Relational Queries

kueri relasional di react native menggunakan parse pendahuluan dalam panduan ini, anda akan melakukan kueri relasional di parse dan mengimplementasikan komponen react native menggunakan kueri ini anda akan belajar cara menyiapkan dan mengkueri data realistis menggunakan back4app dan react native prasyarat untuk menyelesaikan tutorial ini, anda akan membutuhkan sebuah aplikasi react native yang dibuat dan terhubung ke back4app jika anda ingin menguji/menggunakan tata letak layar yang disediakan oleh panduan ini, anda harus menyiapkan react native paper react native paper perpustakaan tujuan kueri data relasional yang disimpan di back4app dari aplikasi react native 1 memahami kelas parse query setiap operasi kueri parse menggunakan tipe objek parse query parse query , yang akan membantu anda mengambil data spesifik dari database anda di seluruh aplikasi anda sangat penting untuk mengetahui bahwa parse query parse query hanya akan terpecahkan setelah memanggil metode ambil (seperti parse query find parse query find atau parse query first parse query first ), jadi kueri dapat disiapkan dan beberapa modifikasi dapat dirangkai sebelum benar benar dipanggil untuk membuat parse query parse query , anda perlu melewatkan sebagai parameter subclass yang diinginkan parse object parse object , yang merupakan yang akan berisi hasil kueri anda contoh kueri dapat dilihat di bawah, di mana subclass fiksi book book sedang dikueri 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(); anda dapat membaca lebih lanjut tentang parse query parse query kelas di sini pada dokumentasi resmi https //parseplatform org/parse sdk js/api/master/parse query html 2 simpan beberapa data di back4app mari kita buat berbagai kelas, yang akan menjadi target kueri kita dalam panduan ini kelas kelas tersebut adalah penulis penulis , buku buku , penerbit penerbit dan toko buku toko buku , di mana buku buku memiliki hubungan 1\ n dengan penerbit penerbit dan n\ n dengan penulis penulis , dan toko buku toko buku memiliki hubungan n\ n dengan buku buku di parse js console, anda dapat menjalankan kode javascript secara langsung, menanyakan dan memperbarui konten database aplikasi anda menggunakan perintah js sdk jalankan kode di bawah ini dari js console anda dan masukkan data di back4app berikut adalah tampilan konsol js di dasbor anda silakan lanjutkan dan buat kelas dengan konten contoh berikut 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 kuery data sekarang setelah anda mengisi semua kelas, kita sekarang dapat melakukan beberapa kueri relasional di dalamnya mari kita mulai dengan memfilter buku buku hasil berdasarkan penerbit, mencari yang termasuk dalam penerbit penerbit “acacia publishings” (atau “penerbit a”) menggunakan parse query equalto parse query equalto metode dasar 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 }; sekarang mari kita kuery objek mana yang bookstore bookstore mengandung book book objek dengan tanggal penerbitan lebih besar dari 01/01/2010, menggunakan kuery dalam dengan parse query greaterthan parse query greaterthan metode dan kemudian parse query matchesquery parse query matchesquery metode 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 }; sekarang mari kita buat kuery relasional yang lebih kompleks, mencari objek bookstore bookstore yang memiliki setidaknya satu book book yang ditulis oleh author author “aaron writer” (atau “authora”), menggunakan equalto equalto dan 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 kueri dari komponen react native mari kita gunakan kueri contoh kita di dalam komponen di react native, dengan antarmuka sederhana yang memiliki daftar yang menunjukkan hasil dan juga tombol untuk memanggil kueri inilah cara kode komponen disusun, perhatikan fungsi doquery doquery yang berisi kode contoh dari sebelumnya 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 querylist = () => { 12 // state variable 13 const \[queryresults, setqueryresults] = usestate(null); 14&#x9; 15 const doquerya = async function () { 16 // get publishera object 17 const publisheraquery = new parse query('publisher'); 18 publisheraquery equalto('name', 'acacia publishings'); 19 const publishera = await publisheraquery first(); 20&#x9; 21 // query books with publishera 22 const bookquery = new parse query('book'); 23 bookquery equalto('publisher', publishera); 24&#x9; 25 try { 26 let results = await bookquery find(); 27 setqueryresults(results); 28 return true; 29 } catch (error) { 30 // error can be caused by lack of internet connection 31 alert alert('error!', error message); 32 return false; 33 } 34 }; 35&#x9; 36 const doqueryb = async function () { 37 // create inner book query 38 const