Query Parameters

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You can use QueryParameters to filter your layers & widgets at the backend side, using the concept of parametrized queries over your sources. You can check our related deck.gl documentation for different providers. In this guide we’re going to create a simple map that shows the earthquakes in Spain and allows to filter it by their magnitude.

Creating a map using QueryParameters

First you’ll need to create a source that supports query parameters. In this case we are getting all the earthquakes from a bigquery connection, whoses magnitude are between min: 4 and max: 5.

import { MAP_TYPES } from '@deck.gl/carto';

const sql = 'select * from `carto-demo-data.demo_tables.spain_earthquakes` where magnitude between @min and @max';

const earthquakesSource = {
  id: 'earthquakes',
  data: sql,
  type: MAP_TYPES.QUERY,
  queryParameters: {
    min: 4,
    max: 5
  }
}

Once you have your source ready to be used, you can create your layer using useCartoLayerProps hook.

import { CartoLayer } from '@deck.gl/carto';
import { useCartoLayerProps } from '@carto/react-api';

const layerProps = useCartoLayerProps({ source: earthquakesSource });
const earthquakesLayer = new CartoLayer({
  ...layerProps,
  id: 'earthquakesLayer',
  pointRadiusUnits: 'pixels',
  lineWidthUnits: 'pixels',
  getLineColor: [0, 0, 0],
  getPointRadius: 3,
});

Now your layer is ready and you can use it in your map, so we’re going to create a <FormulaWidget /> which displays the number of earthquakes in your viewport.

Using queryParameters with widgets

All our widgets are ready to use sources with queryParameters. You just need to pass the datasource properly configured (that basically means declaring its type as MAP_TYPES.QUERY and adding the corresponding queryParameters configuration). After that, you can use any widget as usual, eg:

<FormulaWidget
  id='totalEarthquakes'
  title='Total earthquakes'
  dataSource={earthquakesSource.id}
  operation={AggregationTypes.COUNT}
  />

Filtering with queryParameters using a widget

But the utility of queryParameters is dynamically changing the parametrized values in the app, so now we’re gonna use a widget to modify those values (and as a consequence, to apply new backend filters using queryParameters). Here we’re going to add a <RangeWidgetUI /> to allow filtering earthquakes by magnitude.

First we need to prepare the source to support queryParameters modification, passing those values as parameters to it.

import { MAP_TYPES } from '@deck.gl/carto';

function useEarthquakeSource([min, max]) {
  const sql = 'select * from `carto-demo-data.demo_tables.spain_earthquakes` where magnitude between @min and @max';
  
  const earthquakesSource = {
    id: 'earthquakes',
    data: sql,
    type: MAP_TYPES.QUERY,
    queryParameters: {
      min,
      max,
    }
  };

  return earthquakesSource;
}

Once the datasource is ready we can add a widget to filter by magnitude.

import { useState } from 'react';
import { CartoLayer } from '@deck.gl/carto';
import { useCartoLayerProps } from '@carto/react-api';
import { FormulaWidget } from '@carto/react-widgets';
import { RangeWidgetUI } from '@carto/react-ui';

function Earthquakes() {
  const [magnitudes, setMagnitudes] = useState([0, 10]);
  const earthquakesSource = useEarthquakeSource(magnitudes);
  const layerProps = useCartoLayerProps({ source: earthquakesSource });
  const earthquakesLayer = new CartoLayer({
    ...layerProps,
    id: 'earthquakesLayer',
    pointRadiusUnits: 'pixels',
    lineWidthUnits: 'pixels',
    getLineColor: [0, 0, 0],
    getPointRadius: 3,
  });
  
  return (
    <>
      <RangeWidgetUI
        min={0}
        max={10}
        onSelectedRangeChange={(range) => setMagnitudes(range)}
      />
  
      <FormulaWidget
        id='totalEarthquakes'
        title='Total earthquakes'
        dataSource={earthquakesSource.id}
        operation={AggregationTypes.COUNT}
      />
    </>
  );
}

export default Earthquakes;