Basic Queries

query in react native using parse introduction in this guide, you will perform basic queries in parse and implement a react native component using these queries you will learn how to set up and query realistic data using back4app and react native prerequisites to complete this tutorial, you will need a react native app created and connected to back4app if you want to test/use the screen layout provided by this guide, you should set up the react native paper react native paper library goal query data stored on back4app from a react native app 1 understanding the parse query class any parse query operation uses the parse query 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 parse query will only resolve after calling a retrieve method (like parse query find parse query find or parse query get 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 parse query , you need to pass as a parameter the desired parse object 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 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 parse query class here at the official documentation https //parseplatform org/parse sdk js/api/master/parse query html 2 save some data on back4app let’s create a profile profile 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 user profile profile class with the following example content 1 // add profile objects and create table 2 // adam sandler 3 let profile = new parse object('profile'); 4 profile set('name', 'adam sandler'); 5 profile set('birthday', new date('09/09/1966')); 6 profile set('friendcount', 2); 7 profile set('favoritefoods', \['lobster', 'bread']); 8 await profile save(); 9&#x9; 10 // adam levine 11 profile = new parse object('profile'); 12 profile set('name', 'adam levine'); 13 profile set('birthday', new date('03/18/1979')); 14 profile set('friendcount', 52); 15 profile set('favoritefoods', \['cake', 'bread']); 16 await profile save(); 17&#x9; 18 // carson kressley 19 profile = new parse object('profile'); 20 profile set('name', 'carson kressley'); 21 profile set('birthday', new date('11/11/1969')); 22 profile set('friendcount', 12); 23 profile set('favoritefoods', \['fish', 'cookies']); 24 await profile save(); 25&#x9; 26 // dan aykroyd 27 profile = new parse object('profile'); 28 profile set('name', 'dan aykroyd'); 29 profile set('birthday', new date('07/01/1952')); 30 profile set('friendcount', 66); 31 profile set('favoritefoods', \['jam', 'peanut butter']); 32 await profile save(); 33&#x9; 34 // eddie murphy 35 profile = new parse object('profile'); 36 profile set('name', 'eddie murphy'); 37 profile set('birthday', new date('04/03/1961')); 38 profile set('friendcount', 49); 39 profile set('favoritefoods', \['lettuce', 'pepper']); 40 await profile save(); 41&#x9; 42 // fergie 43 profile = new parse object('profile'); 44 profile set('name', 'fergie'); 45 profile set('birthday', new date('03/27/1975')); 46 profile set('friendcount', 55); 47 profile set('favoritefoods', \['lobster', 'shrimp']); 48 await profile save(); 49&#x9; 50 console log('success!'); 3 query the data now that you have a populated class, we can now perform some basic queries in it let’s begin by filtering profile profile results by name, which is a string type field, searching for values that contain the name adam adam using the parse query contains parse query contains method 1 // create your query 2 let parsequery = new parse query('profile'); 3&#x9; 4 // `contains` is a basic query method that checks if string field 5 // contains a specific substring 6 parsequery contains('name', 'adam'); 7&#x9; 8 // the query will resolve only after calling this method, retrieving 9 // an array of `parse objects` 10 let queryresults = await parsequery find(); 11&#x9; 12 // let's show the results 13 for (let result of queryresults) { 14 // you access `parse objects` attributes by using ` get` 15 console log(result get('name')); 16 }; let’s now query by the number type field friendcount friendcount by using another common query method, parse query greaterthan parse query greaterthan in this case, we want user profiles profiles in which the friend count is greater than 20 1 // create your query 2 let parsequery = new parse query('profile'); 3&#x9; 4 // `greaterthan` is a basic query method that does what it 5 // says on the tin 6 parsequery greaterthan('friendcount', 20); 7&#x9; 8 // the query will resolve only after calling this method, retrieving 9 // an array of `parse objects` 10 let queryresults = await parsequery find(); 11&#x9; 12 // let's show the results 13 for (let result of queryresults) { 14 // you access `parse objects` attributes by using ` get` 15 console log(`name ${result get('name')}, friend count ${result get('friendcount')}`); 16 }; other recurring query methods are parse