bookquery = new parse query('book'); 39 bookquery greaterthan('publishingdate', new date('01/01/2010')); 40&#x9; 41 // query bookstore using inner book query 42 const bookstorequery = new parse query('bookstore'); 43 bookstorequery matchesquery('books', bookquery); 44&#x9; 45 try { 46 let results = await bookstorequery find(); 47 setqueryresults(results); 48 return true; 49 } catch (error) { 50 // error can be caused by lack of internet connection 51 alert alert('error!', error message); 52 return false; 53 } 54 }; 55&#x9; 56 const doqueryc = async function () { 57 // get authora object 58 const authoraquery = new parse query('author'); 59 authoraquery equalto('name', 'aaron writer'); 60 const authora = await authoraquery first(); 61&#x9; 62 // create inner book query 63 const bookquery = new parse query('book'); 64 bookquery equalto('authors', authora); 65&#x9; 66 // query bookstore using inner book query 67 const bookstorequery = new parse query('bookstore'); 68 bookstorequery matchesquery('books', bookquery); 69&#x9; 70 try { 71 let results = await bookstorequery find(); 72 setqueryresults(results); 73 return true; 74 } catch (error) { 75 // error can be caused by lack of internet connection 76 alert alert('error!', error message); 77 return false; 78 } 79 }; 80&#x9; 81 const clearqueryresults = async function () { 82 setqueryresults(null); 83 return true; 84 }; 85&#x9; 86 return ( 87 <> 88 \<view style={styles header}> 89 \<image 90 style={styles header logo} 91 source={ { 92 uri 93 'https //blog back4app com/wp content/uploads/2019/05/back4app white logo 500px png', 94 } } 95 /> 96 \<papertext style={styles header text}> 97 \<papertext style={styles header text bold}> 98 {'react native on back4app '} 99 \</papertext> 100 {' relational queries'} 101 \</papertext> 102 \</view> 103 \<scrollview style={styles wrapper}> 104 \<view> 105 \<title>{'result list'}\</title> 106 {/ query list /} 107 {queryresults !== null && 108 queryresults !== undefined && 109 queryresults map((result) => ( 110 \<list item 111 key={result id} 112 title={ 113 result get('name') !== undefined 114 ? result get('name') 115 result get('title') 116 } 117 titlestyle={styles list text} 118 style={styles list item} 119 /> 120 ))} 121 {queryresults === null || 122 queryresults === undefined || 123 (queryresults !== null && 124 queryresults !== undefined && 125 queryresults length <= 0) ? ( 126 \<papertext>{'no results here!'}\</papertext> 127 ) null} 128 \</view> 129 \<view> 130 \<title>{'query buttons'}\</title> 131 \<paperbutton 132 onpress={() => doquerya()} 133 mode="contained" 134 icon="search web" 135 color={'#208aec'} 136 style={styles list button}> 137 {'query a'} 138 \</paperbutton> 139 \<paperbutton 140 onpress={() => doqueryb()} 141 mode="contained" 142 icon="search web" 143 color={'#208aec'} 144 style={styles list button}> 145 {'query b'} 146 \</paperbutton> 147 \<paperbutton 148 onpress={() => doqueryc()} 149 mode="contained" 150 icon="search web" 151 color={'#208aec'} 152 style={styles list button}> 153 {'query c'} 154 \</paperbutton> 155 \<paperbutton 156 onpress={() => clearqueryresults()} 157 mode="contained" 158 icon="delete" 159 color={'#208aec'} 160 style={styles list button}> 161 {'clear results'} 162 \</paperbutton> 163 \</view> 164 \</scrollview> 165 \</> 166 ); 167 }; 168&#x9; 169 // these define the screen component styles 170 const styles = stylesheet create({ 171 header { 172 alignitems 'center', 173 paddingtop 30, 174 paddingbottom 50, 175 backgroundcolor '#208aec', 176 }, 177 header logo { 178 height 50, 179 width 220, 180 resizemode 'contain', 181 }, 182 header text { 183 margintop 15, 184 color '#f0f0f0', 185 fontsize 16, 186 }, 187 header text bold { 188 color '#fff', 189 fontweight 'bold', 190 }, 191 wrapper { 192 width '90%', 193 alignself 'center', 194 }, 195 list button { 196 margintop 6, 197 marginleft 15, 198 height 40, 199 }, 200 list item { 201 borderbottomwidth 1, 202 borderbottomcolor 'rgba(0, 0, 0, 0 12)', 203 }, 204 list text { 205 fontsize 15, 206 }, 207 });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 doquerya = async function () promise\<boolean> { 16 // get publishera object 17 const publisheraquery parse query = new parse query('publisher'); 18 publisheraquery equalto('name', 'acacia publishings'); 19 const publishera parse object = await publisheraquery first(); 20&#x9; 21 // query books with publishera 22 const bookquery parse query = new parse query('book'); 23 bookquery equalto('publisher', publishera); 24&#x9; 25 try { 26 let results \[parse object] = await bookquery find(); 27 setqueryresults(results); 28 return true; 29 } catch (error) { 30 // error can be caused by lack of internet connection 