Grails GORM loading collection of objects issue

I'm trying to load a list of Evaluations in a class named Contributor but I'm missing something as I cannot get my test passing.

My test is creating and saving objects as expected because when I do Evaluations.list() and Contributor.list() and print the values I see the data I saved.

Furthermore, when I select an Evaluation and print the value of its 'contributor' property it appears to be correct.

However, when I select a Contributor and print the values of its 'evaluations' property it is null.

I assume my mapping is the problem?

class Contributor {
    String name

    static hasMany = [evals:Evaluation]

    static mapping = {
        id column: 'user_id'
        evals joinTable:[name:'ev开发者_如何学编程aluation', column:'eval_id', key:'eval_user_id']
        version false
    }
}

class Evaluation {
    Contributor contributor
    String comment

    static mapping = {
        id column:'eval_id'
        contributor column:'eval_user_id'
        version false
    }
}

Thanks.

You shouldn't assign evals like contributor.evals = [eval]. Rather invoke a dynamic method addTo*(): contributor.addToEvals(eval). This will create a Hibernate collection for evals which will be persisted later.

The first one didn't work because Grails doesn't assign other end of association when you assign eval.contributor, i.e. it doesn't call contributor.addToEvals(eval). I have no idea why - there must be some implementation reason.

So contributor remains with the same empty evals in Hibernate cache. If it falls out of cache and you re-read it, it will have evals filled, because the association is mapped only on Eval table's foreign key.

Empty evals are null - it's another Hibernate feature: when a collection is empty, it can be null. Just know it.

Here's an good short post explaining some Hibernate internals: http://blog.xebia.com/2008/03/advanced-hibernate-proxy-pitfalls/

Ahh I've sussed it. The problem is the way I was saving the objects.

The following does not work:

def contributor = new Contributor([name:'Homer']).save(failOnError:true)
def eval = new Evaluation([contributor:contributor, comment:'Must read article']).save(failOnError:true)

This

def contributor = new Contributor([name:'Homer']).save(failOnError:true)
def eval = new Evaluation([contributor:contributor, comment:'a comment']).save(failOnError:true)
contributor.evals = [eval]
contributor.save(failOnError:true)

Or this, does work:

def contributor = new Contributor([name:'Homer'])
def eval = new Evaluation([contributor:contributor, comment:'a comment'])
contributor.evals = [eval]
contributor.save(failOnError:true)

Not sure I fully understand why the top save method doesn't work when selecting data since the id of the contributor is saved on the evaluation.