Run a job instead of a server#

An application on the database layer alone, whose boot is a unit of work over rows: run once, on a schedule, or by a cron.

The build#

Depend on eezo-db instead of the umbrella, and skip the plugin: there are no routes to generate.

libraryDependencies += "io.eezo" %% "eezo-db" % eezoVersion

With only eezo-db on the classpath, derives Form and derives Resource don't compile, and dev is a command the application doesn't know. That's the point of opting into one layer.

`boot` is the job#

import java.time.LocalDate
import io.eezo.db.*
import io.eezo.db.Scopes.*
import models.Reminder

object Main extends DbApp {

  override def schema: Schema = AppSchema

  override def boot(): Unit = {
    val reminders = Table[Reminder]
    val today     = LocalDate.now()
    val delivered = transact {
      val due = reminders
        .where(_.sent === false)
        .where(_.dueOn <= today)
        .orderBy(_.dueOn.asc)
        .list()
      due.foreach { reminder =>
        println(s"  ${reminder.dueOn}  ${reminder.text}")
        reminders.update(reminder.copy(sent = true))
      }
      due.size
    }
    println(s"$delivered reminder(s) delivered")
  }
}

DbApp installs the database around boot and takes it down after, so sbt run does the work and exits. The query is the typed layer: where on a field, orderBy, list(), inside one transact so the reads and the updates are one transaction.

The schema commands come along#

status, sync, freeze, migrate, reset, drop, dump and ddl work exactly as on a web application, so the table is created the same way:

sbt "run freeze initial schema"
sbt "run migrate --apply"
sbt run

Running it repeatedly#

On a schedule: whatever runs commands on your platform, cron or a Fly scheduled machine, running the same java -cp lib/* Main the staged Dockerfile does.
While developing, re-run on save with sbt's own watch: sbt ~run.

Seeding#

A job that wants data on its first run can check the table and insert:

if (reminders.query.count() == 0L) Reminder.seed(today).foreach(reminders.insert)

The reminders example under examples/reminders is this whole page as a running project.