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Snapshot

Snapshots passed to user-defined function that are used to compute state updates. These allow safe and performant access to the denormalized data based on the current state.

interface Snapshot {
  get(schema, ...args)​ => DenormalizeNullable<typeof schema> | undefined;
  getResponse(endpoint, ...args)​ => { data, expiryStatus, expiresAt };
  getError(endpoint, ...args)​ => ErrorTypes | undefined;
  fetchedAt: number;
  abort: Error;
}
tip

Use Controller.snapshot() to construct a snapshot

Usage​

import { Entity } from '@data-client/rest';

export class Post extends Entity {
  id = 0;
  userId = 0;
  title = '';
  body = '';
  votes = 0;

  pk() {
    return this.id?.toString();
  }
  static key = 'Post';

  get img() {
    return `//loremflickr.com/96/72/kitten,cat?lock=${this.id % 16}`;
  }
}

import { createResource } from '@data-client/rest';
import { Post } from './Post';

export { Post };

export const PostResource = createResource({
  path: '/posts/:id',
  schema: Post,
}).extend('vote', {
  path: '/posts/:id/vote',
  method: 'POST',
  body: undefined,
  schema: Post,
  getOptimisticResponse(snapshot, { id }) {
    const post = snapshot.get(Post, { id });
    if (!post) throw snapshot.abort;
    return {
      id,
      votes: post.votes + 1,
    };
  },
});

import { useController } from '@data-client/react';
import { PostResource, type Post } from './PostResource';

export default function PostItem({ post }: Props) {
  const ctrl = useController();
  const handleVote = () => {
    ctrl.fetch(PostResource.vote, { id: post.id });
  };
  return (
    <div>
      <div className="voteBlock">
        <small className="vote">
          <button className="up" onClick={handleVote}>
            &nbsp;
          </button>
          {post.votes}
        </small>
        <img src={post.img} width="70" height="52" />
      </div>
      <div>
        <h4>{post.title}</h4>
        <p>{post.body}</p>
      </div>
    </div>
  );
}
interface Props { post: Post }

import { schema } from '@data-client/rest';
import { useQuery } from '@data-client/react';
import { Post } from './PostResource';

const queryTotalVotes = new schema.Query(
  new schema.All(Post),
  (posts, { userId } = {}) => {
    if (userId !== undefined)
      posts = posts.filter(post => post.userId === userId);
    return posts.reduce((total, post) => total + post.votes, 0);
  },
);

export default function TotalVotes({ userId }: Props) {
  const totalVotes = useQuery(queryTotalVotes, { userId });
  return (
    <center>
      <small>{totalVotes} votes total</small>
    </center>
  );
}
interface Props { userId: number }

import { useSuspense } from '@data-client/react';
import { PostResource } from './PostResource';
import PostItem from './PostItem';
import TotalVotes from './TotalVotes';

function PostList() {
  const userId = 2;
  const posts = useSuspense(PostResource.getList, { userId });
  return (
    <div>
      {posts.map(post => (
        <PostItem key={post.pk()} post={post} />
      ))}
      <TotalVotes userId={userId} />
    </div>
  );
}
render(<PostList />);
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Members​

get(schema, ...args)​

Looks up any Queryable Schema.

getResponse(endpoint, ...args)​

returns
{
  data: DenormalizeNullable<E['schema']>;
  expiryStatus: ExpiryStatus;
  expiresAt: number;
}

Gets the (globally referentially stable) response for a given endpoint/args pair from state given.

data​

The denormalize response data. Guarantees global referential stability for all members.

expiryStatus​

export enum ExpiryStatus {
  Invalid = 1,
  InvalidIfStale,
  Valid,
}
Valid​
  • Will never suspend.
  • Might fetch if data is stale
InvalidIfStale​
  • Will suspend if data is stale.
  • Might fetch if data is stale
Invalid​
  • Will always suspend
  • Will always fetch

expiresAt​

A number representing time when it expires. Compare to Date.now().

getError(endpoint, ...args)​

Gets the error, if any, for a given endpoint. Returns undefined for no errors.

fetchedAt​

When the fetch was called that resulted in this snapshot.

abort​

This is an Error to be thrown in Endpoint.getOptimisticResponse() to cancel an optimistic update.