31 alert alert('error!', error message); 32 return false; 33 } 34 }; 35&#x9; 36 const doqueryb = async function () promise\<boolean> { 37 // create inner book query 38 const bookquery parse query = new parse query('book'); 39 bookquery greaterthan('publishingdate', new date('01/01/2010')); 40&#x9; 41 // query bookstore using inner book query 42 const bookstorequery parse query = new parse query('bookstore'); 43 bookstorequery matchesquery('books', bookquery); 44&#x9; 45 try { 46 let results \[parse object] = await bookstorequery find(); 47 setqueryresults(results); 48 return true; 49 } catch (error) { 50 // error can be caused by lack of internet connection 51 alert alert('error!', error message); 52 return false; 53 } 54 }; 55&#x9; 56 const doqueryc = async function () promise\<boolean> { 57 // get authora object 58 const authoraquery parse query = new parse query('author'); 59 authoraquery equalto('name', 'aaron writer'); 60 const authora parse object = await authoraquery first(); 61&#x9; 62 // create inner book query 63 const bookquery parse query = new parse query('book'); 64 bookquery equalto('authors', authora); 65&#x9; 66 // query bookstore using inner book query 67 const bookstorequery parse query = new parse query('bookstore'); 68 bookstorequery matchesquery('books', bookquery); 69&#x9; 70 try { 71 let results \[parse object] = await bookstorequery find(); 72 setqueryresults(results); 73 return true; 74 } catch (error) { 75 // error can be caused by lack of internet connection 76 alert alert('error!', error message); 77 return false; 78 } 79 }; 80&#x9; 81 const clearqueryresults = async function () promise\<boolean> { 82 setqueryresults(null); 83 return true; 84 }; 85&#x9; 86 return ( 87 <> 88 \<view style={styles header}> 89 \<image 90 style={styles header logo} 91 source={ { 92 uri 93 'https //blog back4app com/wp content/uploads/2019/05/back4app white logo 500px png', 94 } } 95 /> 96 \<papertext style={styles header text}> 97 \<papertext style={styles header text bold}> 98 {'react native on back4app '} 99 \</papertext> 100 {' relational queries'} 101 \</papertext> 102 \</view> 103 \<scrollview style={styles wrapper}> 104 \<view> 105 \<title>{'result list'}\</title> 106 {/ query list /} 107 {queryresults !== null && 108 queryresults !== undefined && 109 queryresults map((result parse object) => ( 110 \<list item 111 key={result id} 112 title={ 113 result get('name') !== undefined 114 ? result get('name') 115 result get('title') 116 } 117 titlestyle={styles list text} 118 style={styles list item} 119 /> 120 ))} 121 {queryresults === null || 122 queryresults === undefined || 123 (queryresults !== null && 124 queryresults !== undefined && 125 queryresults length <= 0) ? ( 126 \<papertext>{'no results here!'}\</papertext> 127 ) null} 128 \</view> 129 \<view> 130 \<title>{'query buttons'}\</title> 131 \<paperbutton 132 onpress={() => doquerya()} 133 mode="contained" 134 icon="search web" 135 color={'#208aec'} 136 style={styles list button}> 137 {'query a'} 138 \</paperbutton> 139 \<paperbutton 140 onpress={() => doqueryb()} 141 mode="contained" 142 icon="search web" 143 color={'#208aec'} 144 style={styles list button}> 145 {'query b'} 146 \</paperbutton> 147 \<paperbutton 148 onpress={() => doqueryc()} 149 mode="contained" 150 icon="search web" 151 color={'#208aec'} 152 style={styles list button}> 153 {'query c'} 154 \</paperbutton> 155 \<paperbutton 156 onpress={() => clearqueryresults()} 157 mode="contained" 158 icon="delete" 159 color={'#208aec'} 160 style={styles list button}> 161 {'clear results'} 162 \</paperbutton> 163 \</view> 164 \</scrollview> 165 \</> 166 ); 167 }; 168&#x9; 169 // these define the screen component styles 170 const styles = stylesheet create({ 171 header { 172 alignitems 'center', 173 paddingtop 30, 174 paddingbottom 50, 175 backgroundcolor '#208aec', 176 }, 177 header logo { 178 height 50, 179 width 220, 180 resizemode 'contain', 181 }, 182 header text { 183 margintop 15, 184 color '#f0f0f0', 185 fontsize 16, 186 }, 187 header text bold { 188 color '#fff', 189 fontweight 'bold', 190 }, 191 wrapper { 192 width '90%', 193 alignself 'center', 194 }, 195 list button { 196 margintop 6, 197 marginleft 15, 198 height 40, 199 }, 200 list item { 201 borderbottomwidth 1, 202 borderbottomcolor 'rgba(0, 0, 0, 0 12)', 203 }, 204 list text { 205 fontsize 15, 206 }, 207 }); inilah cara komponen seharusnya terlihat setelah dirender dan ditanyakan oleh salah satu fungsi kueri kesimpulan di akhir panduan ini, anda telah mempelajari cara kerja kueri relasional di parse dan cara melakukannya di back4app dari aplikasi react native di panduan berikutnya, anda akan belajar cara bekerja dengan pengguna di parse