[hibernate-issues] [Hibernate-JIRA] Commented: (HHH-4479) We should be able to implement Joins using formulas with Annotations
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http://opensource.atlassian.com/projects/hibernate/browse/HHH-4479?page=c...
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Sharath Reddy commented on HHH-4479:
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Hi Paul,
I think this discussion has segued into 2 different issues:
1. Your comment: 'Because Joins are name-based, not positional-based'
Not necessarily true. Emmanuel told me that 'referencedColumnName' is mandatory as
per the JPA spec. HOWEVER, because of legacy reasons, IF a join refers to a composite
primary key, AND the foreign key columns are specified in the same order as the
corresponding columns of the primary key, then Hibernate does not require this attribute
to be specified (As it is implicit).
Or to put it in another way, if the 'referencedColumnName' attribute is not
specified, Hibernate assumes it is referring to the primary key of the referenced entity.
We want to preserve this going forward.
2. Forgetting about formulas for the moment, from a purely practical stand-point, the way
the AnnotationBinder currently parses the annotated classes, it REQUIRES the @JoinColumns
annotation if a join involves multiple columns. So the following would not work:
@ManyToOne
@JoinColumn(name="order_nbr", referencedColumnName="order_nbr")
@JoinColumn(name="is_default", referencedColumnName="is_default")
public Menu getOrder() {
return order;
}
The parser would arbitarily select either one of the @JoinColumn annotations, or may be
throw an exception (I have to check). If you want to join on multiple columns, you HAVE to
use @JoinColumns.
@JoinColumns{ @JoinColumn(..), @JoinColumn(..) }
So it is probably logically consistent that if you have a join consisting of a join column
AND a formula, you use some kind of wrapper annotation.
However, I do see your point. @JoinColumnsOrFormulas does not sound...elegant.
Let me discuss this again with Emmanual and get back to you.
We should be able to implement Joins using formulas with Annotations
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Key: HHH-4479
URL: http://opensource.atlassian.com/projects/hibernate/browse/HHH-4479
Project: Hibernate Core
Issue Type: New Feature
Components: annotations
Reporter: Sharath Reddy
Assignee: Sharath Reddy
Priority: Minor
Fix For: 3.5
Attachments: HHH-4479.patch, HHH-4479second.patch
This article published on the O'Reilly web site -
http://onjava.com/pub/a/onjava/2005/08/03/hibernate.html?page=3 - describes how to
implement joins with formulas, using the hbm xml files. We should be able to do the same
with annotations:
<hibernate-mapping>
<class name="Company" table="Company">
<id name="id" />
<many-to-one
name="defaultContactPerson"
property-ref="defaultContactPerson">
<column name="id"/>
<formula>1</formula>
</many-to-one>
</class>
<class name="Person" >
<id name="id" />
<properties name="defaultContactPerson">
<property name="companyID" />
<property name="defaultFlag" />
</properties>
</class>
</hibernate-mapping>
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