query ascending parse query ascending and parse query descending parse query descending , responsible for ordering your queries this ordering can be done in most data types, so let’s order a query by the date field birthday birthday by the youngest 1 // create your query 2 let parsequery = new parse query('profile'); 3&#x9; 4 // `descending` and `ascending` can and should be chained 5 // with other query methods to improve your queries 6 parsequery descending('birthday'); 7&#x9; 8 // the query will resolve only after calling this method, retrieving 9 // an array of `parse objects` 10 let queryresults = await parsequery find(); 11&#x9; 12 // let's show the results 13 for (let result of queryresults) { 14 // you access `parse objects` attributes by using ` get` 15 console log(`name ${result get('name')}, birthday ${result get('birthday')}`); 16 }; as stated here before, you can and should chain query methods to achieve more refined results let’s then combine the previous examples in a single query request 1 // create your query 2 let parsequery = new parse query('profile'); 3&#x9; 4 parsequery contains('name', 'adam'); 5 parsequery greaterthan('friendcount', 20); 6 parsequery descending('birthday'); 7&#x9; 8 // the query will resolve only after calling this method, retrieving 9 // an array of `parse objects` 10 let queryresults = await parsequery find(); 11&#x9; 12 // let's show the results 13 for (let result of queryresults) { 14 // you access `parse objects` attributes by using ` get` 15 console log(`name ${result get('name')}, friend count ${result get('friendcount')}, birthday ${result get('birthday')}`); 16 }; 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 4 buttons for calling the queries this is how the component code is laid out, note the doquery doquery functions, containing the example code form before javascript 1 import react, {usestate} from 'react'; 2 import {alert, image, view, scrollview, stylesheet} from 'react native'; 3 import parse from 'parse/react native'; 4 import { 5 list, 6 title, 7 button as paperbutton, 8 text as papertext, 9 } from 'react native paper'; 10&#x9; 11 export const booklist = () => { 12 // state variable 13 const \[queryresults, setqueryresults] = usestate(null); 14&#x9; 15 const doquerybyname = async function () { 16 // create our parse query instance so methods can be chained 17 // reading parse objects is done by using parse query 18 const parsequery = new parse query('profile'); 19&#x9; 20 // `contains` is a basic query method that checks if string field 21 // contains a specific substring 22 parsequery contains('name', 'adam'); 23&#x9; 24 try { 25 let profiles = await parsequery find(); 26 setqueryresults(profiles); 27 return true; 28 } catch (error) { 29 // error can be caused by lack of internet connection 30 alert alert('error!', error message); 31 return false; 32 } 33 }; 34&#x9; 35 const doquerybyfriendcount = async function () { 36 // create our parse query instance so methods can be chained 37 // reading parse objects is done by using parse query 38 const parsequery = new parse query('profile'); 39&#x9; 40 // `greaterthan` is a basic query method that does what it 41 // says on the tin 42 parsequery greaterthan('friendcount', 20); 43&#x9; 44 try { 45 let profiles = await parsequery find(); 46 setqueryresults(profiles); 47 return true; 48 } catch (error) { 49 // error can be caused by lack of internet connection 50 alert alert('error!', error message); 51 return false; 52 } 53 }; 54&#x9; 55 const doquerybyordering = async function () { 56 // create our parse query instance so methods can be chained 57 // reading parse objects is done by using parse query 58 const parsequery = new parse query('profile'); 59&#x9; 60 // `descending` and `ascending` can and should be chained 61 // with other query methods to improve your queries 62 parsequery descending('birthday'); 63&#x9; 64 try { 65 let profiles = await parsequery find(); 66 setqueryresults(profiles); 67 return true; 68 } catch (error) { 69 // error can be caused by lack of internet connection 70 alert alert('error!', error message); 71 return false; 72 } 73 }; 74&#x9; 75 const doquerybyall = async function () { 76 // create our parse query instance so methods can be chained 77 // reading parse objects is done by using parse query 78 const parsequery = new parse query('profile'); 79&#x9; 80 parsequery contains('name', 'adam'); 81 parsequery greaterthan('friendcount', 20); 82 parsequery descending('birthday'); 83&#x9; 84 try { 85 let profiles = await parsequery find(); 86 setqueryresults(profiles); 87 return true; 88 } catch (error) { 89 // error can be caused by lack of internet connection 90 alert alert('error!', error message); 91 return false; 92 } 93 }; 94&#x9; 95 const clearqueryresults = async function () { 96 setqueryresults(null); 97 return true; 98 }; 99&#x9; 100 return ( 101 <> 102 \<view style={styles header}> 103 \<image 104 style={styles header logo} 105 source={ { 106 uri 107 'https //blog back4app com/wp content/uploads/2019/05/back4app white logo 500px png', 108 } } 109 /> 110 \<papertext style={styles header text}> 111 \<papertext style={styles header text bold}> 112 {'react native on back4app '} 113 \</papertext> 114 {' basic queries'} 115 \</papertext> 116 \</view> 117 \<scrollview style={styles wrapper}> 118 \<view> 119 \<title>{'result list'}\</title> 120 {/ book list /} 121 {queryresults !