Dexie.js Docs

Dexie.Observable

Observe changes to database - even when they happen in another browser window.

NOTE!

This addon adds meta tables your database to maintain change tracking. This can slow down the performance. As of dexie version >= 3.2, you no longer need this addon to observe data. We encourage you to look at the docs of liveQuery() and useLiveQuery() - built-in observation in Dexie >= 3.2, before considering this addon.

Install

npm install dexie-observable

Use

import Dexie from 'dexie';
import 'dexie-observable';

// Use Dexie as normally - but you can also subscribe to db.on('changes').

Usage with existing DB

In case you want to use Dexie.Observable with your existing database, you will have to do a schema upgrade. Without it Dexie.Observable will not be able to properly work.

import Dexie from 'dexie';
import 'dexie-observable';

var db = new Dexie('myExistingDb');
db.version(1).stores(... existing schema ...);

// Now, add another version, just to trigger an upgrade for Dexie.Observable
db.version(2).stores({}); // No need to add / remove tables. This is just to allow the addon to install its tables.

Dependency Tree

Source

Dexie.Observable.js

Description

Dexie.Observable is an add-on to Dexie.js makes it possible to listen for changes on the database even if the changes are made in a foreign window. The addon provides a “storage” event for IndexedDB, much like the storage event (onstorage) for localStorage.

In contrary to the Dexie CRUD hooks, this event reacts not only on changes made on the current db instance but also on changes occurring on db instances in other browser windows. This enables a Web Apps to react to database changes and update their views accordingly.

Dexie.Observable is also the base of Dexie.Syncable.js - an add-on that enables two-way replication with a remote server.

Dexie.Observable excludes tables whose names begin with an underscore from observation. Therefore, it is recommended to avoid using such names.

Extended Methods, Properties and Events

UUID key generator

When defining your stores in Version.stores() you may use the $$ (double dollar) prefix to your primary key. This will make it auto-generated to a UUID string. See sample below.

Dexie.Observable.createUUID()

A static method added to Dexie that creates a UUID. This method is used internally when using the \(prefix to primary keys. To change the format of\) primary keys, just override Dexie.createUUID by setting it to your desired function instead.

db.on(‘changes’) event

Subscribe to any database changes no matter if they occur locally or in other browser window.

Parameters to your callback:

changes : Array<DatabaseChange>Array of changes that have occurred in database (locally or in other window) since last time event was triggered, or the time of starting subscribing to changes.
partial: BooleanTrue in case the array does not contain all changes. In this case, your callback will soon be called again with the additional changes and partial=false when all changes are delivered.

Example:

<html>
<head>
  <script src="dexie.min.js"></script>
  <script src="dexie-observable.min.js"></script> <!-- Enable DB observation -->
  <script>
    var db = new Dexie("ObservableTest");
    db.version(1).stores({
        friends: "$$uuid,name"
    });
    db.on('changes', function (changes) {
      changes.forEach(function (change) {
        switch (change.type) {
          case 1: // CREATED
            console.log('An object was created: ' + JSON.stringify(change.obj));
            break;
          case 2: // UPDATED
            console.log('An object with key ' + change.key + ' was updated with modifications: ' + JSON.stringify(change.mods));
            break;
          case 3: // DELETED
            console.log('An object was deleted: ' + JSON.stringify(change.oldObj));
            break;
        }
      });
    });
    db.open();
    // Make an initial put() - will result in a CREATE-change:
    db.friends.put({name: "Kalle"}).then(function(primKey) {
      // Call put() with existing primary key - will result in an UPDATE-change:
      db.friends.put({uuid: primKey, name: "Olle"}).then (function () {
        // Call delete() will result in a DELETE-change:
        db.friends.delete(primKey);
      });
    });

    // Result that will be logged:
    // An object was created: {"uuid": "23bada36-d27a-4e78-a978-1ab3c4129cd0", name: "Kalle"}
    // An object with key: 23bada36-d27a-4e78-a978-1ab3c4129cd0 was updated with modifications: {"name": "Olle"}
    // An object was deleted: {"uuid": "23bada36-d27a-4e78-a978-1ab3c4129cd0", name: "Olle"}
  </script>
</head>
<body></body>
</html>

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