Relational Queries

relational query in react using parse introduction in this guide, you will perform relational 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 relational data stored on back4app from a react 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 first parse query first ), 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 book book subclass is being queried 1 // this will create your query 2 let parsequery = new parse query("book"); 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 an assortment of classes, which will be the target of our queries in this guide the classes are author author , book book , publisher publisher and bookstore bookstore , in which book book has a 1\ n relation with publisher publisher and n\ n with author author , and bookstore bookstore has an n\ n relation with book book on parse js console it 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 classes with the following example content 1 // add objects and create tables 2 // authors 3 const authora = new parse object('author'); 4 authora set('name', 'aaron writer'); 5 await authora save(); 6&#x9; 7 const authorb = new parse object('author'); 8 authorb set('name', 'beatrice novelist'); 9 await authorb save(); 10&#x9; 11 const authorc = new parse object('author'); 12 authorc set('name', 'casey columnist'); 13 await authorc save(); 14&#x9; 15 // publishers 16 const publishera = new parse object('publisher'); 17 publishera set('name', 'acacia publishings'); 18 await publishera save(); 19&#x9; 20 const publisherb = new parse object('publisher'); 21 publisherb set('name', 'birch distributions'); 22 await publisherb save(); 23&#x9; 24 // books 25 const booka = new parse object('book'); 26 booka set('title', 'a love story'); 27 booka set('publisher', publishera); 28 booka set('publishingdate', new date('05/07/1998')); 29 const bookarelation = booka relation("authors"); 30 bookarelation add(authora); 31 await booka save(); 32&#x9; 33 const bookb = new parse object('book'); 34 bookb set('title', 'benevolent elves'); 35 bookb set('publisher', publisherb); 36 bookb set('publishingdate', new date('11/31/2008')); 37 const bookbrelation = bookb relation("authors"); 38 bookbrelation add(authorb); 39 await bookb save(); 40&#x9; 41 const bookc = new parse object('book'); 42 bookc set('title', 'can you believe it?'); 43 bookc set('publisher', publisherb); 44 bookc set('publishingdate', new date('08/21/2018')); 45 const bookcrelation = bookc relation("authors"); 46 bookcrelation add(authora); 47 bookcrelation add(authorc); 48 await bookc save(); 49&#x9; 50 // bookstore 51 const bookstorea = new parse object('bookstore'); 52 bookstorea set('name', 'books of love'); 53 const bookstorearelation = bookstorea relation("books"); 54 bookstorearelation add(booka); 55 await bookstorea save(); 56&#x9; 57 const bookstoreb = new parse object('bookstore'); 58 bookstoreb set('name', 'fantasy books'); 59 const bookstorebrelation = bookstoreb relation("books"); 60 bookstorebrelation add(bookb); 61 await bookstoreb save(); 62&#x9; 63 const bookstorec = new parse object('bookstore'); 64 bookstorec set('name', 'general books'); 65 const bookstorecrelation = bookstorec relation("books"); 66 bookstorecrelation add(booka); 67 bookstorecrelation add(bookc); 68 await bookstorec save(); 69&#x9; 70 console log('success'); 3 query the data now that you have populated all the classes, we can now perform some relational queries in it let’s begin by filtering book book results by the publisher publisher , searching for the ones that belong to the publisher “acacia publishings” (or “publisher a”) using the basic parse query equalto parse query equalto method 1 // get publishera object 2 const publisheraquery = new parse query('publisher'); 3 publisheraquery equalto('name', 'acacia publishings'); 4 const publishera = await publisheraquery first(); 5&#x9; 6 // query books with publishera 7 const bookquery = new parse query('book'); 8 bookquery equalto('publisher', publishera); 9 let queryresults = await bookquery find(); 10&#x9; 11 // let's