Geoqueries
Using React Native geolocation to perform geoqueries using Parse
Introduction
In this guide, you will perform geoqueries in Parse using the React Native geolocation. You will implement a React Native component using these queries and learn how to set up and query realistic data using Back4App and React Native.
Prerequisites
Goal
Perform Geoqueries using geopoints stored on Back4App and React Native geolocation.
1 - Understanding the Parse.Query class
Any Parse query operation uses the Parse.Query object type, which will help you retrieve specific data from your database throughout your app. It is crucial to know that a Parse.Query will only resolve after calling a retrieve method (like Parse.Query.find or Parse.Query.get), so a query can be set up and several modifiers can be chained before actually being called.
To create a new Parse.Query, you need to pass as a parameter the desired Parse.Object subclass, which is the one that will contain your query results. An example query can be seen below, in which a fictional Profile subclass is being queried.
1 // This will create your query
2 let parseQuery = new Parse.Query("Profile");
3 // The query will resolve only after calling this method
4 let queryResult = await parseQuery.find();You can read more about the Parse.Query class here at the official documentation.
2 - Save some data on Back4App
Let’s create a City class, which will be the target of our queries in this guide. On Parse JS Console is possible to run JavaScript code directly, querying and updating your application database contents using the JS SDK commands. Run the code below from your JS Console and insert the data on Back4App.
Here is how the JS Console looks like in your dashboard:
Go ahead and create the City class with the following example content:
1 // Add City objects and create table
2 // Note how GeoPoints are created, passing latitude and longitude as arguments
3 // Montevideo
4 City = new Parse.Object('City');
5 City.set('name', 'Montevideo - Uruguay');
6 City.set('location', new Parse.GeoPoint(-34.85553195363169, -56.207280375137955));
7 await City.save();
8
9 // BrasÃlia
10 City = new Parse.Object('City');
11 City.set('name', 'BrasÃlia - Brazil');
12 City.set('location', new Parse.GeoPoint(-15.79485821477289, -47.88391074690196));
13 await City.save();
14
15 // Bogotá
16 City = new Parse.Object('City');
17 City.set('name', 'Bogotá - Colombia');
18 City.set('location', new Parse.GeoPoint(4.69139880891712, -74.06936691331047));
19 await City.save();
20
21 // Mexico City
22 City = new Parse.Object('City');
23 City.set('name', 'Mexico City - Mexico');
24 City.set('location', new Parse.GeoPoint(19.400977162618933, -99.13311378164776));
25 await City.save();
26
27 // Washington, D.C.
28 City = new Parse.Object('City');
29 City.set('name', 'Washington, D.C. - USA');
30 City.set('location', new Parse.GeoPoint(38.930727220189944, -77.04626261880388));
31 await City.save();
32
33 // Ottawa
34 City = new Parse.Object('City');
35 City.set('name', 'Ottawa - Canada');
36 City.set('location', new Parse.GeoPoint(45.41102167733425, -75.695414598736));
37 await City.save();
38
39 console.log('Success!');3 - Query the data
Now that you have a populated class, we can now perform some GeoPoint queries in it. Let’s begin by ordering City results by the nearest from Kingston in Jamaica (latitude 18.01808695059913 and longitude -76.79894232253473), using the Parse.Query.near method:
1 // Create your query
2 let parseQuery = new Parse.Query('City');
3
4 // Create our GeoPoint for the query
5 let kingstonGeoPoint = new Parse.GeoPoint(18.018086950599134, -76.79894232253473);
6
7 // `near` will order results based on distance between the GeoPoint type field from the class and the GeoPoint argument
8 parseQuery.near('location', kingstonGeoPoint);
9
10 // The query will resolve only after calling this method, retrieving
11 // an array of `Parse.Objects`
12 let queryResults = await parseQuery.find();
13
14 // Let's show the results
15 for (let result of queryResults) {
16 // You access `Parse.Objects` attributes by using `.get`
17 console.log(result.get('name'));
18 };Let’s now query using the methodParse.Query.withinKilometers, which will retrieve all results whose GeoPoint field is located within the max distance. Kingston will be used once again as a reference and the distance limit will be 3000 km.
