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From Craig L Russell <Craig.Russ...@Sun.COM>
Subject Re: Query objects and hashCode() + equals()
Date Fri, 23 Oct 2009 16:57:18 GMT
Hi Jörg,

On Oct 16, 2009, at 9:50 AM, Joerg von Frantzius wrote:

> Hi,
>
> it would be nice if the spec would mandate that implementations of
> javax.jdo.Query do correctly implement hashCode() and equals().

As users execute mutator methods on queries, the string representation  
would change. And for proper use in sets or map keys, hashCode and  
equals should be  immutable after construction. So I don't see how we  
can mandate that hashCode and equals rely in any internal state.

> Alternatively, Query.toString() could be required to return the
> single-string representation of the query, or some dedicated method  
> was
> added to provide it.
>
Having the single-string version of a query is useful but adds  
implementation complexity. While there is a requirement for an  
implementation to parse a single string query into executable form,  
there's no current requirement to create the single string form from  
the internal form.

> This would make it easier to e.g. implement some custom cache for  
> query
> results, or, more generally, it would make it easier to put Query
> objects as keys into Maps.

It seems to me that if you want this functionality at the application  
framework layer, then the framework can mandate that the single string  
form be used and at the time the query is created, the single string  
form be used as the key into a framework map.

Regards,

Craig
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Craig L Russell
Architect, Sun Java Enterprise System http://db.apache.org/jdo
408 276-5638 mailto:Craig.Russell@sun.com
P.S. A good JDO? O, Gasp!


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