Geoqueries

utilizzare la geolocalizzazione di react native per eseguire geoquery utilizzando parse introduzione in questa guida, eseguirai geoquery in parse utilizzando la geolocalizzazione di react native implementerai un componente react native utilizzando queste query e imparerai come configurare e interrogare dati realistici utilizzando back4app e react native prerequisiti per completare questo tutorial, avrai bisogno di un'app react native creata e connessa a https //www back4app com/docs/react native/parse sdk/react native sdk se desideri testare/utilizzare il layout dello schermo fornito da questa guida, dovresti configurare il react native paper react native paper https //github com/callstack/react native paper e anche react native geolocation service react native geolocation service obiettivo eseguire geoquery utilizzando geopunti memorizzati su back4app e la geolocalizzazione di react native 1 comprendere la classe parse query qualsiasi operazione di query parse utilizza il parse query parse query tipo di oggetto, che ti aiuterà a recuperare dati specifici dal tuo database in tutta l'app è fondamentale sapere che un parse query parse query si risolverà solo dopo aver chiamato un metodo di recupero (come parse query find parse query find o parse query get parse query get ), quindi una query può essere impostata e diversi modificatori possono essere concatenati prima di essere effettivamente chiamati per creare un nuovo parse query parse query , è necessario passare come parametro la parse object parse object desiderata, che sarà quella che conterrà i risultati della tua query un esempio di query può essere visto qui sotto, in cui viene interrogata una profile profile fittizia 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(); puoi leggere di più sulla parse query parse query classe https //parseplatform org/parse sdk js/api/master/parse query html 2 salva alcuni dati su back4app creiamo una city city classe, che sarà l'obiettivo delle nostre query in questa guida sulla console js di parse è possibile eseguire codice javascript direttamente, interrogando e aggiornando i contenuti del database della tua applicazione utilizzando i comandi del sdk js esegui il codice qui sotto dalla tua console js e inserisci i dati su back4app ecco come appare la console js nel tuo dashboard procedi e crea la city city classe con il seguente contenuto di esempio 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&#x9; 9 // brasília 10 city = new parse object('city'); 11 city set('name', 'brasília brazil'); 12 city set('location', new parse geopoint( 15 79485821477289, 47 88391074690196)); 13 await city save(); 14&#x9; 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&#x9; 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&#x9; 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&#x9; 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&#x9; 39 console log('success!'); 3 interroga i dati ora che hai una classe popolata, possiamo ora eseguire alcune interrogazioni geopoint in essa iniziamo ordinando city city i risultati in base alla prossimità da kingston in giamaica (latitudine 18 01808695059913 e longitudine 76 79894232253473), utilizzando il parse query near parse query near metodo 1 // create your query 2 let parsequery = new parse query('city'); 3&#x9; 4 // create our geopoint for the query 5 let kingstongeopoint = new parse geopoint(18 018086950599134, 76 79894232253473); 6&#x9; 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&#x9; 10 // the query will resolve only after calling this method, retrieving 11 // an array of `parse objects` 12 let queryresults = await parsequery find(); 13&#x9; 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 }; ora interroghiamo utilizzando il metodo parse query withinkilometers parse query withinkilometers , che recupererà tutti i risultati il cui campo geopoint si trova entro la distanza massima kingston sarà utilizzato ancora una volta come riferimento e il limite di distanza sarà di 3000 km 1 // create your query 2 let parsequery = new parse query('city'); 3&#x9; 4 // create our geopoint for the query 5 let kingstongeopoint = new parse geopoint(18 018086950599134, 76 79894232253473); 6&#x9; 7 // you can also use `withinmiles` and `withinradians` the same way, 8 // but with different measuring unities 9 parsequery withinkilometers('location', kingstongeopoint, 3000); 10&#x9; 11 // the query will resolve only after calling this method, retrieving 12 // an array of `parse objects` 13 let queryresults = await parsequery find(); 14&#x9; 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 }; un altro metodo di query utile è parse query withinpolygon parse query withinpolygon , che