docs: def restrict_joins(self, q, bindings):
          """
          Restrict the joins across all tables referenced in the database
          query to those specified in the model for the relevant dimensions.
          If a single table is used for the query, no unnecessary joins are
          performed. If more than one table are referenced, this ensures
          their returned rows are connected via the fact table.
          """
          if len(q.froms) == 1:
              return q
          else:
              for binding in bindings:
                  if binding.table == self.fact_table:
                      continue
                  concept = self.model[binding.ref]
                  if isinstance(concept, Dimension):
                      dimension = concept
                  else:
                      dimension = concept.dimension
                  dimension_table, key_col = dimension.key_attribute.bind(self)
                  if binding.table != dimension_table:
                      raise BindingException('Attributes must be of same table as '
                                             'as their dimension key')
  
                  join_column_name = dimension.join_column_name
                  if isinstance(join_column_name, string_types):
                      try:
                          join_column = self.fact_table.columns[join_column_name]
                      except KeyError:
                          raise BindingException("Join column '%s' for %r not in fact table."
                                                 % (dimension.join_column_name, dimension))
                  else:
                      if not isinstance(join_column_name, list) or len(join_column_name) != 2:
                          raise BindingException("Join column '%s' for %r should be either a string or a 2-tuple."
                                                 % (join_column_name, dimension))
                      try:
                          join_column = self.fact_table.columns[join_column_name[0]]
                      except KeyError:
                          raise BindingException("Join column '%s' for %r not in fact table."
                                                 % (dimension.join_column_name[0], dimension))
                      try:
                          key_col = dimension_table.columns[join_column_name[1]]
                      except KeyError:
                          raise BindingException("Join column '%s' for %r not in dimension table."
                                                 % (dimension.join_column_name[1], dimension))
  
                  q = q.where(join_column == key_col)
          return q