code: static String toEntityCategory(String table, List<String> fields) {
  		if (fields == null || fields.size() == 0) {
  			return table + "[]";
  		}
  		StringBuffer buffer = new StringBuffer();
  		buffer.append(table).append('[').append(fields.get(0));
  		for (int i = 1; i < fields.size(); i++) {
  			buffer.append(',').append(fields.get(i));
  		}
  		buffer.append(']');
  		return buffer.toString();
  	}
docs: Converts an entity type and scalar field name list to an 'entity category'
  Entity category is represented as String: "table[field1,field2]"
  
  @param table  entity type
  @param fields scalar field names the entity should be initialized with
  @return       entity category