Grails: how to return instance of domain class when using projections

Question

I have a domain class which has around 20 properties. A findBy on the domain class results in a select query which has all the columns selected from the database, which can be a performance hit when the required column could be only 1.

So I thought of using, withCriteria.

def sampleDomainInst = SampleDomain.withCriteria{
    projections {
        property('fieldOne')
       }
     eq('id', idVal)
  } 

The value returned is a list. But what I need is an instance of SampleDomain How do I do that?

Thank You. Regards, Jay Chandran

Answer 1

The goal of projections is IMHO not to have domain instances returned. In theory you might add 'id' to the projections closure and then you can do a DomainClass.get(id). But that is the same as working completely without the projection.

If your domain class has so many properties that a you're using projections to get only parts of them, you should consider splitting up the domain class in multiple joined classes. A good design practice is that each class should only represent one single abstraction.

Answer 2

Try withCriteria(uniqueResult: true) {...} or, longer, SampleDomain.createCriteria().get {...} .

OTOH, how can you select only 1 column, if you're selecting whole SampleDomain object (unless most of its properties are lazily-fetched)? That sounds unclear.

// And I believe you'll get more performance hits then selecting 20 fields for 1 record.

Answer 3

def whatYouWant = sampleDomainInst[0] 

除非我错过了什么。