Java/JPA/Find

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Find All Objects

   <source lang="java">

File: Professor.java

import javax.persistence.Entity; import javax.persistence.Id; @Entity public class Professor {

 @Id
 private int id;
 private String name;
 private long salary;
 public Professor() {
 }
 public Professor(int id) {
   this.id = id;
 }
 public int getId() {
   return id;
 }
 public void setId(int id) {
   this.id = id;
 }
 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() + " salary: " + getSalary();
 }

}

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(int id, String name, long salary) {
   Professor emp = new Professor(id);
   emp.setName(name);
   emp.setSalary(salary);
   em.persist(emp);
   return emp;
 }
 public void removeProfessor(int id) {
   Professor emp = findProfessor(id);
   if (emp != null) {
     em.remove(emp);
   }
 }
 public Professor raiseProfessorSalary(int id, long raise) {
   Professor emp = em.find(Professor.class, id);
   if (emp != null) {
     emp.setSalary(emp.getSalary() + raise);
   }
   return emp;
 }
 public Professor findProfessor(int id) {
   return em.find(Professor.class, id);
 }
 public Collection<Professor> findAllProfessors() {
   Query query = em.createQuery("SELECT e FROM Professor e");
   return (Collection<Professor>) query.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("\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: Main.java // find all employees import java.util.Collection; 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();
   Professor emp = service.createProfessor(158, "AAA", 45000);
   em.getTransaction().rumit();
   System.out.println("Persisted " + emp);
   util.checkData("select * from Professor");
   // 
   Collection<Professor> emps = service.findAllProfessors();
   for (Professor e : emps)
     System.out.println("Found Professor: " + e);
   em.close();
   emf.close();
 }

}


File: persistence.xml <persistence xmlns="http://java.sun.ru/xml/ns/persistence"

            xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
            xsi:schemaLocation="http://java.sun.ru/xml/ns/persistence http://java.sun.ru/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>


      </source>
   
  
 
  



Find Object By Class

   <source lang="java">

File: Professor.java

import javax.persistence.Entity; import javax.persistence.Id; @Entity public class Professor {

   @Id
   private int id;
   private String name;
   private long salary;
   public Professor() {}
   public Professor(int id) {
       this.id = id;
   }
   public int getId() {
       return id;
   }
   
   public void setId(int id) {
       this.id = id;
   }
   
   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() + " salary: " + getSalary();
   }

}

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(int id, String name, long salary) {
   Professor emp = new Professor(id);
   emp.setName(name);
   emp.setSalary(salary);
   em.persist(emp);
   return emp;
 }
 public void removeProfessor(int id) {
   Professor emp = findProfessor(id);
   if (emp != null) {
     em.remove(emp);
   }
 }
 public Professor raiseProfessorSalary(int id, long raise) {
   Professor emp = em.find(Professor.class, id);
   if (emp != null) {
     emp.setSalary(emp.getSalary() + raise);
   }
   return emp;
 }
 public Professor findProfessor(int id) {
   return em.find(Professor.class, id);
 }
 public Collection<Professor> findAllProfessors() {
   Query query = em.createQuery("SELECT e FROM Professor e");
   return (Collection<Professor>) query.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("\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: Main.java import java.util.Collection; import java.util.Iterator; 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();
   Professor emp = service.createProfessor(1, "name", 100);
   emp = service.createProfessor(2, "name 2", 100);
   Integer userId = 1;
   emp = em.find(Professor.class, userId);
   if (emp == null) {
     System.out.println(userId + " not found! ");
   } else {
     System.out.println("Found " + emp);
   }
   for (Object o : em.createQuery("SELECT u FROM Professor u").getResultList()) {
     System.out.println(o);
   }
   util.checkData("select * from Professor");
   em.getTransaction().rumit();
   em.close();
   emf.close();
 }

}


File: persistence.xml <persistence xmlns="http://java.sun.ru/xml/ns/persistence"

            xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
            xsi:schemaLocation="http://java.sun.ru/xml/ns/persistence http://java.sun.ru/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>