interrogherà i risultati il cui valore del campo geopoint è all'interno del poligono specificato, composto da un array di geopoints (almeno tre) se il percorso del poligono è aperto, verrà chiuso automaticamente da parse collegando l'ultimo e il primo punto per questo esempio, utilizzerai un semplice poligono che contiene approssimativamente il continente sudamericano, composto da 5 geopoints distanti nell'oceano 1 // create your query 2 let parsequery = new parse query('city'); 3&#x9; 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&#x9; 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&#x9; 14 // the query will resolve only after calling this method, retrieving 15 // an array of `parse objects` 16 let queryresults = await parsequery find(); 17&#x9; 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 da un componente react native utilizziamo ora le nostre query di esempio all'interno di un componente in react native, con un'interfaccia semplice che mostra un elenco di risultati e anche 3 pulsanti per chiamare le query il componente recupera anche la posizione attuale del dispositivo utilizzando react native geolocation service react native geolocation service , quindi le query utilizzeranno dati reali ecco come è strutturato il codice del componente, nota le doquery doquery funzioni, contenenti l'esempio di codice di prima javascript 1 import react, {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&#x9; 20 export const querylist = () => { 21 // state variable 22 const \[queryresults, setqueryresults] = usestate(null); 23&#x9; 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 = 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&#x9; 48 const doquerynear = async function () { 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 // create our geopoint 55 let currentlocationgeopoint = new parse geopoint( 56 currentposition coords latitude, 57 currentposition coords longitude, 58 ); 59&#x9; 60 // create our query 61 let parsequery = new parse query('city'); 62&#x9; 63 // `near` will order results based on distance between the geopoint type field from the class and the geopoint argument 64 parsequery near('location', currentlocationgeopoint); 65&#x9; 66 try { 67 let results = await parsequery find(); 68 // set query results to state variable 69 setqueryresults(results); 70 } catch (error) { 71 // error can be caused by lack of internet connection 72 alert alert('error!', error message); 73 } 74 }, 75 error => { 76 alert alert( 77 'error!', 78 'this app needs your location permission to query this!', 79 ); 80 }, 81 {enablehighaccuracy true, timeout 15000, maximumage 10000}, 82 ); 83 return true; 84 }; 85&#x9; 86 const doquerywithinkilometers = async function () { 87 // request location permissions 88 await requestlocationpermissions(); 89 // get current location and create the geopoint for the query 90 geolocation getcurrentposition( 91 async (currentposition) => { 92 // create our geopoint 93 let currentlocationgeopoint = new parse geopoint( 94 currentposition coords latitude, 95 currentposition coords longitude, 96 ); 97&#x9; 98 // create our query 99 let parsequery = new parse query('city'); 100&#x9; 101 // you can also use `withinmiles` and `withinradians` the same way, 102 // but with different measuring unities 103 parsequery withinkilometers('location', currentlocationgeopoint, 3000); 104&#x9; 105 try { 106 let results = await parsequery find(); 107 // set query results to state variable 108 setqueryresults(results); 109 } catch (error) { 110 // error can be caused by lack of internet connection 111 alert alert('error!', error message); 112 } 113 }, 114 error => { 115 alert alert( 116 'error!', 117 'this app needs your location permission to query this!', 118 ); 119 }, 120 {enablehighaccuracy true, timeout 15000, maximumage 10000}, 121 ); 122 return true; 123 }; 124&#x9; 125 const doquerywithinpolygon = async function () { 126 // create our geopoint polygon points 127 let geopoint1 = new parse geopoint(15 822238344514378, 72 42845934415942); 128 let geopoint2 = new parse geopoint( 0 7433770196268968, 97 44765968406668); 129 let geopoint3 = new parse geopoint( 59 997149373299166, 76 52969196322749); 130 let geopoint4 = new parse geopoint( 9 488786415007201, 18 346101586021952); 131 let geopoint5 = new parse geopoint(15 414859532811047, 60 00625459569375); 132&#x9; 133 // create our query 134 let parsequery = new parse query('city'); 135&#x9; 136 // 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 137 parsequery withinpolygon('location', \[ 138 geopoint1, 139 geopoint2, 140 geopoint3, 141 geopoint4, 142 geopoint5, 143 ]); 144&#x9; 145 try { 146 let results = await parsequery find(); 147 // set query results to state