*/
public String asString(UpdateOp update) {
StringBuilder sb = new StringBuilder("[");
boolean needComma = false;
for (Map.Entry<Key, Operation> change : update.getChanges().entrySet()) {
Operation op = change.getValue();
Key key = change.getKey();
// exclude properties that are serialized into special columns
if (columnProperties.contains(key.getName()) && null == key.getRevision())
continue;