show the results 12 for (let result of queryresults) { 13 // you access `parse objects` attributes by using ` get` 14 console log(result get('title')); 15 }; let’s now query which bookstore bookstore objects contain book book objects with publishing date greater than 01/01/2010, using an inner query with the parse query greaterthan parse query greaterthan method and then the parse query matchesquery parse query matchesquery method 1 // create inner book query 2 const bookquery = new parse query('book'); 3 bookquery greaterthan('publishingdate', new date('01/01/2010')); 4&#x9; 5 // query bookstore using inner book query 6 const bookstorequery = new parse query('bookstore'); 7 bookstorequery matchesquery('books', bookquery); 8 let queryresults = await bookstorequery find(); 9&#x9; 10 // let's show the results 11 for (let result of queryresults) { 12 // you access `parse objects` attributes by using ` get` 13 console log(result get('name')); 14 }; let’s now create a more complex relational query, looking for bookstore bookstore objects that have at least one book book written by author author “aaron writer” (or “authora”), using equalto equalto and matchesquery matchesquery 1 // get authora object 2 const authoraquery = new parse query('author'); 3 authoraquery equalto('name', 'aaron writer'); 4 const authora = await authoraquery first(); 5&#x9; 6 // create inner book query 7 const bookquery = new parse query('book'); 8 bookquery equalto('authors', authora); 9&#x9; 10 // query bookstore using inner book query 11 const bookstorequery = new parse query('bookstore'); 12 bookstorequery matchesquery('books', bookquery); 13 let queryresults = await bookstorequery 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 }; 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 buttons for calling the queries this is how the component code is laid out, note the doquery doquery functions, containing the example code from 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 queryrelational = () => { 8 // state variable 9 const \[queryresults, setqueryresults] = usestate(); 10&#x9; 11 const doquerya = async function () { 12 // get publishera object 13 const publisheraquery = new parse query('publisher'); 14 publisheraquery equalto('name', 'acacia publishings'); 15 const publishera = await publisheraquery first(); 16&#x9; 17 // query books with publishera 18 const bookquery = new parse query('book'); 19 bookquery equalto('publisher', publishera); 20&#x9; 21 try { 22 let results = await bookquery find(); 23 setqueryresults(results); 24 return true; 25 } catch (error) { 26 // error can be caused by lack of internet connection 27 alert(`error! ${error message}`); 28 return false; 29 } 30 }; 31&#x9; 32 const doqueryb = async function () { 33 // create inner book query 34 const bookquery = new parse query('book'); 35 bookquery greaterthan('publishingdate', new date('01/01/2010')); 36&#x9; 37 // query bookstore using inner book query 38 const bookstorequery = new parse query('bookstore'); 39 bookstorequery matchesquery('books', bookquery); 40&#x9; 41 try { 42 let results = await bookstorequery find(); 43 setqueryresults(results); 44 return true; 45 } catch (error) { 46 // error can be caused by lack of internet connection 47 alert(`error! ${error message}`); 48 return false; 49 } 50 }; 51&#x9; 52 const doqueryc = async function () { 53 // get authora object 54 const authoraquery = new parse query('author'); 55 authoraquery equalto('name', 'aaron writer'); 56 const authora = await authoraquery first(); 57&#x9; 58 // create inner book query 59 const bookquery = new parse query('book'); 60 bookquery equalto('authors', authora); 61&#x9; 62 // query bookstore using inner book query 63 const bookstorequery = new parse query('bookstore'); 64 bookstorequery matchesquery('books', bookquery); 65&#x9; 66 try { 67 let results = await bookstorequery find(); 68 setqueryresults(results); 69 return true; 70 } catch (error) { 71 // error can be caused by lack of internet connection 72 alert(`error! ${error message}`); 73 return false; 74 } 75 }; 