Disallow entry of negative quantities of green coffee in new batch window

config/Windows/newbatch.xml

                                 <label>Green Coffee:</label>
                                 <sqltablearray columns="3" id="greens">
                                     <column name="Coffee" delegate="sql" showdata="true" null="true" nulltext="Delete" nulldata="delete" data="0" display="1">SELECT id, name FROM coffees WHERE quantity &lt;&gt; 0 ORDER BY name</column>
-                                    <column name="Weight" delegate="numeric" />
+                                    <column name="Weight" delegate="positivenumeric" />
                                     <column name="Remaining" />
                                 </sqltablearray>
                                 <layout type="horizontal">

src/typica.w

 {
     @<Assign numeric column delegate@>@;
 }
+else if(currentElement.attribute("delegate") == "positivenumeric")
+{
+	@<Assign positive numeric column delegate@>@;
+}
 
 @ When using a |SaltModel|, there are times where the array values being
 inserted are identification numbers representing some record that already exists
 delegate->setWidget(widget);
 view->setItemDelegateForColumn(currentColumn, delegate);
 
-@ Another common use is allowing numeric values. At present this only
-restricts input to numbers, however it may be useful to provide other options
-such as restricting the range of allowed values in the future.
+@ Another common use is allowing numeric values.
 
 @<Assign numeric column delegate@>=
 NumericDelegate *delegate = new NumericDelegate;
 view->setItemDelegateForColumn(currentColumn, delegate);
 
+@ It is also possible to restrict allowed numeric values to non-negative
+values.
+
+@<Assign positive numeric column delegate@>=
+NumericDelegate *delegate = new NumericDelegate(true);
+view->setItemDelegateForColumn(currentColumn, delegate);
+
 @ The |NumericDelegate| will only set the display value to a number, but it
 will perform mathematical calculations that are entered into the editor as
 well. This allows a person to type something like $13.26+5.06$ with the result
 {
     @[Q_OBJECT@]@;
     public:@/
-        NumericDelegate(QObject *parent = NULL);
+        NumericDelegate(bool positiveOnly = false, QObject *parent = NULL);
         QWidget *createEditor(QWidget *parent,
                               const QStyleOptionViewItem &option,@|
                               const QModelIndex &index) const;
         void updateEditorGeometry(QWidget *editor,
                                   const QStyleOptionViewItem &option,@|
                                   const QModelIndex &index) const;
+	private:
+		bool m_positiveOnly;
 };
 
 @ There is nothing special about the constructor.
 
 @<NumericDelegate implementation@>=
-NumericDelegate::NumericDelegate(QObject *parent) :
-    QItemDelegate(parent)
+NumericDelegate::NumericDelegate(bool positiveOnly, QObject *parent) :
+    QItemDelegate(parent), m_positiveOnly(positiveOnly)
 {
     /* Nothing needs to be done here. */
 }
     QScriptValue result = engine->evaluate(line->text());
     if(result.isNumber())
     {
-        model->setData(index, result.toVariant(), Qt::DisplayRole);
+		if(m_positiveOnly)
+		{
+			if(result.toNumber() < 0)
+			{
+				model->setData(index, QVariant(), Qt::DisplayRole);
+			}
+			else
+			{
+				model->setData(index, result.toVariant(), Qt::DisplayRole);
+			}
+		}
+		else
+		{
+			model->setData(index, result.toVariant(), Qt::DisplayRole);
+		}
     }
     else
     {