IDE Environment: Eclipse-3.4
DB Environment: Apache-Derby-10.5.1.1
JDK Environment: Sun JDK-1.6.0_07
Jar Environment: from
http://openjpa.apache.org/builds/latest/downloads/apache-openjpa-2.0.0-SNAPSHOT-binary.zip
Eclipse PlugIn Environment:Apache-Derby, JUnit4
I want to test the @ManyToMany(the example is Teacher and Student, many to
many)
The code is this:
Student.java
@Entity
public class Student {
private int id;
private String name;
private Set<Teacher> teachers = new HashSet<Teacher>();
@Id
@GeneratedValue
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
@Column(length = 10, nullable = false)
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
@ManyToMany(cascade = { CascadeType.REFRESH })
@JoinTable(
name = "STUDENT_TEACHER",
inverseJoinColumns = @JoinColumn(name = "TEACHER_ID"),
joinColumns = @JoinColumn(name = "STUDENT_ID")
)
public Set<Teacher> getTeachers() {
return teachers;
}
public void setTeachers(Set<Teacher> teachers) {
this.teachers = teachers;
}
public void addTeacher(Teacher teacher) {
this.teachers.add(teacher);
}
public void removeTeacher(Teacher teacher) {
if (this.teachers.contains(teacher)) {
this.teachers.remove(teacher);
}
}
}
Teacher.java
@Entity
public class Teacher {
private int id;
private String name;
private Set<Student> students = new HashSet<Student>();
@Id
@GeneratedValue
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
@Column(length=10, nullable=false)
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
@ManyToMany(cascade={CascadeType.REFRESH}, mappedBy="teachers" )
public Set<Student> getStudents() {
return students;
}
public void setStudents(Set<Student> students) {
this.students = students;
}
@Override
public int hashCode() {
final int prime = 31;
int result = 1;
result = prime * result + id;
return result;
}
@Override
public boolean equals(Object obj) {
if (this == obj)
return true;
if (obj == null)
return false;
if (getClass() != obj.getClass())
return false;
Teacher other = (Teacher) obj;
if (id != other.id)
return false;
return true;
}
}
ManyToManyTest.java
public class ManyToManyTest {
@Test
public void testPersist(){
EntityManagerFactory emf =
Persistence.createEntityManagerFactory("sample");
EntityManager em = emf.createEntityManager();
EntityTransaction et = em.getTransaction();
et.begin();
Student student = new Student();
student.setName("student1");
Teacher teacher = new Teacher();
teacher.setName("teacher1");
em.persist(student);
em.persist(teacher);
et.commit();
em.close();
emf.close();
}
@Test
public void testPersistJoinTable(){
EntityManagerFactory emf =
Persistence.createEntityManagerFactory("sample");
EntityManager em = emf.createEntityManager();
EntityTransaction et = em.getTransaction();
et.begin();
Student student = em.find(Student.class, 1);
Teacher teacher = em.getReference(Teacher.class, 51);
student.addTeacher(teacher);
et.commit();
em.close();
emf.close();
}
}
and META-INF/persistence.xml is
<persistence-unit name="sample" transaction-type="RESOURCE_LOCAL">
<provider>org.apache.openjpa.persistence.PersistenceProviderImpl</provider>
<!-- Many to many Type -->
<class>org.sample.demo.jpa.entity.manytomany.Student</class>
<class>org.sample.demo.jpa.entity.manytomany.Teacher</class>
<properties>
<property name="openjpa.jdbc.DBDictionary"
value="derby"/>
<property name="openjpa.ConnectionURL"
value="jdbc:derby://localhost:1527/sample;create=true" />
<property name="openjpa.ConnectionDriverName"
value="org.apache.derby.jdbc.ClientDriver" />
<property name="openjpa.ConnectionUserName"
value="user" />
<property name="openjpa.ConnectionPassword"
value="secret" />
<property name="openjpa.jdbc.SynchronizeMappings"
value="buildSchema(ForeignKeys=true)"/>
</properties>
</persistence-unit>
---------------------------------------------------------
I tested the method testPersist(), everythind is right.
Question is when I tested the method testPersistJoinTable() It throws a
NullPointException, when it processed in Student student =
em.find(Student.class, 1);, the student object's Set<Teacher> is null, and I
could not insert into table STUDENT_TEACHER.(The student's id and teacher's
id were exist).
after that I use Hibernate, It's right, and I can do addTeacher(Teacher)
method. and Set<Teacher> is not null.
I think a use JPA and it should be both right……
Does someone can fix this question? any help is OK.
---
Thanks.
Open Gloves
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