Add Item To List With LookUp Column Programmatically

In my previous posts on "Working With SharePoint List" I have discussed how we can Read, Add and Update SharePoint List. If you have to add new Item to a list which has lookup column, you have to follow a different procedure.

If you look at the following figure, you can easily understand what I'm going to do. I'm going to add a new record to List_B, which has a lookup column from List_A's Title Field.

This is a sample code to get the above task done,

        
    public void addToLookUp()
    {
        /* open the web */
        SPSite site = new SPSite("http://merdev-moss:5050/testsara");
        SPWeb web = site.OpenWeb();

        string targetList = "List_B";
        string sourceList = "List_A";
        string sourceListField = "Title";

        /* we are going to add new row to List_B,
        * It (List_B) has a lookup column called "A_Column",
        * It (A_Column) get data from Title field of List_A.
        * (List_A has value called "test2" in Title field)
        */

        SPListItemCollection listItems = web.Lists[targetList].Items;
        SPListItem item = listItems.Add();
        item["Title"] = "New Title";
        int ID = get_ID(web, sourceList, sourceListField, "test2");
        if (ID != 0)
            item["A_Column"] = ID;
        item.Update();
    }

    public static int get_ID(SPWeb web, string list, string field, string itemname)
    {
        int id = 0;
        SPList sharedDocumentList = web.ServerRelativeUrl.Equals("/") ? web.GetList(web.ServerRelativeUrl + list) : web.GetList(web.ServerRelativeUrl + "/" + list);
        SPListItemCollection listItems = sharedDocumentList.Items;
        foreach (SPListItem item in listItems)
        {
            if (item[field].ToString() == itemname.ToString())
                id = item.ID;
            break;
        }
        return (id);
    }