Java/JPA/Join Columns

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Inversion Join Column

File: Professor.java

import java.util.ArrayList;
import java.util.Collection;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.JoinTable;
import javax.persistence.ManyToMany;
@Entity
public class Professor {
    @Id @GeneratedValue(strategy=GenerationType.IDENTITY)
    private int id;
    private String name;
    private long salary;
    
    @ManyToMany 
    @JoinTable(name="EMP_PROJ", 
          joinColumns=@JoinColumn(name="EMP_ID"),
          inverseJoinColumns=@JoinColumn(name="PROJ_ID"))
    private Collection<Project> projects;
    
    
    public Professor() {
        projects = new ArrayList<Project>();
    }
    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 void addProject(Project project) {
        if (!getProjects().contains(project)) {
            getProjects().add(project);
        }
        if (!project.getProfessors().contains(this)) {
            project.getProfessors().add(this);
        }
    }
    public Collection<Project> getProjects() {
        return projects;
    }
    public String toString() {
        return "Professor id: " + getId() + " name: " + getName() + 
               " with " + getProjects().size() + " projects";
    }
}

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 Project createProject(String name) {
    Project proj = new Project();
    proj.setName(name);
    em.persist(proj);
    return proj;
  }
  public Collection<Project> findAllProjects() {
    Query query = em.createQuery("SELECT p FROM Project p");
    return (Collection<Project>) query.getResultList();
  }
  public Professor createProfessor(String name, long salary) {
    Professor emp = new Professor();
    emp.setName(name);
    emp.setSalary(salary);
    em.persist(emp);
    return emp;
  }
  public Professor addProfessorProject(int empId, int projId) {
    Professor emp = em.find(Professor.class, empId);
    Project proj = em.find(Project.class, projId);
    proj.addProfessor(emp);
    return emp;
  }
  public Collection<Professor> findAllProfessors() {
    Query query = em.createQuery("SELECT e FROM Professor e");
    return (Collection<Professor>) query.getResultList();
  }
}

File: Project.java

import java.util.ArrayList;
import java.util.Collection;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.ManyToMany;
@Entity
public class Project {
    @Id @GeneratedValue(strategy=GenerationType.IDENTITY)
    protected int id;
    protected String name;
    @ManyToMany(mappedBy="projects")
    private Collection<Professor> employees;
    public Project() {
        employees = new ArrayList<Professor>();
    }
    public int getId() {
        return id;
    }
    
    public void setId(int projectNo) {
        this.id = projectNo;
    }
    
    public String getName() {
        return name;
    }
    
    public void setName(String projectName) {
        this.name = projectName;
    }
    
    public Collection<Professor> getProfessors() {
        return employees;
    }
    
    public void addProfessor(Professor employee) {
        if (!getProfessors().contains(employee)) {
            getProfessors().add(employee);
        }
        if (!employee.getProjects().contains(this)) {
            employee.getProjects().add(this);
        }
    }
    
    public String toString() {
        return "Project id: " + getId() + ", name: " + getName() +
               " with " + getProfessors().size() + " employees";
    }
}

File: Main.java
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("empName",100);
    Project proj = service.createProject("projName");

    emp = service.addProfessorProject(emp.getId(),proj.getId());
    Collection<Professor> emps = service.findAllProfessors();
    if (emps.isEmpty()) {
        System.out.println("No Professors found ");
    } else {
      System.out.println("Found Professors:");
        for (Professor emp1 : emps) {
          System.out.println(emp1);
        }
    }
    
    Collection<Project> projs = service.findAllProjects();
    if (projs.isEmpty()) {
      System.out.println("No Projects found ");
    } else {
      System.out.println("Found Projects:");
        for (Project proj1 : projs) {
          System.out.println(proj1);
        }
    }
    util.checkData("select * from Professor");
    
    util.checkData("select * from Project");
    em.getTransaction().rumit();
    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: 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>





Join Two Entities With Parameter

File: Department.java

import java.util.ArrayList;
import java.util.Collection;
import javax.persistence.Entity;
import javax.persistence.Id;
import javax.persistence.OneToMany;
@Entity
public class Department {
    @Id
    private int id;
    private String name;
    @OneToMany(mappedBy="department")
    private Collection<Professor> employees;
    public Department() {
        employees = new ArrayList<Professor>();
    }
    
    public int getId() {
        return id;
    }
    
    public String getName() {
        return name;
    }
    
    public Collection<Professor> getProfessors() {
        return employees;
    }
    public String toString() {
        return "Department no: " + getId() + 
               ", name: " + getName();
    }
}

