Source Code : Query Hints Example

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Query Hints Example

File: Professor.java



import javax.persistence.Entity;
import javax.persistence.Id;
import javax.persistence.NamedQuery;
import javax.persistence.QueryHint;

@Entity
@NamedQuery(name="findProfessorNoCache",
            query="SELECT e FROM Professor e WHERE e.id = ?1",
            hints={@QueryHint(name="toplink.cache-usage", value="DoNotCheckCache")})
public class Professor {
    @Id
    private int id;
    private String name;
    private long salary;

    public int getId() {
        return id;
    }
    
    public String getName() {
        return name;
    }

    public long getSalary() {
        return salary;
    }
    
    public String toString() {
        return "Professor " + getId() + 
               ": name: " + getName() +
               ", salary: " + getSalary();
    }
}


File: ProfessorService.java

import java.util.Collection;

import javax.persistence.EntityManager;
import javax.persistence.NoResultException;
import javax.persistence.Query;

public class ProfessorService {
  protected EntityManager em;

  public ProfessorService(EntityManager em) {
    this.em = em;
  }

  public Professor findProfessor(int empId) {
    Query q = em.createQuery("SELECT e FROM Professor e WHERE e.id =  ?1");
    q.setParameter(1, empId);
    try {
      return (Professor) q.getSingleResult();
    } catch (NoResultException e) {
      return null;
    }
  }

  public Professor findProfessorNoCache(int empId) {
    Query q = em.createQuery("SELECT e FROM Professor e WHERE e.id = ?1");
    // force read from database
    q.setHint("cacheUsage", oracle.toplink.essentials.queryframework.ObjectLevelReadQuery.DoNotCheckCache);
    q.setParameter(1, empId);
    try {
      return (Professor) q.getSingleResult();
    } catch (NoResultException e) {
      return null;
    }
  }

  public Professor findProfessorNoCacheNamed(int empId) {
    Query q = em.createNamedQuery("findProfessorNoCache");
    q.setParameter(1, empId);
    try {
      return (Professor) q.getSingleResult();
    } catch (NoResultException e) {
      return null;
    }
  }

  public Collection<Professor> findAllProfessors() {
    return (Collection<Professor>) em.createQuery("SELECT e FROM Professor e").getResultList();
  }

}


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("	"+ metadata.getColumnLabel(i + 1)); 
    }
    System.out.println("
----------------------------------");

    while (rs.next()) {
      for (int i = 0; i < metadata.getColumnCount(); i++) {
        Object value = rs.getObject(i + 1);
        if (value == null) {
          System.out.print("	       ");
        } else {
          System.out.print("	"+value.toString().trim());
        }
      }
      System.out.println("");
    }
  }
}


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.removeDepartment2();
    
    util.checkData("select * from Professor");
    util.checkData("select * from Department");

    em.getTransaction().commit();
    em.close();
    emf.close();
  }
}




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>

           
       

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