1 // Create your query
2 let parseQuery = new Parse.Query('City');
3
4 // Create our GeoPoint for the query
5 let kingstonGeoPoint = new Parse.GeoPoint(18.018086950599134, -76.79894232253473);
6
7 // You can also use `withinMiles` and `withinRadians` the same way,
8 // but with different measuring unities
9 parseQuery.withinKilometers('location', kingstonGeoPoint, 3000);
10
11 // The query will resolve only after calling this method, retrieving
12 // an array of `Parse.Objects`
13 let queryResults = await parseQuery.find();
14
15 // Let's show the results
16 for (let result of queryResults) {
17 // You access `Parse.Objects` attributes by using `.get`
18 console.log(result.get('name'));
19 };Another useful query method isParse.Query.withinPolygon, which will query results whose GeoPoint field value is within the specified polygon, composed of an array of GeoPoints (at least three). If the polygon path is open, it will be closed automatically by Parse connecting the last and first points.
For this example, you will be using a simple polygon that roughly contains the South American continent, composed of 5 distant GeoPoints in the ocean.
1 // Create your query
2 let parseQuery = new Parse.Query('City');
3
4 // Create our GeoPoint polygon for the query
5 let geoPoint1 = new Parse.GeoPoint(15.822238344514378, -72.42845934415942);
6 let geoPoint2 = new Parse.GeoPoint(-0.7433770196268968, -97.44765968406668);
7 let geoPoint3 = new Parse.GeoPoint(-59.997149373299166, -76.52969196322749);
8 let geoPoint4 = new Parse.GeoPoint(-9.488786415007201, -18.346101586021952);
9 let geoPoint5 = new Parse.GeoPoint(15.414859532811047, -60.00625459569375);
10
11 // Note that the polygon is merely an array of GeoPoint objects and that the first and last are not connected, so Parse connects them for you
12 parseQuery.withinPolygon('location', [geoPoint1, geoPoint2, geoPoint3, geoPoint4, geoPoint5]);
13
14 // The query will resolve only after calling this method, retrieving
15 // an array of `Parse.Objects`
16 let queryResults = await parseQuery.find();
17
18 // Let's show the results
19 for (let result of queryResults) {
20 // You access `Parse.Objects` attributes by using `.get`
21 console.log(result.get('name'));
22 };4 - Query from a React Native component
Let’s now use our example queries inside a component in React Native, with a simple interface having a list showing results and also 3 buttons for calling the queries. The component also retrieves the device’s current location using react-native-geolocation-service, so the queries will be using real data.
This is how the component code is laid out, note the doQuery functions, containing the example code form before.
1 import React, {FC, ReactElement, useState} from 'react';
2 import {
3 Alert,
4 Image,
5 View,
6 PermissionsAndroid,
7 Platform,
8 ScrollView,
9 StyleSheet,
10 } from 'react-native';
11 import Parse from 'parse/react-native';
12 import {
13 List,
14 Title,
15 Button as PaperButton,
16 Text as PaperText,
17 } from 'react-native-paper';
18 import Geolocation from 'react-native-geolocation-service';
19
20 export const QueryList: FC<{}> = ({}): ReactElement => {
21 // State variable
22 const [queryResults, setQueryResults] = useState(null);
23
24 // This function asks for location permission on iOS and Android
25 const requestLocationPermissions = async () => {
26 if (Platform.OS === 'ios') {
27 // iOS can be asked always, since the OS handles if user already gave permission
28 await Geolocation.requestAuthorization('whenInUse');
29 } else if (Platform.OS === 'android') {
30 let permissionCheck: boolean = await PermissionsAndroid.check(
31 PermissionsAndroid.PERMISSIONS.ACCESS_FINE_LOCATION,
32 );
