Mapping a column with comma seperated values

Question

Hi,
I have two tables
1. Tasks (task_id, task_description)
2. Task_assignment (username, task_assignment_value)
the task_assignment_value has a comma seperated list of task_ids.
What is the best ways to map the tables ?
Thanks in advance.
Moinuddin Mohammed

Answer 1

I have a couple of attributes where I do this. From TopLink's perspective, I just map it as a String. Then, in my accessors for the attribute, I transform the primitive between the String and an Array or however the rest of the app wants to see the attribute.
Here's an example that's actually more complicated than absolutely necessary. The mapped attributed is indicatorValueListString. It is lazily converted to an Array of Enums when it is first accessed. And it is converted back to a String in the preWriteEventCallback that is mapped in the TopLink descriptor.
This implementation attempts to minimize the number of times the String<->Array conversion takes place, but if that's not a concern, it could be made much more simple. Also, at my company we privately manage collections with the Collection classes for dynamic allocation, but publicly exchange Arrays for type-safety. This could also be factored out. ValuedEnumUtils basically manages asking the enum for its delimiter and performing the actual conversion between a String and an Array or back.
private String indicatorValueListString;
private List indicatorValueSelections;
private List indicatorValueSelections() {
        if (indicatorValueSelections == null) {
                indicatorValueSelections = new ArrayList();
                if (indicatorValueListString != null) {
                        indicatorValueSelections =
                                java.util.Arrays.asList(ValuedEnumUtils.decodeEnumString(
                                     IndicatorValueEnum.class,indicatorValueListString));
        return indicatorValueSelections;
private void indicatorValueSelections(List newIndicatorValueSelections) {
        indicatorValueSelections = newIndicatorValueSelections;
public IndicatorValueEnum[] getIndicatorValueSelections() {
        return (IndicatorValueEnum[])indicatorValueSelections().toArray(new IndicatorValueEnum[0]);
public void setIndicatorValueSelections(IndicatorValueEnum[] newIvSelections) {
        indicatorValueSelections(java.util.Arrays.asList(newIvSelections));
public boolean addIndicatorValueSelection(IndicatorValueEnum anIvEnum) {
        return indicatorValueSelections().add(anIvEnum);
public boolean removeIndicatorValueSelection(IndicatorValueEnum anIvEnum) {
        return indicatorValueSelections().remove(anIvEnum);
public void preWriteEventCallback(DescriptorEvent aDescriptorEvent) {
        // Note: Not using accessor to avoid lazy initialization if no changes
        // are necessary.
        if (indicatorValueSelections != null) {
                indicatorValueListString =
                        ValuedEnumUtils.encodeEnumString((ValuedEnum[])indicatorValueSelections.toArray());
}