How to change data before saving in Entity Framework + DataGridView?

Question

C++ / C#

There is a datagridview with bound data from the Entity Framework - the model. One of the fields is external and can be NULL. But, when I pick up values ​​for it from another table, when I click on the field itself, the first record from the external table is automatically selected, and I want to leave the option to leave NULL in this field. I tried to add a new empty record with id = 0 - it is still recognized as a value, and I get a foreign key error when saving the data. Is it possible to somehow change something in the data before saving?

Answer 1

I solved the problem like this: when changing the data in the desired column (CellValueChanged event), I check which one is set, and if 0 is set, I change it to null.