docs: def database_forwards(self, app_label, schema_editor, from_state, to_state):
          """Perform forward migration."""
          Process = from_state.apps.get_model('flow', 'Process')  # pylint: disable=invalid-name
          Data = from_state.apps.get_model('flow', 'Data')  # pylint: disable=invalid-name
          try:
              # pylint: disable=invalid-name
              ProcessMigrationHistory = from_state.apps.get_model('flow', 'ProcessMigrationHistory')
              DataMigrationHistory = from_state.apps.get_model('flow', 'DataMigrationHistory')
          except LookupError:
              raise LookupError(
                  "Unable to retrieve migration history models. Perhaps you need "
                  "to add a migration dependency to a recent enough Resolwe flow "
                  "app in your migration?"
              )
  
          # Migrate processes.
          processes = Process.objects.filter(slug=self.process)
          if not processes.exists():
              return
  
          migrated_processes = set()
          schema_field = '{}_schema'.format(self.schema_type)
          for process in processes:
              current_schema = getattr(process, schema_field)
              if not self.migrate_process_schema(process, current_schema, from_state):
                  continue
  
              setattr(process, schema_field, current_schema)
              process.save()
              migrated_processes.add(process)
  
              # Update process migration log.
              ProcessMigrationHistory.objects.create(
                  migration=self.migration_id,
                  process=process,
                  metadata=self.describe_process_migration(process),
              )
  
          if not migrated_processes:
              return
  
          # Migrate all data objects.
          data = Data.objects.filter(process__in=migrated_processes)
          self.migrate_data(data, from_state)
  
          # Update data migration log.
          for datum in data:
              DataMigrationHistory.objects.create(
                  migration=self.migration_id,
                  data=datum,
                  metadata=self.describe_data_migration(datum)
              )