AW: [Fwd: RE: [OJB-developers] Mapping Question]

[Mahler T. <tho...@it...>]

Hi Vikas,

> 
> I hope this time I am posting my question on the right mailing list.
> 
> Thomas, thank you so much for your reply to my original question on 
> Developer's mailing list.  However, I am still not clear.  I read 
> tutorial3.html and it does pretty good job of explaining inheritance 
> mapping.  My situation has additional quirk of relation 
> mapping.  Let me 
> try to explain..........
> 
>  >From the classes point of view: there is class M with attributes as 
> follows:
> 
> Class M
> ---------
> m_id                   integer
> someValue          String
> child_type           String
> child_id              integer
>


Does one M instance have a D attribute ?
m_myD		D ?
 
> There is Class D and subclasses D1,D2,D3... (that need persistence)
> 
> Class D
> ---------
> child_id                       integer
> someData                   String
> 
> class D1
> ----------
> child_id                  integer
> aaValue                  String
> bbValue                  String
> 
> 
> Class D2
> ------------
> child_id                 integer
> ccValue                 String
> ddValue                 String
> 
> Class D3
> ------------
> child_id                 integer
> eeValue                 String
> ffValue                 String
> 
> The relation ship between M and instance of D (really D1 or 
> D2 or D3) is 
> determined by 'child_type' of class M.
> 
> I understand inheritance mapping of class D and subclasses 
> D1,D2,D3.  I 
> am leaning towards mapping each subclass with distinct table (with 
> FieldDescriptor for all attributes including inherited 
> attributes).  How 
> do I map the relationship between M and D1,D2,D3 as they are 
> joined by 
> child_id to the appropriate table based on value of 'child_type'.
> 

OJB supports polymorphism. That is you simply declare that M has a reference
attribute of type D.
To enable polymorph loading of D instances you must declare an extent for
Class D that contains classes D1, D2, D3.
This is also explained in Tutorial 3
(http://objectbridge.sourceforge.net/tutorial3.html#extents-and-polymorphism
). There is also plenty of sample code for similar problems in the
test.ojb.broker package.
The attribute child_type is not needed for OJB.

HTH,

Thomas

> Does this make sense?
> 
> Thanks for any help you can provide.
> 
> Vikas
> 
> 
> 
> 
> -----Original Message-----
> From: Thomas Mahler [mailto:tho...@ho...]
> Sent: Thursday, April 04, 2002 2:22 AM
> To: Vikas Javiya
> Cc: obj...@li...
> Subject: Re: [OJB-developers] Mapping Question
> 
> 
> Hi Vikas,
> 
> please refer to the tutorial3.html. It explains how to build mappings
> for inheritance hierarchies.
> It also explains how mappings for 1:1, 1:n and m:n 
> associations are build.
> 
> If you have further question that are not answered in the mentioned
> document don't hesitate to post your questions to the 
> objectbridge-users
> mailinglist.
> 
> 
> HTH,
> Thomas
> 
> Vikas Javiya wrote:
> 
>  > Hello,
>  >
>  >
>  >
>  > A simple question regarding mapping;
>  >
>  >
>  >
>  > I have a class operation and a table OPERATION for 
> persistence.  Two
>  > main attributes of operation are; resource_type and resource_id.
>  > Possible values for resource_type are 'Phone_number' , 
> 'Email_address',
>  > 'JMS_Queue', 'EJB_methods'.  There is class 'resource' and 
> sub classes
>  > 'Phone_resource', 
> 'email_resource','JMS_resource','EJB_resource'.  There
>  > are tables to map all of these sub classes of resource.  
> An OPERATION
>  > table is linked to any of these resource table via 
> resource_ID column
>  > depending on the resource_type column.  In a way it is 
> dynamic mapping
>  > between 'operation' class and any of the resource classes 
> based on the
>  > value of resource_type.
>  >
>  >
>  >
>  > How do I map this in repository.xml??????????????
>  >
>  >
>  >
>  > Thanks for your help.
>  >
>  >
>  >
>  > Vikas
>  >
>  >
>  >
>  >
>  >
>  > Vikas Javiya
>  >
>  > ThatOne Company
>  >
>  > 408.869.8112 (Phone)
>  >
>  > 408.487.9801 (Fax)
>  >
>  > www.ThatOne.com <http://www.thatone.com/>
>  >
>  > 
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