76&#x9; 77 const clearqueryresults = async function () { 78 setqueryresults(undefined); 79 return true; 80 }; 81&#x9; 82 return ( 83 \<div> 84 \<div classname="header"> 85 \<img 86 classname="header logo" 87 alt="back4app logo" 88 src={ 89 'https //blog back4app com/wp content/uploads/2019/05/back4app white logo 500px png' 90 } 91 /> 92 \<p classname="header text bold">{'react on back4app'}\</p> 93 \<p classname="header text">{'relational queries'}\</p> 94 \</div> 95 \<div classname="container"> 96 \<div classname="flex between"> 97 \<h2 classname="heading">{'query list'}\</h2> 98 \<div classname="flex"> 99 \<button 100 onclick={() => doquerya()} 101 type="primary" 102 classname="heading button" 103 color={'#208aec'} 104 icon={\<searchoutlined />} 105 > 106 query a 107 \</button> 108 \<button 109 onclick={() => doqueryb()} 110 type="primary" 111 classname="heading button" 112 color={'#208aec'} 113 icon={\<searchoutlined />} 114 > 115 query b 116 \</button> 117 \<button 118 onclick={() => doqueryc()} 119 type="primary" 120 classname="heading button" 121 color={'#208aec'} 122 icon={\<searchoutlined />} 123 > 124 query c 125 \</button> 126 \<button 127 onclick={() => clearqueryresults()} 128 type="primary" 129 classname="heading button" 130 color={'#208aec'} 131 icon={\<closeoutlined />} 132 > 133 clear results 134 \</button> 135 \</div> 136 \</div> 137 \<divider /> 138 \<div classname="flex between"> 139 \<div classname="flex child"> 140 {/ query list /} 141 {queryresults !== undefined && 142 queryresults map((result, index) => ( 143 \<div classname="list item" key={`${index}`}> 144 \<p classname="list item title">{`${ 145 result get('name') !== undefined 146 ? result get('name') 147 result get('title') 148 }`}\</p> 149 \</div> 150 ))} 151 {queryresults !== undefined && queryresults length <= 0 ? ( 152 \<p>{'no results here!'}\</p> 153 ) null} 154 \</div> 155 \</div> 156 \</div> 157 \</div> 158 ); 159 }; 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 queryrelational fc<{}> = () reactelement => { 8 // state variable 9 const \[queryresults, setqueryresults] = usestate\<parse object\[]>(); 10&#x9; 11 const doquerya = async function () promise\<boolean> { 12 // get publishera object 13 const publisheraquery parse query = new parse query('publisher'); 14 publisheraquery equalto('name', 'acacia publishings'); 15 const publishera parse object | undefined = await publisheraquery first(); 16&#x9; 17 // query books with publishera 18 const bookquery parse query = new parse query('book'); 19 bookquery equalto('publisher', publishera); 20&#x9; 21 try { 22 let results parse object\[] = await bookquery find(); 23 setqueryresults(results); 24 return true; 25 } catch (error) { 26 // error can be caused by lack of internet connection 27 alert(`error! ${error message}`); 28 return false; 29 } 30 }; 31&#x9; 32 const doqueryb = async function () promise\<boolean> { 33 // create inner book query 34 const bookquery parse query = new parse query('book'); 35 bookquery greaterthan('publishingdate', new date('01/01/2010')); 36&#x9; 37 // query bookstore using inner book query 38 const bookstorequery parse query = new parse query('bookstore'); 39 bookstorequery matchesquery('books', bookquery); 40&#x9; 41 try { 42 let results parse object\[] = await bookstorequery find(); 43 setqueryresults(results); 44 return true; 45 } catch (error) { 46 // error can be caused by lack of internet connection 47 alert(`error! ${error message}`); 48 return false; 49 } 50 }; 51&#x9; 52 const doqueryc = async function () promise\<boolean> { 53 // get authora object 54 const authoraquery parse query = new parse query('author'); 55 authoraquery equalto('name', 'aaron writer'); 56 const authora parse object | undefined = await authoraquery first(); 57&#x9; 58 // create inner book query 59 const bookquery parse query = new parse query('book'); 60 bookquery equalto('authors', authora); 61&#x9; 62 // query bookstore using inner book query 63 const bookstorequery parse query = new parse query('bookstore'); 64 bookstorequery matchesquery('books', bookquery); 