code: private String redisKey(ModelExt<?> m) {
  		Table table = m.table();
  		StringBuilder key = new StringBuilder();
  		key.append(RECORDS);
  		key.append(table.getName());
  		key.append(":");
  		//fetch primary keys' values
  		String[] primaryKeys = table.getPrimaryKey();
  		//format key
  		for (int idx = 0; idx < primaryKeys.length; idx++) {
  			Object primaryKeyVal = m.get(primaryKeys[idx]);
  			if (null != primaryKeyVal) {
  				if (idx > 0) {
  					key.append("|");
  				}
  				key.append(primaryKeyVal);
  			}
  		}
  		return key.toString();
  	}
docs: redis key: records:tablename: id1 | id2 | id3...
  eg: the user has three primarykeys id1=1,id2=2,id3=3, so the redisKey is 'records:user:1|2|3'.
  @return redis key