variable 148 setqueryresults(results); 149 } catch (error) { 150 // error can be caused by lack of internet connection 151 alert alert('error!', error message); 152 } 153 }; 154&#x9; 155 const clearqueryresults = async function () { 156 setqueryresults(null); 157 return true; 158 }; 159&#x9; 160 return ( 161 <> 162 \<view style={styles header}> 163 \<image 164 style={styles header logo} 165 source={ { 166 uri 167 'https //blog back4app com/wp content/uploads/2019/05/back4app white logo 500px png', 168 } } 169 /> 170 \<papertext style={styles header text}> 171 \<papertext style={styles header text bold}> 172 {'react native on back4app '} 173 \</papertext> 174 {' geopoint queries'} 175 \</papertext> 176 \</view> 177 \<scrollview style={styles wrapper}> 178 \<view> 179 \<title>{'result list'}\</title> 180 {/ query list /} 181 {queryresults !== null && 182 queryresults !== undefined && 183 queryresults map((result) => ( 184 \<list item 185 key={result id} 186 title={result get('name')} 187 titlestyle={styles list text} 188 style={styles list item} 189 /> 190 ))} 191 {queryresults === null || 192 queryresults === undefined || 193 (queryresults !== null && 194 queryresults !== undefined && 195 queryresults length <= 0) ? ( 196 \<papertext>{'no results here!'}\</papertext> 197 ) null} 198 \</view> 199 \<view> 200 \<title>{'query buttons'}\</title> 201 \<paperbutton 202 onpress={() => doquerynear()} 203 mode="contained" 204 icon="search web" 205 color={'#208aec'} 206 style={styles list button}> 207 {'query near'} 208 \</paperbutton> 209 \<paperbutton 210 onpress={() => doquerywithinkilometers()} 211 mode="contained" 212 icon="search web" 213 color={'#208aec'} 214 style={styles list button}> 215 {'query within km'} 216 \</paperbutton> 217 \<paperbutton 218 onpress={() => doquerywithinpolygon()} 219 mode="contained" 220 icon="search web" 221 color={'#208aec'} 222 style={styles list button}> 223 {'query within polygon'} 224 \</paperbutton> 225 \<paperbutton 226 onpress={() => clearqueryresults()} 227 mode="contained" 228 icon="delete" 229 color={'#208aec'} 230 style={styles list button}> 231 {'clear results'} 232 \</paperbutton> 233 \</view> 234 \</scrollview> 235 \</> 236 ); 237 }; 238&#x9; 239 // these define the screen component styles 240 const styles = stylesheet create({ 241 header { 242 alignitems 'center', 243 paddingtop 30, 244 paddingbottom 50, 245 backgroundcolor '#208aec', 246 }, 247 header logo { 248 height 50, 249 width 220, 250 resizemode 'contain', 251 }, 252 header text { 253 margintop 15, 254 color '#f0f0f0', 255 fontsize 16, 256 }, 257 header text bold { 258 color '#fff', 259 fontweight 'bold', 260 }, 261 wrapper { 262 width '90%', 263 alignself 'center', 264 }, 265 list button { 266 margintop 6, 267 marginleft 15, 268 height 40, 269 }, 270 list item { 271 borderbottomwidth 1, 272 borderbottomcolor 'rgba(0, 0, 0, 0 12)', 273 }, 274 list text { 275 fontsize 15, 276 }, 277 });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&#x9; 20 export const querylist fc<{}> = ({}) reactelement => { 21 // state variable 22 const \[queryresults, setqueryresults] = usestate(null); 23&#x9; 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&#x9; 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&#x9; 62 // create our query 63 let parsequery parse query = new parse query('city'); 64&#x9; 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&#x9; 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&#x9; 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&#x9; 102 // create our query 103 let parsequery parse query = new parse query('city'); 104&#x9; 105 // you can also use `withinmiles` and `withinradians` the same way, 106 // but with different measuring unities 107 parsequery withinkilometers('location', currentlocationgeopoint, 3000); 108&#x9; 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&#x9; 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&#x9; 152 // create our query 153 let parsequery parse query = new parse query('city'); 154&#x9; 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&#x9; 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&#x9; 174 const clearqueryresults = async function () promise\<boolean> { 175 setqueryresults(null); 176 return true; 177 }; 178&#x9; 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&#x9; 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 }); ecco come dovrebbe apparire il componente dopo il rendering e la query di una delle funzioni di query conclusione alla fine di questa guida, hai imparato come funzionano le query sui dati geopoint su parse e come eseguirle su back4app da un'app react native nella prossima guida, verificherai come creare e gestire gli utenti in parse