Add values to a list contains a Lookup Field - sharepoint

Question

I have a list named "Designation" that contains a Designation Code and Designation Name.
I have another list named "Employee" that contains Employee Name and Designation Name (as a Lookup Field).
I am able to insert values to "Employee" list using the following code.
protected void AddEmp(object sender, EventArgs e)
{
string emp_name = txtEmployeeName.Text;
string emp_designation = ddlDesignation.SelectedValue;
using (SPSite site = new SPSite("My Site"))
{
using (SPWeb web = site.OpenWeb())
{
SPSecurity.RunWithElevatedPrivileges(delegate()
{
web.AllowUnsafeUpdates = true;
SPList splist_employees = web.Lists["Employee"];
SPList splist_designations = web.Lists["Designations"];
SPListItemCollection splc_items = splist_employees.Items;
SPListItem spli_item = splc_items.Add();
SPFieldLookup lookup = splist_employees.Fields["Designated"] as SPFieldLookup;
string fieldName = lookup.LookupField;
spli_item["Employee Name"] = emp_name;
spli_item[fieldName] = GetLookFieldIDS(emp_designation, splist_designations);
spli_item.Update();
});
}
}
}
public static string GetLookFieldIDS(string lookupValues, SPList lookupSourceList)
{
string id = string.Empty;
SPFieldLookupValueCollection lookupIds = new SPFieldLookupValueCollection();
SPQuery query = new Microsoft.SharePoint.SPQuery();
query.Query = "<Where><Eq><FieldRef Name='Designation' /><Value type='Text'>"+lookupValues + "</Value></Eq></Where>";
SPListItemCollection listItems = lookupSourceList.GetItems(query);
foreach (Microsoft.SharePoint.SPListItem item in listItems)
{
id = item.ID.ToString();
}
return id;
}
Here I have given the field name as 'Designation' inside the query.
But, I want to find the field name based on the value given from the user end instead of hard-coding the field name as 'Designation'.
Any help is greatly appreciated. Thanks in advance.

Answer 1

Not sure about your request but, you could pass SPFieldLookup.LookupField property to your GetLookFieldIDS method and use that variable instead of "Designation"
spli_item[fieldName] = GetLookFieldIDS(emp_designation, splist_designations, lookup.LookupField);