code: def get_ris(self):
          
          if self.aggregationType != 'Journal':
              raise ValueError('Only Journal articles supported.')
          # Basic information
          ris = "TY  - JOUR\nTI  - {title}\nJO  - {jour}\nVL  - {vol}\n"\
                "DA  - {date}\nPY  - {year}\nSP  - {pages}\n".format(
                  title=self.title, jour=self.publicationName, vol=self.volume,
                  date=self.coverDate, year=self.coverDate[0:4],
                  pages=self.pageRange)
          # Authors
          for au in self.authors:
              ris += 'AU  - {}\n'.format(au.indexed_name)
          # DOI
          if self.doi is not None:
              ris += 'DO  - {0}\nUR  - https://doi.org/{0}\n'.format(self.doi)
          # Issue
          if self.issueIdentifier is not None:
              ris += 'IS  - {}\n'.format(self.issueIdentifier)
          ris += 'ER  - \n\n'
          return ris
docs: Bibliographic entry in RIS (Research Information System Format)
          format for journal articles.
  
          Raises
          ------
          ValueError
              If the item's aggregationType is not Journal.