code: def check_reaction_on_surface(self, chemical_composition, reactants,
                                    products):
          
          con = self.connection or self._connect()
          self._initialize(con)
          cur = con.cursor()
          statement = """SELECT reaction.id FROM reaction WHERE
          reaction.chemical_composition='{}' and reaction.reactants='{}'
          and reaction.products='{}';""".format(chemical_composition,
                                                json.dumps(reactants),
                                                json.dumps(products))
  
          cur.execute(statement)
          rows = cur.fetchall()
          if len(rows) > 0:
              id = rows[0][0]
          else:
              id = None
          return id
docs: Check if entry with same surface and reaction is allready written
          to database file
  
          Parameters
          ----------
          chemcial_composition: str
          reactants: dict
          products: dict
  
          Returns id or None