      </source>
   
  
 
  



Find One Object

   <source lang="java">

File: Professor.java

import javax.persistence.Entity; import javax.persistence.Id; @Entity public class Professor {

 @Id
 private int id;
 private String name;
 private long salary;
 public Professor() {
 }
 public Professor(int id) {
   this.id = id;
 }
 public int getId() {
   return id;
 }
 public void setId(int id) {
   this.id = id;
 }
 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() + " salary: " + getSalary();
 }

}

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(int id, String name, long salary) {
   Professor emp = new Professor(id);
   emp.setName(name);
   emp.setSalary(salary);
   em.persist(emp);
   return emp;
 }
 public void removeProfessor(int id) {
   Professor emp = findProfessor(id);
   if (emp != null) {
     em.remove(emp);
   }
 }
 public Professor raiseProfessorSalary(int id, long raise) {
   Professor emp = em.find(Professor.class, id);
   if (emp != null) {
     emp.setSalary(emp.getSalary() + raise);
   }
   return emp;
 }
 public Professor findProfessor(int id) {
   return em.find(Professor.class, id);
 }
 public Collection<Professor> findAllProfessors() {
   Query query = em.createQuery("SELECT e FROM Professor e");
   return (Collection<Professor>) query.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("\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: Main.java // find a specific employee 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();
   Professor emp = service.createProfessor(158, "AAA", 45000);
   em.getTransaction().rumit();
   System.out.println("Persisted " + emp);
   util.checkData("select * from Professor");
   // 
   emp = service.findProfessor(158);
   System.out.println("Found " + emp);    
   
   em.close();
   emf.close();
 }

}


File: persistence.xml <persistence xmlns="http://java.sun.ru/xml/ns/persistence"

            xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
            xsi:schemaLocation="http://java.sun.ru/xml/ns/persistence http://java.sun.ru/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>


      </source>
   
  
 
  



Get Entity by ID

   <source lang="java">

File: Professor.java

import javax.persistence.Entity; import javax.persistence.Id; @Entity public class Professor {

   @Id
   private int id;
   private String name;
   private long salary;
   public Professor() {}
   public Professor(int id) {
       this.id = id;
   }
   public int getId() {
       return id;
   }
   
   public void setId(int id) {
       this.id = id;
   }
   
   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() + " salary: " + getSalary();
   }

}

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(int id, String name, long salary) {
   Professor emp = new Professor(id);
   emp.setName(name);
   emp.setSalary(salary);
   em.persist(emp);
   return emp;
 }
 public void removeProfessor(int id) {
   Professor emp = findProfessor(id);
   if (emp != null) {
     em.remove(emp);
   }
 }
 public Professor raiseProfessorSalary(int id, long raise) {
   Professor emp = em.find(Professor.class, id);
   if (emp != null) {
     emp.setSalary(emp.getSalary() + raise);
   }
   return emp;
 }
 public Professor findProfessor(int id) {
   return em.find(Professor.class, id);
 }
 public Collection<Professor> findAllProfessors() {
   Query query = em.createQuery("SELECT e FROM Professor e");
   return (Collection<Professor>) query.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("\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: Main.java import java.util.Collection; import java.util.Iterator; 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();
   Professor emp = service.createProfessor(1, "name", 100);
   emp = service.createProfessor(2, "name 2", 100);
   Integer userId = 1;
   emp = em.find(Professor.class, userId);
   if (emp == null) {
     System.out.println(userId + " not found! ");
   } else {
     System.out.println("Found " + emp);
   }
   for (Object o : em.createQuery("SELECT u FROM Professor u").getResultList()) {
     System.out.println(o);
   }
   util.checkData("select * from Professor");
   em.getTransaction().rumit();
   em.close();
   emf.close();
 }

}


File: persistence.xml <persistence xmlns="http://java.sun.ru/xml/ns/persistence"

            xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
            xsi:schemaLocation="http://java.sun.ru/xml/ns/persistence http://java.sun.ru/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>

      </source>