protected String getDBFieldString(Set<String> requestedIds) {
    String[] tmp = new String[requestedIds.size()];
    int i = 0;
    for (String s : requestedIds)
      if (dbFields.containsKey(s))
        tmp[i++] = dbFields.get(s).toString();
    return StringUtils.join(tmp, ",", 0, i);
  }
Gets a comma-separated list of db fields corresponding to set of requested
ids.

@param requestedIds
         the requested ids
@return a comma-separated list of db fields
ambari-server/src/main/java/org/apache/ambari/server/controller/internal/AbstractJDBCResourceProvider.java