By Redid Team

To add an event to a Stream we need to use the XADD command. Node Redis exposes that as .xAdd(). So, we need to add a call to .xAdd() in our route. Modify location-router.js to import our connection:

import { connection } from '../om/client.js'

And then in the route itself add a call to .xAdd():

 ...snip...
  const person = await personRepository.fetch(id)
  person.location = { longitude, latitude }
  person.locationUpdated = locationUpdated
  await personRepository.save(person)

  let keyName = `${person.keyName}:locationHistory`
  await connection.xAdd(keyName, '*', person.location)
  ...snip...

.xAdd() takes a key name, an event ID, and a JavaScript object containing the keys and values that make up the event, i.e. the event data. For the key name, we're building a string using the .keyName property that Person inherited from Entity (which will return something like Person:01FYC7CTPKYNXQ98JSTBC37AS1) combined with a hard-coded value. We're passing in * for our event ID, which tells Redis to just generate it based on the current time and previous event ID. And we're passing in the location—with properties of longitude and latitude—as our event data.

Now, whenever this route is exercised, the longitude and latitude will be logged and the event ID will encode the time. Go ahead and use Swagger to move Joan Jett around a few times.

Now, go into RedisInsight and take a look at the Stream. You'll see it there in the list of keys but if you click on it, you'll get a message saying that "This data type is coming soon!". If you don't get this message, congratualtions, you live in the future! For us here in the past, we'll just issue the raw command instead:

XRANGE Person:01FYC7CTPKYNXQ98JSTBC37AS1:locationHistory - +

This tells Redis to get a range of values from a Stream stored in the given the key name—Person:01FYC7CTPKYNXQ98JSTBC37AS1:locationHistory in our example. The next values are the starting event ID and the ending event ID. - is the beginning of the Stream. + is the end. So this returns everything in the Stream:

1) 1) "1647536562911-0"
  2) 1) "longitude"
      2) "45.678"
      3) "latitude"
      4) "45.678"
2) 1) "1647536564189-0"
  2) 1) "longitude"
      2) "45.679"
      3) "latitude"
      4) "45.679"
3) 1) "1647536565278-0"
  2) 1) "longitude"
      2) "45.680"
      3) "latitude"
      4) "45.680"

And just like that, we're tracking Joan Jett.

So, now you know how to use Express + Redis OM to build an API backed by Redis Stack. And, you've got yourself some pretty decent started code in the process. Good deal! If you want to learn more, you can check out the documentation for Redis OM. It covers the full breadth of Redis OM's capabilities.

And thanks for taking the time to work through this. I sincerely hope you found it useful. If you have any questions, the Redis Discord server is by far the best place to get them answered. Join the server and ask away!