File: Professor.java

import java.util.ArrayList;
import java.util.Collection;
import java.util.Date;
import javax.persistence.Entity;
import javax.persistence.Id;
import javax.persistence.ManyToMany;
import javax.persistence.ManyToOne;
import javax.persistence.OneToMany;
import javax.persistence.Temporal;
import javax.persistence.TemporalType;
@Entity
public class Professor {
    @Id
    private int id;
    private String name;
    private long salary;
    @Temporal(TemporalType.DATE)
    private Date startDate;
    
    @ManyToOne
    private Professor manager;
    
    @OneToMany(mappedBy="manager")
    private Collection<Professor> directs;
    @ManyToOne
    private Department department;
    
    @ManyToMany 
    private Collection<Project> projects;
    public Professor() {
        projects = new ArrayList<Project>();
        directs = new ArrayList<Professor>();
    }
    public int getId() {
        return id;
    }
    
    public String getName() {
        return name;
    }
    public long getSalary() {
        return salary;
    }
    public Date getStartDate() {
        return startDate;
    }
    
    public Department getDepartment() {
        return department;
    }
    
    public Collection<Professor> getDirects() {
        return directs;
    }
    
    public Professor getManager() {
        return manager;
    }
    public Collection<Project> getProjects() {
        return projects;
    }
    
    public String toString() {
        return "Professor " + getId() + 
               ": name: " + getName() +
               ", salary: " + getSalary() +
               ", dept: " + ((getDepartment() == null) ? null : getDepartment().getName());
    }
}

File: ProfessorService.java
import java.util.Collection;
import javax.persistence.EntityManager;
import javax.persistence.NoResultException;
public class ProfessorService {
  protected EntityManager em;
  public ProfessorService(EntityManager em) {
    this.em = em;
  }
  public long queryEmpSalary(String deptName, String empName) {
    String query = "SELECT e.salary " + "FROM Professor e " + "WHERE e.department.name = ""
        + deptName + "" AND " + " e.name = "" + empName + """;
    try {
      return (Long) em.createQuery(query).getSingleResult();
    } catch (NoResultException e) {
      return 0;
    }
  }
  public long queryEmpSalaryUsingParams(String deptName, String empName) {
    try {
      return (Long) em.createQuery(
          "SELECT e.salary " + "FROM Professor e " + "WHERE e.department.name = :deptName AND "
              + " e.name = :empName ").setParameter("deptName", deptName).setParameter("empName",
          empName).getSingleResult();
    } catch (NoResultException e) {
      return 0;
    }
  }
}

File: Project.java

import java.util.ArrayList;
import java.util.Collection;
import javax.persistence.Entity;
import javax.persistence.Id;
import javax.persistence.ManyToMany;
@Entity
public class Project {
    @Id
    protected int id;
    protected String name;
    @ManyToMany(mappedBy="projects")
    private Collection<Professor> employees;
    public Project() {
        employees = new ArrayList<Professor>();
    }
    public int getId() {
        return id;
    }
    
    public String getName() {
        return name;
    }
    
    public Collection<Professor> getProfessors() {
        return employees;
    }
    
    public String toString() {
        return "Project id: " + getId() + ", name: " + getName();
    }
}

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 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();
    long l = service.queryEmpSalary("deptName", "empName");
    
    long q = service.queryEmpSalaryUsingParams("deptName", "empName");
    
    
    util.checkData("select * from Professor");
    util.checkData("select * from Department");
    
    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>





Mark Joined Column As Nullable

File: Address.java
import javax.persistence.Entity;
import javax.persistence.Id;
@Entity
public class Address {
    @Id
    private int id;
    private String street;
    private String city;
    private String state;
    private String zip;
    
    public int getId() {
        return id;
    }
    
    public void setId(int id) {
        this.id = id;
    }
    
    public String getStreet() {
        return street;
    }
    
    public void setStreet(String address) {
        this.street = address;
    }
    public String getCity() {
        return city;
    }
    public void setCity(String city) {
        this.city = city;
    }
    public String getState() {
        return state;
    }
    public void setState(String state) {
        this.state = state;
    }
    public String getZip() {
        return zip;
    }
    public void setZip(String zip) {
        this.zip = zip;
    }
    public String toString() {
        return "Address id: " + getId() + 
               ", street: " + getStreet() +
               ", city: " + getCity() +
               ", state: " + getState() +
               ", zip: " + getZip();
    }
}

