The Amber Query API resembles the JDBC PreparedStatement with enhanced SQL and direct support for objects.

Files in this tutorial

WEB-INF/resin-web.xml	resin-web.xml configuration
WEB-INF/classes/META-INF/persistence.xml	persistence.xml configuration
WEB-INF/classes/example/Student.java	The student bean
WEB-INF/classes/example/House.java	The house bean
WEB-INF/classes/example/QueryServlet.java	The course servlet

Database Schema

House.java

@Entity public class House { @Id @Column (name="id") public long getId() @Basic public String getName() @OneToMany (targetEntity=Student.class, mappedBy="house") public Collection getStudentList() }

Student.java

@Entity public class Student { @Id @Column (name="id") public long getId() @Basic public String getName() @ManyToOne @JoinColumn (name="house") public House getHouse() }

Query

QueryServlet.java

private void doService(PrintWriter out) throws java.io.IOException { Query allHouse = _entityManager.createQuery("SELECT o FROM House o"); String sql = ("SELECT s" + " FROM House h, IN(h.studentList) s" + " WHERE h.id=?1 AND s.gender='M'"); Query boysInHouse = _entityManager.createQuery(sql); List houses = allHouse.getResultList(); for (int i = 0; i < houses.size(); i++) { House house = (House) houses.get(i); out.println("<H3>Boys living in " + house.getName() + ":</H3>"); boysInHouse.setParameter(1, new Long(house.getId())); List boys = boysInHouse.getResultList(); if (boys.size() == 0) out.println("No boys are living in " + house.getName()); for (int j = 0; j < boys.size(); j++) { Student boy = (Student) boys.get(j); out.println(boy.getName() + "<br>"); } } } }

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