symmetric getter and setter methods

Doc/course.xml

@@ -18909,6 +18909,44 @@ public class Laptop {
 ...
 @OneToOne (<emphasis role="bold">mappedBy="laptop"</emphasis>)
   public Employee getOwner() { return owner;} ...</programlisting>
+
+          <qandaset role="exercise">
+            <title>Symmetric implementation of getter and setter
+            methods</title>
+
+            <qandadiv>
+              <qandaentry>
+                <question>
+                  <para>The current implementation is not symmetric with
+                  respect to entity.company5.model.Employee.setLaptop and
+                  entity.company5.model.Laptop.setOwner. Implement a better
+                  solution allowing both variants:</para>
+
+                  <programlisting>Employee e ...;
+
+Laptop l ... ;
+
+e.setLaptop(l);
+...
+l.setOwner(e);</programlisting>
+                </question>
+              </qandaentry>
+            </qandadiv>
+          </qandaset>
+
+          <qandaset role="exercise">
+            <title>Transactions and data integrity</title>
+
+            <qandadiv>
+              <qandaentry>
+                <question>
+                  <para>Use your implementation to exchange the laptops of two
+                  users. Which problem possibly arises? Is there a
+                  solution?</para>
+                </question>
+              </qandaentry>
+            </qandadiv>
+          </qandaset>
         </section>
       </section>
     </chapter>

ws/eclipse/HibIntro/src/main/java/entity/company5/hibernate.cfg.xml

@@ -15,7 +15,7 @@
   <property name="hibernate.format_sql">true</property>
   <property name="hibernate.hbm2ddl.auto">update</property>
   
-  <mapping class="entity.company5.Laptop"/>
-  <mapping class="entity.company5.Employee"/>
+  <mapping class="entity.company5.model.Laptop"/>
+  <mapping class="entity.company5.model.Employee"/>
  </session-factory>
 </hibernate-configuration>

ws/eclipse/HibIntro/src/main/java/entity/company6/ExchangeLaptops.java

+package entity.company6;
+
+import hibintro.util.HibernateUtil;
+
+import org.hibernate.Session;
+import org.hibernate.Transaction;
+
+import entity.company6.model.Employee;
+import entity.company6.model.Laptop;
+
+/**
+ * Removing {@link Laptop} from {@link Employee} 
+ */
+public class ExchangeLaptops {
+  /**
+   * @param args not used.
+   */
+  public static void main(String[] args) {
+    final Session session = HibernateUtil.createSessionFactory("entity/company6/hibernate.cfg.xml").openSession();
+    {
+      final Transaction transaction = session.beginTransaction();
+      final Employee martin = (Employee) session.load(Employee.class, 1L),
+          eve = (Employee) session.load(Employee.class, 2L);
+      
+      final Laptop currentMartin2214 = (Laptop) session.load(Laptop.class, 1L),
+          currentEve2213 = (Laptop) session.load(Laptop.class, 2L);
+      
+      eve.setLaptop(currentMartin2214);
+      currentEve2213.setOwner(martin);
+      
+      System.out.println("Martin:" + martin.getLaptop().getId());
+      System.out.println("Eve:" + eve.getLaptop().getId());
+      
+      System.out.println("currentEve2213:" + currentEve2213.getOwner().getCname());
+      System.out.println("currentMartin2214:" + currentMartin2214.getOwner().getCname());
+
+      transaction.commit();
+    }
+  }
+}
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ws/eclipse/HibIntro/src/main/java/entity/company6/Persist.java

+package entity.company6;
+
+import hibintro.util.HibernateUtil;
+
+import org.hibernate.Session;
+import org.hibernate.Transaction;
+
+import entity.company6.model.Employee;
+import entity.company6.model.Laptop;
+
+public class Persist {
+  public static void main(String[] args) {
+    final Session session = HibernateUtil.createSessionFactory("entity/company6/hibernate.cfg.xml").openSession();
+    {
+      final Transaction transaction = session.beginTransaction();
+      final Employee  martin = new Employee(123, "Martin Goik"),
+          eve = new Employee(140, "Eve Blix");
+
+      final Laptop superCoolGadget = new Laptop(2213),
+          g2 = new Laptop(2214),
+          g3 = new Laptop(2215); // Not being referenced later
+
+      martin.setLaptop(g2);
+      eve.setLaptop(superCoolGadget);
+      // Now only save the employee transients,
+      // superCoolGadget will be saved automatically due to
+      // CascadeType.ALL 
+      session.save(martin);
+      session.save(eve);
+      session.save(g3);
+      transaction.commit();
+    }
+  }
+}
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ws/eclipse/HibIntro/src/main/java/entity/company6/hibernate.cfg.xml

