Re: findBy referencing another entity reference
Adam, Thanks, this looks nice. However I have the problem that I want to use "GROUP BY" in my statements which is a kind of a problem as the "defined finder" methods requires that exact the same parameters are returned which isn't true in case of "GROUP BY" (the Sum() returns something that isn't in the orginally resultset). How can I still receive the result set form this Group by statement ? I was thinking about defining an entity bean that contains the fields that the Group by statement returns, but how ??? (Just like the elefantwalker mentioned: have another entitybean that performs all the heavy stuff) Can someone help me with this, as I don't knwo what the xml definition of this entity bean should look like, as untill now was using simple entity beans that are directly related to database tables, which isn't true in this case. Eddie - Original Message - From: Adam Cassar [EMAIL PROTECTED] To: Orion-Interest [EMAIL PROTECTED] Sent: Tuesday, April 17, 2001 3:41 AM Subject: Re: findBy referencing another entity reference I found this reply to an earlier posting quite usefull. http://www.mail-archive.com/orion-interest@orionserver.com/msg12085.html On 16 Apr 2001 17:23:15 -0700, Rian Schmidt wrote: Oh boy... OK, maybe that was a bad example. "Read more about entity beans" is not very useful advice in any case. I just didn't want to explain our business model to ask the question. Try the situation where the top level is Vehicle - Manufacturer - Model or something many-to-many on each layer. My point is that I want to be able to "skip a layer" in the finder. Is that possible? If you don't know, or the answer is no, please just say that or ignore my question and move on. If you have an actual answer or alternative approach that might work, I'd be very appreciative to hear it. For what it's worth, I want to do it this way, as opposed to using some kind of bean-based (logical model) test or pseudo-BMP thing because, due to the volume of "3rd level (in my example)" entities running a findAll on them is performance-limiting and I'd rather not stick SQL directly in my beans. Thanks, Rian -- Rian Schmidt [EMAIL PROTECTED] - Original Message - From: "elephantwalker" [EMAIL PROTECTED] To: "Orion-Interest" [EMAIL PROTECTED] Sent: Monday, April 16, 2001 2:54 PM Subject: RE: findBy referencing another entity reference Rian, This is much too sql centric. You should resolve your entity beans around business methods. So I would start off by reading more about entity beans. Theserverside.com, for example has a download on an excellent book for entity beans. As for the sql, you are talking a one to one relationship for the car/model and a one to many relationship for the manufacturer/model. There should be some examples of this on the sun's j2ee site. I know that they specifically discuss this issue. Regards, the elephantwalker -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]On Behalf Of Rian Schmidt Sent: Monday, April 16, 2001 2:23 PM To: Orion-Interest Subject: findBy referencing another entity reference Hi all, How about this scenario: There are three entities: manufacturer, model, car (as an example) model knows directly which manufacturer it is, car knows which model it is, but car has to do a model.getManufacturer to find out its manufacturer... OK, so what I wanna know is can I a findByManufacturer for car? I'd like to be able to do something like this: query="$model.manufacturer = $1" Now, I know that I could specify a sub-query with the actual persistence name of the other entity's thang, something like: query="$model in (select $model from model where manufacturer_id = $1)" but it strikes me that Orion won't know what I'm going on about, and best case, will have to talk to the database each time. Either way, I had to put the persistence name into the orion-ejb-jar.xml file, which is not goodness. Is it possible maybe to say something like: query="model in ($1)" where $1 is a Collection of models taken from ModelHome.findByManufacturer? Any thoughts on the best way to approach this? Thanks, Rian -- Rian Schmidt [EMAIL PROTECTED] -- Adam Cassar Technical Development Manager ___ NetRegistry http://www.netregistry.au.com Tel: +61 2 9641 8609 | Fax: +61 2 9699 6088 PO Box 270 Broadway NSW 2007 Australia
RE: findBy referencing another entity reference
Rian, This is much too sql centric. You should resolve your entity beans around business methods. So I would start off by reading more about entity beans. Theserverside.com, for example has a download on an excellent book for entity beans. As for the sql, you are talking a one to one relationship for the car/model and a one to many relationship for the manufacturer/model. There should be some examples of this on the sun's j2ee site. I know that they specifically discuss this issue. Regards, the elephantwalker -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]On Behalf Of Rian Schmidt Sent: Monday, April 16, 2001 2:23 PM To: Orion-Interest Subject: findBy referencing another entity reference Hi all, How about this scenario: There are three entities: manufacturer, model, car (as an example) model knows directly which manufacturer it is, car knows which model it is, but car has to do a