| 22. 10. 2. Many To Many Mapping and Remove Operation |
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File: Project.java |
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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();
}
}
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File: Student.java |
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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() ;
}
}
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File: Main.java |
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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();
}
}
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File: Helper.java |
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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");
}
}
}
}
}
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File: persistence.xml |
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<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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 Download: JPA-ManyToManyRemove.zip( 5,288 k) |