Question

Hi I have two Lists in sharepoint 2007.
I have a lookup column in on list which looks the other field.
I want to use the sharepoint object model to add an item to the second list.
How to i set the lookup field value. (The value is already in the other list).?

SPListItem Employee = web.Lists["Employee"].Items.Add();
Employee["Name"] = account.Name;
Employee["Department"] = <lookup value must come here>
Employee.Update();                 

Answer 1

Lookup fields will contain a combination of the row’s id and the value of the column to display, separated by :#, in your case that could be 1:#HumanResources or 12:#Engineering.

So to reference a lookup simply setting the id won’t be enough, instead the above mentioned string needs to be set. Luckily SharePoint provides the class SPFieldLookupValue that does exactly this:

var department = web.Lists["Department"].GetItemById(1);
var employee = web.Lists["Employee"].Items.Add();
employee["Name"] = account.Name;
employee["Department"] = new SPFieldLookupValue(department.ID, department.Title);
employee.Update();