react-native-onyx

Persistent storage solution wrapped in a Pub/Sub library.

Features

• Onyx stores and retrieves data from persistent storage
• Data is stored as key/value pairs, where the value can be anything from a single piece of data to a complex object
• Collections of data are usually not stored as a single key (e.g. an array with multiple objects), but as individual keys+ID (e.g. report_1234, report_4567, etc.). Store collections as individual keys when a component will bind directly to one of those keys. For example: reports are stored as individual keys because SidebarLink.js binds to the individual report keys for each link. However, report actions are stored as an array of objects because nothing binds directly to a single report action.
• Onyx allows other code to subscribe to changes in data, and then publishes change events whenever data is changed
• Anything needing to read Onyx data needs to:
  1. Know what key the data is stored in (for web, you can find this by looking in the JS console > Application > local storage)
  2. Subscribe to changes of the data for a particular key or set of keys. React components use withOnyx() and non-React libs use Onyx.connect().
  3. Get initialized with the current value of that key from persistent storage (Onyx does this by calling setState() or triggering the callback with the values currently on disk as part of the connection process)
• Subscribing to Onyx keys is done using a constant defined in ONYXKEYS. Each Onyx key represents either a collection of items or a specific entry in storage. For example, since all reports are stored as individual keys like report_1234, if code needs to know about all the reports (e.g. display a list of them in the nav menu), then it would subscribe to the key ONYXKEYS.COLLECTION.REPORT.

Getting Started

Installation

At the moment, Onyx is not yet published to npm. To use in your project, reference the latest sha of the main branch directly in package.json

  "dependencies": {
    "react-native-onyx": "git+https://github.com/Expensify/react-native-onyx.git#ccb64c738b8bbe933b8997eb177f864e5139bd8d"
  }

Initialization

To initialize Onyx we call Onyx.init() with a configuration object.

import Onyx from 'react-native-onyx';

const ONYXKEYS = {
    SESSION: 'session',
};

const config = {
    keys: ONYXKEYS,
};

Onyx.init(config);

Setting data

To store some data we can use the Onyx.set() method.

API.Authenticate(params)
    .then((response) => {
        Onyx.set(ONYXKEYS.SESSION, {token: response.token});
    });

The data will then be cached and stored via AsyncStorage.

Merging data

We can also use Onyx.merge() to merge new Object or Array data in with existing data.

For Array the default behavior is to concatenate new items.

Onyx.merge(ONYXKEYS.EMPLOYEE_LIST, ['Joe']); // -> ['Joe']
Onyx.merge(ONYXKEYS.EMPLOYEE_LIST, ['Jack']); // -> ['Joe', 'Jack']

For Object values the default behavior uses lodash/merge under the hood to do a deep extend of the object.

Onyx.merge(ONYXKEYS.POLICY, {id: 1}); // -> {id: 1}
Onyx.merge(ONYXKEYS.POLICY, {name: 'My Workspace'}); // -> {id: 1, name: 'My Workspace'}

One caveat to be aware of is that lodash/merge follows the behavior of jQuery's deep extend and will not concatenate nested arrays in objects. It might seem like this code would concat these arrays, but it does not.

Onyx.merge(ONYXKEYS.POLICY, {employeeList: ['Joe']}); // -> {employeeList: ['Joe']}
Onyx.merge(ONYXKEYS.POLICY, {employeeList: ['Jack']}); // -> {employeeList: ['Jack']}

Should I use merge() or set() or both?

• Use merge() if we want to merge partial data into an existing Array or Object
• Use set() if we are working with simple values (String, Boolean, etc), need to completely overwrite a complex property of an Object, or reset some data entirely.

Consecutive calls to Onyx.merge() with the same key are batched in a stack and processed in the order that they were called. This helps avoid race conditions where one merge possibly finishes before another. However, it's important to note that calls to Onyx.set() are not batched together with calls to Onyx.merge(). For this reason, it is usually preferable to use one or the other, but not both. Onyx is a work-in-progress so always test code to make sure assumptions are correct!

Subscribing to data changes

To set up a basic subscription for a given key use the Onyx.connect() method.

let session;
const connectionID = Onyx.connect({
    key: ONYXKEYS.SESSION,
    callback: (val) => session = val || {},
});

To teardown the subscription call Onyx.disconnect() with the connectionID returned from Onyx.connect(). It's recommended to clean up subscriptions anytime you are connecting from within a function to prevent memory leaks.

Onyx.disconnect(connectionID);

We can also access values inside React components via the withOnyx() higher order component. When the data changes the component will re-render.

import React from 'react';
import {withOnyx} from 'react-native-onyx';

const App = ({session}) => (
    <View>
        {session.token ? <Text>Logged in</Text> : <Text>Logged out</Text> }
    </View>
);

export default withOnyx({
    session: {
        key: ONYXKEYS.SESSION,
    },
})(App);

It is preferable to use the HOC over Onyx.connect() in React code as withOnyx() will delay the rendering of the wrapped component until all keys have been accessed and made available.