65&#x9; 66 try { 67 let results parse object\[] = await bookstorequery find(); 68 setqueryresults(results); 69 return true; 70 } catch (error) { 71 // error can be caused by lack of internet connection 72 alert(`error! ${error message}`); 73 return false; 74 } 75 }; 76&#x9; 77 const clearqueryresults = async function () promise\<boolean> { 78 setqueryresults(undefined); 79 return true; 80 }; 81&#x9; 82 return ( 83 \<div> 84 \<div classname="header"> 85 \<img 86 classname="header logo" 87 alt="back4app logo" 88 src={ 89 'https //blog back4app com/wp content/uploads/2019/05/back4app white logo 500px png' 90 } 91 /> 92 \<p classname="header text bold">{'react on back4app'}\</p> 93 \<p classname="header text">{'relational queries'}\</p> 94 \</div> 95 \<div classname="container"> 96 \<div classname="flex between"> 97 \<h2 classname="heading">{'query list'}\</h2> 98 \<div classname="flex"> 99 \<button 100 onclick={() => doquerya()} 101 type="primary" 102 classname="heading button" 103 color={'#208aec'} 104 icon={\<searchoutlined />} 105 > 106 query a 107 \</button> 108 \<button 109 onclick={() => doqueryb()} 110 type="primary" 111 classname="heading button" 112 color={'#208aec'} 113 icon={\<searchoutlined />} 114 > 115 query b 116 \</button> 117 \<button 118 onclick={() => doqueryc()} 119 type="primary" 120 classname="heading button" 121 color={'#208aec'} 122 icon={\<searchoutlined />} 123 > 124 query c 125 \</button> 126 \<button 127 onclick={() => clearqueryresults()} 128 type="primary" 129 classname="heading button" 130 color={'#208aec'} 131 icon={\<closeoutlined />} 132 > 133 clear results 134 \</button> 135 \</div> 136 \</div> 137 \<divider /> 138 \<div classname="flex between"> 139 \<div classname="flex child"> 140 {/ query list /} 141 {queryresults !== undefined && 142 queryresults map((result parse object, index number) => ( 143 \<div classname="list item" key={`${index}`}> 144 \<p classname="list item title">{`${result get('name') !== undefined ? result get('name') result get('title')}`}\</p> 145 \</div> 146 ))} 147 {queryresults !== undefined && 148 queryresults length <= 0 ? ( 149 \<p>{'no results here!'}\</p> 150 ) null} 151 \</div> 152 \</div> 153 \</div> 154 \</div> 155 ); 156 }; also add these classes to your app css app css file to fully render the component layout app css 1 @import ' antd/dist/antd css'; 2&#x9; 3 app { 4 text align center; 5 } 6&#x9; 7 html { 8 box sizing border box; 9 outline none; 10 overflow auto; 11 } 12&#x9; 13 , 14 before, 15 after { 16 margin 0; 17 padding 0; 18 box sizing inherit; 19 } 20&#x9; 21 h1, 22 h2, 23 h3, 24 h4, 25 h5, 26 h6 { 27 margin 0; 28 font weight bold; 29 } 30&#x9; 31 p { 32 margin 0; 33 } 34&#x9; 35 body { 36 margin 0; 37 background color #fff; 38 } 39&#x9; 40 container { 41 width 100%; 42 max width 900px; 43 margin auto; 44 padding 20px 0; 45 text align left; 46 } 47&#x9; 48 header { 49 align items center; 50 padding 25px 0; 51 background color #208aec; 52 } 53&#x9; 54 header logo { 55 height 55px; 56 margin bottom 20px; 57 object fit contain; 58 } 59&#x9; 60 header text bold { 61 margin bottom 3px; 62 color rgba(255, 255, 255, 0 9); 63 font size 16px; 64 font weight bold; 65 } 66&#x9; 67 header text { 68 color rgba(255, 255, 255, 0 9); 69 font size 15px; 70 } 71&#x9; 72 heading { 73 font size 22px; 74 } 75&#x9; 76 flex { 77 display flex; 78 } 79&#x9; 80 flex between { 81 display flex; 82 justify content space between; 83 } 84&#x9; 85 flex child { 86 flex 0 0 45%; 87 } 88&#x9; 89 heading button { 90 margin left 12px; 91 } 92&#x9; 93 list item { 94 padding bottom 15px; 95 margin bottom 15px; 96 border bottom 1px solid rgba(0,0,0,0 06); 97 text align left; 98 } 99&#x9; 100 list item title { 101 color rgba(0,0,0,0 87); 102 font size 17px; 103 } this is how the component should look like after rendering and querying by one of the query functions conclusion at the end of this guide, you learned how relational queries work on parse and how to perform them on back4app from a react app in the next guide, you will learn how to work with users in parse