Panduan Kueri Data dengan ParseSwift SDK di iOS

kueri dasar pendahuluan dalam sebagian besar kasus penggunaan, kita perlu mengambil data dari basis data dengan kondisi tertentu kondisi ini mungkin termasuk perbandingan yang kompleks dan persyaratan pengurutan oleh karena itu, dalam aplikasi apa pun, sangat penting untuk membangun kueri yang efisien dan, pada saat yang sama, basis data harus dapat mengeksekusinya secepat mungkin sdk parseswift sdk parseswift sdk menyediakan alat yang diperlukan bagi anda untuk membangun kueri apa pun sesuai dengan kebutuhan aplikasi dalam tutorial ini, kami menjelajahi alat alat ini dan menggunakannya dalam aplikasi dunia nyata tutorial ini menggunakan aplikasi dasar yang dibuat di xcode 12 dan ios 14 kapan saja, anda dapat mengakses proyek lengkap melalui repositori github kami https //github com/templates back4app/ios crud to do list tujuan untuk memahami cara membuat kueri dasar untuk mengambil data dari database back4app prasyarat untuk menyelesaikan panduan cepat ini, anda memerlukan xcode sebuah aplikasi yang dibuat di back4app ikuti https //www back4app com/docs/get started/new parse app untuk belajar cara membuat aplikasi parse di back4app catatan ikuti https //www back4app com/docs/ios/parse swift sdk untuk membuat proyek xcode yang terhubung ke back4app memahami aplikasi kontak kami template proyek adalah aplikasi kontak di mana pengguna menambahkan informasi kontak untuk menyimpannya di database back4app di layar utama aplikasi, anda akan menemukan serangkaian tombol untuk berbagai jenis kueri menggunakan tombol + + yang terletak di sisi kanan atas bilah navigasi, kita dapat menambahkan sebanyak mungkin kontak kontak sesuai kebutuhan referensi cepat perintah yang akan kita gunakan untuk contoh ini, kita menggunakan objek kontak kontak 1 import foundation 2 import parseswift 3 4 struct contact parseobject { 5 // required properties from parseobject protocol 6 var originaldata data? 7 var objectid string? 8 var createdat date? 9 var updatedat date? 10 var acl parseacl? 11 12 // custom fields for the contact's information 13 var name string? 14 var birthday date? 15 var numberoffriends int? 16 var favoritefoods \[string]? 17 18 19 } metode berikut akan memungkinkan kita untuk menyimpan dan mengquery kontak kontak objek create contact //when creating and saving a new instance of contact we can use 1 var newcontact contact = contact(name "john doe", birthday date(), numberoffriends 5, favoritefoods \["bread", "pizza"]) 2 3 // saves newcontact on your back4app database synchronously and returns the new saved item it throws and error if something went wrong 4 let savedcontact = try? newcontact save() 5 6 // saves newcontact on your back4app database asynchronously, and passes a result\<contact, parseerror> object to the completion block to handle the save process 7 newcontact save { result in 8 // handle the result to check wether the save process was successfull or not 9 } query all //for retrieving all the contact items saved on a back4app database, we construct a query\<contact> object and call the find() method on it 1 let contactsquery = contact query() // a query to fetch all contact items on your back4app database 2 3 // fetches the items synchronously or throws an error if found 4 let fetchedcontacts = try? query find() 5 6 // fetches the items asynchronously and calls a completion block passing a result object containing the result of the operation 7 query find { result in 8 // handle the result 9 } query by name //in order to create a query with a specific condition, we use the static method query( ) provided by the parseobject protocol we pass a queryconstraint object to the method as a parameter this queryconstraint object represents the type of constraint we are imposing on the query for queries involving comparison constraints, the parseswift sdk provides the following methods to create them 1 import parseswift 2 3 // a constraint to retreive all contact items that have exactly the string 'jhon doe' in their 'name' field 4 let constraint1 = try? equalto(key "name", value "john doe") 5 6 // an operator like implementation for the equalto(key\ value ) method 7 let constraint2 queryconstraint = "name" == "jhon doe" 8 9 // a constraint to retrieve all contact items that have the string 'john' in their 'name' field (only workd with string type fields) 10 let constraint3 queryconstraint = containsstring(key "name", substring "jhon") 11 12 let query = contact query(constrint1) // depending on your use case, you can send any of the above constraints as parameter 13 14 // executes the query synchronously it throws an error if something happened 15 let fetchedcontacts = try? query find() 16 17 // executes que query asynchronously and returns a result<\[contact], parseerror> object with the result 18 query find() { result in 19 // handle the result 20 } query by friend count //when we want to query contacts which have a certain amount of friends or more, we do it in the following way 1 import parseswift 2 3 // a constraint to retrieve all contact items that have 30 or more number of friends 4 let constraint1 queryconstraint = "numberoffriends" >= 30 5 6 // a constraint to retrieve all contact items that have more than 30 number of friends 7 let constraint2 queryconstraint = "numberoffriends" > 