Re: [appengine-java] Can't fetch a dataset using primary key

[Ikai Lan (Google)]

Try:

SELECT * from DB WHERE __key__ = KEY('1')

You can find more documentation on this here:

http://code.google.com/appengine/docs/python/datastore/gqlreference.html

--
Ikai Lan
Developer Programs Engineer, Google App Engine
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On Sun, Jan 23, 2011 at 2:00 PM, herber.m...@googlemail.com wrote:

 Hi all,

 I'm pretty new using GQL so hopefully someone can help me solving this easy
 (?) problem.

 I store my Entities in the DB using datastore.put( Entity ) without using
 an ID. But if I look at the Datastore Viewer I see that these entities are
 stored with an unique id called *ID/Name*. Now I'm trying to load such an
 entity using this code:

 SELECT * from DB WHERE ID/Name = 'id=1' - Error
 SELECT * from DB WHERE ID = 'id=1' - empty resultset
 SELECT * from DB WHERE Name = 'id=1' - empty resultset
 SELECT * from DB WHERE ID/Name = '1' - Error
 SELECT * from DB WHERE ID = '1' - empty resultset
 SELECT * from DB WHERE Name = '1' - empty resultset

 Can anybody tell me what to use to get this entry?

 Thanks in advance!

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Re: [appengine-java] Can't fetch a dataset using primary key

[Marc Herber]

Thanks for your help. Unfortunatelly this syntax isn't working at all :(

I tried to run this statement within the datastore viewer but I get an error 
GQL Query.
Apart from that the link you posted is for python, but I would need it for 
java. Can you/anybody help me with that too?

Thanks in advance.

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Re: [appengine-java] Can't fetch a dataset using primary key

[Marc Herber]

Meanwhile I tried this *java* code:
PersistenceManagerFactory pmf = JDOHelper.getPersistenceManagerFactory( 
transactions-optional );
PersistenceManager pm = pmf.getPersistenceManager();
Antwort objectById = pm.getObjectById( Antwort.class, parameters.getLong( 
Constants.ID ) );

And this is my *jdocnfig.xml*:
?xml version=1.0 encoding=utf-8?
jdoconfig xmlns=http://java.sun.com/xml/ns/jdo/jdoconfig;
   xmlns:xsi=http://www.w3.org/2001/XMLSchema-instance;
   xsi:noNamespaceSchemaLocation=http://java.sun.com/xml/ns/jdo/jdoconfig;

   persistence-manager-factory name=transactions-optional
   
   property name=javax.jdo.PersistenceManagerFactoryClass 
value=org.datanucleus.store.appengine.jdo.DatastoreJDOPersistenceManagerFactory/
   property name=javax.jdo.option.ConnectionURL value=appengine/
   property name=javax.jdo.option.NontransactionalRead value=true/
   property name=javax.jdo.option.NontransactionalWrite 
value=true/
   property name=javax.jdo.option.RetainValues value=true/
   property name=datanucleus.appengine.autoCreateDatastoreTxns 
value=true/
   
   /persistence-manager-factory
   
/jdoconfig


But I get the subsequent exception:
javax.jdo.JDOFatalUserException: Application code attempted to create a 
PersistenceManagerFactory named transactions-optional, but one with this 
name already exists!  Instances of PersistenceManagerFactory are extremely 
slow to create and it is usually not necessary to create one with a given 
name more than once.  Instead, create a singleton and share it throughout 
your code.  If you really do need to create a duplicate 
PersistenceManagerFactory (such as for a unittest suite), set the 
appengine.orm.disable.duplicate.pmf.exception system property to avoid this 
error.

Can anybody help me out?!

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Re: [appengine-java] Can't fetch a dataset using primary key

[Stephen Johnson]

Try changing Ikai's code to include the entity name like:

SELECT * from DB WHERE __key__ = KEY('DB','1')

if your key is a number then

SELECT * from DB WHERE __key__ = KEY('DB',1)

Documentation:

an entity key literal, with either a string-encoded
keyhttp://code.google.com/appengine/docs/python/datastore/keyclass.html#Keyor
a complete
path of kinds and key
names/IDshttp://code.google.com/appengine/docs/python/datastore/keysandentitygroups.html:


   - KEY('*encoded key*')
   - KEY('*kind*', *'name'/ID* [, '*kind*', *'name'/ID*...])