33 // Only asks for permission on Android if not given before
34 if (permissionCheck !== true) {
35 await PermissionsAndroid.request(
36 PermissionsAndroid.PERMISSIONS.ACCESS_FINE_LOCATION,
37 {
38 title: 'Location Permission Request',
39 message:
40 'This app needs you permission for using your location for querying GeoPoints in Parse!',
41 buttonPositive: 'OK',
42 },
43 );
44 }
45 }
46 };
47
48 const doQueryNear = async function (): Promise<boolean> {
49 // Request location permissions
50 await requestLocationPermissions();
51 // Get current location and create the GeoPoint for the query
52 Geolocation.getCurrentPosition(
53 async (currentPosition: {
54 coords: {latitude: number; longitude: number};
55 }) => {
56 // Create our GeoPoint
57 let currentLocationGeoPoint: Parse.GeoPoint = new Parse.GeoPoint(
58 currentPosition.coords.latitude,
59 currentPosition.coords.longitude,
60 );
61
62 // Create our query
63 let parseQuery: Parse.Query = new Parse.Query('City');
64
65 // `near` will order results based on distance between the GeoPoint type field from the class and the GeoPoint argument
66 parseQuery.near('location', currentLocationGeoPoint);
67
68 try {
69 let results: [Parse.Object] = await parseQuery.find();
70 // Set query results to state variable
71 setQueryResults(results);
72 } catch (error) {
73 // Error can be caused by lack of Internet connection
74 Alert.alert('Error!', error.message);
75 }
76 },
77 _error => {
78 Alert.alert(
79 'Error!',
80 'This app needs your location permission to query this!',
81 );
82 },
83 {enableHighAccuracy: true, timeout: 15000, maximumAge: 10000},
84 );
85 return true;
86 };
87
88 const doQueryWithinKilometers = async function (): Promise<boolean> {
89 // Request location permissions
90 await requestLocationPermissions();
91 // Get current location and create the GeoPoint for the query
92 Geolocation.getCurrentPosition(
93 async (currentPosition: {
94 coords: {latitude: number; longitude: number};
95 }) => {
96 // Create our GeoPoint
97 let currentLocationGeoPoint: Parse.GeoPoint = new Parse.GeoPoint(
98 currentPosition.coords.latitude,
99 currentPosition.coords.longitude,
100 );
101
102 // Create our query
103 let parseQuery: Parse.Query = new Parse.Query('City');
104
105 // You can also use `withinMiles` and `withinRadians` the same way,
106 // but with different measuring unities
107 parseQuery.withinKilometers('location', currentLocationGeoPoint, 3000);
108
109 try {
110 let results: [Parse.Object] = await parseQuery.find();
111 // Set query results to state variable
112 setQueryResults(results);
113 } catch (error) {
114 // Error can be caused by lack of Internet connection
115 Alert.alert('Error!', error.message);
116 }
117 },
118 _error => {
119 Alert.alert(
120 'Error!',
121 'This app needs your location permission to query this!',
122 );
123 },
124 {enableHighAccuracy: true, timeout: 15000, maximumAge: 10000},
125 );
126 return true;
127 };
128
129 const doQueryWithinPolygon = async function (): Promise<boolean> {
130 // Create our GeoPoint polygon points
131 let geoPoint1: Parse.GeoPoint = new Parse.GeoPoint(
132 15.822.238.344.514.300,00
133 -7.242.845.934.415.940,00
134 );
135 let geoPoint2: Parse.GeoPoint = new Parse.GeoPoint(
136 -0.7433770196268968,
137 -9.744.765.968.406.660,00
138 );
139 let geoPoint3: Parse.GeoPoint = new Parse.GeoPoint(
140 -59.997.149.373.299.100,00
141 -7.652.969.196.322.740,00
142 );
143 let geoPoint4: Parse.GeoPoint = new Parse.GeoPoint(
144 -9.488.786.415.007.200,00
145 -18.346.101.586.021.900,00
146 );
147 let geoPoint5: Parse.GeoPoint = new Parse.GeoPoint(
148 15.414.859.532.811.000,00
149 -6.000.625.459.569.370,00
150 );
151
152 // Create our query
