Lookup Field : Invalid data has been used to update the list item. The field you are trying to update may be read only.

One of friend came up with this error while updating a lookup column in a list in SharePoint event handler.

When updating the look up column, we should not assign the value directly. Instead,we need to assign the Id of the lookup value.

I have a lookup column Country which gets the value from another list named “Country”.

If I update the value as

item[“Country”]=”India”;

results in the above error : Invalid data has been used to update the list item. The field you are trying to update may be read only.

Here I wrote one helper function which will return the SPLookupFieldValueCollection which can be set to the field.

public static SPFieldLookupValueCollection GetLookFieldIDS(string lookupValues,

SPList lookupSourceList)

{

SPFieldLookupValueCollection lookupIds = new SPFieldLookupValueCollection();

string[] lookups = lookupValues.Split(new char[] { ‘,’ },StringSplitOptions.RemoveEmptyEntries);

foreach (string lookupValue in lookups)

{

SPQuery query = new Microsoft.SharePoint.SPQuery();

query.Query = String.Format(“<Where><Eq><FieldRef Name=’Title’/><Value Type=’Text’>{0}</Value></Eq></Where>”, lookupValue);

SPListItemCollection listItems = lookupSourceList.GetItems(query);

foreach (Microsoft.SharePoint.SPListItem item in listItems)

{

SPFieldLookupValue value = new SPFieldLookupValue(item.ID.ToString());

lookupIds.Add(value);

break;

}

}

return lookupIds;

}

• Call this method like this

item[“Country”] = GetLookFieldIDS(“Australia”, lookupFieldList);

• If the LookupField allows multiple values

item[“Country”] = GetLookFieldIDS(“Australia,India”, lookupFieldList);