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Records

Records are the main building blocks of deepstream's data-sync capabilities. They are atomic bits of JSON data that can be manipulated and observed. Any change to a record is instantly synced across all connected clients.

Using records

Records are requested using client.record.getRecord(name). If a record with the specified name doesn't exist yet, it will be created on the fly. If you just want to check if a record exists without creating it, you can use client.record.has(name, callback).

Records have set() and get() methods to interact with their data and subscribe() to inform you about updates. Here's what that would look like in action:

// Client A: Hungry customer sees pizza delivery approach on map
const driver = client.record.getRecord('driver/jack')
driver.subscribe('coords', updateMapPointer)
// Client B: Delivery driver's smartphone feeds position into record
const driver = client.record.getRecord('driver/jack')
navigator.geolocation.watchPosition(position => {
  driver.set('coords', position.coords)
})

Paths

get(), set() and subscribe() can be used to get the entire record's data, but also support "paths". Paths let you access sub-parts of your record's data using JSON notation, e.g. pets[1].fur.color. If a value for a path that doesn't exist yet is set, the path will be created on the fly.

Record lifecycle

When calling client.record.getRecord(), one of three things can happen:

  • If the record doesn't exist on the client or the server yet, it will be created. The initial data of a newly created record is an empty object {}.

  • If the record exists on the server, but hasn't been loaded on the client yet, it will be retrieved.

  • If the record is already loaded on the client, its instance will be returned.

Independent of whether the record has been loaded yet, getRecord() will return a record instance straight away. You can already start setting values or subscribing to updates at this point, however get() calls might return null.

To ensure a record is fully loaded, use the whenReady() method. Please note: This method will execute synchronously when the record is already available or asynchronously if its still being loaded.

Discarding Records

To inform the server that you're no longer interested in updates for a record, call discard(). Discard calls are aggregated, meaning that if a record was requested in three different places using getRecord(), it also needs to be discarded three times in order for the server to be notified.

Deleting Records

Records can be deleted using delete(). Deleting also discards the record. Whenever a record is deleted by one client, the same record on all other clients will emit a delete event.

Unsubscribe, Discard and Delete - what's the difference?

unsubscribe() removes an existing subscription to updates to a record or path. This is purely a client side operation and doesn't notify the server.

discard() tells the server that you're no longer interested in receiving updates for the record.

delete() irreversibly deletes the record from the database and cache and notifies all servers and clients within the cluster of the deletion.

Getting a snapshot

If you just require a static one-off view into a record's data, but not bother with the entire lifecycle you can also use client.record.snapshot(name, callback)

Naming records

Each record is identified by a name that needs to be unique across the entire system. So what does a great recordname look like? Something like this:

const book = client.record.getRecord('book/iq6auu7d-p9i1vz3q0yi')

This name consists of different parts: book is the category of the record. / is used as a split-character by many database connectors to sort records into tables. iq6auu7d-p9i1vz3q0yi is a unique id. Unique ids can be generated on the client using client.getUid(). They consist of a base64 encoded millisecond timestamp and a random string. UIDs are a common concept in distributed systems as they eliminate the need for a centralized, incremental id.

Can't unique id's clash?

Theoretically: yes. But the chances for two ids that were generated within the exact same millisecond to be the same are 1:1x10^16 - or one to 10 quadrillion - which is considered an acceptable risk.

Can I use more descriptive record names?

Absolutely, any string can be used as a record name. But you need to be certain that the string never changes. This is the case for many institutional usecases that are already based on unique ids. If you're building a stock trading platform, it's perfectly fine to name your record for Microsoft's stock stock/msft.

Making the username part of the record name

Many permissioning strategies in deepstream are based on record, event or rpc-names and the data they contain. To make sure that only johndoe can change his settings, you would call your record settings/johndoe and specify an associated Valve rule:

record:
  settings/$username:
    write: "$username === user.id"

Listening

Records also support a concept called "listening". Every client can register as a listener for record name patterns, e.g. ^settings/.*. Whenever other clients start subscribing to records that match said pattern, the listener will be notified.

// Client B
client.record.listen('settings/.*', (match, isSubscribed, response) => {
  console.log(match) // 'settings/security'
  if (isSubscribed) {
    if (/* if you want to provide */) {
      response.accept()
      // star publishing to this record via `client.record.getRecord(match).set(/* data */)`
    } else {
      response.reject() // let deepstream ask another provider
    }
  } else {
    // stop publishing data
    client.record.getRecord(match).discard()
  }
})

This is useful to create "active" data providers - backend processes that only send out data that's actually requested. A few things worth mentioning about listening:

  • The listen-callback is called with isSubscribed = true once the first client subscribes to a matching record and with isSubscribed = false once the last subscriber for a matching record unsubscribes.

  • Listening also keeps state. Registering as a listener for a pattern that already has matching subscriptions will call the callback multiple times straight away, once for every matching subscription.

Video Demo

If you would like to learn more find out our video tutorial with Yasser Fadl, explaining more in detail about records in deepstream.


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