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Calculations of field values using other tables [message #390286]

Tue, 14 July 2009 08:51

Philipp Kursawe

Messages: 135
Registered: July 2009

Senior Member

Hello,

is it possible to calculate a fields value using a SQL statement?
I have a progress and a status field that would have to be calculated by
values from another table.

OrderEntity {
float progress;
int shortageLines;
}

The shortageLines field would be calculated by the number of line items
from the line_items table that have been picked with a shortage. The
progress field is the overal % of already picked line items versus the
total number of line items to pick.

Any idea if something like that is possible to "inject" into the object
using JPA?

Thanks,
Phil

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Re: Calculations of field values using other tables [message #390294 is a reply to message #390286]

Thu, 16 July 2009 14:04

James Sutherland

Messages: 1939
Registered: July 2009
Location: Ottawa, Canada

Senior Member

You could change this to a query instead of a persistence attribute.

If you need to map it, you could use a TransformationMapping in
EclipseLink, or use a postBuild event to query the data. You could also
just lazy initialize the field using a query.

Another solution would be define a database view that include the computed
values and map your object to the view.

---
James
http://www.nabble.com/EclipseLink---Users-f26658.html

James : Wiki : Book : Blog : Twitter

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Re: Calculations of field values using other tables [message #390298 is a reply to message #390294]

Thu, 16 July 2009 14:30

Philipp Kursawe

Messages: 135
Registered: July 2009

Senior Member

James wrote:
> You could change this to a query instead of a persistence attribute.

What you mean by that? How would I annotate that or create this query?

>
> If you need to map it, you could use a TransformationMapping in
> EclipseLink, or use a postBuild event to query the data. You could also
> just lazy initialize the field using a query.
>
> Another solution would be define a database view that include the
> computed values and map your object to the view.
I am doing that right now, it might be the most performant solution.
But anyway I am interested, in case the DB does not support views, how I
would use a TransformationMapping in my particular case. Do you have an
example of that for me?

Thanks,
Phil

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