I m using JDO version 2 Data nucleus with App engine SDK 1.7.3. I am having problem retrieving child objects in one to many relationship.
contents = (Collection<ContentType>) persistenceManager.newQuery(ContentType.class).execute();
This query returns all instances of ContentType but ContentType also contains a list of its children “Content” which are not fetched from Database.
ContentType.java
public Collection<ContentType> getAllContents() {
PersistenceManager persistenceManager = PersistenceFactory
.getInstance().getPersistenceManager();
Transaction transaction = persistenceManager.currentTransaction();
Collection<ContentType> contents = null;
try {
transaction.begin();
contents = (Collection<ContentType>) persistenceManager.newQuery(ContentType.class).execute();
Logging.log("contents in getAllContents=== "+ contents);
if(contents!=null)
{
Logging.log("contents size in getAllContents=== "+ contents.size());
}
for (ContentType contentTypeElement : contents) {
Logging.log("inside main loop in getAllContents, contentTypeElement=== "+ contentTypeElement);
if(contentTypeElement!=null)
{
Logging.log("inside main loop in getAllContents, contentTypeElement having list === "+ contentTypeElement.getContentList());
}
if(contentTypeElement.getContentList()!=null)
{
for (Content contentElement : contentTypeElement.getContentList()) {
Logging.log("inside second loop in getAllContents");
String contentPath = Constants.CONTENT_BASE_URL
+ contentElement.getContentPath();
contentElement.setContentPath(contentPath);
}
}
Logging.log("At end of main loop iteration");
}
transaction.commit();
} catch (Exception e) {
transaction.rollback();
e.printStackTrace();
Logging.log("Exception retriving all content, detail in getAllContents: "
+ e.toString());
} finally {
persistenceManager.close();
}
return contents;
}
Here is the log
2012-12-14 13:27:14.101
org.datanucleus.TransactionImpl internalPreCommit: >> calling preCommit on org.datanucleus.store.connection.ConnectionManagerImpl$2@873b9f
I 2012-12-14 13:27:14.102
org.datanucleus.TransactionImpl internalPreCommit: >> calling preCommit on org.datanucleus.ObjectManagerImpl@c6b8b0
I 2012-12-14 13:27:14.102
org.datanucleus.TransactionImpl preFlush: >> calling preFlush on org.datanucleus.store.connection.ConnectionManagerImpl$2@873b9f
I 2012-12-14 13:27:14.102
org.datanucleus.TransactionImpl preFlush: >> calling preFlush on org.datanucleus.ObjectManagerImpl@c6b8b0
I 2012-12-14 13:27:14.135
com.test.igreetings.util.Logging log: contents in getAllContents=== [com.test.igreetings.persistence.domain.ContentType@14fdb76, com.test.igreetings.persistence.domain.ContentType@1d15a18, com.test.igreetings.persistence.domain.ContentType@171f735, com.test.igreetings.persistence.domain.ContentType@1bf496b]
I 2012-12-14 13:27:14.135
com.test.igreetings.util.Logging log: contents size in getAllContents=== 4
I 2012-12-14 13:27:14.135
com.test.igreetings.util.Logging log: inside main loop in getAllContents, contentTypeElement=== com.test.igreetings.persistence.domain.ContentType@14fdb76
I 2012-12-14 13:27:14.135
com.test.igreetings.util.Logging log: inside main loop in getAllContents, contentTypeElement having list === null
I 2012-12-14 13:27:14.135
com.test.igreetings.util.Logging log: At end of main loop iteration
I 2012-12-14 13:27:14.135
com.test.igreetings.util.Logging log: inside main loop in getAllContents, contentTypeElement=== com.test.igreetings.persistence.domain.ContentType@1d15a18
I 2012-12-14 13:27:14.135
com.test.igreetings.util.Logging log: inside main loop in getAllContents, contentTypeElement having list === null
I 2012-12-14 13:27:14.135
com.test.igreetings.util.Logging log: At end of main loop iteration
I 2012-12-14 13:27:14.135
com.test.igreetings.util.Logging log: inside main loop in getAllContents, contentTypeElement=== com.test.igreetings.persistence.domain.ContentType@171f735
I 2012-12-14 13:27:14.135
com.test.igreetings.util.Logging log: inside main loop in getAllContents, contentTypeElement having list === null
I 2012-12-14 13:27:14.135
com.test.igreetings.util.Logging log: At end of main loop iteration
I 2012-12-14 13:27:14.135
com.test.igreetings.util.Logging log: inside main loop in getAllContents, contentTypeElement=== com.test.igreetings.persistence.domain.ContentType@1bf496b
I 2012-12-14 13:27:14.135
com.test.igreetings.util.Logging log: inside main loop in getAllContents, contentTypeElement having list === null
I 2012-12-14 13:27:14.135
com.test.igreetings.util.Logging log: At end of main loop iteration
I 2012-12-14 13:27:14.136
org.datanucleus.TransactionImpl internalPreCommit: >> calling preCommit on org.datanucleus.store.connection.ConnectionManagerImpl$2@66da2c
I 2012-12-14 13:27:14.136
org.datanucleus.TransactionImpl internalPreCommit: >> calling preCommit on org.datanucleus.ObjectManagerImpl@274608
DATA NUCLEUS LOGS
1. org.datanucleus.store.connection.ConnectionManagerImpl allocateConnection: Connection added to the pool : com.google.appengine.datanucleus.DatastoreConnectionFactoryImpl$DatastoreManagedConnection@74ece8 for key=org.datanucleus.ObjectManagerImpl@107c76b in factory=ConnectionFactory:tx[com.google.appengine.datanucleus.DatastoreConnectionFactoryImpl@119549e]
2.