== null && 122 queryresults !== undefined && 123 queryresults map((profile) => ( 124 \<list item 125 key={profile id} 126 title={profile get('name')} 127 description={`friend count ${profile get( 128 'friendcount', 129 )}, birthday ${profile get('birthday')}`} 130 titlestyle={styles list text} 131 style={styles list item} 132 /> 133 ))} 134 {queryresults === null || 135 queryresults === undefined || 136 (queryresults !== null && 137 queryresults !== undefined && 138 queryresults length <= 0) ? ( 139 \<papertext>{'no results here!'}\</papertext> 140 ) null} 141 \</view> 142 \<view> 143 \<title>{'query buttons'}\</title> 144 \<paperbutton 145 onpress={() => doquerybyname()} 146 mode="contained" 147 icon="search web" 148 color={'#208aec'} 149 style={styles list button}> 150 {'query by name'} 151 \</paperbutton> 152 \<paperbutton 153 onpress={() => doquerybyfriendcount()} 154 mode="contained" 155 icon="search web" 156 color={'#208aec'} 157 style={styles list button}> 158 {'query by friend count'} 159 \</paperbutton> 160 \<paperbutton 161 onpress={() => doquerybyordering()} 162 mode="contained" 163 icon="search web" 164 color={'#208aec'} 165 style={styles list button}> 166 {'query by ordering'} 167 \</paperbutton> 168 \<paperbutton 169 onpress={() => doquerybyall()} 170 mode="contained" 171 icon="search web" 172 color={'#208aec'} 173 style={styles list button}> 174 {'query by all'} 175 \</paperbutton> 176 \<paperbutton 177 onpress={() => clearqueryresults()} 178 mode="contained" 179 icon="delete" 180 color={'#208aec'} 181 style={styles list button}> 182 {'clear results'} 183 \</paperbutton> 184 \</view> 185 \</scrollview> 186 \</> 187 ); 188 }; 189&#x9; 190 // these define the screen component styles 191 const styles = stylesheet create({ 192 header { 193 alignitems 'center', 194 paddingtop 30, 195 paddingbottom 50, 196 backgroundcolor '#208aec', 197 }, 198 header logo { 199 height 50, 200 width 220, 201 resizemode 'contain', 202 }, 203 header text { 204 margintop 15, 205 color '#f0f0f0', 206 fontsize 16, 207 }, 208 header text bold { 209 color '#fff', 210 fontweight 'bold', 211 }, 212 wrapper { 213 width '90%', 214 alignself 'center', 215 }, 216 list button { 217 margintop 6, 218 marginleft 15, 219 height 40, 220 }, 221 list item { 222 borderbottomwidth 1, 223 borderbottomcolor 'rgba(0, 0, 0, 0 12)', 224 }, 225 list text { 226 fontsize 15, 227 }, 228 });1 import react, {fc, reactelement, usestate} from 'react'; 2 import {alert, image, view, scrollview, stylesheet} from 'react native'; 3 import parse from 'parse/react native'; 4 import { 5 list, 6 title, 7 button as paperbutton, 8 text as papertext, 9 } from 'react native paper'; 10&#x9; 11 export const querylist fc<{}> = ({}) reactelement => { 12 // state variable 13 const \[queryresults, setqueryresults] = usestate(null); 14&#x9; 15 const doquerybyname = async function () promise\<boolean> { 16 // create our parse query instance so methods can be chained 17 // reading parse objects is done by using parse query 18 const parsequery parse query = new parse query('profile'); 19&#x9; 20 // `contains` is a basic query method that checks if string field 21 // contains a specific substring 22 parsequery contains('name', 'adam'); 23&#x9; 24 try { 25 let profiles \[parse object] = await parsequery find(); 26 setqueryresults(profiles); 27 return true; 28 } catch (error) { 29 // error can be caused by lack of internet connection 30 alert alert('error!', error message); 31 return false; 32 } 33 }; 34&#x9; 35 const doquerybyfriendcount = async function () promise\<boolean> { 36 // create our parse query instance so methods can be chained 37 // reading parse objects is done by using parse query 38 const parsequery parse query = new parse query('profile'); 39&#x9; 40 // `greaterthan` is a basic query method that does what it 41 // says on the tin 42 parsequery greaterthan('friendcount', 20); 43&#x9; 44 try { 45 let profiles \[parse object] = await parsequery find(); 46 setqueryresults(profiles); 47 return true; 48 } catch (error) { 49 // error can be caused by lack of internet connection 50 alert alert('error!', error message); 51 return false; 52 } 53 }; 54&#x9; 