File: Professor.java

import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.ManyToOne;
@Entity
public class Professor {
    @Id private int id;
    @Column(nullable=false)
    private String name;
    private long salary;
    @ManyToOne 
    @JoinColumn(nullable=false)
    private Address address;
    
    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 Address getAddress() {
        return address;
    }
    
    public void setAddress(Address address) {
        this.address = address; 
    }
    
    public String toString() {
        return "Professor id: " + getId() + " name: " + getName();
    }
}

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 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 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.findAllProfessors();
    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>





Primary Key Column as Joined Column

File: ParkingSpace.java

import javax.persistence.Entity;
import javax.persistence.Id;
import javax.persistence.OneToOne;
import javax.persistence.PrimaryKeyJoinColumn;
import javax.persistence.Table;
@Entity
public class ParkingSpace {
    @Id
    private int id;
    private int lot;
    private String location;
    @OneToOne
    @PrimaryKeyJoinColumn
    private Professor employee;
    public int getId() {
        return id;
    }
    
    public void setId(int id) {
        this.id = id;
    }
    public int getLot() {
        return lot;
    }
    public void setLot(int lot) {
        this.lot = lot;
    }
    
    public String getLocation() {
        return location;
    }
    
    public void setLocation(String deptName) {
        this.location = deptName;
    }
    public Professor getProfessor() {
        return employee;
    }
    public void setProfessor(Professor employee) {
        this.employee = employee;
    }
    
    public String toString() {
        return "ParkingSpace id: " + getId() + " lot: " + getLot() +
               ", location: " + getLocation();
    }
}

File: Professor.java

import javax.persistence.Entity;
import javax.persistence.Id;
import javax.persistence.OneToOne;
@Entity
public class Professor {
    @Id
    private int id;
    private String name;
    private long salary;
    
    @OneToOne(mappedBy="employee") 
    private ParkingSpace parkingSpace;
    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 ParkingSpace getParkingSpace() {
        return parkingSpace;
    }
    
    public void setParkingSpace(ParkingSpace parkingSpace) {
        this.parkingSpace = parkingSpace;
    }
    public String toString() {
        return "Professor id: " + getId() + " name: " + getName() + 
               " with " + getParkingSpace();
    }
}

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();
    emp.setId(id);
    emp.setName(name);
    emp.setSalary(salary);
    em.persist(emp);
    return emp;
  }
  public Collection<Professor> findAllProfessors() {
    Query query = em.createQuery("SELECT e FROM Professor e");
    return (Collection<Professor>) query.getResultList();
  }
  public ParkingSpace createParkingSpace(Professor emp, int lot, String location) {
    ParkingSpace space = new ParkingSpace();
    space.setId(emp.getId());
    space.setLot(lot);
    space.setLocation(location);
    emp.setParkingSpace(space);
    space.setProfessor(emp);
    em.persist(space);
    return space;
  }
  public Collection<ParkingSpace> findAllParkingSpaces() {
    Query query = em.createQuery("SELECT p FROM ParkingSpace p");
    return (Collection<ParkingSpace>) 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 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, "empName", 100L);
    service.createParkingSpace(emp, 1, "location");
    System.out.println("Created " + emp);
    Collection<Professor> emps = service.findAllProfessors();
    if (emps.isEmpty()) {
      System.out.println("No Professors found ");
    } else {
      System.out.println("Found Professors:");
      for (Professor emp1 : emps) {
        System.out.println(emp1);
      }
    }
    Collection<ParkingSpace> pSpaces = service.findAllParkingSpaces();
    if (pSpaces.isEmpty()) {
      System.out.println("No ParkingSpaces found ");
    } else {
      System.out.println("Found ParkingSpaces:");
      for (ParkingSpace pSpace : pSpaces) {
        System.out.println(pSpace);
      }
    }
    util.checkData("select * from Professor");
    util.checkData("select * from ParkingSpace");
    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>





