Javascript Live Objects/Collections

All data returned by the SDK are wrapped in the SDK's LiveObject API. The LiveObject API allows you to easily retrieve the queried data asynchronously, as well as subscribe to any new changes to the data.

LiveObject

Observing live changes to any object queries can be done by observing the dataUpdated event on the Live Object:

// observe data changes
const currentUser = client.currentUser;

currentUser.on('dataUpdated', model => {
  console.log(`Current user is: ${model.displayName}`);
})

// unobserve data changes once you are finished
currentUser.removeAllListeners('dataUpdated');

In this example, the block observes the data of the currently authenticated user and prints out the displayName. The observe block can be called multiple times throughout the lifetime of the application:

If the requested object data is stored locally on the device, the block will be called immediately with the local version of the data (you can verify this through the dataStatus property).
In parallel, a network request for the latest version of the data is fired. Once the network returns the data, the observe block will be called again with the updated data.
Any future changes to the data (whenever the user changes its displayName on another device, for example) can trigger additional callbacks.

We recommend you to always call removeAllListeners() whenever you are done observing an event to avoid any unnecessary callbacks.

Model

The data provided by LiveObject is directly accessible via the model property. The model property is always kept up to date with the latest state changes; wheneverdataUpdated event is fired, the model property has already been updated.

Data Status

If you want to exclusively display fresh data in your UI (without using the potientially out-of-date local data), you can do so by reading the object's dataStatus property, which reflects the status of the callback data, and check that its value is set to fresh.

import { LoadingStatus, DataStatus } from '@amityco/js-sdk';

if (currentUser.dataStatus === DataStatus.Fresh) {
  // the data field of this object is up to date
  console.log(currentUser.model);
}

You can also use the object's loadingStatus property to determine the current state of network operations being performed by the LiveObject. This is useful for any UI element that needs to provide the loading state.

if (currentUser.loadingStatus === LoadingStatus.Loading) {
  // this object is current loading, show loading UI
}

The LiveObject can also emit events for updates for dataStatus as well as loadingStatus. As with other events, please make sure to call removeAllListeners() when you are done observing changes to these values in order to prevent memory leaks.

currentUser.on('dataStatusChanged', callback);
currentUser.on('loadingStatusChanged', callback);

Events Order

The LiveObject updates statuses and data in strict order and emits related events accordingly when an instance is created. Few different cases might occurs when you create a LiveObject instance:

Data is not cached.

Initial values:

loadingStatus = LoadingStatus.Loading
dataStatus = DataStatus.NotExist
model = undefined

Process received data:

emits loadingStatusChanged
emits dataStatusChanged
emits dataUpdated

Data is cached, but is not fresh.

Initial values:

loadingStatus = LoadingStatus.Loading
dataStatus = DataStatus.Local
model = localData

Process received data (same order):

emits loadingStatusChanged
emits dataStatusChanged
emits dataUpdated - only if data is really different

Data is cached and is fresh.

loadingStatus = LoadingStatus.Loaded
dataStatus = DataStatus.Fresh
model = localFreshData

Interface

This is the list of LiveObject members and methods.

Members

model = model that the live object should fetch
loadingStatus = determine the current state of network operations being performed by the LiveObject
dataStatus = reflects the status of the callback data

Methods

on(event, callback) = listens to event and executes callback when event is fired
once= same as the on method but can only be called once
removeAllListeners = removes all listeners from on
dispose = causes the LiveObject to be destroyed and cleaned up

Get Post data

Here is a sample code on how the get Post data.

const livePost = PostRepository.getPost(postId)
console.log(livePost.model)

LiveCollection

The LiveObject API supports queries that return a list of objects, this is known as a LiveCollection. LiveCollection has the same methods and properties as its object counterpart, but contains a few other helper methods around pagination.

import { MessageRepository } from '@amityco/js-sdk';

const messageRepo = new MessageRepository('channel1');
const messages = messageRepo.messagesForChannel({ channelId: 'channel1234' });
messages.on('dataUpdated', models => {
  // models will be an array of message objects
  models.forEach(message => {
    console.log('Message: ', message);
  });
});

Pagination

Pagination with LiveCollections is very simple: the collection offers a convenient nextPage method that you can call which will automatically trigger a local cache lookup, a network call, and multiple LiveObject updates once new data is returned. Every collection starts with one page of 20 models. After nextPage() is successful, the dataUpdated event will be triggered with a new array combining both the old objects as well as 20 newly fetched objects.

const liveCollection = MessageRepository.queryMessages({
    channelId: 'channelId',
    type: 'text'
});

liveCollection.on(“dataUpdated”, messages => console.log(messages))

const loadMore = () => {
  if (liveCollection.nextPage) {
    liveCollection.nextPage();
  }
};

The dataUpdated event will be dispatched when the first set of data from the server is loaded. Calling nextPage will load the next set of data. Once all data are loaded, the dataUpdated event will once again be dispatched.

You can use the nextPage property to determine if you've scrolled to the end of the list. The nextPage property initially returns false until the first collection query is finished.

Lastly, if there is a need to shrink the list of objects exported back to only the first 20 records (for example, if you pass the LiveCollection object to a new view), you can simply call resetPage().

Models

Similar to model property of the LiveObject, the LiveCollection provides models property what is basically is an array of LiveObject's model objects. models is mutable and always contains same data as one what returned by dataUpdated event.

Errors

Both LiveObject and LiveCollection can be subscribed to the dataError event which is fired every time an error happens during the data update process. In other words, every time the LiveObject or LiveCollection fails to get data from the server - this error will be emitted.

const messages = messageRepo.messagesForChannel({ channelId: 'channel1234' });

messages.on('dataError', error => {
  // Every error has a code. You can control how your application should behave in response to the error.
  if (error.code !== YYYYYY) {
    throw error;
  }
});

Dispose LiveObject and LiveCollection

We recommend you to always call dispose() whenever you are done working with any LiveObject/LiveCollection.

// create an user LiveObject and a messages LiveCollection when you mount your component or view
const currentUser = client.currentUser;
const messages = messageRepo.messagesForChannel({ channelId: 'channel1234' });

...

// before leaving page, unmounting component etc
currentUser.dispose();
messages.dispose();

Dispose is a very important functionality of the LiveObject. It allows you to avoid memory leaks and keeps your application performant. What does dispose() do:

unsubscribe all listeners attached to the LiveObject instance;
stop all internall observers related to the LiveObject instance;
clean up an internall buffer of the LiveObject instance;

After you call dispose() on a LiveObject instance, dataStatus and loadingStatus switch to Error.

Last updated 2 years ago