153 let parseQuery: Parse.Query = new Parse.Query('City');
154
155 // Note that the polygon is merely an array of GeoPoint objects and that the first and last are not connected, so Parse connects them for you
156 parseQuery.withinPolygon('location', [
157 geoPoint1,
158 geoPoint2,
159 geoPoint3,
160 geoPoint4,
161 geoPoint5,
162 ]);
163
164 try {
165 let results: [Parse.Object] = await parseQuery.find();
166 // Set query results to state variable
167 setQueryResults(results);
168 } catch (error) {
169 // Error can be caused by lack of Internet connection
170 Alert.alert('Error!', error.message);
171 }
172 };
173
174 const clearQueryResults = async function (): Promise<boolean> {
175 setQueryResults(null);
176 return true;
177 };
178
179 return (
180 <>
181 <View style={Styles.header}>
182 <Image
183 style={Styles.header_logo}
184 source={ {
185 uri:
186 'https://blog.back4app.com/wp-content/uploads/2019/05/back4app-white-logo-500px.png',
187 } }
188 />
189 <PaperText style={Styles.header_text}>
190 <PaperText style={Styles.header_text_bold}>
191 {'React Native on Back4App - '}
192 </PaperText>
193 {' GeoPoint Queries'}
194 </PaperText>
195 </View>
196 <ScrollView style={Styles.wrapper}>
197 <View>
198 <Title>{'Result List'}</Title>
199 {/* Query list */}
200 {queryResults !== null &&
201 queryResults !== undefined &&
202 queryResults.map((result: Parse.Object) => (
203 <List.Item
204 key={result.id}
205 title={result.get('name')}
206 titleStyle={Styles.list_text}
207 style={Styles.list_item}
208 />
209 ))}
210 {queryResults === null ||
211 queryResults === undefined ||
212 (queryResults !== null &&
213 queryResults !== undefined &&
214 queryResults.length <= 0) ? (
215 <PaperText>{'No results here!'}</PaperText>
216 ) : null}
217 </View>
218 <View>
219 <Title>{'Query buttons'}</Title>
220 <PaperButton
221 onPress={() => doQueryNear()}
222 mode="contained"
223 icon="search-web"
224 color={'#208AEC'}
225 style={Styles.list_button}>
226 {'Query Near'}
227 </PaperButton>
228 <PaperButton
229 onPress={() => doQueryWithinKilometers()}
230 mode="contained"
231 icon="search-web"
232 color={'#208AEC'}
233 style={Styles.list_button}>
234 {'Query Within KM'}
235 </PaperButton>
236 <PaperButton
237 onPress={() => doQueryWithinPolygon()}
238 mode="contained"
239 icon="search-web"
240 color={'#208AEC'}
241 style={Styles.list_button}>
242 {'Query Within Polygon'}
243 </PaperButton>
244 <PaperButton
245 onPress={() => clearQueryResults()}
246 mode="contained"
247 icon="delete"
248 color={'#208AEC'}
249 style={Styles.list_button}>
250 {'Clear Results'}
251 </PaperButton>
252 </View>
253 </ScrollView>
254 </>
255 );
256 };
257
258 // These define the screen component styles
259 const Styles = StyleSheet.create({
260 header: {
261 alignItems: 'center',
262 paddingTop: 30,
263 paddingBottom: 50,
264 backgroundColor: '#208AEC',
265 },
266 header_logo: {
267 height: 50,
268 width: 220,
269 resizeMode: 'contain',
270 },
271 header_text: {
272 marginTop: 15,
273 color: '#f0f0f0',
274 fontSize: 16,
275 },
276 header_text_bold: {
277 color: '#fff',
278 fontWeight: 'bold',
279 },
280 wrapper: {
281 width: '90%',
282 alignSelf: 'center',
283 },
284 list_button: {
285 marginTop: 6,
286 marginLeft: 15,
287 height: 40,
288 },
289 list_item: {
290 borderBottomWidth: 1,
291 borderBottomColor: 'rgba(0, 0, 0, 0.12)',
292 },
293 list_text: {
294 fontSize: 15,
295 },
296 });This is how the component should look like after rendering and querying one of the query functions:
Conclusion
At the end of this guide, you learned how GeoPoint data queries work on Parse and how to perform them on Back4App from a React Native App. In the next guide, you will check how to create and manage users in Parse.