Define And Use Compound Primary Key : Primary Key « JPA « Java
Define And Use Compound Primary Key
File: Main.java
import javax.persistence.EntityManager;
import javax.persistence.EntityManagerFactory;
import javax.persistence.Persistence;
public class Main {
public static void main(String[] a) throws Exception {
JPAUtil util = new JPAUtil();
EntityManagerFactory emf = Persistence.createEntityManagerFactory("ProfessorService");
EntityManager em = emf.createEntityManager();
ProfessorService service = new ProfessorService(em);
em.getTransaction().begin();
service.createProfessor("country", 1, "name", 100);
Professor emp = service.findProfessor("country", 1);
System.out.println("Found " + emp);
System.out.println("Professors:");
for (Professor emp1 : service.findAllProfessors()) {
System.out.print(emp1);
}
util.checkData("select * from Professor");
em.getTransaction().commit();
em.close();
emf.close();
}
}
File: JPAUtil.java
import java.io.Reader;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.ResultSetMetaData;
import java.sql.Statement;
public class JPAUtil {
Statement st;
public JPAUtil() throws Exception{
Class.forName("org.hsqldb.jdbcDriver");
System.out.println("Driver Loaded.");
String url = "jdbc:hsqldb:data/tutorial";
Connection conn = DriverManager.getConnection(url, "sa", "");
System.out.println("Got Connection.");
st = conn.createStatement();
}
public void executeSQLCommand(String sql) throws Exception {
st.executeUpdate(sql);
}
public void checkData(String sql) throws Exception {
ResultSet rs = st.executeQuery(sql);
ResultSetMetaData metadata = rs.getMetaData();
for (int i = 0; i < metadata.getColumnCount(); i++) {
System.out.print("\t"+ metadata.getColumnLabel(i + 1));
}
System.out.println("\n----------------------------------");
while (rs.next()) {
for (int i = 0; i < metadata.getColumnCount(); i++) {
Object value = rs.getObject(i + 1);
if (value == null) {
System.out.print("\t ");
} else {
System.out.print("\t"+value.toString().trim());
}
}
System.out.println("");
}
}
}
File: Professor.java
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.Id;
import javax.persistence.IdClass;
@Entity
@IdClass(ProfessorId.class)
public class Professor {
@Id private String country;
@Id
@Column(name="EMP_ID")
private int id;
private String name;
private long salary;
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getCountry() {
return country;
}
public void setCountry(String country) {
this.country = country;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public long getSalary() {
return salary;
}
public void setSalary(long salary) {
this.salary = salary;
}
public String toString() {
return "Professor id: " + getId() + " name: " + getName() +
" country: " + getCountry();
}
}
File: ProfessorId.java
import java.io.Serializable;
public class ProfessorId implements Serializable {
private String country;
private int id;
public ProfessorId() {
}
public ProfessorId(String country, int id) {
this.country = country;
this.id = id;
}
public String getCountry() {
return country;
}
public int getId() {
return id;
}
public boolean equals(Object o) {
return ((o instanceof ProfessorId) && country.equals(((ProfessorId) o).getCountry()) && id == ((ProfessorId) o)
.getId());
}
public int hashCode() {
return country.hashCode() + id;
}
}
File: ProfessorService.java
import java.util.Collection;
import javax.persistence.EntityManager;
import javax.persistence.Query;
public class ProfessorService {
protected EntityManager em;
public ProfessorService(EntityManager em) {
this.em = em;
}
public Professor createProfessor(String country, int id, String name, long salary) {
Professor emp = new Professor();
emp.setCountry(country);
emp.setId(id);
emp.setName(name);
emp.setSalary(salary);
em.persist(emp);
return emp;
}
public Professor findProfessor(String country, int id) {
return em.find(Professor.class, new ProfessorId(country, id));
}
public Collection<Professor> findAllProfessors() {
Query query = em.createQuery("SELECT e FROM Professor e");
return (Collection<Professor>) query.getResultList();
}
}
File: persistence.xml
<persistence xmlns="http://java.sun.com/xml/ns/persistence"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://java.sun.com/xml/ns/persistence http://java.sun.com/xml/ns/persistence/persistence" version="1.0">
<persistence-unit name="JPAService" transaction-type="RESOURCE_LOCAL">
<properties>
<property name="hibernate.dialect" value="org.hibernate.dialect.HSQLDialect"/>
<property name="hibernate.hbm2ddl.auto" value="update"/>
<property name="hibernate.connection.driver_class" value="org.hsqldb.jdbcDriver"/>
<property name="hibernate.connection.username" value="sa"/>
<property name="hibernate.connection.password" value=""/>
<property name="hibernate.connection.url" value="jdbc:hsqldb:data/tutorial"/>
</properties>
</persistence-unit>
</persistence>
JPA-DefineAndUseCompoundPrimaryKey.zip( 5,335 k)