Question

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:'evaluation', 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.

Answer 1

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/