problem with a request with m:n relations (ojb)

[kristen <kr...@yahoo.fr>]

Hello !

First, sorry for my english...

I would like to create a request which are based on a m:n relationships.

For example :

a book can be written by several authors and several authors can write books.


This is the relation :

book <-> writtenBy <-> author

For example, How can I obtain the name of all the author who have written the 
book "my book" ?

I have the following code but I don't know how can I put several classes after 
the "from" :

Transaction tx = odmg.newTransaction();
tx.begin();
OQLQuery query = odmg.newOQLQuery();
String queryStr = "select auhors from " + Author.class.getName()+ .... ?

query.create(queryStr);
GroupsList = (List) query.execute();
tx.commit();


Thank you for your help


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Re: problem with a request with m:n relations (ojb)

[Jakob Braeuchi <jb...@gmx.ch>]

hi kristen,

ojb does the join automatically:

query.create("select authors ...Autor where books.title like ?");

this sample need a relationship-definition named 'books' and an attribute 
'title' in class Books. the relationship 'books' is a bidirectional m:n 
relationship based on the table writtenBy.

jakob

kristen schrieb:

> Hello !
> 
> First, sorry for my english...
> 
> I would like to create a request which are based on a m:n relationships.
> 
> For example :
> 
> a book can be written by several authors and several authors can write books.
> 
> 
> This is the relation :
> 
> book <-> writtenBy <-> author
> 
> For example, How can I obtain the name of all the author who have written the 
> book "my book" ?
> 
> I have the following code but I don't know how can I put several classes after 
> the "from" :
> 
> Transaction tx = odmg.newTransaction();
> tx.begin();
> OQLQuery query = odmg.newOQLQuery();
> String queryStr = "select auhors from " + Author.class.getName()+ .... ?
> 
> query.create(queryStr);
> GroupsList = (List) query.execute();
> tx.commit();
> 
> 
> Thank you for your help
> 
> 
> ---------------------------------------------------------------------
> To unsubscribe, e-mail: ojb-user-unsubscribe@db.apache.org
> For additional commands, e-mail: ojb-user-help@db.apache.org
> 
> 

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