[hibernate-issues] [Hibernate-JIRA] Commented: (HHH-879) Enable joining the same association twice with Criteria

[James Olsen (JIRA)]

    [ http://opensource.atlassian.com/projects/hibernate/browse/HHH-879?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_30511 ] 

James Olsen commented on HHH-879:
---------------------------------

WORKAROUND

I use extra 'query keys' (a term borrowed from a competing product) as shown below.

This first mapping is the standard one.  In my case it's protected, FetchType.LAZY and ignores any data as I never use it to retrieve data directly.  It's just metadata for a query key so that I have transitive closure for these objects in a distributed system but still have all the relationships defined for querying purposes.  You could have this first mapping as a proper mapping if you want.

@OneToMany(targetEntity = TradeOrderAuditImpl.class, fetch = FetchType.LAZY, mappedBy = "tradeOrder")
protected Set<TradeOrderAudit> getTradeOrderAudits() {
	return null;
}

protected void setTradeOrderAudits(Set<TradeOrderAudit> tradeOrderAudits) {
}

This second mapping is to the same entity.  Again, it's just a query key.  In this case it also happens to have a constraint which uniquely identifies the target object (making this suit a single purpose).  This is completely optional, you could leave the @Where off and use criteria to constrain in the normal way (making it as general purpose as the standard mapping).

@OneToMany(targetEntity = TradeOrderAuditImpl.class, fetch = FetchType.LAZY, mappedBy = "tradeOrder")
@Where(clause="ORDER_ACTION_EN = 6")
protected Set<TradeOrderAudit> getFillTradeOrderAudit() {
	return null;
}

protected void setFillTradeOrderAudit(Set<TradeOrderAudit> tradeOrderAudits) {
}

Now I can refer to both 'tradeOrderAudits' and 'fillTradeOrderAudit' which relate to the same table and use them in query restrictions and projections.

These query keys don't seem to affect performance too much.  On merge hibernate thinks the collections have simply been dereferenced and ignores them (no cascading).

I rely on these a lot (more for the transitive-closure-with-full-relationship-metadata benefit) so it would actually be nice to have the notion of a 'query key' promoted to a first class item rather than this hack.  Perhaps equivalents of the existing relationship annotations but with 'QK' prefixed and placed at the class level?

> Enable joining the same association twice with Criteria
> -------------------------------------------------------
>
>                 Key: HHH-879
>                 URL: http://opensource.atlassian.com/projects/hibernate/browse/HHH-879
>             Project: Hibernate3
>          Issue Type: Improvement
>          Components: core
>            Reporter: Vladimir Bayanov
>
> Make double joining the same association with Criteria.createCriteria possible. See: http://forum.hibernate.org/viewtopic.php?t=931249

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