useGetMany

This hook calls dataProvider.getMany() when the component mounts. It queries the data provider for several records, based on an array of ids.

Syntax

const { data, isPending, error, refetch } = useGetMany(
    resource,
    { ids, meta },
    options
);

Usage

import { useGetMany, useRecordContext } from 'ra-core';

const PostTags = () => {
    const record = useRecordContext();
    const { data, isPending, error } = useGetMany(
        'tags',
        { ids: record.tagIds }
    );
    if (isPending) { return <div>Loading...</div>; }
    if (error) { return <p>ERROR</p>; }
    return (
         <ul>
             {data.map(tag => (
                 <li key={tag.id}>{tag.name}</li>
             ))}
         </ul>
     );
};

useGetMany deduplicates and aggregates the calls made for a given resource during a render pass. This means that if a page makes several calls to useGetMany for a given resource, ra-core will only call the dataProvider.getMany() once.

// three calls to useGetMany on the same resource
useGetMany('tags', { ids: [1, 2, 3] });
useGetMany('tags', { ids: [3, 4, 5] });
useGetMany('tags', { ids: [5, 6, 7] });

// will result in a single call to the dataProvider
dataProvider.getMany('tags', { ids: [1, 2, 3, 4, 5, 6, 7] });

Ra-core uses useGetMany in the <ReferenceFieldBase> component, to overcome the n+1 problem when using this component in a list.

TypeScript

The useGetMany hook accepts a generic parameter for the record type:

import { useGetMany, useRecordContext } from 'ra-core';

type Post = {
    id: number;
    title: string;
    tagIds: number[];
};

type Tag = {
    id: number;
    name: string;
}

const PostTags = () => {
    const post = useRecordContext<Post>();

    const { data: tags, isPending, error } = useGetMany<Tag>(
        'tags',
        { ids: post.tagIds }
    );
    if (isPending) { return <div>Loading...</div>; }
    if (error) { return <p>ERROR</p>; }
    return (
        <ul>
            {/* TypeScript knows that tags is of type Tag[] */}
            {tags.map(tag => (
                <li key={tag.id}>{tag.name}</li>
            ))}
        </ul>
    );
};