Source Code : Relationship On Id

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Relationship On Id

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<Project> projects;

    public Department() {
        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 deptName) {
        this.name = deptName;
    }
    
    public Collection<Project> getProjects() {
        return projects;
    }

    public String toString() {
        return "Department 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 Department createDepartment(String name, int id) {
    Department dept = new Department();
    dept.setId(id);
    dept.setName(name);
    em.persist(dept);

    return dept;
  }
  public Project createProject(String name, int deptId) {
    Project proj = new Project(findDepartment(deptId));
    proj.setName(name);
    em.persist(proj);

    return proj;
  }

  public Department findDepartment(int id) {
    return em.find(Department.class, id);
  }

  public Collection<Project> findAllProjects() {
    Query query = em.createQuery("SELECT p FROM Project p");
    return (Collection<Project>) query.getResultList();
  }

  public Collection<Department> findAllDepartments() {
    Query query = em.createQuery("SELECT d FROM Department d");
    return (Collection<Department>) query.getResultList();
  }
}


File: Project.java

import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.Id;
import javax.persistence.IdClass;
import javax.persistence.JoinColumn;
import javax.persistence.ManyToOne;

@Entity
@IdClass(ProjectId.class)
public class Project {
  @Id
  @Column(name = "DEPT_ID", insertable = false, updatable = false)
  private int deptId;

  @Id
  private String name;

  @ManyToOne
  @JoinColumn(name = "DEPT_ID")
  private Department department;

  public Project() {
  }

  public Project(Department dept) {
    this.department = dept;
    this.deptId = dept.getId();
  }

  public String getName() {
    return name;
  }

  public void setName(String projectName) {
    this.name = projectName;
  }

  public int getDeptId() {
    return deptId;
  }

  public Department getDepartment() {
    return department;
  }

  public String toString() {
    return "Project name: " + getName();
  }
}


File: ProjectId.java


import java.io.Serializable;

public class ProjectId implements Serializable {
    private int deptId;
    private String name;

    public ProjectId() {}
    public ProjectId(int deptId, String name) {
        this.deptId = deptId;
        this.name = name;
    }

    public String getName() {
        return name;
    }

    public int getId() {
        return deptId;
    }

    public boolean equals(Object o) {
        return ((o instanceof ProjectId) && 
                name.equals(((ProjectId) o).getName()) && 
                deptId == ((ProjectId) o).getId());

    }

    public int hashCode() {
        return name.hashCode() + deptId;
    }
}


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();

    Department dept = service.createDepartment("name",1);
    System.out.print("Created" + dept);
    
    Project proj = service.createProject("name", 1);
    System.out.print("Created" + proj);

    System.out.println("Project:");
    for (Project p : service.findAllProjects()) {
      System.out.println(p + " " + p.getDepartment());
    }

    System.out.println("Departments:");
    for (Department d : service.findAllDepartments()) {
      System.out.println(d + " " + d.getProjects().size());
    }

    util.checkData("select * from Project");

    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("	"+ 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: 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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