Re: Casting an Object to a subclass

[Armin Waibel]

Hi,

I never used this feature and don't know much about it, but some things 
may problematic:

test.Point, field-descriptor for PK "id" is declared anonymous

test.NamedPoint, field-descriptor for PK "id" is anonymous
and no seperate reference field for reference (PK and reference
id field are the same)
regards,
Armin
[EMAIL PROTECTED] wrote:




Hello,

I am using the ODMG API.
i don't know whether this behaviour is to be expected:
I am mapping a child class to it's parent class via multiple joined tables.
When I retrive objects of the parent class from the Database, some of the
returned objects should be members of a child class.
But if i ask  for the objects of the parent class, I only get them as
instances of the parent class.
In the spy.log - File I can see that only parent objects are retrieved.
What can I do to get the "real" objects?



The repository:
<class-descriptor class="test.Point" table="point">

<field-descriptor
id="1"
name="id"
column="id"
jdbc-type="INTEGER"
primarykey="true"
autoincrement="true"
access="anonymous"/>
<field-descriptor id="2"
name="region"
column="region"
jdbc-type="VARCHAR"/>
</class-descriptor>
<class-descriptor class="test.NamedPoint" table="namedpoint">
<field-descriptor id="1"
name="id"
column="id"
jdbc-type="INTEGER"
primarykey="true"
autoincrement="true"
access="anonymous"/>
<field-descriptor id="2"
name="name"
column="name"
jdbc-type="VARCHAR"/>
<reference-descriptor name="super" class-ref="test.Point">
<foreignkey field-ref="id" /> 
</reference-descriptor>

</class-descriptor>

the table definitions:
CREATE TABLE point (id INT PRIMARY KEY, region VARCHAR (20)) ;
CREATE TABLE namedpoint (id INT PRIMARY KEY,name VARCHAR (20)) ;
the main - Method (Class definitions are as expected from the repository):
      public static void main(String[] args) {
            // Open Database
            Implementation theOdmg = OJB.getInstance();
            Database theDb = theOdmg.newDatabase();
            try {
                  theDb.open("default", Database.OPEN_READ_WRITE);
            } catch (ODMGException ex) {
                  ex.printStackTrace();
            }
            //Create a NamedPoint
            Transaction tx = theOdmg.newTransaction();
            tx.begin();
            NamedPoint np = new NamedPoint();
            np.setRegion("region");
            np.setName("test");
            tx.lock(np, Transaction.WRITE);
            tx.commit();
            //get Point
            tx = theOdmg.newTransaction();
            tx.begin();
            OQLQuery query = theOdmg.newOQLQuery();
            DList pointList = null;
            try {
                  String queryString =
                        "select all from " + Point.class.getName() + "
where region =\"region\"";
                  query.create(queryString);
                  pointList = (DList) query.execute();
                  java.util.Iterator iter = pointList.iterator();
                  while (iter.hasNext()) {
                        Point point = (Point) iter.next();
                        if (point instanceof NamedPoint) {
                              System.out.println("Named Point!");
                        } else {
                              System.out.println("No Named Point!");
                        }
                  }
            } catch (QueryInvalidException ex) {
                  ex.printStackTrace();
            } catch (QueryException ex) {
                  ex.printStackTrace();
            }
      }
the text on the Screen:
No Named Point!
thanks,
Birgitta
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