3. D2012-12-14 17:20:11.232
4. org.datanucleus.store.query.QueryManager getQueryCompilationForQuery: Query "SELECT FROM com.test.igreetings.persistence.domain.ContentType" of language "JDOQL" has been run before so reusing existing generic compilation
5. D2012-12-14 17:20:11.232
6. com.google.appengine.datanucleus.query.JDOQLQuery performExecute: JDOQL Query : Executing "SELECT FROM com.test.igreetings.persistence.domain.ContentType" ...
7. D2012-12-14 17:20:11.233
8. com.google.appengine.datanucleus.query.JDOQLQuery performExecute: Query compiled as : Kind=com.test.igreetings.persistence.domain.ContentType
9. D2012-12-14 17:20:11.233
10. com.google.appengine.datanucleus.query.DatastoreQuery executeNormalQuery: Executing query in datastore for SELECT FROM com.test.igreetings.persistence.domain.ContentType
11. D2012-12-14 17:20:11.233
12. org.datanucleus.store.connection.ConnectionManagerImpl allocateConnection: Connection found in the pool : com.google.appengine.datanucleus.DatastoreConnectionFactoryImpl$DatastoreManagedConnection@74ece8 for key=org.datanucleus.ObjectManagerImpl@107c76b in factory=ConnectionFactory:tx[com.google.appengine.datanucleus.DatastoreConnectionFactoryImpl@119549e]
13. D2012-12-14 17:20:11.234
14. com.google.appengine.datanucleus.query.JDOQLQuery performExecute: JDOQL Query : Execution Time = 2 ms
15. D2012-12-14 17:20:11.279
16. org.datanucleus.ObjectManagerImpl getObjectFromLevel1Cache: Object with id "com.test.igreetings.persistence.domain.ContentType:ContentType(3)" not found in Level 1 cache [cache size = 0]
17. D2012-12-14 17:20:11.279
18. org.datanucleus.ObjectManagerImpl putObjectIntoLevel1Cache: Object "com.test.igreetings.persistence.domain.ContentType@165d118" (id="com.test.igreetings.persistence.domain.ContentType:ContentType(3)") added to Level 1 cache (loadedFlags="[NNYNN]")
19. D2012-12-14 17:20:11.279
20. org.datanucleus.state.JDOStateManager wrapSCOField: Object "com.test.igreetings.persistence.domain.ContentType@165d118" (id="com.test.igreetings.persistence.domain.ContentType:ContentType(3)") is having the value in field "endDate" replaced by a SCO wrapper
21. D2012-12-14 17:20:11.280
22. org.datanucleus.state.JDOStateManager wrapSCOField: Object "com.test.igreetings.persistence.domain.ContentType@165d118" (id="com.test.igreetings.persistence.domain.ContentType:ContentType(3)") is having the value in field "startDate" replaced by a SCO wrapper
23. D2012-12-14 17:20:11.280
24. org.datanucleus.ObjectManagerImpl enlistInTransaction: Object "com.test.igreetings.persistence.domain.ContentType@165d118" (id="com.google.appengine.api.datastore.Key:ContentType(3)") enlisted in transactional cache
25. D2012-12-14 17:20:11.280
26. org.datanucleus.ObjectManagerImpl getObjectFromLevel2Cache: Object with id="com.test.igreetings.persistence.domain.ContentType:ContentType(3)" taken from Level 2 cache (fields="[0, 1, 2, 3, 4]", version="") - represented as "com.test.igreetings.persistence.domain.ContentType@165d118"
27. D2012-12-14 17:20:11.280
org.datanucleus.store.connection.ConnectionManagerImpl allocateConnection: Connection found in the pool : com.google.appengine.datanucleus.DatastoreConnectionFactoryImpl$DatastoreManagedConnection@74ece8 for key=org.datanucleus.ObjectManagerImpl@107c76b in factory=ConnectionFactory:tx[com.google.appengine.datanucleus.DatastoreConnectionFactoryImpl@119549e]
So contentList is fetched empty although in admin console Data viewer there are many instances of Content associated with Content Types. What am i missing?
Since you now say that there is no property in ContentType for the List then you didn’t persist the data with v2 of the GAE JDO plugin. Consequently you can’t expect it to know about elements in the Collection.
Solution : fix your data.