The text property of the combo box returns the current value of the edit box according to MSDN documentation.
So, you must validate your data through code before saving it into your database. In other words, if the text in the edit box has been changed, your program must make sure that that data can actually be saved in that particular field of your oracle recordset.
You can do this in the change event of the combo control. This only works, if the style property is set to 0 or 1.
Private Sub Combo1_Change()
' Code to validate the new value
End Sub
Otherwise, you'll have to write a function to check the data before saving it to the database.
Private Sub CheckData()
'
End Sub