Skip to main content

useQuery()

Data rendering without the fetch.

Access any Queryable Schema's store value; like Entity, All, Collection, Query, and Union. Lazy fields also work via their .query accessor. If the value does not exist, returns undefined.

useQuery() is reactive to data mutations; rerendering only when necessary. Returns undefined when data is Invalid.

tip

Queries are a great companion to efficiently render aggregate computations like those that use groupBy, map, reduce, and filter.

Usage​

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

const queryTotalVotes = new Query(
  PostResource.getList.schema,
  posts => 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;
}
🔴 Live Preview
Store▶

See truthiness narrowing for more information about type handling

Types​

function useQuery(
  schema: Queryable,
  ...args: SchemaArgs<typeof schema>
): DenormalizeNullable<typeof endpoint.schema> | undefined;

Queryable​

Queryable schemas require an queryKey() method that returns something. These include Entity, All, Collection, Query, and Union. Lazy fields produce a Queryable via their .query accessor.

interface Queryable {
  queryKey(
    args: readonly any[],
    queryKey: (...args: any) => any,
    getEntity: GetEntity,
    getIndex: GetIndex,
    // Must be non-void
  ): {};
}

Examples​

Sorting & Filtering​

Query provides programmatic access to the Reactive Data Client store.

import { Query } from '@data-client/rest';
import { useQuery, useFetch } from '@data-client/react';
import { UserResource, User } from './UserResource';

interface Args {
  asc: boolean;
  isAdmin?: boolean;
}
const sortedUsers = new Query(
  new All(User),
  (entries, { asc, isAdmin }: Args = { asc: false }) => {
    let sorted = [...entries].sort((a, b) => a.name.localeCompare(b.name));
    if (isAdmin !== undefined)
      sorted = sorted.filter(user => user.isAdmin === isAdmin);
    if (asc) return sorted;
    return sorted.reverse();
  },
);

function UsersPage() {
  useFetch(UserResource.getList);
  const users = useQuery(sortedUsers, { asc: true });
  if (!users) return <div>No users in cache yet</div>;
  return (
    <div>
      {users.map(user => (
        <div key={user.pk()}>{user.name}</div>
      ))}
    </div>
  );
}
render(<UsersPage />);
🔴 Live Preview
Store▶

Remaining Todo total​

Queries can also be used to compute aggregates

More Demos

Lazy relationships​

Lazy fields keep raw IDs during parent denormalization. Use .query with useQuery to resolve them on demand, isolating re-renders to only the components that need the related data.

import { useQuery, useFetch } from '@data-client/react';
import { DepartmentResource, Department } from './Resources';

function BuildingList({ dept }: { dept: Department }) {
  const buildings = useQuery(
    Department.schema.buildings.query,
    dept.buildings,
  );
  if (!buildings) return null;
  return (
    <span>{buildings.map(b => b.name).join(', ')}</span>
  );
}

function DepartmentsPage() {
  useFetch(DepartmentResource.getList);
  const departments = useQuery(new All(Department));
  if (!departments) return <div>Loading...</div>;
  return (
    <div>
      {departments.map(dept => (
        <div key={dept.pk()}>
          <strong>{dept.name}</strong>: <BuildingList dept={dept} />
        </div>
      ))}
    </div>
  );
}
render(<DepartmentsPage />);
🔴 Live Preview
Store▶

Data fallbacks​

In this case Ticker is constantly updated from a websocket stream. However, there is no bulk/list fetch for Ticker - making it inefficient for getting the prices on a list view.

So in this case we can fetch a list of Stats as a fallback since it has price data as well.

More Demos