Textbox bound to primary key fields problem

[besmart2000]

Hi
I have a form with bindingsource ,biningnavigator and bound textboxes generated using VS2005 wizard.
I want to use the same textbox controls for entering search criteria , by writing code in a command button control.
The problem:
When i focuse on textbox bound to primary key field,I can't leave the textbox control an i should enter a value, but really i want to let it blank (null) to be out of search criteria.
The Question:
how can I let the Textboxes relaxed for all PK constraints, and leave them blank for search.
I used :
MyTable.DataSet.EnforceConstraints = False , but it has no effect.

Thanks

 

[cjard]

EnforceCOnstraints=False should do it. Can you show me the code in your Search button click handler?