You typically do it on a schedule, e.g. once per hour, or once every day.

In the post the whenever gem (https://github.com/javan/whenever) is used, but you could use anything that is able to run things periodically.

If you'd want to stay solely within Postgres, there is also pg_cron (https://github.com/citusdata/pg_cron) which could be used to call REFRESH MATERIALIZED VIEW from within the database.

The post covers this under the section "Refreshing a materialized view".

In addition to what the other commenters mentioned, if you’re importing data, you can refresh the affected materialized views after the data import is complete.