Clean up

To clear all data from Onyx we can use Onyx.clear().

function signOut() {
    Onyx.clear();
}

Storage Providers

Onyx.get/set and the rest of the API accesses the underlying storage differently depending on the platform

Under the hood storage access calls are delegated to a StorageProvider Some platforms (like web and desktop) might use the same storage provider

If a platform needs to use a separate library (like using MMVK for react-native) it should be added in the following way:

1. Create a StorageProvider.js at lib/storage/providers
   Reference an existing StorageProvider for the interface that has to be implemented
2. Update the factory at lib/storage/index.js to return the newly created Provider for the desired Platform(s)

API Reference

Docs

Storage Eviction

Different platforms come with varying storage capacities and Onyx has a way to gracefully fail when those storage limits are encountered. When Onyx fails to set or modify a key the following steps are taken:

1. Onyx looks at a list of recently accessed keys (access is defined as subscribed to or modified) and locates the key that was least recently accessed
2. It then deletes this key and retries the original operation

By default, Onyx will not evict anything from storage and will presume all keys are "unsafe" to remove unless explicitly told otherwise.

To flag a key as safe for removal:

• Add the key to the safeEvictionKeys option in Onyx.init(options)
• Implement canEvict in the Onyx config for each component subscribing to a key
• The key will only be deleted when all subscribers return true for canEvict

e.g.

Onyx.init({
    safeEvictionKeys: [ONYXKEYS.COLLECTION.REPORT_ACTIONS],
});

export default withOnyx({
    reportActions: {
        key: ({reportID}) => `${ONYXKEYS.COLLECTION.REPORT_ACTIONS}${reportID}_`,
        canEvict: props => !props.isActiveReport,
    },
})(ReportActionsView);

Benchmarks

Provide the captureMetrics boolean flag to Onyx.init to capture call statistics

Onyx.init({
    keys: ONYXKEYS,
    safeEvictionKeys: [ONYXKEYS.COLLECTION.REPORT_ACTIONS],
    captureMetrics: Config.BENCHMARK_ONYX,
});

At any point you can get the collected statistics using Onyx.getMetrics(). This will return an object containing totalTime, averageTime and summaries. summaries is a collection of statistics for each method it contains data about:

• method name
• total, max, min, average times for this method calls
• calls - a list of individual calls with each having: start time; end time; call duration; call arguments
  • start/end times are relative to application launch time - 0.00 being exactly at launch

If you wish to reset the metrics and start over use Onyx.resetMetrics()

Finally, there's a Onyx.printMetrics() method which prints human statistics information on the dev console. You can use this method during debugging. For example add an Onyx.printMetrics() line somewhere in code or call it through the dev console. It supports 3 popular formats MD - human friendly markdown, CSV and JSON. The default is MD if you want to print another format call Onyx.printMetrics({ format: 'csv' }) or Onyx.printMetrics({ format: 'json' }).

Sample output of Onyx.printMetrics()

### Onyx Benchmark
  - Total: 1.5min
  - Last call finished at: 12.55sec

|     method      | total time spent |    max    |   min    |    avg    | time last call completed | calls made |
|-----------------|-----------------:|----------:|---------:|----------:|-------------------------:|-----------:|
| Onyx:getAllKeys |           1.2min |   2.16sec |  0.159ms | 782.230ms |                 12.55sec |         90 |
| Onyx:merge      |          4.73sec |   2.00sec | 74.412ms | 591.642ms |                 10.24sec |          8 |
| Onyx:set        |          3.90sec | 846.760ms | 43.663ms | 433.056ms |                  7.47sec |          9 |
| Onyx:get        |          8.87sec |   2.00sec |  0.063ms |  61.998ms |                 10.24sec |        143 |


|                           Onyx:set                            |
|---------------------------------------------------------------|
| start time | end time  | duration  |           args           |
|-----------:|----------:|----------:|--------------------------|
|  291.042ms | 553.079ms | 262.037ms | session, [object Object] |
|  293.719ms | 553.316ms | 259.597ms | account, [object Object] |
|  294.541ms | 553.651ms | 259.109ms | network, [object Object] |
|  365.378ms | 554.246ms | 188.867ms | iou, [object Object]     |
|    1.08sec |   2.20sec |   1.12sec | network, [object Object] |
|    1.08sec |   2.20sec |   1.12sec | iou, [object Object]     |
|    1.17sec |   2.20sec |   1.03sec | currentURL, /            |