55 const doquerybyordering = async function () promise\<boolean> { 56 // create our parse query instance so methods can be chained 57 // reading parse objects is done by using parse query 58 const parsequery parse query = new parse query('profile'); 59&#x9; 60 // `descending` and `ascending` can and should be chained 61 // with other query methods to improve your queries 62 parsequery descending('birthday'); 63&#x9; 64 try { 65 let profiles \[parse object] = await parsequery find(); 66 setqueryresults(profiles); 67 return true; 68 } catch (error) { 69 // error can be caused by lack of internet connection 70 alert alert('error!', error message); 71 return false; 72 } 73 }; 74&#x9; 75 const doquerybyall = async function () promise\<boolean> { 76 // create our parse query instance so methods can be chained 77 // reading parse objects is done by using parse query 78 const parsequery parse query = new parse query('profile'); 79&#x9; 80 parsequery contains('name', 'adam'); 81 parsequery greaterthan('friendcount', 20); 82 parsequery descending('birthday'); 83&#x9; 84 try { 85 let profiles \[parse object] = await parsequery find(); 86 setqueryresults(profiles); 87 return true; 88 } catch (error) { 89 // error can be caused by lack of internet connection 90 alert alert('error!', error message); 91 return false; 92 } 93 }; 94&#x9; 95 const clearqueryresults = async function () promise\<boolean> { 96 setqueryresults(null); 97 return true; 98 }; 99&#x9; 100 return ( 101 <> 102 \<view style={styles header}> 103 \<image 104 style={styles header logo} 105 source={ { 106 uri 107 'https //blog back4app com/wp content/uploads/2019/05/back4app white logo 500px png', 108 } } 109 /> 110 \<papertext style={styles header text}> 111 \<papertext style={styles header text bold}> 112 {'react native on back4app '} 113 \</papertext> 114 {' basic queries'} 115 \</papertext> 116 \</view> 117 \<scrollview style={styles wrapper}> 118 \<view> 119 \<title>{'result list'}\</title> 120 {/ book list /} 121 {queryresults !== null && 122 queryresults !== undefined && 123 queryresults map((profile parse object) => ( 124 \<list item 125 key={profile id} 126 title={profile get('name')} 127 description={`friend count ${profile get( 128 'friendcount', 129 )}, birthday ${profile get('birthday')}`} 130 titlestyle={styles list text} 131 style={styles list item} 132 /> 133 ))} 134 {queryresults === null || 135 queryresults === undefined || 136 (queryresults !== null && 137 queryresults !== undefined && 138 queryresults length <= 0) ? ( 139 \<papertext>{'no results here!'}\</papertext> 140 ) null} 141 \</view> 142 \<view> 143 \<title>{'query buttons'}\</title> 144 \<paperbutton 145 onpress={() => doquerybyname()} 146 mode="contained" 147 icon="search web" 148 color={'#208aec'} 149 style={styles list button}> 150 {'query by name'} 151 \</paperbutton> 152 \<paperbutton 153 onpress={() => doquerybyfriendcount()} 154 mode="contained" 155 icon="search web" 156 color={'#208aec'} 157 style={styles list button}> 158 {'query by friend count'} 159 \</paperbutton> 160 \<paperbutton 161 onpress={() => doquerybyordering()} 162 mode="contained" 163 icon="search web" 164 color={'#208aec'} 165 style={styles list button}> 166 {'query by ordering'} 167 \</paperbutton> 168 \<paperbutton 169 onpress={() => doquerybyall()} 170 mode="contained" 171 icon="search web" 172 color={'#208aec'} 173 style={styles list button}> 174 {'query by all'} 175 \</paperbutton> 176 \<paperbutton 177 onpress={() => clearqueryresults()} 178 mode="contained" 179 icon="delete" 180 color={'#208aec'} 181 style={styles list button}> 182 {'clear results'} 183 \</paperbutton> 184 \</view> 185 \</scrollview> 186 \</> 187 ); 188 }; 189&#x9; 190 // these define the screen component styles 191 const styles = stylesheet create({ 192 header { 193 alignitems 'center', 194 paddingtop 30, 195 paddingbottom 50, 196 backgroundcolor '#208aec', 197 }, 198 header logo { 199 height 50, 200 width 220, 201 resizemode 'contain', 202 }, 203 header text { 204 margintop 15, 205 color '#f0f0f0', 206 fontsize 16, 207 }, 208 header text bold { 209 color '#fff', 210 fontweight 'bold', 211 }, 212 wrapper { 213 width '90%', 214 alignself 'center', 215 }, 216 list button { 217 margintop 6, 218 marginleft 15, 219 height 40, 220 }, 221 list item { 222 borderbottomwidth 1, 223 borderbottomcolor 'rgba(0, 0, 0, 0 12)', 224 }, 225 list text { 226 fontsize 15, 227 }, 228 }); this is how the component should look like after rendering and querying by all the query functions conclusion at the end of this guide, you learned how basic data queries work on parse and how to perform them on back4app from a react native app in the next guide, you will explore the parse query parse query full potential using all the methods available on this class