Forms Data Controls :: Edit GridView Row With ObjectDataSource

I have a grid that receives products over a GetList methods via ObjectDataSource. The Product class contains also a Object Supplier. If I change in the drop down list of the grid the supplier for a product and I click update the ID of the suppliier is still the same. I have debugged the call of the update method and checked the parameter in the product object. I wrote the following code in the SelectedIndexChanged event and the text box shows the right id but not the update method.

DropDownList supplier = (DropDownList) sender;
txtTest.Text = supplier.SelectedValue;

Here is the code of my grid view:

[Code]....

My Object Data Source calls the following Update Method:

[Code]....

The next work around idea would be to call the update method manually in the Update Event of the grid view.