Java/JPA/Many to Many Mapping

Содержание

1 Many To Many Bidirectional Mapping
2 Many To Many Joined Table
3 Many to Many Mapping Key Table Is Created Automatically
4 Many To Many Mapping Remove Action

Many To Many Bidirectional Mapping

   <source lang="java">

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.ManyToMany; @Entity public class Professor {

   @Id @GeneratedValue(strategy=GenerationType.IDENTITY)
   private int id;
   private String name;
   private long salary;
   
   @ManyToMany 
   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 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();

}

   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();

} }

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: 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("empName", 100L);
   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: 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>

Many To Many Joined Table

   <source lang="java">

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: 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("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: 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>

Many to Many Mapping Key Table Is Created Automatically

   <source lang="java">

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.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;
   
   @ManyToMany 
   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 void setProjects(Collection<Project> projects) {
     this.projects = projects;
   }
   public void setSalary(long salary) {
     this.salary = salary;
   }
   public void setStartDate(Date startDate) {
     this.startDate = startDate;
   }
   public long getSalary() {
       return salary;
   }
   public Date getStartDate() {
       return startDate;
   }
   
   public Collection<Project> getProjects() {
       return projects;
   }
   
   public String toString() {
       return "Professor " + getId() + 
              ": name: " + getName() +
              ", salary: " + getSalary();
   }

}

File: ProfessorService.java import java.util.Collection; import javax.persistence.EntityManager; public class ProfessorService {

 protected EntityManager em;
 public ProfessorService(EntityManager em) {
   this.em = em;
 }
 public Professor createProfessor(String name, long salary) {
   Professor emp = new Professor();
   emp.setName(name);
   emp.setSalary(salary);
   em.persist(emp);
   return emp;
 }

 public Project createProject(String name) {
   Project space = new Project();
   space.setName(name);
   em.persist(space);
   return space;
 }

 public Collection<Professor> findAllProfessors() {
   return (Collection<Professor>) em.createQuery("SELECT e FROM Professor e").getResultList();
 }
 public void assignProfessorToProject(int empId, int projectId) {
   Project project = em.find(Project.class, projectId);
   Professor employee = em.find(Professor.class, empId);
   project.getProfessors().add(employee);
   employee.getProjects().add(project);
 }
 public Collection<Project> findAllProjects() {
   return (Collection<Project>) em.createQuery("SELECT p FROM Project p").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")
   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 void setProfessors(Collection<Professor> employees) {
     this.employees = employees;
   }
   public void setId(int id) {
     this.id = id;
   }
   public void setName(String name) {
     this.name = name;
   }
   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();
   Professor emp = service.createProfessor("name",100);
   Project proj = service.createProject("proj name");
   
   service.assignProfessorToProject(emp.getId(),proj.getId());

for (Object o : service.findAllProfessors()) { System.out.println(o ); } for (Object o : service.findAllProjects()) {

 System.out.println(o);

}

   util.checkData("select * from Professor");
   util.checkData("select * from Project");
   
   util.checkData("select * from Professor_Project");
   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>

Many To Many Mapping Remove Action

   <source lang="java">

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().rumit();
   em.close();
   emf.close();
   
   Helper.checkData();
 }

}

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>

Java/JPA/Many to Many Mapping

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Many To Many Bidirectional Mapping

Many To Many Joined Table

Many to Many Mapping Key Table Is Created Automatically

Many To Many Mapping Remove Action

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