model.getManufacturer to find out its manufacturer... OK, so what I wanna know is can I a findByManufacturer for car? I'd like to be able to do something like this: query="$model.manufacturer = $1" Now, I know that I could specify a sub-query with the actual persistence name of the other entity's thang, something like: query="$model in (select $model from model where manufacturer_id = $1)" but it strikes me that Orion won't know what I'm going on about, and best case, will have to talk to the database each time. Either way, I had to put the persistence name into the orion-ejb-jar.xml file, which is not goodness. Is it possible maybe to say something like: query="model in ($1)" where $1 is a Collection of models taken from ModelHome.findByManufacturer? Any thoughts on the best way to approach this? Thanks, Rian -- Rian Schmidt [EMAIL PROTECTED]
Re: findBy referencing another entity reference
Oh boy... OK, maybe that was a bad example. "Read more about entity beans" is not very useful advice in any case. I just didn't want to explain our business model to ask the question. Try the situation where the top level is Vehicle - Manufacturer - Model or something many-to-many on each layer. My point is that I want to be able to "skip a layer" in the finder. Is that possible? If you don't know, or the answer is no, please just say that or ignore my question and move on. If you have an actual answer or alternative approach that might work, I'd be very appreciative to hear it. For what it's worth, I want to do it this way, as opposed to using some kind of bean-based (logical model) test or pseudo-BMP thing because, due to the volume of "3rd level (in my example)" entities running a findAll on them is performance-limiting and I'd rather not stick SQL directly in my beans. Thanks, Rian -- Rian Schmidt [EMAIL PROTECTED] - Original Message - From: "elephantwalker" [EMAIL PROTECTED] To: "Orion-Interest" [EMAIL PROTECTED] Sent: Monday, April 16, 2001 2:54 PM Subject: RE: findBy referencing another entity reference Rian, This is much too sql centric. You should resolve your entity beans around business methods. So I would start off by reading more about entity beans. Theserverside.com, for example has a download on an excellent book for entity beans. As for the sql, you are talking a one to one relationship for the car/model and a one to many relationship for the manufacturer/model. There should be some examples of this on the sun's j2ee site. I know that they specifically discuss this issue. Regards, the elephantwalker -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]On Behalf Of Rian Schmidt Sent: Monday, April 16, 2001 2:23 PM To: Orion-Interest Subject: findBy referencing another entity reference Hi all, How about this scenario: There are three entities: manufacturer, model, car (as an example) model knows directly which manufacturer it is, car knows which model it is, but car has to do a model.getManufacturer to find out its manufacturer... OK, so what I wanna know is can I a findByManufacturer for car? I'd like to be able to do something like this: query="$model.manufacturer = $1" Now, I know that I could specify a sub-query with the actual persistence name of the other entity's thang, something like: query="$model in (select $model from model where manufacturer_id = $1)" but it strikes me that Orion won't know what I'm going on about, and best case, will have to talk to the database each time. Either way, I had to put the persistence name into the orion-ejb-jar.xml file, which is not goodness. Is it possible maybe to say something like: query="model in ($1)" where $1 is a Collection of models taken from ModelHome.findByManufacturer? Any thoughts on the best way to approach this? Thanks, Rian -- Rian Schmidt [EMAIL PROTECTED]
RE: findBy referencing another entity reference
This is the right idea; you want to do a join in the finder. Relational databases were designed to do exactly this sort of thing. Putting extra information in the EJBs would just lead to consistency problems, IMHO. The EJB 2.0 specification defines EJB QL, which is a database-independent query language reminiscent of SQL and the preferred solution to your problem. Unfortunately Orion does not yet support EJB QL, so you need to manually specify the join in SQL in the orion-ejb-jar.xml finder definition. You will need to use a partial="false" finder to do a join, which means you need to be very careful about how you specify the select. Select table.* should work if you allowed Orion to create the table in the first place. Otherwise you'll need to make sure that the columns are specified in the same order as the fields in ejb-jar.xml. You will probably want to put this new finder definition in an orion-ejb-jar.xml fragment included in your ejb jar file so that deploying your j2ee app on a new server will automatically include the changes. There is much discussion in the archives about how to do this. Good luck! Jeff -Original Message- From: Adam Cassar [mailto:[EMAIL PROTECTED]] Sent: Monday, April 16, 2001 6:41 PM To: Orion-Interest Subject: Re: findBy referencing another entity reference I found this reply to an earlier posting quite usefull. http://www.mail-archive.com/orion-interest@orionserver.com/msg1 2085.html
