many to one mapping not working

gagan.techm · **Posted:** Thu May 05, 2011 8:39 am

Hi I am new to hibernate. I am facing problem while retriving data from DB using hibernates many to one mapping below is the mapping and code.
I want to retirive the list of a students who lives at XXX Street

Thnks in advance

Code:

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping SYSTEM
    "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<hibernate-mapping>
   <class name="com.test.dto.StudentDTO" table="TAB_STUDENT">
      <!-- Shared primary key generator, dependend on "user" property -->
      <id name="studentId" column="STUDENT_ID">
         <generator class="increment" />
      </id>
      <property name="firstName" column="FIRST_NAME" />
      <property name="lastName" column="LAST_NAME" />
      
      <many-to-one name="address" class="com.test.dto.Address" 
      cascade="all" not-null="true" />
      
   </class>
</hibernate-mapping>

Code:

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping SYSTEM
    "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<hibernate-mapping>
   <class name="com.test.dto.Address" table="TAB_ADDRESS">
      <!-- Shared primary key generator, dependend on "user" property -->
      <id name="addressId" column="ADDRESS_ID">
         <generator class="native" />
      </id>
      <property name="street" column="ADDRESS_STREET" />
      <property name="city" column="ADDRESS_CITY" />
      <property name="zipcode" column="ADDRESS_ZIP_CODE" />
      <property name="state" column="ADDRESS_STATE" />
      
   </class>
</hibernate-mapping>

Code:

Criteria criteria = session.createCriteria(Address.class)
      .add(Restrictions.eq("street", "NIBM"));
      
      List l = criteria.list();
      
      List s = new ArrayList();
      Address dto = null;
      for (Iterator iterator = l.iterator(); iterator.hasNext();) {
         dto = (Address) iterator.next();
         System.out.println("ADDRESS ID : "+dto.getAddressId());
      }
      
      s = new TestMain().getStudentFromAddress(dto.getAddressId());
      
      for (Iterator iterator = s.iterator(); iterator.hasNext();) {
         StudentDTO object = (StudentDTO) iterator.next();
         System.out.println("STUDENT FIRST NAME IS "+object.getFirstName());
         System.out.println("ADDRESS IS "+ object.getAddress().getStreet());
         
      }

public List getStudentFromAddress(Long id){
      Session session = HibernateUtils.getSessionFactory().getCurrentSession();
      session.getTransaction().begin();
      Criteria criteria = session.createCriteria(StudentDTO.class)
      .add(Restrictions.eq("addressId", id));
      
      List l = criteria.list();
      
      return l;
   }

Evan1988 · **Posted:** Fri May 06, 2011 5:10 am

Hi, I think you may need to do a one-to-many mapping in the class com.test.dto.Address.

You have the many-to-one mapping in the StudentDTO class with a Address class reference "address", and you can use it to find out the street a specific student lives in.

Also you need to have a one-to-many mapping with a StudentDTO reference in your Address class so that you can use it to find who lives in a specific street.

I am not good at English so you may just test the following codes in case I didnt make myself clear.

Noted that a column name"addressId" has been added to the property "address"

Code:

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping SYSTEM
    "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<hibernate-mapping>
   <class name="com.test.dto.StudentDTO" table="TAB_STUDENT">
      <!-- Shared primary key generator, dependend on "user" property -->
      <id name="studentId" column="STUDENT_ID">
         <generator class="increment" />
      </id>
      <property name="firstName" column="FIRST_NAME" />
      <property name="lastName" column="LAST_NAME" />
      
      <many-to-one name="address" column="addressId" class="com.test.dto.Address" 
      cascade="all" not-null="true" />      
   </class>
</hibernate-mapping>

Code:

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping SYSTEM
    "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<hibernate-mapping>
   <class name="com.test.dto.Address" table="TAB_ADDRESS">
      <!-- Shared primary key generator, dependend on "user" property -->
      <id name="addressId" column="ADDRESS_ID">
         <generator class="native" />
      </id>
      <property name="street" column="ADDRESS_STREET" />
      <property name="city" column="ADDRESS_CITY" />
      <property name="zipcode" column="ADDRESS_ZIP_CODE" />
      <property name="state" column="ADDRESS_STATE" />
      <set name="students"  inverse="true"> 
          <key column="addressId" /> 
          <one-to-many class="com.test.dto.StudentDTO" /> 
      </set>      
   </class>
</hibernate-mapping>

Also you need to add the following into your Address class. Noted that the set name"student" is the "student" used in your mapping above.

Code:

Set<StudentDTO> students = new HashSet<StudentDTO>();