I believe you're going to have to change this to
class User {
String name;
List <String> workNames; // or List <Long> workIds;
}
class Work {
String name;
String userName; // or Long userId;
}
This is actually you'd design this under the MDA paradigm, actually. You
need to be able to change each independently of the other. As far as
"automatic population", like an ORM would do, I don't think this is
possible. You'll have to do this manually. Honestly, you won't lose much
by doing two queries.
On Wed, Jun 2, 2010 at 2:12 PM, RAVINDER MAAN <rsmaan...@gmail.com> wrote:
> Thank you so much for your answer Bill
> yes you are rite the way i wrote its many to many relation.Actually I
> want relation as below
>
> class User{
> Long id;
> String username;
> List<Work> workList;
> }
>
> class Work{
> Long id;
> String workname;
> String username;
>
> }
> you can see work class has username and user class too has username.In
> both classes primary key is id. I just want to know is there any way to get
> workList populated automatically on retrieval of user object.we can do it
> with 2 queries easily.we can reteriev user first then we can retrieve work
> object with second query.
>
>
> On Wed, Jun 2, 2010 at 10:35 PM, Bill Milligan <bill.milli...@gmail.com>wrote:
>
>>
>> Are you trying one-to-many or many-to-many? By using a third table it
>> sounds like you're trying to do many-to-many, not one-to-many.
>>
>> As best I can determine, the only real way to do this in GAE is to have a
>> User class with a collection of string properties, containing the list of
>> all Work ids. In this case a bidirectional link would be probably quite
>> useful, so that a Work could be identified by its User id.
>>
>> Here's a scenario: Retrieve User by user id. Then, retrieve all Works in
>> the list of work ids owned by the User.
>>
>> Note that this is not true object composition, with a User containing a
>> List of Collection, but rather an indirect reference. This pattern is
>> useful in a lot of circumstances where you want to be able to break up your
>> object model into more modular deployable applications. On the other hand,
>> I'd hate to be completely boxed in by this restriction.
>>
>> I'm just getting started with GAE so I'm very much not an expert. I'd
>> love to know anybody else's thoughts on the matter.
>>
>> On Wed, Jun 2, 2010 at 12:10 AM, RAVINDER MAAN <rsmaan...@gmail.com>wrote:
>>
>>> Hello all
>>> can anybody please tell me how to implement simple one many
>>> relation in java.I have user table and work table .Any user can do
>>> many type of works.In user table i have userid but it is not primary
>>> key of the user table.Then i have work table which has workid it is
>>> also not primary key of the table.Normally in relation db we ca make
>>> third table table which contains workid for every userid.What how can
>>> we implement this thing appengine datastore.I want to have collection
>>> all works in user object .can anybody please tell me how to define
>>> this mapping?please note that in userid and workid are not primary
>>> keys in both objects or tables.
>>> Thanks in adavance.
>>>
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>
>
>
> --
> Regards,
> Ravinder Singh Maan
>
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