Basic Queries

query in react using parse introduction in this guide, you will perform basic queries in parse and implement a react component using these queries you will learn how to set up and query realistic data using back4app and react prerequisites to complete this tutorial, you will need a react app created and connected to back4app if you want to run this guide’s example project, you should set up the ant design ant design library goal query data stored on back4app from a react application 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 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 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 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 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 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 50 console log('success!'); 3 querying 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 4 // `contains` is a basic query method that checks if string field 5 // contains a specific substring 6 parsequery contains('name', 'adam'); 7 8 // the query will resolve only after calling this method, retrieving 9 // an array of `parse objects` 10 let queryresults = await parsequery find(); 11 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 4 // `greaterthan` is a basic query method that does what it 5 // says on the tin 6 parsequery greaterthan('friendcount', 20); 7 8 // the query will resolve only after calling this method, retrieving 9 // an array of `parse objects` 10 let queryresults = await parsequery find(); 11 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 4 // `descending` and `ascending` can and should be chained 5 // with other query methods to improve your queries 6 parsequery descending('birthday'); 7 8 // the query will resolve only after calling this method, retrieving 9 // an array of `parse objects` 10 let queryresults = await parsequery find(); 11 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 4 parsequery contains('name', 'adam'); 5 parsequery greaterthan('friendcount', 20); 6 parsequery descending('birthday'); 7 8 // the query will resolve only after calling this method, retrieving 9 // an array of `parse objects` 10 let queryresults = await parsequery find(); 11 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 component let’s now use our example queries inside a component in react, 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 parse from 'parse/dist/parse min js'; 3 import ' /app css'; 4 import { button, divider } from 'antd'; 5 import { closeoutlined, searchoutlined } from '@ant design/icons'; 6&#x9; 7 export const querybasic = () => { 8 // state variable 9 const \[queryresults, setqueryresults] = usestate(); 10&#x9; 11 const doquerybyname = async function () { 12 // create our parse query instance so methods can be chained 13 // reading parse objects is done by using parse query 14 const parsequery = new parse query('profile'); 15&#x9; 16 // `contains` is a basic query method that checks if string field 17 // contains a specific substring 18 parsequery contains('name', 'adam'); 19&#x9; 20 try { 21 let profiles = await parsequery find(); 22 setqueryresults(profiles); 23 return true; 24 } catch (error) { 25 // error can be caused by lack of internet connection 26 alert(`error! ${error message}`); 27 return false; 28 } 29 }; 30&#x9; 31 const doquerybyfriendcount = async function () { 32 // create our parse query instance so methods can be chained 33 // reading parse objects is done by using parse query 34 const parsequery = new parse query('profile'); 35&#x9; 36 // `greaterthan` is a basic query method that does what it 37 // says on the tin 38 parsequery greaterthan('friendcount', 20); 39&#x9; 40 try { 41 let profiles = await parsequery find(); 42 setqueryresults(profiles); 43 return true; 44 } catch (error) { 45 // error can be caused by lack of internet connection 46 alert(`error! ${error message}`); 47 return false; 48 } 49 }; 50&#x9; 51 const doquerybyordering = async function () { 52 // create our parse query instance so methods can be chained 53 // reading parse objects is done by using parse query 54 const parsequery = new parse query('profile'); 55&#x9; 56 // `descending` and `ascending` can and should be chained 57 // with other query methods to improve your queries 58 parsequery descending('birthday'); 59&#x9; 60 try { 61 let profiles = await parsequery find(); 62 setqueryresults(profiles); 63 return true; 64 } catch (error) { 65 // error can be caused by lack of internet connection 66 alert(`error! ${error message}`); 67 return false; 68 } 69 }; 70&#x9; 71 const doquerybyall = async function () { 72 // create our parse query instance so methods can be chained 73 // reading parse objects is done by using parse query 74 const parsequery = new parse