Hi,

What dou you think about adding a new attribute to the PROPERTY element in the Hibernate 3 mapping, so you are able to define what must be treated as a null value within a property?

This would be very helpful, for example, when working with searching criteria represented as combos. Imagine you have a property which is an Integer, and the user has to select in a combo its value, but can also select all the possible values. If we could set its null-value property as follows:



Then we could add a new selection to the combo named "ALL THE COUNTRIES", which will be initialized to -1, so when the search criteria arrives to the DAO, then Hibernate knows it's like null, so Hibernate will just ignore it.

What do you think? Could this be interesting? If you agree I could post an improvement in JIRA :-)

This is an interesting addition because it influence something I've been thinking about for a while: we could hide the ternary operators IS [NOT] NULL and make SQL a little bit easier to use. I didn't spend much time trying to figure out the consequences of this. Please post to JIRA as Improvement and include my response. Thanks

OK. Done.

http://opensource.atlassian.com/project ... se/HHH-555

Please, friends, vote it so we can get it done soon ;-)

I cannot see how null-value='-1' is helpfull since the null value actually is not -1 its NULL....

and NULL is not equal to "ALL THE XXX", its actually the complete opposite.

what you are looking for (with respect to your search criteria example)sounds more like a custom Example.PropertySelector.
(and you can use <meta> to add your wanted behavior)

Well, it's not intended to substitute the NULL value, but to provide a mechanism to tell the Criteria API that if the <null-value> arrives, just skip it.

How could it be achieved then using the PropertySelector? And what is that <meta> about?

Exactly and it surely has nothing to do with NULL ;)

meta attribute is something you can apply to class'es and assocations, e.g.


and now that stuff is available via Property.getMetaAttributes()

PropertySelector is what is used to tell hibernate which attributes to consider in Criteria/Example queries:

s.createCriteria(Account.class)
.add( Example.create(accountBean). setPropertySelector(new YourCustomSelector());

Then your propery selector is passed each property name and the example value on which you can decide wether you want it included or not.

Hibernate already has a few built in which is activated by calling excludeZeroes(), and excludeNone().

So an example for your usecase would be:

class NotNullOrMinusPropertySelector implements PropertySelector {
public boolean include(Object object, String propertyName, Type type) {
return object!=null && (
!(object instanceof Number) || ( (Number) object ).longValue()!=-1
);
}
}

OK. Did some investigation:



I will complete this example with the use of a <meta> tag to define the "skip" value ;-)

By the way, how can that Property.getMetaAttributes() method be accesed if I only have the property's name that the include method gives me as a parameter?

its accessible via the SessionFactory getclassMetaData and you can then just pass in the correct metadata to your property selector.

/max

Sorry, but what method should I call in getClassMetadata to obtain those meta attributes?

Could you possibly provide a working example? Thanks.

sorry they are not on sessionfactory, but on the Configuration.

look at getClassMapping("whatever").getProperty("prop").getMetaAttribute("doh")