[hibernate-issues] [Hibernate-JIRA] Commented: (HHH-4479) We should be able to implement Joins using formulas with Annotations

[Paul Benedict (JIRA)]

    [ http://opensource.atlassian.com/projects/hibernate/browse/HHH-4479?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=34149#action_34149 ] 

Paul Benedict commented on HHH-4479:
------------------------------------

Let's take a step back and make a differentiation here. There's a difference between supporting legacy behavior and how it is accomplished. Translating legacy behavior from HBM files to annotations doesn't mean it's a black-and-white mechanical translation. In fact, how could it be? Converting mapping files to annotations is a task in itself, and not even the attributes are identical. Therefore, making referencedColumnName mandatory with a formula-joins seems like such a small price to pay when making the jump to annotation-based configuration. Rhetorically speaking, what's the problem with saying joins must be name-based when using annotations? If someone needs to do positional-based joins, HBM  (i.e., legacy) files are there for them. 

About your second point, Java does not allow annotations to be repeated. Only one type may be annotated per target, or otherwise you have to use a container (like @JoinColumns) that accepts an array. Here's an expanded example:

@ManyToOne
@JoinColumn(name="order_nbr", referencedColumnName="order_nbr")
@JoinFormulas({
    @JoinFormula(value="'true'", referencedColumnName="is_default"),
    @JoinFormula(value="'true'", referencedColumnName="is_personalized")
})
public Menu getOrder() {
    return order;
}

> We should be able to implement Joins using formulas with Annotations 
> ---------------------------------------------------------------------
>
>                 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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