Question

I’ve got 2 tables, Question and Answer, with a many-to-many relationship (i.e. Questions can have multiple Answers and Answers can be reused by multiple Questions). For normalization, I have a cross-reference table between them named Question_Answer that has a many-to-one relationship with both tables. These are their class definitions:

class Question {
    int id
    int text

    static hasMany = [questionAnswers : QuestionAnswer]
}

class Answer {
    int id
    int text

    static hasMany = [questionAnswers : QuestionAnswer]
}

class QuestionAnswer {
    int id
    Question question
    Answer answer
}

I’m trying to get a list of Answers based on certain criteria. Here is my criteria query (using Grails’ withCriteria function):

def listing = Answer.withCriteria {
    cache false
    order "id", "asc"

    eq("id", myAnswerID)

    questionAnswers {
        question {
            isNotNull("text")
        }
    }
}

Here’s an example of the problem I’m having:

I have an Answer that matches 3 different Questions. What I want in the “listing” is 1 Answer object, with its questionAnswers list populated with the 3 matching QuestionAnswer objects. Instead, I’m getting 3 identical Answer objects, all with their questionAnswers lists populated.

Is there a simple way to achieve what I want? I’m hoping I’m just missing something small.

Any help/suggestions are much appreciated.

Thanks,
B.J.

Answer 1

Try adding this to your query to tell the Criteria to return only distinct Answer objects:

resultTransformer org.hibernate.Criteria.DISTINCT_ROOT_ENTITY