Combo box value in Popup editor

[Just]

I have a custom popup template attached to grid for edit and add. In the template I've a drop down (combo box) column. I can get it populated fine.
The problem is it always defaults to the first value. How can I get it to set to the value that was in the row being edited.

The combobox is defined like below

<input name="ProductType" data-source="myDataSource" data-text-field="productName"

                    data-value-field="productId" data-bind="value:ProductType" data-role="dropdownlist" />

The grid shows the "ProductType" column.

Thanks.

[Just]

I changed it to

<input name="ProductType" data-source="myDataSource" data-text-field="productName"

                    data-value-field="productName" data-bind="value:ProductType" data-role="dropdownlist" />

and it works.

But now how do I get the Product Id of the selected product?

In the grid the ProductName is a read only label.