report query question

[David Mitchell <da...@factorylogic.com>]

 I have a question regarding report queries. 

 What is the purpose of having to provide a OJB persistent class reference
when supplying the query code that will be 
executed? I can see why you need to provide the following String array with
the names of the fields you want, but why do I
need to pass a specific persistent class type when creating the query?

 In the java API docs for the ReportQueryByCriteria, the variable is named
"targetClass", as if that was the type of object that
the query is populating, but it ISNT really, is it? Could I just pass a null
in there in lieu of having to pretend that some real OJB
object applies to my query?

 yours,
 David Mitchell



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Re: report query question

[Thomas Mahler <th...@web.de>]

Hi David,

David Mitchell wrote:
>  I have a question regarding report queries. 
> 
>  What is the purpose of having to provide a OJB persistent class reference
> when supplying the query code that will be 
> executed? I can see why you need to provide the following String array with
> the names of the fields you want, but why do I
> need to pass a specific persistent class type when creating the query?

The reason is stated in the javadoc for 
PersistenceBroker.getReportQueryIteratorByQuery(Query query):

Returns an Iterator that iterates Object[] calling the .next() method. 
The Elements returned come from a SELECT ... WHERE sqlStatement

*The Class c is only used to provide the associated JDBC Connection*

OJB must know against which datasource a query should be performed. This 
  information is taken from the ClassDescriptor of class c.

>  In the java API docs for the ReportQueryByCriteria, the variable is named
> "targetClass", as if that was the type of object that
> the query is populating, but it ISNT really, is it? Could I just pass a null
> in there in lieu of having to pretend that some real OJB
> object applies to my query?

Try it out. But IMO it will result in an error as OJB tries to lookup a 
datasource from the ClassDescriptor of the class parameter.
If the parameter is null a NullPointerException could be a likely result...

cheers,
Thomas

> 
>  yours,
>  David Mitchell
> 
> 
> 
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Re: report query question

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

hi david,

the class is used to get the classdescriptor describing the table, the 
columns etc. from repository.
field names are translated into column names using this descriptor.

hth
jakob

David Mitchell wrote:

> I have a question regarding report queries. 
>
> What is the purpose of having to provide a OJB persistent class reference
>when supplying the query code that will be 
>executed? I can see why you need to provide the following String array with
>the names of the fields you want, but why do I
>need to pass a specific persistent class type when creating the query?
>
> In the java API docs for the ReportQueryByCriteria, the variable is named
>"targetClass", as if that was the type of object that
>the query is populating, but it ISNT really, is it? Could I just pass a null
>in there in lieu of having to pretend that some real OJB
>object applies to my query?
>
> yours,
> David Mitchell
>
>
>
>+---------------------------------------------------------+ 
>This message may contain confidential and/or privileged information.  If you
>are not the addressee or authorized to receive this for the addressee, you
>must not use, copy, disclose or take any action based on this message or any
>information herein.  If you have received this message in error, please
>advise the sender immediately by reply e-mail and delete this message.
>Thank you for your cooperation.
>+---------------------------------------------------------+
>
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