query('profile'); 75&#x9; 76 parsequery contains('name', 'adam'); 77 parsequery greaterthan('friendcount', 20); 78 parsequery descending('birthday'); 79&#x9; 80 try { 81 let profiles = await parsequery find(); 82 setqueryresults(profiles); 83 return true; 84 } catch (error) { 85 // error can be caused by lack of internet connection 86 alert(`error! ${error message}`); 87 return false; 88 } 89 }; 90&#x9; 91 const clearqueryresults = async function () { 92 setqueryresults(undefined); 93 return true; 94 }; 95&#x9; 96 return ( 97 \<div> 98 \<div classname="header"> 99 \<img 100 classname="header logo" 101 alt="back4app logo" 102 src={ 103 'https //blog back4app com/wp content/uploads/2019/05/back4app white logo 500px png' 104 } 105 /> 106 \<p classname="header text bold">{'react on back4app'}\</p> 107 \<p classname="header text">{'basic queries'}\</p> 108 \</div> 109 \<div classname="container"> 110 \<div classname="flex between"> 111 \<h2 classname="heading">{'query list'}\</h2> 112 \<div classname="flex"> 113 \<button 114 onclick={() => doquerybyname()} 115 type="primary" 116 classname="heading button" 117 color={'#208aec'} 118 icon={\<searchoutlined />} 119 > 120 by name 121 \</button> 122 \<button 123 onclick={() => doquerybyfriendcount()} 124 type="primary" 125 classname="heading button" 126 color={'#208aec'} 127 icon={\<searchoutlined />} 128 > 129 by friend count 130 \</button> 131 \<button 132 onclick={() => doquerybyordering()} 133 type="primary" 134 classname="heading button" 135 color={'#208aec'} 136 icon={\<searchoutlined />} 137 > 138 by ordering 139 \</button> 140 \<button 141 onclick={() => doquerybyall()} 142 type="primary" 143 classname="heading button" 144 color={'#208aec'} 145 icon={\<searchoutlined />} 146 > 147 by all 148 \</button> 149 \<button 150 onclick={() => clearqueryresults()} 151 type="primary" 152 classname="heading button" 153 color={'#208aec'} 154 icon={\<closeoutlined />} 155 > 156 clear 157 \</button> 158 \</div> 159 \</div> 160 \<divider /> 161 \<div classname="flex between"> 162 \<div classname="flex child"> 163 {/ query list /} 164 {queryresults !== undefined && 165 queryresults map((profile, index) => ( 166 \<div classname="list item" key={`${index}`}> 167 \<p classname="list item title">{`${profile get('name')}`}\</p> 168 \<p classname="list item description">{`friend count ${profile get( 169 'friendcount' 170 )}, birthday ${profile get('birthday')}`}\</p> 171 \</div> 172 ))} 173 {queryresults !== undefined && queryresults length <= 0 ? ( 174 \<p>{'no results here!'}\</p> 175 ) null} 176 \</div> 177 \</div> 178 \</div> 179 \</div> 180 ); 181 }; typescript 1 import react, { usestate, fc, reactelement } from 'react'; 2 import ' /app css'; 3 import { button, divider } from 'antd'; 4 import { closeoutlined, searchoutlined } from '@ant design/icons'; 5 const parse = require('parse/dist/parse min js'); 6&#x9; 7 export const querybasic fc<{}> = () reactelement => { 8 // state variable 9 const \[queryresults, setqueryresults] = usestate\<parse object\[]>(); 10&#x9; 11 const doquerybyname = async function () promise\<boolean> { 12 // create our parse query instance so methods can be chained 13 // reading parse objects is done by using parse query 14 const parsequery parse query = new parse query('profile'); 15&#x9; 16 // `contains` is a basic query method that checks if string field 17 // contains a specific substring 18 parsequery contains('name', 'adam'); 19&#x9; 20 try { 21 let profiles parse object\[] = await parsequery find(); 22 setqueryresults(profiles); 23 return true; 24 } catch (error any) { 25 // error can be caused by lack of internet connection 26 alert(`error! ${error message}`); 27 return false; 28 } 29 }; 30&#x9; 31 const doquerybyfriendcount = async function () promise\<boolean> { 32 // create our parse query instance so methods can be chained 33 // reading parse objects is done by using parse query 34 const parsequery parse query = new parse query('profile'); 35&#x9; 36 // `greaterthan` is a basic query method that does what it 37 // says on the tin 38 parsequery greaterthan('friendcount', 20); 39&#x9; 40 try { 41 let profiles parse object\[] = await parsequery find(); 42 setqueryresults(profiles); 43 return true; 44 } catch (error any) { 45 // error can be caused by lack of internet connection 46 alert(`error! ${error message}`); 47 return false; 48 } 49 }; 50&#x9; 51 const doquerybyordering = async function () promise\<boolean> { 52 // create our parse query instance so methods can be chained 53 // reading parse objects is done by using parse query 54 const parsequery parse query = new parse query('profile'); 55&#x9; 56 // `descending` and `ascending` can and should be chained 57 // with other query methods to improve your queries 58 parsequery descending('birthday'); 59&#x9; 60 try { 