public class MyConstraint extends AbstractModelConstraint
{
    @Override
    public IStatus validate(IValidationContext ctx)
    {
        Diagnostician diagnostician = new Diagnostician();
        Diagnostic diagnostics = diagnostician.validate(ctx.getTarget());

        if (diagnostics.getSeverity() == Diagnostic.OK)
        {
            return createSuccessReport(ctx, target);
        }

        List<Diagnostic> diagnosticsChildren = diagnostics.getChildren();
        if (diagnosticsChildren.size() == 1)
        {
            Diagnostic child = diagnosticsChildren.get(0);
            return createFailureReport(ctx, target, child.getMessage());
        }

        // Create multiple failure reports and combine into a multistatus report
        List<IStatus> statusList = new ArrayList<IStatus>(diagnosticsChildren.size());
        for (Diagnostic child : diagnosticsChildren)
        {
            statusList.add(createFailureReport(ctx, target, child.getMessage()));
        }

        return ConstraintStatus.createMultiStatus(ctx, statusList);
    }
}