+<?xml version="1.0" encoding="UTF-8"?>
+
+<!DOCTYPE hibernate-configuration PUBLIC
+	"-//Hibernate/Hibernate Configuration DTD 3.0//EN"
+	"http://www.hibernate.org/dtd/hibernate-configuration-3.0.dtd">
+
+<hibernate-configuration>
+ <session-factory >
+  <property name="hibernate.connection.driver_class">com.mysql.jdbc.Driver</property>
+  <property name="hibernate.connection.password">XYZ</property>
+  <property name="hibernate.connection.url">jdbc:mysql://localhost:3306/hdm</property>
+  <property name="hibernate.connection.username">hdmuser</property>
+  <property name="hibernate.dialect">org.hibernate.dialect.MySQL5InnoDBDialect</property>
+  <property name="hibernate.show_sql">true</property>
+  <property name="hibernate.format_sql">true</property>
+  <property name="hibernate.hbm2ddl.auto">update</property>
+  
+  <mapping class="entity.company6.model.Laptop"/>
+  <mapping class="entity.company6.model.Employee"/>
+ </session-factory>
+</hibernate-configuration>

ws/eclipse/HibIntro/src/main/java/entity/company6/model/Employee.java

+package entity.company6.model;
+
+import javax.persistence.CascadeType;
+import javax.persistence.Entity;
+import javax.persistence.GeneratedValue;
+import javax.persistence.Id;
+import javax.persistence.OneToOne;
+import javax.persistence.Table;
+import javax.persistence.UniqueConstraint;
+
+
+/**
+ * 
+ *         {@link Employee} instances related to {@link Department}
+ * 
+ */
+@Entity
+@Table(uniqueConstraints={@UniqueConstraint(columnNames={"staffNumber"})})
+public class Employee {
+
+  @Id
+  @GeneratedValue
+  public Long getId() {return id;}
+  protected void setId(Long id) {this.id = id;}
+  private Long id;
+
+  public int getStaffNumber() { return staffNumber;}
+  public void setStaffNumber(int staffNumber) { this.staffNumber = staffNumber;}
+  int staffNumber = Integer.MIN_VALUE;
+
+  public String getCname() { return cname;}
+  public void setCname(String cname) { this.cname = cname;}
+  private String cname; // Common name
+
+  /**
+   * One {@link Laptop} per {@link Employee}.
+   * 
+   * @return {@link Laptop}  "owned" by {@link Employee}.
+   */
+  @OneToOne(optional=false, cascade={CascadeType.ALL})
+  public Laptop getLaptop() { return laptop;}
+  
+  public void setLaptop(final Laptop laptop) {
+    if (getLaptop() == laptop) {
+      return;
+    }
+    if (null != getLaptop()) {
+      getLaptop().setOwnerInternal(null);
+    }
+    setLaptopInternal(laptop);
+    if (null != getLaptop()) {
+      getLaptop().setOwnerInternal(this);
+    }
+  }
+  protected  void setLaptopInternal(final Laptop laptop) {
+    this.laptop = laptop;
+  }
+  
+  private Laptop laptop;// Workstation for employees.
+
+  protected Employee(){}
+
+  public Employee(final int staffNumber, final String cname) {
+    setStaffNumber(staffNumber);
+    setCname(cname);
+  }
+  @Override
+  public boolean equals(Object other) {
+    if (this == other) {
+      return true;
+    } else if (Integer.MIN_VALUE == getStaffNumber()) {
+      return false;
+    } else if (other instanceof Employee) {
+      final Employee that = (Employee) other;
+      return this.getStaffNumber() == that.getStaffNumber();
+    } else {
+      return false;
+    }
+  }
+  @Override
+  public int hashCode() {
+    if (Integer.MIN_VALUE == getStaffNumber()) {
+      return System.identityHashCode(this);
+    } else {
+      return getStaffNumber();
+    }
+  }
+}
\ No newline at end of file

ws/eclipse/HibIntro/src/main/java/entity/company6/model/Laptop.java

+package entity.company6.model;
+
+import javax.persistence.CascadeType;
+import javax.persistence.Entity;
+import javax.persistence.GeneratedValue;
+import javax.persistence.Id;
+import javax.persistence.OneToOne;
+import javax.persistence.Table;
+import javax.persistence.UniqueConstraint;
+
+
+/**
+ * 
+ * Laptops possibly being assigned to {@link Employee}   
+ * 
+ */
+@Entity
+@Table(uniqueConstraints={@UniqueConstraint(columnNames={"idNumber"})})
+public class Laptop {
+
+  @Id
+  @GeneratedValue
+  public Long getId() {return id;}
+  protected void setId(Long id) {this.id = id;}
+  private Long id;
+
+  /**
+   * @return The device's unique part number
+   */
+  public int getIdNumber() { return idNumber;}
+  public void setIdNumber(int idNumber) { this.idNumber = idNumber;}
+  int idNumber;
+
+  @OneToOne (mappedBy="laptop",cascade={CascadeType.ALL})
+  public Employee getOwner() { return owner;}
+  
+  public void setOwner(Employee owner) {
+    if (getOwner() == owner) {
+      return;
+    }
+    if (null != getOwner()) {
+      getOwner().setLaptopInternal(null);
+    }
+    setOwnerInternal(owner);
+    if (null != getOwner()) {
+      getOwner().setLaptopInternal(this);
+    }
+  }
+  protected void setOwnerInternal(Employee owner) {
+    this.owner = owner;
+  }
+  Employee owner;
+
+  protected Laptop(){}
+
+  public Laptop(final int idNumber) {
+    setIdNumber(idNumber);
+  }
+  @Override
+  public boolean equals(Object other) {
+    if (this == other) {
+      return true;
+    } else if (Integer.MIN_VALUE == getIdNumber()) {
+      return false;
+    } else if (other instanceof Laptop) {
+      final Laptop that = (Laptop) other;
+      return this.getIdNumber() == that.getIdNumber();
+    } else {
+      return false;
+    }
+  }
+  @Override
+  public int hashCode() {
+    if (Integer.MIN_VALUE == getIdNumber()) {
+      return System.identityHashCode(this);
+    } else {
+      return getIdNumber();
+    }
+  }
+}
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