Set Referenced Column Inverse Join Column

File: Professor.java

import java.util.ArrayList;
import java.util.Collection;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.Id;
import javax.persistence.IdClass;
import javax.persistence.JoinColumn;
import javax.persistence.JoinColumns;
import javax.persistence.JoinTable;
import javax.persistence.ManyToMany;
import javax.persistence.ManyToOne;
import javax.persistence.OneToMany;
@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;
    @ManyToOne 
    @JoinColumns({
        @JoinColumn(name="MGR_COUNTRY", referencedColumnName="COUNTRY"),
        @JoinColumn(name="MGR_ID", referencedColumnName="EMP_ID")
    })
    private Professor manager;
    @OneToMany(mappedBy="manager")
    private Collection<Professor> directs;
    @ManyToMany 
    @JoinTable(
        name="EMP_PROJECT", 
        joinColumns={
            @JoinColumn(name="EMP_COUNTRY", referencedColumnName="COUNTRY"),
            @JoinColumn(name="EMP_ID", referencedColumnName="EMP_ID")},
        inverseJoinColumns=@JoinColumn(name="PROJECT_ID"))
    private Collection<Project> projects;
    public Professor() {
        directs = new ArrayList<Professor>();
        projects = new ArrayList<Project>();
    }
    
    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 Collection<Professor> getDirects() {
        return directs;
    }
    
    public Professor getManager() {
        return manager;
    }
    
    public void setManager(Professor manager) {
        this.manager = manager;
    }
    
    public Collection<Project> getProjects() {
        return projects;
    }
    public String toString() {
        return "Professor id: " + getId() + " name: " + getName() +
               " country: " + getCountry();
    }
}

File: ProfessorId.java
import java.io.Serializable;
import javax.persistence.Column;
import javax.persistence.Embeddable;
@Embeddable
public class ProfessorId implements Serializable{
  private String country;
  @Column(name = "EMP_ID")
  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 void createProject(String projName) {
    Project proj = new Project();
    proj.setName(projName);
    em.persist(proj);
  }
  public void setProfessorManager(String country, int id, String mgrCountry, int mgrId) {
    Professor emp = findProfessor(country, id);
    Professor mgr = findProfessor(mgrCountry, mgrId);
    emp.setManager(mgr);
    mgr.getDirects().add(emp);
  }
  public void addProfessorProject(String country, int id, int projId) {
    Professor emp = findProfessor(country, id);
    Project proj = em.find(Project.class, projId);
    emp.getProjects().add(proj);
    proj.getProfessors().add(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();
  }
  public Collection<Project> findAllProjects() {
    Query query = em.createQuery("SELECT p FROM Project p");
    return (Collection<Project>) query.getResultList();
  }
}

File: Project.java
import java.util.ArrayList;
import java.util.Collection;
import javax.persistence.Entity;
import javax.persistence.Id;
import javax.persistence.ManyToMany;
@Entity
public class Project {
  @Id
  protected int id;
  protected String name;
  @ManyToMany(mappedBy = "projects")
  protected Collection<Professor> employees = new ArrayList<Professor>();
  public int getId() {
    return id;
  }
  public void setId(int projectNo) {
    this.id = projectNo;
  }
  public String getName() {
    return name;
  }
  public void setName(String projectName) {
    this.name = projectName;
  }
  public Collection<Professor> getProfessors() {
    return employees;
  }
  public void addProfessor(Professor employee) {
    if (!getProfessors().contains(employee)) {
      getProfessors().add(employee);
    }
    if (!employee.getProjects().contains(this)) {
      employee.getProjects().add(this);
    }
  }
  public String toString() {
    return getClass().getName().substring(getClass().getName().lastIndexOf(".") + 1) + " no: "
        + getId() + ", name: " + getName();
  }
}

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 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);
    service.createProfessor("mgrcountry", 2, "mgrName", 100);
    service.createProject("proj");
    service.addProfessorProject("empCountry2", 1, 1);
    service.setProfessorManager("Country", 1, "mgrCountry", 1);

    System.out.println("Professors:");
    for (Professor emp : service.findAllProfessors()) {
      System.out.println(emp + " " + emp.getProjects().size());
      System.out.println(emp + " " + emp.getManager());
    }
    System.out.println("Projects:");
    for (Project p : service.findAllProjects()) {
      System.out.print(p + " " + p.getProfessors().size());
    }
    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>


Источник — «http://jexp.ru/index.php?title=Java/JPA/Join_Columns&oldid=8961»