`useParamValue`

The useParamValue hook returns the current value of a single parameter in a query.

useParamValue(
  queryId: string,
  paramId: string,
  queriesOrQueriesId?: QueriesOrQueriesId,
): ParamValue | undefined

	Type	Description
`queryId`	`string`	The `Id` of the query to get the parameter value from.
`paramId`	`string`	The `Id` of the parameter to get the value of.
`queriesOrQueriesId?`	`QueriesOrQueriesId`	The `Queries` object to be accessed: omit for the default context `Queries` object, provide an `Id` for a named context `Queries` object, or provide an explicit reference.
returns	`ParamValue \| undefined`	The value of the parameter, or undefined if it doesn't exist.

A Provider component is used to wrap part of an application in a context, and it can contain a default Queries object or a set of Queries objects named by Id. The useParamValue hook lets you indicate which Queries object to get data for: omit the optional final parameter for the default context Queries object, provide an Id for a named context Queries object, or provide a Queries object explicitly by reference.

When first rendered, this hook will create a listener so that changes to the parameter value will cause a re-render. When the component containing this hook is unmounted, the listener will be automatically removed.

Examples

This example creates a Queries object outside the application, which is used in the useParamValue hook by reference. A change to the parameter value re-renders the component.

import React from 'react';
import {createQueries, createStore} from 'tinybase';
import {createRoot} from 'react-dom/client';
import {useParamValue} from 'tinybase/ui-react';

const store = createStore().setTable('pets', {
  fido: {species: 'dog', color: 'brown'},
  felix: {species: 'cat', color: 'black'},
});
const queries = createQueries(store);
queries.setQueryDefinition(
  'petsBySpecies',
  'pets',
  ({select, where, param}) => {
    select('species');
    where('species', param('species'));
  },
  {species: 'dog'},
);

const App = () => (
  <span>{useParamValue('petsBySpecies', 'species', queries)}</span>
);

const app = document.createElement('div');
createRoot(app).render(<App />);
console.log(app.innerHTML);
// -> '<span>dog</span>'

queries.setParamValue('petsBySpecies', 'species', 'cat');
console.log(app.innerHTML);
// -> '<span>cat</span>'

This example creates a Provider context into which a default Queries object is provided. A component within it then uses the useParamValue hook.

import {Provider, useParamValue} from 'tinybase/ui-react';
import React from 'react';
import {createQueries, createStore} from 'tinybase';
import {createRoot} from 'react-dom/client';

const App = ({queries}) => (
  <Provider queries={queries}>
    <Pane />
  </Provider>
);
const Pane = () => (
  <span>{useParamValue('petsBySpecies', 'species')}</span>
);

const store = createStore().setTable('pets', {
  fido: {species: 'dog'},
  felix: {species: 'cat'},
});
const queries = createQueries(store);
queries.setQueryDefinition(
  'petsBySpecies',
  'pets',
  ({select, where, param}) => {
    select('species');
    where('species', param('species'));
  },
  {species: 'dog'},
);

const app = document.createElement('div');
createRoot(app).render(<App queries={queries} />);
console.log(app.innerHTML);
// -> '<span>dog</span>'

This example creates a Provider context into which a Queries object is provided, named by Id. A component within it then uses the useParamValue hook.

import {Provider, useParamValue} from 'tinybase/ui-react';
import React from 'react';
import {createQueries, createStore} from 'tinybase';
import {createRoot} from 'react-dom/client';

const App = ({queries}) => (
  <Provider queriesById={{petQueries: queries}}>
    <Pane />
  </Provider>
);
const Pane = () => (
  <span>{useParamValue('petsBySpecies', 'species', 'petQueries')}</span>
);

const store = createStore().setTable('pets', {
  fido: {species: 'dog'},
  felix: {species: 'cat'},
});
const queries = createQueries(store);
queries.setQueryDefinition(
  'petsBySpecies',
  'pets',
  ({select, where, param}) => {
    select('species');
    where('species', param('species'));
  },
  {species: 'dog'},
);

const app = document.createElement('div');
createRoot(app).render(<App queries={queries} />);
console.log(app.innerHTML);
// -> '<span>dog</span>'

Since

v7.2.0