Optimistic Updates
Optimistic updates enable highly responsive and fast interfaces by avoiding network wait times. An update is optimistic by assuming the network is successful. In the case of any errors, Rest Hooks will then roll back any changes in a way that deals with all possible race conditions.
Partial updates
One common use case is for quick toggles. Here we demonstrate a publish button for an
article. Note that we need to include the primary key (id in this case) in the response
body to ensure the normalized cache gets updated correctly.
import { Entity, createResource } from '@rest-hooks/rest';
export class Article extends Entity {
readonly id: string | undefined = undefined;
readonly title: string = '';
readonly content: string = '';
readonly published: boolean = false;
pk() {
return this.id;
}
}
const BaseArticleResource = createResource({
path: '/articles/:id',
schema: Article,
});
export const ArticleResource = {
...BaseArticleResource,
partialUpdate: BaseArticleResource.partialUpdate.extend({
getOptimisticResponse(snap, params, body) {
return {
// we absolutely need the primary key here,
// but won't be sent in a partial update
id: params.id,
...body,
};
},
}),
};
import { useController } from 'rest-hooks';
import { ArticleResource } from 'api/Article';
export default function PublishButton({ id }: { id: string }) {
const controller = useController();
return (
<button
onClick={() =>
controller.fetch(
ArticleResource.partialUpdate,
{ id },
{ published: true },
)
}
>
Publish
</button>
);
}
Optimistic create with instant updates
Optimistic updates can also be combined with immediate updates, enabling updates to other endpoints instantly. This is most commonly seen when creating new items while viewing a list of them.
Here we demonstrate what could be used in a list of articles with a modal to create a new article. On submission of the form it would instantly add to the list of articles the newly created article - without waiting on a network response.
import { Entity, createResource } from '@rest-hooks/rest';
import uuid from 'uuid/v4';
export class Article extends Entity {
readonly id: string | undefined = undefined;
readonly title: string = '';
readonly content: string = '';
readonly published: boolean = false;
pk() {
return this.id;
}
}
const BaseArticleResource = createResource({
path: '/articles/:id',
schema: Article,
});
export const ArticleResource = {
...BaseArticleResource,
create: BaseArticleResource.create.extend({
getRequestInit(body) {
if (body) {
return this.constructor.prototype.getRequestInit.call(this, {
id: uuid(),
...body,
});
}
return this.constructor.prototype.getRequestInit.call(this, body);
},
getOptimisticResponse(snap, params, body) {
return body;
},
update(newResourcePk: string) {
return {
[list.key({})]: (resourcePks: string[] = []) => [
...resourcePks,
newResourcePk,
],
};
},
}),
};
Since the actual id of the article is created on the server, we will need to fill
in a temporary fake id here, so the primary key can be generated. This is needed
to properly normalize the article to be looked up in the cache.
Once the network responds, it will have a different id, which will replace the existing
data. This is often seamless, but care should be taken if the fake id is used in any
renders - like to issue subsequent requests. We recommend disabling edit type features
that rely on the primary key until the network fetch completes.
import { useController } from 'rest-hooks';
import { ArticleResource } from 'api/Article';
export default function CreateArticle() {
const { fetch } = useController();
const submitHandler = useCallback(
data => fetch(ArticleResource.create, data),
[create],
);
return <Form onSubmit={submitHandler}>{/* rest of form */}</Form>;
}
Optimistic Deletes
Since deletes automatically update the cache correctly upon fetch success, making your delete endpoint do this optimistically is as easy as adding the getOptimisticResponse function to your options.
We return an empty string because that's the response we expect from the server. Although by default, the server response is ignored.
import { Entity, createResource } from '@rest-hooks/rest';
export class Article extends Entity {
readonly id: string | undefined = undefined;
readonly title: string = '';
readonly content: string = '';
readonly published: boolean = false;
pk() {
return this.id;
}
}
const BaseArticleResource = createResource({
path: '/articles/:id',
schema: Article,
});
export const ArticleResource = {
...BaseArticleResource,
delete: BaseArticleResource.delete.extend({
getOptimisticResponse(snap, params, body) {
return params;
},
}),
};
Optimistic Transforms
Sometimes user actions should result in data transformations that are dependent on the previous state of data. The simplest examples of this are toggling a boolean, or incrementing a counter; but the same principal applies to more complicated transforms. To make it more obvious we're using a simple counter here.
{"count":0,"updatedAt":"2023-03-20T19:56:26.702Z"}
export class CountEntity extends Entity {count = 0;pk() {return `SINGLETON`;}}export const getCount = new RestEndpoint({path: '/api/count',schema: CountEntity,name: 'get',});export const increment = new RestEndpoint({path: '/api/count/increment',method: 'POST',name: 'increment',schema: CountEntity,getRequestInit() {// substitute for super.getRequestInit()return this.constructor.prototype.getRequestInit.call(this, {updatedAt: Date.now(),});},getOptimisticResponse(snap) {const { data } = snap.getResponse(getCount);if (!data) throw new AbortOptimistic();return {count: data.count + 1,};},});
Try removing getOptimisticResponse from the increment RestEndpoint. Even without optimistic updates, this race condition can be a real problem. While it is less likely with fast endpoints;
slower or less reliable internet connections means a slow response time no matter how fast the server is.
The problem is that the responses come back in a different order than they are computed. If we can determine the correct 'total order', we would be able to solve this problem.
Without optimistic updates, this can be achieved simply by having the server return a timestamp of when it was last updated. The client can then choose to ignore responses that are out of date by their time of resolution.
Tracking order with updatedAt
To handle potential out of order resolutions, we can track the last update time in updatedAt.
Overriding our useIncoming, we can check which data is newer, and disregard old data
that resolves out of order.
We use snap.fetchedAt in our getOptimisticResponse. This respresents the moment the fetch is triggered, which is when the optimistic update first applies.
{"count":0,"updatedAt":"2023-03-20T19:56:26.702Z"}
export class CountEntity extends Entity {count = 0;updatedAt = 0;pk() {return `SINGLETON`;}static useIncoming(existingMeta, incomingMeta, existing, incoming) {return existing.updatedAt <= incoming.updatedAt;}}export const getCount = new RestEndpoint({path: '/api/count',schema: CountEntity,name: 'get',});export const increment = new RestEndpoint({path: '/api/count/increment',method: 'POST',name: 'increment',schema: CountEntity,getRequestInit() {// substitute for super.getRequestInit()return this.constructor.prototype.getRequestInit.call(this, {updatedAt: Date.now(),});},getOptimisticResponse(snap) {const { data } = snap.getResponse(getCount);if (!data) throw new AbortOptimistic();return {count: data.count + 1,updatedAt: snap.fetchedAt,};},});