30 8 9 let query = contact query(constraint1) // depending on your use case, you can send any of the above constraints as parameter 10 11 // executes the query synchronously it throws an error if something happened 12 let fetchedcontacts = try? query find() 13 14 // executes que query asynchronously and returns a result<\[contact], parseerror> object with the result 15 query find() { result in 16 // handle the result 17 } query with ordering //adding an ordering option to queries is straightforward any query\<contact> object has the order( ) method to do so a simple query using the birthday as descending order can be implemented in the folowing way 1 import parseswift 2 3 // a query without order to retrieve all the contact items 4 let unorderedquery = contact query() 5 6 // sorts the result by the brithday field the parameter in the enumeration is the key of the field used to order the results 7 let descendingorder = query\<contact> order descending("birthday") 8 9 let orderedquery = unorderedquery order(\[descendingorder]) // returns a new query with the requested (descending) ordering option 10 11 // executes the query synchronously it throws an error if something happened 12 let orderedcontacts = try? orderedquery find() 13 14 // executes que query asynchronously and returns a result<\[contact], parseerror> object with the result 15 orderedcontacts find() { result in 16 // handle the result 17 } 1 unduh template aplikasi kontak proyek xcode xcode memiliki struktur berikut kapan saja, anda dapat mengakses proyek lengkap melalui repositori github kami https //github com/templates back4app/ios crud to do list untuk fokus pada tujuan utama panduan ini, kami hanya akan merinci bagian yang secara ketat terkait dengan kueri dan parseswift sdk 2 alur crud tambahan sebelum memulai dengan kueri, perlu untuk memiliki beberapa kontak yang sudah disimpan di database back4app anda di dalam kelas newcontactcontroller newcontactcontroller , kami mengimplementasikan formulir dasar untuk menambahkan sebuah contact contact untuk menyimpan sebuah instance dari objek contact contact , kami menggunakan metode handleaddcontact() handleaddcontact() yang diimplementasikan di dalam kelas newcontactcontroller newcontactcontroller 1 // newcontactcontroller swift file 2 3 4 extension newcontactcontroller { 5 /// retrieves the info the user entered for a new contact and stores it on your back4app database 6 @objc fileprivate func handleaddcontact() { 7 view\ endediting(true) 8 9 // collect the contact's information from the form 10 guard let name = nametextfield text, 11 let numberoffriendsstring = numberoffriendstextfield text, 12 let numberoffriends = int(numberoffriendsstring), 13 let favoritefoods = favoritefoodstextfield text? split(separator ",") else { 14 return showalert(title "error", message "the data you entered is con valid ") 15 } 16 17 // once the contact's information is collected, instantiate a contact object to save it on your back4app database 18 let contact = contact( 19 name name, 20 birthday birthdaydatepicker date, 21 numberoffriends numberoffriends, 22 favoritefoods favoritefoods compactmap { string($0) trimmingcharacters(in whitespaces) } 23 ) 24 25 // save the new contact 26 contact save { \[weak self] result in 27 switch result { 28 case success( ) 29 self? showalert(title "success", message "contact saved ") { 30 self? dismiss(animated true, completion nil) 31 } 32 case failure(let error) 33 self? showalert(title "error", message "failed to save contact \\(error message)") 34 } 35 } 36 } 37 } untuk detail lebih lanjut tentang langkah ini, anda dapat pergi ke https //www back4app com/docs/ios/parse swift sdk/data objects/swift crud database operations 3 melakukan kueri dasar \ berdasarkan nama contoh pertama yang kita lihat adalah kueri yang memungkinkan kita untuk mengambil kontak yang memiliki substring tertentu di nama nama field untuk melakukan ini, kita pertama tama membuat sebuah queryconstraint queryconstraint objek objek ini akan berisi batasan yang kita inginkan parseswift sdk parseswift sdk menyediakan metode berikut untuk (secara tidak langsung) membuat sebuah queryconstraint queryconstraint 1 // queryconstraint swift file 2 3 / 4 add a constraint for finding string values that contain a provided substring 5 warning this will be slow for large datasets 6 parameter key the key that the string to match is stored in 7 parameter substring the substring that the value must contain 8 parameter modifiers any of the following supported pcre modifiers (defaults to nil) 9 `i` case insensitive search 10 `m` search across multiple lines of input 11 returns the resulting `queryconstraint` 12 / 13 public func containsstring(key string, substring string, modifiers string? = nil) > queryconstraint 14 15 / 16 add a constraint that requires that a key is equal to a value 17 parameter key the key that the value is stored in 18 parameter value the value to compare 19 returns the same instance of `queryconstraint` as the receiver 20 warning see `equalto` for more information 21 behavior changes based on `parseswift configuration isusingequalqueryconstraint` 22 where isusingequalqueryconstraint == true is known not to work for livequery on 23 parse servers <= 5 0 0 24 / 25 public func == \<t>(key string, value t) > queryconstraint where t