Sto usando Hibernate per tutte le operazioni CRUD nel mio progetto. Non funziona per le relazioni uno-a-molti e molti-a-uno. Mi dà il seguente errore.
org.hibernate.MappingException: Could not determine type for: java.util.List, at table: College, for columns: [org.hibernate.mapping.Column(students)]
Poi di nuovo ho seguito questo video tutorial . Per me è molto semplice, all'inizio. Ma non riesco a farlo funzionare. Anche adesso, dice
org.hibernate.MappingException: Could not determine type for: java.util.List, at table: College, for columns: [org.hibernate.mapping.Column(students)]
Ho eseguito alcune ricerche su Internet, qualcuno dice che è un bug in Hibernate e alcuni dicono che, aggiungendo @GenereatedValue, questo errore verrà cancellato, ma non funziona per me.
College.java
@Entity
public class College {
@Id
@GeneratedValue(strategy=GenerationType.AUTO)
private int collegeId;
private String collegeName;
private List<Student> students;
@OneToMany(targetEntity=Student.class, mappedBy="college", fetch=FetchType.EAGER)
public List<Student> getStudents() {
return students;
}
public void setStudents(List<Student> students) {
this.students = students;
}//Other gettters & setters omitted
Student.java
@Entity
public class Student {
@Id
@GeneratedValue(strategy=GenerationType.AUTO)
private int studentId;
private String studentName;
private College college;
@ManyToOne
@JoinColumn(name="collegeId")
public College getCollege() {
return college;
}
public void setCollege(College college) {
this.college = college;
}//Other gettters & setters omitted
Main.java:
public class Main {
private static org.hibernate.SessionFactory sessionFactory;
public static SessionFactory getSessionFactory() {
if (sessionFactory == null) {
initSessionFactory();
}
return sessionFactory;
}
private static synchronized void initSessionFactory() {
sessionFactory = new AnnotationConfiguration().configure().buildSessionFactory();
}
public static Session getSession() {
return getSessionFactory().openSession();
}
public static void main (String[] args) {
Session session = getSession();
Transaction transaction = session.beginTransaction();
College college = new College();
college.setCollegeName("Dr.MCET");
Student student1 = new Student();
student1.setStudentName("Peter");
Student student2 = new Student();
student2.setStudentName("John");
student1.setCollege(college);
student2.setCollege(college);
session.save(student1);
session.save(student2);
transaction.commit();
}
}
Console:
Exception in thread "main" org.hibernate.MappingException: Could not determine type for: java.util.List, at table: College, for columns: [org.hibernate.mapping.Column(students)]
at org.hibernate.mapping.SimpleValue.getType(SimpleValue.java:306)
at org.hibernate.mapping.SimpleValue.isValid(SimpleValue.java:290)
at org.hibernate.mapping.Property.isValid(Property.java:217)
at org.hibernate.mapping.PersistentClass.validate(PersistentClass.java:463)
at org.hibernate.mapping.RootClass.validate(RootClass.java:235)
at org.hibernate.cfg.Configuration.validate(Configuration.java:1330)
at org.hibernate.cfg.Configuration.buildSessionFactory(Configuration.java:1833)
at test.hibernate.Main.initSessionFactory(Main.java:22)
at test.hibernate.Main.getSessionFactory(Main.java:16)
at test.hibernate.Main.getSession(Main.java:27)
at test.hibernate.Main.main(Main.java:43)
L'XML:
<?xml version='1.0' encoding='utf-8'?>
<!DOCTYPE hibernate-configuration PUBLIC
"-//Hibernate/Hibernate Configuration DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd">
<hibernate-configuration>
<session-factory>
<!-- Database connection settings -->
<property name="connection.driver_class">com.mysql.jdbc.Driver</property>
<property name="connection.url">jdbc:mysql://localhost:3306/dummy</property>
<property name="connection.username">root</property>
<property name="connection.password">1234</property>
<!-- JDBC connection pool (use the built-in) -->
<property name="connection.pool_size">1</property>
<!-- SQL dialect -->
<property name="dialect">org.hibernate.dialect.MySQLDialect</property>
<!-- Enable Hibernate's automatic session context management -->
<property name="current_session_context_class">thread</property>
<!-- Disable the second-level cache -->
<property name="cache.provider_class">org.hibernate.cache.NoCacheProvider</property>
<!-- Echo all executed SQL to stdout -->
<property name="show_sql">true</property>
<!-- Drop and re-create the database schema on startup -->
<property name="hbm2ddl.auto">update</property>
<mapping class="test.hibernate.Student" />
<mapping class="test.hibernate.College" />
</session-factory>