Project.java Source code

Introduction

Here is the source code for Project.java

Source

    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<Student> students;

    public Project() {
        students = new ArrayList<Student>();
    }
    public void setId(int i){
      id = i;
    }
    public int getId() {
        return id;
    }
    
    public String getName() {
        return name;
    }
    
    public Collection<Student> getStudents() {
        return students;
    }
    
    public String toString() {
        return "Project id: " + getId() + ", name: " + getName();
    }
}

    File:Student.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.Temporal;
    import javax.persistence.TemporalType;

@Entity
public class Student {
    @Id
    private int id;
    private String name;

    
    @ManyToMany 
    private Collection<Project> projects;

    public Student() {
        projects = new ArrayList<Project>();
    }

    public int getId() {
        return id;
    }
    
    public void setId(int id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    
    public Collection<Project> getProjects() {
        return projects;
    }
    
    public String toString() {
        return "Student " + getId() + 
               ": name: " + getName() ;
    }
}

    File:Helper.java

    import java.sql.Connection;
    import java.sql.DriverManager;
    import java.sql.ResultSet;
    import java.sql.ResultSetMetaData;
    import java.sql.Statement;

public class Helper {
  public static void checkData() throws Exception {
    Class.forName("org.hsqldb.jdbcDriver");
    Connection conn = DriverManager.getConnection("jdbc:hsqldb:data/tutorial", "sa", "");
    Statement st = conn.createStatement();

    ResultSet mrs = conn.getMetaData().getTables(null, null, null, new String[] { "TABLE" });
    while (mrs.next()) {
      String tableName = mrs.getString(3);
      System.out.println("\n\n\n\nTable Name: "+ tableName);

      ResultSet rs = st.executeQuery("select * from " + tableName);
      ResultSetMetaData metadata = rs.getMetaData();
      while (rs.next()) {
        System.out.println(" Row:");
        for (int i = 0; i < metadata.getColumnCount(); i++) {
          System.out.println("    Column Name: "+ metadata.getColumnLabel(i + 1)+ ",  ");
          System.out.println("    Column Type: "+ metadata.getColumnTypeName(i + 1)+ ":  ");
          Object value = rs.getObject(i + 1);
          System.out.println("    Column Value: "+value+"\n");
        }
      }
    }
  }
}

    File:Main.java

    import java.util.List;

    import javax.persistence.EntityManager;
    import javax.persistence.EntityManagerFactory;
    import javax.persistence.Persistence;
    import javax.persistence.Query;

    public class Main {
        static EntityManagerFactory emf = Persistence.createEntityManagerFactory("JPAService");
        static EntityManager em = emf.createEntityManager();

        public static void main(String[] a) throws Exception {
            em.getTransaction().begin();

            Student student = new Student();
            student.setId(1);
            em.persist(student);

            Project dept = new Project();
            dept.setId(1);
            em.persist(dept);

            em.flush();

            em.remove(dept);

            Query query = em.createQuery("SELECT e FROM Student e");
            List<Student> list = (List<Student>) query.getResultList();
            System.out.println(list);

            query = em.createQuery("SELECT d FROM Project d");
            List<Project> dList = (List<Project>) query.getResultList();
            System.out.println(dList);

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

            Helper.checkData();
        }
    }

    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>