encodable sebagai contoh, kueri yang memungkinkan kita untuk mengambil semua kontak kontak yang memiliki john di nama nama mereka dapat dibuat dengan 1 // create the query sending the constraint as parameter 2 let constraint queryconstraint = containsstring(key "name", substring "john") // the first parameter (key) referres to the name of the field 3 let query = contact query(constrain) 4 5 // retrieve the contacts asynchronously (or sinchronously if needed) 6 query find() { result in 7 // handle the result and do the corresponding ui update 8 } jika batasan mengharuskan nama nama field untuk cocok dengan tepat string yang diberikan, kita bisa menggunakan 1 // create the query sending the constraint as parameter 2 let value = "john" 3 let constraint queryconstraint = "name" == value 4 let query = contact query(constrain) \ berdasarkan jumlah teman sebuah kueri dengan batasan yang melibatkan perbandingan numerik dapat dibangun dengan membuat sebuah queryconstraint queryconstraint dengan 1 / 2 add a constraint that requires that a key is greater than a value 3 parameter key the key that the value is stored in 4 parameter value the value to compare 5 returns the same instance of `queryconstraint` as the receiver 6 / 7 public func > \<t>(key string, value t) > queryconstraint where t encodable 8 9 / 10 add a constraint that requires that a key is greater than or equal to a value 11 parameter key the key that the value is stored in 12 parameter value the value to compare 13 returns the same instance of `queryconstraint` as the receiver 14 / 15 public func >= \<t>(key string, value t) > queryconstraint where t encodable 16 17 / 18 add a constraint that requires that a key is less than a value 19 parameter key the key that the value is stored in 20 parameter value the value to compare 21 returns the same instance of `queryconstraint` as the receiver 22 / 23 public func < \<t>(key string, value t) > queryconstraint where t encodable 24 25 / 26 add a constraint that requires that a key is less than or equal to a value 27 parameter key the key that the value is stored in 28 parameter value the value to compare 29 returns the same instance of `queryconstraint` as the receiver 30 / 31 public func <= \<t>(key string, value t) > queryconstraint where t encodable untuk mengkueri semua kontak dengan 30 atau lebih teman, kita menggunakan 1 let query = contacts query("numberoffriends" >= 30) 2 3 // retrieve the contacts asynchronously (or sinchronously if needed) 4 query find() { result in 5 // handle the result and do the corresponding ui update 6 } \ mengurutkan hasil kueri untuk mengurutkan hasil dari sebuah kueri, objek query\<contacts> query\<contacts> menyediakan metode order( ) order( ) yang mengembalikan sebuah query\<contact> query\<contact> baru dengan mempertimbangkan opsi pengurutan yang diminta sebagai parameter, kita mengirimkan sebuah enumerasi ( query\<contact> order query\<contact> order ) untuk menunjukkan pengurutan yang kita inginkan potongan kode berikut menerapkan urutan menurun berdasarkan bidang birthday birthday 1 // a query without order to retrieve all the contact items 2 let unorderedquery = contact query() 3 4 // sorts the contacts based on their brithday the parameter in the enumeration is the key of the field used to order the results 5 let descendingorder = query\<contact> order descending("birthday") 6 7 let orderedquery = unorderedquery order(\[descendingorder]) // returns a new query with the requested (descending) ordering option 8 9 // executes que query asynchronously and returns a result<\[contact], parseerror> object with the result 10 orderedcontacts find() { result in 11 // handle the result 12 } dalam https //github com/templates back4app/ios basic queries example , kami menerapkan kuery yang disebutkan di atas kelas contactscontroller contactscontroller memiliki metode fetchcontacts() fetchcontacts() di mana anda akan menemukan cuplikan berikut 1 2 3 class contactscontroller { 4 let querytype querytype 5 6 7 8 private func fetchcontacts() { 9 // we create a query\<contact> according to the querytype enumeration 10 let query query\<contact> = { 11 switch querytype { 12 case byname(let value) 13 return contact query(containsstring(key "name", substring value)) 14 case bynumberoffriends(let quantity) 15 return contact query("numberoffriends" >= quantity) 16 case byordering(let order) 17 let query = contact query() 18 switch order { 19 case ascending return query order(\[ ascending("birthday")]) 20 case descending return query order(\[ descending("birthday")]) 21 } 22 case all 23 return contact query() 24 } 25 }() 26 27 // execute the query 28 query find { \[weak self] result in 29 switch result { 30 case success(let contacts) 31 self? contacts = contacts 32 33 // update the ui 34 dispatchqueue main async { self? tableview\ reloaddata() } 35 case failure(let error) 36 // notify the user about the error that happened during the fetching process 37 self? showalert(title "error", message "failed to retrieve contacts \\(error message)") 38 return 39 } 40 } 41 } 42 } 4 jalankan aplikasi! sebelum menekan tombol jalankan di xcode xcode , jangan lupa untuk mengonfigurasi back4app back4app aplikasi anda di appdelegate appdelegate kelas! menggunakan tombol + + di bilah navigasi, tambahkan beberapa kontak dan uji berbagai kueri