How to generate a Collection of objects?

goetzi · **Joined:** Wed May 17, 2006 11:52 am **Posts:** 5

I try to get the following: One user can have many Trainings. How can I achieve that?
I think I need one-to-many or many-to-one. Whats the difference between the both?

Here the SQL statements for creating the tables, so you know my structure:

Code:

create table saTaUser(  
    sUserId varchar(10) not null,  
    sVorname varchar(30) not null,  
    sNachname varchar(30) not null,  
    sPLZ varchar(10) not null,  
    sOrt varchar(30) not null,  
    sStrasse varchar(30) not null,  
    primary key (sUserId)  
)

create table saTaTraining (
    nId identity,
    tEinheitStart date not null,
    tEinheitEnde date not null,
    sBeschreibung varchar(200) not null,
    nAnzahlKm double not null,
    sUserId varchar(10),
    primary key (nId),
    foreign key (sUserId) references saTaUser(sUserId) on delete cascade
)

Mapping documents:

Code:

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping SYSTEM "hibernate-mapping-3.0.dtd">

<hibernate-mapping>
    <class name="sa.bo.UserDAO" table="saTaUser">
      <id name="Id" >
            <column name="sUserId" not-null="true"/>
        </id>
        
        <property name="Vorname">
            <column name="sVorname" length="60" not-null="false" />
        </property>
        
        <property name="Nachname">
           <column name="sNachname" length="60" not-null="false" />
        </property>
        
        <property name="Plz">
           <column name="sPlz" length="30" not-null="false" />
        </property>
        
        <property name="Ort">
           <column name="sOrt" length="60" not-null="false" />
        </property>
        
        <property name="Strasse">
           <column name="sStrasse" length="60" not-null="false" />
        </property>
        
       <set name="Trainings">
           <key column="sUserId" not-null="true"/>
           <one-to-many class="sa.bo.TrainingDAO"/>
       </set>
    </class>
    
    <class name="sa.bo.TrainingDAO" table="saTaTraining">
      <id name="Id">
           <column name="nId" not-null="true" />
           <generator class="identity">
           
           </generator>
        </id>   
        
        <property name="EinheitStart">
            <column name="tEinheitStart" not-null="false" />
        </property>
        
        <property name="EinheitEnde">
           <column name="tEinheitEnde" not-null="false" />
        </property>
        
        <property name="Beschreibung">
           <column name="sBeschreibung" length="240" not-null="false" />
        </property>
        
        <property name="AnzahlKm">
           <column name="nAnzahlKm" not-null="false" />
        </property>     
        
        <property name="UserId">
           <column name="sUserId" not-null="false" />
        </property>
    </class>
</hibernate-mapping>

Full stack trace of any exception that occurs:

Code:

log4j:WARN No appenders could be found for logger (org.hibernate.cfg.Environment).
log4j:WARN Please initialize the log4j system properly.
Exception in thread "main" java.lang.ExceptionInInitializerError
   at util.HibernateUtil.<clinit>(HibernateUtil.java:39)
   at sa.admin.Userverwaltung.find(Userverwaltung.java:242)
   at sa.admin.Userverwaltung.main(Userverwaltung.java:78)
Caused by: org.hibernate.MappingException: Repeated column in mapping for entity: sa.bo.TrainingDAO column: sUserId (should be mapped with insert="false" update="false")
   at org.hibernate.mapping.PersistentClass.checkColumnDuplication(PersistentClass.java:575)
   at org.hibernate.mapping.PersistentClass.checkPropertyColumnDuplication(PersistentClass.java:597)
   at org.hibernate.mapping.PersistentClass.checkColumnDuplication(PersistentClass.java:615)
   at org.hibernate.mapping.PersistentClass.validate(PersistentClass.java:405)
   at org.hibernate.mapping.RootClass.validate(RootClass.java:192)
   at org.hibernate.cfg.Configuration.validate(Configuration.java:984)
   at org.hibernate.cfg.Configuration.buildSessionFactory(Configuration.java:1169)
   at util.HibernateUtil.<clinit>(HibernateUtil.java:34)
   ... 2 more

Name and version of the database you are using:
HSQL

tenwit · **Joined:** Thu Dec 23, 2004 9:08 pm **Posts:** 2008

Many-to-one is used for the reverse direction. User has a one-to-many relation with Training, Training has a many-to-one relation with User.

Have you removed something from your mapping? The error says that sUserId is mapped twice in Training, but it's not mapped twice in the mapping you've posted.

