HEllo everybody,
I'm facing an issue with JDO which is presented elsewhere in the
group, but with no workaround.
I simply need to retrieve an object from JDO using only the key.
That is do something like this
PersistenceManager pm = pmf.getPersistenceManager();
SimpleObject ll = new SimpleObject;
try{
pm.makePersistent(ll);
Key leftKey = ll.getKey();
Object retriveved = pm.getObjectById(leftKey);
}
finally{
pm.close();
}
This does not work. Documentation at
http://code.google.com/appengine/docs/java/datastore/creatinggettinganddeletingdata.html#Getting_an_Object_By_Key
states you must provide a class identifier to retrieve objects using
keys, so call
SimpleObject retriveved = pm.getObjectById(SimpleObject.class,
leftKey);
And that works, indeed.
The point is in the real application. I need to retrieve objects
without knowing the class, then treat them differently according to
their type. Actually I must model something similar to a tree (which
is not possible to do without using key references due to the way keys
are generated). I need to save the keys for left and right child of
the tree, then retrieve the objects and treat inner nodes differently
from leafs.
Are there workarounds to get an object using its key in JDO? Maybe I
should use low-level API to detect the kind of the entity.
Thanks for any advice
Lorenzo
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