Upserts with Generic sObjects - Salesforce

sObjectUpsert.cls

list < sObject > sObjList = new list < sObject > (); //This routine would get the rows to update/insert from some business logic 
sObjList = myClass.getObjectRowsToUpdate();
set < string > newExtIDSet = new set < string > ();

string myExternalIDField = 'myExternalID__c'; //Loop through and build a set of External IDs that should be used for a query 
for (sObject sObjItem: sObjList) {
    tempStr = string.ValueOf(sObjItem.get(myExternalIDField));
    if (string.isBlank(tempStr) == false) {
        newExtIDSet.add(tempStr);
    }
}
list < sObject > sObjExistingList = new list < sObject > (); //Now use those external IDs for matching 
string sQuery = 'Select ID, ' + myExternalIDField + ' From myUpdateObj__c' + ' Where ' + myExternalIDField + ' IN :newExtIDSet';
sObjExistingList = database.query(sQuery); //Now loop through the matches and build a map of that external ID to the actual Salesforce ID 
map < string, string > extIDToIDMap = new map < string, string > ();
for (sObject sObjItem: sObjExistingList) {
    extIDToIDMap.put(string.valueOf(sObjItem.get(myExternalIDField)), sObjItem.ID);
} //Now loop through the items to be updated/inserted and assign the Salesforce IDs to that items that matches by the External ID 
list < sObject > sObjInsertList = new list < sObject > ();
list < sObject > sObjUpdateList = new list < sObject > ();
for (sObject sObjItem: sObjList) {
    if (extIDToIDMap.containsKey(string.ValueOf(sObjItem.get(myExternalIDField)))) {
        sObjItem.ID = extIDToIDMap.get(string.ValueOf(sObjItem.get(myExternalIDField)));
        sObjUpdateList.add(sObjItem);
    } else {
        sObjInsertList.add(sObjItem);
    }
}

if (sObjUpdateList.size() > 0) {
    update sObjUpdateList;
}
if (sObjInsertList.size() > 0) {
    insert sObjInsertList;
}