Java/JPA/Many to Many Mapping
Содержание
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>