I've created an interface PMF: PMF.java package com.turbomanage.gwt.server;
import javax.jdo.PersistenceManager; public interface PMF { PersistenceManager getPersistenceManager(); } and a default implementation that I inject via Guice into my service classes: DefaultPMF.java package com.turbomanage.gwt.server; import javax.jdo.PersistenceManager; public interface PMF { PersistenceManager getPersistenceManager(); } Each service then calls pmf.getPersistenceManager(). I hope this is right :-) A benefit of the injection approach is that you can easily create a TestPMF that is injected for unit tests. I've written a little about this at http://turbomanage.wordpress.com/2009/10/27/more-on-unit-testing-with-an-injected-jdo-persistencemanager/ /dmc David Chandler http://turbomanage.wordpress.com On Dec 7, 1:17 pm, Larry Cable <larry.ca...@gmail.com> wrote: > I am not sure it/there is a "right" way, but in my application I am > injecting (via Spring) > a (singleton) PMF into my Controller(s) (which are singletons) and > instantiating a PM for each (concurrent) query/request... > > On Dec 4, 11:30 pm, Fan Lin <linfa...@gmail.com> wrote: > > > Hi, I'm new in JDO, so I think this problem may sounds stupid... > > I'm working on my application on App-engine, and feel really confused > > about how to use the PersistenceManager in my app... > > > 1) At the very beginning I tried to maintain only one static pm > > instance in my app, but I found that when I try to update the entities > > in datastore, it does not write back, since I do not close the pm. > > > 2) Then, I tried to get a new pm in every request, and after the > > request I close it. But I still store the pm as a static field in a > > DaoBase class. the code looks like: > > > PersistenceManager pm = PFM.get().getPersistenceManager(); > > DaoBase.setPm(pm); > > > ....do the request... > > > DaoBase.getPm().close(); > > DaoBase.setPm(null); > > > But when multiple requests come concurrently, things becomes messy and > > sometimes the DaoBase.getPm() will returns null during a request. > > > 3) Use new pm each time when reading the datastore, then detach the > > object from pm, close the pm. Then during update time, use a new pm to > > update it. But the problem here is when there is some owned > > relationship between datastore entities, a detatched object will not > > fetch the data automatically, like: > > > ///////////////////////////// > > class Address { > > .... > > > } > > > class Employee { > > private List<Address> addressList; > > > public List<Address> getAddressList() { > > return addressList; > > }} > > > /////////////////////////////// > > the getAddressList() will always return null. > > > So...What is the right way to use PersistenceManager? -- You received this message because you are subscribed to the Google Groups "Google App Engine for Java" group. To post to this group, send email to google-appengine-j...@googlegroups.com. To unsubscribe from this group, send email to google-appengine-java+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/google-appengine-java?hl=en.