I guess that makes sense and your example is dot on. I was wondering are there real life applications on GAE where people are using JDO/JPA relationships. The more the problems that I face with relationships and the more I read about it, it seems that unowned is the way to go.
Thanks, Vikas On Aug 4, 12:53 am, Frederik Pfisterer <pfiste...@gmail.com> wrote: > There are many Use Cases where it makes sense to keep relationships or > you at least want to leverage the power of entity groups even with > JDO. The school-of-thought is a bit different than in other > environments though. While JDO parent to child access is comfortable > it makes not the best use of GAE's massive scalability and performance > advantages. One example: > > Say you have a user and all his comments are children in his entity > group. Now in an old school way you would check how many there are is > user.getComments().size() ... well that works but would have to load > the entire array from the store. The new school way of doing this > would be running a query filtered on keys that is an order of > magnitude > faster:http://code.google.com/intl/de-DE/appengine/docs/java/datastore/queri... > You can always retrieve the parent object (user) because its key is > encoded in any of the child keys. > > There are many more examples where you have to think different, but in > general: It makes sense to have entity groups where they persist in > reality: users - comments, users - addresses, bank accounts - > transactions, and so forth... > > Hope this helps, > Fred > > On 3 Aug., 20:28, Vikas Hazrati <vhazr...@gmail.com> wrote: > > > > > Hi Fred, > > > Thanks for your response. This is what I suspected too that the entity > > groups might not be able to change. This actually brings me to the > > conclusion that we might not want to keep any owned entities at all. > > We are in the process of converting a legacy application to GAE and in > > the process we have been breaking out relationships due to multiple > > problems. I would write about all the problems that we faced and the > > workarounds and link it here. > > This relationship was probably one of the last bastions that we had > > remaining. With what you mentioned this might have to be broken too > > since a user can move around departments as a valid business case. > > > So let me ask the community this question, does anyone see the benefit > > of maintaining relations at all? using JPA/JDO. From the complex > > queries that a normal web app would have you would fall into > > situations where you would need to use more and more of unowned > > relationships. Is that true? or am I missing something. > > > Regards | Vikaswww.inphina.comwww.thoughts.inphina.com > > > On Aug 3, 10:00 pm, Frederik Pfisterer <pfiste...@gmail.com> wrote: > > > > You have to use unowned relationships and not place the department and > > > the user in the same entity group. > > > See:http://code.google.com/intl/de-DE/appengine/docs/java/datastore/relat... > > > use for UserDepartment: > > > private Set<Key> users = new HashSet<Key>(); > > > and for User: > > > private Key userDepartmentKey; > > > > Entity groups cannot be changed once being established. > > > If you want the relationships like you have them, you would have to > > > change the Key of the User object (it's identity) to place it in the > > > entity group of another department, since the department's (parent) > > > key is part of the user key like in a path. > > > > Cheers, > > > Fred > > > > On 3 Aug., 15:09, Vikas Hazrati <vhazr...@gmail.com> wrote: > > > > > Oops I somehow managed to hit the submit without the full question... > > > > Apologies...Let me start again > > > > > I have 2 entities UserDepartment and User, which are defined as > > > > follows > > > > @Entity > > > > public class UserDepartment extends DomainObject<Long, > > > > UserDepartment> > > > > { > > > > @Id > > > > @GeneratedValue(strategy = GenerationType.IDENTITY) > > > > private Long departmentId; > > > > @OneToMany(mappedBy = "userDepartment", cascade = > > > > CascadeType.ALL, fetch=FetchType.EAGER) > > > > private Set<User> users = new HashSet<User>(); > > > > > and > > > > > @Entity > > > > public class User extends DomainObject<Long, User> { > > > > @Id > > > > @GeneratedValue(strategy = GenerationType.IDENTITY) > > > > @Extension(vendorName = "datanucleus", key = "gae.encoded-pk", > > > > value = "true") > > > > private String encodedKey; > > > > @Extension(vendorName = "datanucleus", key = "gae.pk-id", > > > > value = "true") > > > > private Long userId; > > > > private String username; > > > > @ManyToOne(fetch = FetchType.EAGER) > > > > private UserDepartment userDepartment; > > > > > As you would notice that UserDepartment is the parent of the User. Now > > > > once I persist the entity group, i want to modify the user so that it > > > > belongs to a different department now. > > > > > What is the best way to do that? > > > > > If i remove the UserDepartment from the User and then assign a new > > > > UserDepartment to it then I get into the issue of trying to access > > > > multiple entity groups in the same transaction. > > > > > Regards | Vikaswww.inphina.com > > > > > On Aug 3, 6:05 pm, Vikas Hazrati <vhazr...@gmail.com> wrote: > > > > > > I have 2 entities UserDepartment and User, which are defined as > > > > > follows > > > > > > @Entity > > > > > public class UserDepartment extends DomainObject<Long, UserDepartment> > > > > > { > > > > > > @Id > > > > > @GeneratedValue(strategy = GenerationType.IDENTITY) > > > > > private Long departmentId; > > > > > > and > > > > > > @Entity > > > > > public class User extends DomainObject<Long, User> { > > > > > > @Id > > > > > @GeneratedValue(strategy = GenerationType.IDENTITY) > > > > > @Extension(vendorName = "datanucleus", key = > > > > > "gae.encoded-pk", value > > > > > = "true") > > > > > private String encodedKey; > > > > > > @Extension(vendorName = "datanucleus", key = "gae.pk-id", > > > > > value = > > > > > "true") > > > > > private Long userId; > > > > > > private String username; > > > > > @ManyToOne(fetch = FetchType.EAGER) > > > > > private UserDepartment userDepartment; -- You received this message because you are subscribed to the Google Groups "Google App Engine for Java" group. 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