I'm guessing from your mapping that you want to use the sUserId column in saTaTraining to join with the sUserId column in saTaUser. Your mapping is joining on the nId column. To fix that, you either have to add in the many-to-one association from Training to User, or change your mapping to a many-to-many so that you can add a property-ref attribute.

mschulz · **Joined:** Sat Jan 31, 2004 7:19 pm **Posts:** 39

You should take the hint in the exception literally and everything
should fall into place. At the end of sa.bo.TrainingDAO:

Code:

        ...
        <property name="UserId" insert="false" update="false">
           <column name="sUserId" not-null="false" />
        </property> 

tenwit · **Joined:** Thu Dec 23, 2004 9:08 pm **Posts:** 2008

That sidesteps the problem, but it doesn't explain it. Plus, when that mapping gets converted to many-to-one (and it almost certainly should be a many-to-one, IDs shouldn't be mapped using <property> without good reason), having it insert=false update=false means that you won't ever be able to put any Training into a User's collection.

Better to investigate now than simply make the error disappear.

goetzi · **Joined:** Wed May 17, 2006 11:52 am **Posts:** 5

Quote:

Have you removed something from your mapping?

No, I didn't. The error occured with the mapping I posted.

I don't get it working. Can you post the mapping file that is needed for my example?

What I exactly want: The User should have a collection which contains all Trainings where the sUserId is the UserId.

tenwit · **Joined:** Thu Dec 23, 2004 9:08 pm **Posts:** 2008

Code:

<class name="User" ...>
  ...
  <set name="Trainings" ...>
    <key column="sUserId"/>
    <one-to-many class="Training"/>
  </set>
  ...
</class>

<class name="Training" ...>
  ...
  <many-to-one name="User" column="sUserId" .../>
  ...
</class>

You shouldn't map sUserId in Training as a property. If you need it as a property, you can map it, but you must use insert="false" update="false".

goetzi · **Joined:** Wed May 17, 2006 11:52 am **Posts:** 5

Hi,

I reached a point where no errors occur. But I have the problem that there are no elements in the set.

My mapping file:

Code:

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping SYSTEM "hibernate-mapping-3.0.dtd">

<hibernate-mapping>
    <class name="sa.bo.UserDAO" table="saTaUser">
      <id name="Id" >
            <column name="sUserId" not-null="true"/>
        </id>
        
        <property name="Vorname">
            <column name="sVorname" length="60" not-null="false" />
        </property>
        
        <property name="Nachname">
           <column name="sNachname" length="60" not-null="false" />
        </property>
        
        <property name="Plz">
           <column name="sPlz" length="30" not-null="false" />
        </property>
        
        <property name="Ort">
           <column name="sOrt" length="60" not-null="false" />
        </property>
        
        <property name="Strasse">
           <column name="sStrasse" length="60" not-null="false" />
        </property>
        
       <set name="TrainingSet" table="saTaUser">
           <key column="sUserId" />
           <one-to-many class="sa.bo.TrainingDAO"/>
       </set>
    </class>
    
    <class name="sa.bo.TrainingDAO" table="saTaTraining">
      <id name="Id">
           <column name="nId" not-null="true" />
           <generator class="identity">
           
           </generator>
        </id>   
               
        <property name="EinheitStart">
            <column name="tEinheitStart" not-null="false" />
        </property>
        
        <property name="EinheitEnde">
           <column name="tEinheitEnde" not-null="false" />
        </property>
        
        <property name="Beschreibung">
           <column name="sBeschreibung" length="240" not-null="false" />
        </property>
        
        <property name="AnzahlKm">
           <column name="nAnzahlKm" not-null="false" />
        </property>     
        
        <property name="UserId">
           <column name="sUserId" not-null="false" />
        </property>
        
        <!-- <many-to-one name="User" class="sa.bo.UserDAO" column="sUserId" /> -->
    </class>
</hibernate-mapping>

That's my set (defined in UserDAO):

Code:

private Set<TrainingDAO> _soTrainingSet = new HashSet<TrainingDAO>();

The getter and setter methods of the Set:

Code:

    public Set<TrainingDAO> getTrainingSet()
    {
        return _soTrainingSet;
    }

    public void setTrainingSet(Set<TrainingDAO> soTrainings)
    {
        _soTrainingSet = soTrainings;
    }

tenwit · **Joined:** Thu Dec 23, 2004 9:08 pm **Posts:** 2008

I'm guessing that it has something to do with your join. In UserDAO, you're using sUserId as the key to the set: that looks like a string of some sort, though you haven't specified the type (you really should be explicit about types: hibernate might be able to figure it out automatically, but we mere mortals can't...). In TrainingDAO, the PK is nId, which I'm guessing is an int of some kind. If that's the case, it's probable that no rows are matching the join, hence your set is correctly empty.