Well, not really. Your code looks like it's examining the database to find
the right ClassDescriptor, which I don't really need to do. I'm looking
for a way to override readObjectFromRow, so that I can simply return an
object of the correct class. All the different classes come from the same
table, so I want to have only one class descriptor.
David
|---------+--------------------------->
| | "Jim Shingler" |
| | <[EMAIL PROTECTED]|
| | et> |
| | |
| | 06/25/2003 05:16|
| | PM |
| | Please respond |
| | to "OJB Users |
| | List" |
| | |
|---------+--------------------------->
>--------------------------------------------------------------------------------------------------------------------------------------------------|
|
|
| To: "'OJB Users List'" <[EMAIL PROTECTED]>
|
| cc:
|
| Subject: RE: Getting the correct class instantiated
|
|
|
>--------------------------------------------------------------------------------------------------------------------------------------------------|
I do the same thing.
Below you will find a segment of my row reader below.
Table
ContactPoint
ID
TypeID
EmailAddress
PhoneNumber
...
ID TypeID EmailAddress PhoneNumber
1 1 [EMAIL PROTECTED]
2 2 NA
123-345.6789
Type Table
ID
classOf
ID ClassOF
1 sd.loc.Email
2 sd.loc.PhoneNumber
Objects
ContactPoint
|- sd.loc.PhoneNumber
|- sd.loc.Email
Obvious disclaimers, I haven't had this reviewed by the experts yet.
Maybe some experts can comment.
ClassDescriptor cld = getClassDescriptor();
// check if there is an attribute which tells us which concrete
class is to be instantiated
//FieldDescriptor concreteClassFD =
cld.getFieldDescriptorByName(ClassDescriptor.OJB_CONCRETE_CLASS);
FieldDescriptor concreteClassFD =
cld.getFieldDescriptorByName("classOf");
FieldDescriptor concreteClassFD2 =
cld.getFieldDescriptorByName("typeID");
ClassDescriptor result = null;
// JLS IDEA:
// IF ClassOf isnt present check for TypeID and Load the underlying
TypeClass to get the "ClassOF"
// TypeID should be the preferred method
if (concreteClassFD == null && concreteClassFD2 == null)
return cld;
if (concreteClassFD2 != null)
{
// Load the Type and pull classof off it
Type typeQuery = new Type();
typeQuery.setObjID((String)
row.get(concreteClassFD2.getColumnName()));
Query query = new
QueryByCriteria(typeQuery);
//uery.
Type type = null;
String concreteClass = null;
PersistenceBroker broker = null;
try
{
broker =
PersistenceBrokerFactory.defaultPersistenceBroker();
//broker.beginTransaction
();
Object o =
broker.getObjectByQuery(query);
type =
(Type)ProxyHelper.getRealObject(o);
//broker.commitTransaction
();
concreteClass =
type.getClassOf();
if (concreteClass == null
||
concreteClass.trim().length() == 0)
{
throw new
PersistenceBrokerException(
"type.classOf
field returned null or 0-length string");
}
else
{
concreteClass
=
concreteClass.trim();
}
result =
broker.getClassDescriptor(Class.forName(concreteClass,
true,
Thread.currentThread().getContextClassLoader()));
//PersistenceBrokerFactory.releaseInstance(broker);
//Constructor con =
result.getZeroArgumentConstructor();
//Object oo =
ConstructorHelper.instantiate(con);
//ClassDescriptor result =
cld.getRepository().getDescriptorFor(concreteClass);
if (result == null)
{
result = cld;
}
return result;
}
catch (PBFactoryException e)
{
throw new
PersistenceBrokerException(e);
}
catch (Throwable t)
{
//broker.abortTransaction
();
t.printStackTrace();
}
}
else if (concreteClassFD != null)
{
try
{
String concreteClass = (String)
row.get(concreteClassFD.getColumnName());
if (concreteClass == null ||
concreteClass.trim().length() == 0)
{
throw new PersistenceBrokerException(
"ojbConcreteClass field returned null or
0-length string");
}
else
{
concreteClass = concreteClass.trim();
}
result =
cld.getRepository().getDescriptorFor(concreteClass);
if (result == null)
{
result = cld;
}
return result;
}
catch (PBFactoryException e)
{
throw new PersistenceBrokerException(e);
}
}
return null;
}
-----Original Message-----
From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]
Sent: Wednesday, June 25, 2003 11:28 AM
To: [EMAIL PROTECTED]
Subject: Getting the correct class instantiated
We would like to have a table that represents 3 or 4 different classes
that share a common base class. When objects are created out of the
table, one column in the table indicates which concrete class should be
instantiated. These objects are refered to by a handful of different
classes. I thought this was a perfect job for a RowReader, but the
RowReader example seems to be a case of instantiating two objects out of
one row, and our attempts at variations have not met with success.
What is the correct approach to this?
David
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