On Mon, Jan 24, 2011 at 3:14 PM, Marc Herber herber.m...@googlemail.comwrote:

 Thanks for your help. Unfortunatelly this syntax isn't working at all :(

 I tried to run this statement within the datastore viewer but I get an
 error GQL Query.
 Apart from that the link you posted is for python, but I would need it for
 java. Can you/anybody help me with that too?


 Thanks in advance.

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Re: [appengine-java] Can't fetch a dataset using primary key

[Stephen Johnson]

Hi Marc,
As the error message says, you should use a singleton to share your
persistence manager. Your code must be allocating it more than once. Here ya
go:

import javax.jdo.JDOHelper;
import javax.jdo.PersistenceManagerFactory;
import javax.jdo.PersistenceManager;

final public class PMF {
private final static PersistenceManagerFactory pmf =
JDOHelper.getPersistenceManagerFactory(transactions-optional);

private PMF() {}

static public PersistenceManager getPersistenceManager() {
return pmf.getPersistenceManager();
}
}

Then to use it, just:

 PersistenceManager pm = PMF.getPersistenceManager();

Stephen

On Mon, Jan 24, 2011 at 3:19 PM, Marc Herber herber.m...@googlemail.comwrote:

 Meanwhile I tried this *java* code:
 PersistenceManagerFactory pmf = JDOHelper.getPersistenceManagerFactory(
 transactions-optional );
 PersistenceManager pm = pmf.getPersistenceManager();
 Antwort objectById = pm.getObjectById( Antwort.class, parameters.getLong(
 Constants.ID ) );

 And this is my *jdocnfig.xml*:
 ?xml version=1.0 encoding=utf-8?
 jdoconfig xmlns=http://java.sun.com/xml/ns/jdo/jdoconfig;
xmlns:xsi=http://www.w3.org/2001/XMLSchema-instance;
xsi:noNamespaceSchemaLocation=http://java.sun.com/xml/ns/jdo/jdoconfig
 

persistence-manager-factory name=transactions-optional

property name=javax.jdo.PersistenceManagerFactoryClass
 value=org.datanucleus.store.appengine.jdo.DatastoreJDOPersistenceManagerFactory/
property name=javax.jdo.option.ConnectionURL value=appengine/
property name=javax.jdo.option.NontransactionalRead
 value=true/
property name=javax.jdo.option.NontransactionalWrite
 value=true/
property name=javax.jdo.option.RetainValues value=true/
property name=datanucleus.appengine.autoCreateDatastoreTxns
 value=true/

/persistence-manager-factory

 /jdoconfig


 But I get the subsequent exception:
 javax.jdo.JDOFatalUserException: Application code attempted to create a
 PersistenceManagerFactory named transactions-optional, but one with this
 name already exists!  Instances of PersistenceManagerFactory are extremely
 slow to create and it is usually not necessary to create one with a given
 name more than once.  Instead, create a singleton and share it throughout
 your code.  If you really do need to create a duplicate
 PersistenceManagerFactory (such as for a unittest suite), set the
 appengine.orm.disable.duplicate.pmf.exception system property to avoid this
 error.

 Can anybody help me out?!

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[appengine-java] Can't fetch a dataset using primary key

[herber . marc]

Hi all,

I'm pretty new using GQL so hopefully someone can help me solving this easy 
(?) problem.

I store my Entities in the DB using datastore.put( Entity ) without using an 
ID. But if I look at the Datastore Viewer I see that these entities are 
stored with an unique id called *ID/Name*. Now I'm trying to load such an 
entity using this code:

SELECT * from DB WHERE ID/Name = 'id=1' - Error
SELECT * from DB WHERE ID = 'id=1' - empty resultset
SELECT * from DB WHERE Name = 'id=1' - empty resultset
SELECT * from DB WHERE ID/Name = '1' - Error
SELECT * from DB WHERE ID = '1' - empty resultset
SELECT * from DB WHERE Name = '1' - empty resultset

Can anybody tell me what to use to get this entry?

Thanks in advance!

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