`useCreateIndexes`

The useCreateIndexes hook is used to create an Indexes object within a React application with convenient memoization.

useCreateIndexes(
  store: Store,
  create: (store: Store) => Indexes,
  createDeps?: DependencyList,
): Indexes

	Type	Description
`store`	`Store`	A reference to the `Store` for which to create a new `Indexes` object.
`create`	`(store: Store) => Indexes`	A function for performing the creation steps of the `Indexes` object for the `Store`, plus any additional steps such as adding definitions or listeners, and returning it.
`createDeps?`	`DependencyList`	An optional array of dependencies for the `create` function, which, if any change, result in its rerun. This parameter defaults to an empty array.
returns	`Indexes`	A reference to the `Indexes` object.

It is possible to create an Indexes object outside of the React app with the regular createIndexes function and pass it in, but you may prefer to create it within the app, perhaps inside the top-level component. To defend against a new Indexes object being created every time the app renders or re-renders, the useCreateIndexes hook wraps the creation in a memoization.

The useCreateIndexes hook is a very thin wrapper around the React useMemo hook, defaulting to the provided Store as its dependency, so that by default, the creation only occurs once per Store.

If your create function contains other dependencies, the changing of which should also cause the Indexes object to be recreated, you can provide them in an array in the optional second parameter, just as you would for any React hook with dependencies.

This hook ensures the Indexes object is destroyed whenever a new one is created or the component is unmounted.

Examples

This example creates an Indexes object at the top level of a React application. Even though the App component is rendered twice, the Indexes object creation only occurs once by default.

const App = () => {
  const store = useCreateStore((store) =>
    createStore().setTable('pets', {
      fido: {species: 'dog'},
      felix: {species: 'cat'},
      cujo: {species: 'dog'},
    }),
  );
  const indexes = useCreateIndexes(store, (store) => {
    console.log('Indexes created');
    return createIndexes(store).setIndexDefinition(
      'bySpecies',
      'pets',
      'species',
    );
  });
  return <span>{JSON.stringify(indexes.getSliceIds('bySpecies'))}</span>;
};

const app = document.createElement('div');
const root = ReactDOMClient.createRoot(app);
root.render(<App />);
// -> 'Indexes created'

root.render(<App />);
// No second Indexes creation

console.log(app.innerHTML);
// -> '<span>["dog","cat"]</span>'

This example creates an Indexes object at the top level of a React application. The App component is rendered twice, each with a different top-level prop. The useCreateIndexes hook takes the cellToIndex prop as a dependency, and so the Indexes object is created again on the second render.

const App = ({cellToIndex}) => {
  const store = useCreateStore(() =>
    createStore().setTable('pets', {
      fido: {species: 'dog', color: 'brown'},
      felix: {species: 'cat', color: 'black'},
      cujo: {species: 'dog', color: 'brown'},
    }),
  );
  const indexes = useCreateIndexes(
    store,
    (store) => {
      console.log(`Index created for ${cellToIndex} cell`);
      return createIndexes(store).setIndexDefinition(
        'byCell',
        'pets',
        cellToIndex,
      );
    },
    [cellToIndex],
  );
  return <span>{JSON.stringify(indexes.getSliceIds('byCell'))}</span>;
};

const app = document.createElement('div');
const root = ReactDOMClient.createRoot(app);
root.render(<App cellToIndex="species" />);
// -> 'Index created for species cell'

console.log(app.innerHTML);
// -> '<span>["dog","cat"]</span>'

root.render(<App cellToIndex="color" />);
// -> 'Index created for color cell'

console.log(app.innerHTML);
// -> '<span>["brown","black"]</span>'