Adding, removing objects from a ForeignCollection

Question

I have an entity that contains a ForeignCollection with a getter & setter for the Collection

public class TextQuestion{

    @ForeignCollectionField
    private ForeignCollection<TextAnswer> answers;
    ....

I have a Servicer wrapper class that encapsulates a DAO

public class TextQuestionService
{

    private static TextQuestionService instance;
    private static Dao<TextQuestion, Integer> textQuestionDAO;
    private static DatabaseHelper dbHelper = new DatabaseHelper();


    public void addAnswer( TextQuestion textQuestion, TextAnswer answer )
    {
        List<Answer> answers = (List)textQuestion.getAnswers();
        if( answers == null )
        {
            try
            {
                answers = (List)textQuestionDAO.getEmptyForeignCollection("answers");
            } catch (SQLException e)
            {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        }
        answers.add(answer);
    }

My Question is How do I add, remove items from this collection via the Wrapper service class? Above is my effort but I have just got completely lost, casting Collections to Lists etc. The problem is when I want to add an Answer to the Questions ForeignCollection there would be no problem if the Answers Collection was not null but I want to build the Question up, add Answers to it before persisting it. From a previous question I understand I need to call the getEmptyForeignCollection if the parent has not been retrieved from the DB. There must be a simple way to do this? Any worked similar example would be nice

Answer 1

The problem is when I want to add an Answer to the Questions ForeignCollection there would be no problem if the Answers Collection was not null but I want to build the Question up,

I think you are close. You should be able to do:

ForeignCollection<TextAnswer> answers = textQuestion.getAnswers();
if (answers == null) {
    answers = textQuestionDAO.getEmptyForeignCollection("answers");
}
answers.add(answer);

answers can also be a Collection<TextAnswer> but it is not a List.