61 let profiles parse object\[] = await parsequery find(); 62 setqueryresults(profiles); 63 return true; 64 } catch (error any) { 65 // error can be caused by lack of internet connection 66 alert(`error! ${error message}`); 67 return false; 68 } 69 }; 70&#x9; 71 const doquerybyall = async function () promise\<boolean> { 72 // create our parse query instance so methods can be chained 73 // reading parse objects is done by using parse query 74 const parsequery parse query = new parse query('profile'); 75&#x9; 76 parsequery contains('name', 'adam'); 77 parsequery greaterthan('friendcount', 20); 78 parsequery descending('birthday'); 79&#x9; 80 try { 81 let profiles parse object\[] = await parsequery find(); 82 setqueryresults(profiles); 83 return true; 84 } catch (error any) { 85 // error can be caused by lack of internet connection 86 alert(`error! ${error message}`); 87 return false; 88 } 89 }; 90&#x9; 91 const clearqueryresults = async function () promise\<boolean> { 92 setqueryresults(undefined); 93 return true; 94 }; 95&#x9; 96 return ( 97 \<div> 98 \<div classname="header"> 99 \<img 100 classname="header logo" 101 alt="back4app logo" 102 src={ 103 'https //blog back4app com/wp content/uploads/2019/05/back4app white logo 500px png' 104 } 105 /> 106 \<p classname="header text bold">{'react on back4app'}\</p> 107 \<p classname="header text">{'basic queries'}\</p> 108 \</div> 109 \<div classname="container"> 110 \<div classname="flex between"> 111 \<h2 classname="heading">{'query list'}\</h2> 112 \<div classname="flex"> 113 \<button 114 onclick={() => doquerybyname()} 115 type="primary" 116 classname="heading button" 117 color={'#208aec'} 118 icon={\<searchoutlined />} 119 > 120 by name 121 \</button> 122 \<button 123 onclick={() => doquerybyfriendcount()} 124 type="primary" 125 classname="heading button" 126 color={'#208aec'} 127 icon={\<searchoutlined />} 128 > 129 by friend count 130 \</button> 131 \<button 132 onclick={() => doquerybyordering()} 133 type="primary" 134 classname="heading button" 135 color={'#208aec'} 136 icon={\<searchoutlined />} 137 > 138 by ordering 139 \</button> 140 \<button 141 onclick={() => doquerybyall()} 142 type="primary" 143 classname="heading button" 144 color={'#208aec'} 145 icon={\<searchoutlined />} 146 > 147 by all 148 \</button> 149 \<button 150 onclick={() => clearqueryresults()} 151 type="primary" 152 classname="heading button" 153 color={'#208aec'} 154 icon={\<closeoutlined />} 155 > 156 clear 157 \</button> 158 \</div> 159 \</div> 160 \<divider /> 161 \<div classname="flex between"> 162 \<div classname="flex child"> 163 {/ query list /} 164 {queryresults !== undefined && 165 queryresults map((profile parse object, index number) => ( 166 \<div classname="list item" key={`${index}`}> 167 \<p classname="list item title">{`${profile get('name')}`}\</p> 168 \<p classname="list item description">{`friend count ${profile get( 169 'friendcount' 170 )}, birthday ${profile get('birthday')}`}\</p> 171 \</div> 172 ))} 173 {queryresults !== undefined && 174 queryresults length <= 0 ? ( 175 \<p>{'no results here!'}\</p> 176 ) null} 177 \</div> 178 \</div> 179 \</div> 180 \</div> 181 ); 182 }; also append these classes to your app css app css file to properly render all the interface elements 1 html { 2 box sizing border box; 3 outline none; 4 overflow auto; 5 } 6 7 , 8 before, 9 after { 10 margin 0; 11 padding 0; 12 box sizing inherit; 13 } 14 15 h1, 16 h2, 17 h3, 18 h4, 19 h5, 20 h6 { 21 margin 0; 22 font weight bold; 23 } 24 25 p { 26 margin 0; 27 } 28 29 body { 30 margin 0; 31 background color #fff; 32 } 33 34 container { 35 width 100%; 36 max width 900px; 37 margin auto; 38 padding 20px 0; 39 text align left; 40 } 41 42 header { 43 align items center; 44 padding 25px 0; 45 background color #208aec; 46 } 47 48 header logo { 49 height 55px; 50 margin bottom 20px; 51 object fit contain; 52 } 53 54 header text bold { 55 margin bottom 3px; 56 color rgba(255, 255, 255, 0 9); 57 font size 16px; 58 font weight bold; 59 } 60 61 header text { 62 color rgba(255, 255, 255, 0 9); 63 font size 15px; 64 } 65 66 heading { 67 font size 22px; 68 } 69 70 flex { 71 display flex; 72 } 73 74 flex between { 75 display flex; 76 justify content space between; 77 } 78 79 flex child { 80 flex 0 0 45%; 81 } 82 83 heading button { 84 margin left 12px; 85 } 86 87 list item { 88 padding bottom 15px; 89 margin bottom 15px; 90 border bottom 1px solid rgba(0,0,0,0 06); 91 text align left; 92 } 93 94 list item title { 95 color rgba(0,0,0,0 87); 96 font size 17px; 97 } 98 99 list item description { 100 color rgba(0,0,0,0 5); 101 font size 15px; 102 } 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 app in the next guide, you will explore the parse query parse query full potential using all the methods available on this class