Entity

import { Entity } from 'rest-hooks';

export default class Article extends Entity {
  readonly id: number | undefined = undefined;
  readonly title: string = '';
  readonly content: string = '';
  readonly author: number | null = null;
  readonly tags: string[] = [];

  pk() {
    return this.id?.toString();
  }
}

import { Entity } from 'rest-hooks';

export default class Article extends Entity {
  id = undefined;
  title = '';
  content = '';
  author = null;
  tags = [];

  pk() {
    return this.id?.toString();
  }
}

Entity extends SimpleRecord

Entity is an abstract base class used to define data with some form of primary key (or pk for short). When representing data from a relational database, this makes an Entity roughly map 1:1 with a table, where each row represents an instance of the Entity.

By defining a pk() member, Rest Hooks will normalize entities, ensuring consistency and improve performance by increasing cache hit rates.

For common REST patterns, inheriting from Resource is recommended. However, for other cases Entity is a great place to start.

Methods

static fromJS\<T extends typeof SimpleRecord>(this: T, props: Partial\<AbstractInstanceType\<T>>): AbstractInstanceType\<T>

Inherited from SimpleRecord

This is used to create new entities when normalizing data. These are stored in the entities cache.

abstract pk: (parent?: any, key?: string): string | number | undefined

PK stands for primary key and is intended to provide a standard means of retrieving a key identifier for any Entity. In many cases there will simply be an 'id' field member to return. In case of multicolumn you can simply join them together.

undefined value

A undefined can be used as a default to indicate the entity has not been created yet. This is useful when initializing a creation form using Entity.fromJS() directly. If pk() resolves to null it is considered not persisted to the server, and thus will not be kept in the cache.

Other uses

While the pk() definition is key (pun intended) for making the normalized cache work; it also becomes quite convenient for sending to a react element when iterating on list results:

//....
return (
  <div>
    {results.map(result => <TheThing key={result.pk()} thing={result} />)}
  </div>
)

Singleton Entities

What if there is only ever once instance of a Entity for your entire application? You don't really need to distinguish between each instance, so likely there was no id or similar field defined in the API. In these cases you can just return a literal like 'the_only_one'.

pk() {
  return 'the_only_one';
}

static get key(): string

This defines the key for the Entity itself, rather than an instance. This needs to be a globally unique value.

static merge(first, second): mergedValue

static merge<T extends typeof SimpleRecord>(first: InstanceType<T>, second: InstanceType<T>) => InstanceType<T>

Inherited from SimpleRecord

Merge is used to resolve the same entity. This can be because it was previously put in the cache, or it was found in multiple places nested in one response. By default it is the SimpleRecord merge, which prefers values from the newer item but only if they are actually set.

Override this to change the algorithm - for instance if having the absolutely correct latest value is important, adding a timestamp to the entity and then using it to select the return value will solve any race conditions.

Example

class LatestPriceEntity extends Entity {
  readonly id: string = '';
  readonly timestamp: string = '';
  readonly price: string = '0.0';
  readonly symbol: string = '';

  static merge<T extends typeof SimpleRecord>(first: InstanceType<T>, second: InstanceType<T>) {
    if (first.timestamp > second.timestamp) return first;
    return second;
  }
}

static schema: { [k: keyof this]: Schema }

Set this to define entities nested inside this one.

static asSchema() => Entity

Returns this Entity with the TypeScript type set properly. Using asSchema() instead of this directly is key to getting correct typing from the hooks.

This can be used as a Schema or to build other Schemas.

import { universalFetchFunction } from 'utils';
import ArticleEntity from './ArticleEntity';

export const articleListShape = {
  type: 'read',
  schema: { results: [ArticleEntity.asSchema()], nextPage: '', prevPage: '' },
  getFetchKey(params: Readonly<object>): {return `article/${JSON.stringify(params)}`;},
  fetch: universalFetchFunction,
}