -399,7 +399,92 @@ public class Airline {
     <section xml:id="persistSectAirlineSimpleKey">
       <title>Advocating simple key definitions</title>
 
-      <para/>
+      <qandaset defaultlabel="qanda"
+                xml:id="persistQandaAirlineKeyAutoIncrementSimple">
+        <qandadiv>
+          <qandaentry>
+            <question>
+              <para>We might choose a simpler model to achieve non-nullable
+              keys:</para>
+
+              <programlisting language="java">@Entity
+public class Airline {
+   @Id
+   @GeneratedValue(strategy=GenerationType.IDENTITY)
+   Long id;
+   
+   @Column(unique=true, nullable=false)
+   String name;
+
+   @Column(unique=true, nullable=false)
+   String icaoCode;
+   
+   public Airline(final String name, final String icaoCode) {
+      this.name = name;
+      this.icaoCode = icaoCode;
+   }
+   protected Airline(){}   
+}</programlisting>
+
+              <para>Discuss the pros and cons of this approach compared to
+              <xref linkend="persistQandaAirlineKeyAutoIncrement"/>.</para>
+            </question>
+
+            <answer>
+              <glosslist>
+                <glossentry>
+                  <glossterm>Pros:</glossterm>
+
+                  <glossdef>
+                    <orderedlist>
+                      <listitem>
+                        <para>This approach is easier to understand.</para>
+                      </listitem>
+
+                      <listitem>
+                        <para>Stable approach with respect to <xref
+                        linkend="glo_Java"/> code refactoring: If e.g. the
+                        property <property>icaoCode</property> gets
+                        consistently renamed to
+                        <property>icaoCode</property>Number <xref
+                        linkend="glo_SqlDdl"/> code will still be properly
+                        generated. However this problem may be overcome by
+                        providing stable <xref linkend="glo_SqlDdl"/>
+                        attribute names via <code>@Column(name="icaoCode"
+                        ...)</code> thereby protecting the database from
+                        unnecessary schema evolution issues being inflicted by
+                        <xref linkend="glo_Java"/> code refactoring.</para>
+                      </listitem>
+                    </orderedlist>
+                  </glossdef>
+                </glossentry>
+
+                <glossentry>
+                  <glossterm>Cons:</glossterm>
+
+                  <glossdef>
+                    <orderedlist>
+                      <listitem>
+                        <para>Does not work for composed keys.</para>
+                      </listitem>
+
+                      <listitem>
+                        <para>Does not allow for self explanatory constraint
+                        names. We end up with e.g. :</para>
+
+                        <programlisting language="sql">...
+  UNIQUE KEY `UK_s759kv0st7r42c85xqjjiusde` (`icaoCode`),
+  UNIQUE KEY `UK_swdntm8xd26ugm3t78mkkted2` (`name`)
+...</programlisting>
+                      </listitem>
+                    </orderedlist>
+                  </glossdef>
+                </glossentry>
+              </glosslist>
+            </answer>
+          </qandaentry>
+        </qandadiv>
+      </qandaset>
     </section>
   </section>
 </chapter>