code: public List distinct(final String fieldName, final DBObject query) {
          return distinct(fieldName, query, getReadPreference());
      }
docs: Find the distinct values for a specified field across a collection and returns the results in an array.
  
  @param fieldName Specifies the field for which to return the distinct values
  @param query     specifies the selection query to determine the subset of documents from which to retrieve the distinct values
  @return an array of the distinct values
  @mongodb.driver.manual reference/command/distinct Distinct Command