Query on collection descriptors

["Kollivakkam R. Raghavan" <rk...@cisco.com>]

If I have a 1-n relationship between two entities represented as a
collection-descriptor in OJB, how can I use the PB Query API to retrieve
items in the collections based on some constraint on the n side of the
relationship.  In other words I don't want to get all the entries in the
collection but only the ones that satisfy the constraint.

For example:
If I had a classroom table and a student table which has a 1-n
relationship (each classroom has n students male or female), I want to
write a PB query that returns me all male (or female) students in a
given classroom (assume that gender is an attribute in the student
table).  Is this possible?

Thanks in advance
Raghavan


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Re: Query on collection descriptors

[Armin Waibel <ar...@apache.org>]

Hi Raghavan,

Kollivakkam R. Raghavan wrote:

> If I have a 1-n relationship between two entities represented as a
> collection-descriptor in OJB, how can I use the PB Query API to retrieve
> items in the collections based on some constraint on the n side of the
> relationship.  In other words I don't want to get all the entries in the
> collection but only the ones that satisfy the constraint.
> 

you can try to implement a QueryCustomizer
http://db.apache.org/ojb/tutorial3.html#Customizing collection queries

regards,
Armin

> For example:
> If I had a classroom table and a student table which has a 1-n
> relationship (each classroom has n students male or female), I want to
> write a PB query that returns me all male (or female) students in a
> given classroom (assume that gender is an attribute in the student
> table).  Is this possible?
> 
> Thanks in advance
> Raghavan
> 
> 
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