Panduan Kueri Data dengan ParseSwift SDK di iOS

15min
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 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.
﻿Repositori Contoh iOS﻿
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 tutorial Aplikasi Parse Baru untuk belajar cara membuat aplikasi Parse di Back4App.
Catatan: Ikuti Tutorial Instalasi Parse SDK (Swift) 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 sesuai kebutuhan.
Referensi cepat perintah yang akan kita gunakan
Untuk contoh ini, kita menggunakan objek Kontak﻿
Swift
 import Foundation
 import ParseSwift
3
 struct Contact: ParseObject {
     // Required properties from ParseObject protocol
     var originalData: Data?
     var objectId: String?
     var createdAt: Date?
     var updatedAt: Date?
    var ACL: ParseACL?
  
    // Custom fields for the contact's information
    var name: String?
    var birthday: Date?
    var numberOfFriends: Int?
    var favoriteFoods: [String]?
  
    ...
}
 import Foundation
 import ParseSwift
3
 struct Contact: ParseObject {
     // Required properties from ParseObject protocol
     var originalData: Data?
     var objectId: String?
     var createdAt: Date?
     var updatedAt: Date?
    var ACL: ParseACL?
  
    // Custom fields for the contact's information
    var name: String?
    var birthday: Date?
    var numberOfFriends: Int?
    var favoriteFoods: [String]?
  
    ...
}
﻿
Metode berikut akan memungkinkan kita untuk menyimpan dan mengqueryKontak objek:
Create contact
Query all
Query by name
Query by friend count
Query with ordering
//When creating and saving a new instance of Contact we can use
 var newContact: Contact = Contact(name: "John Doe", birthday: Date(), numberOfFriends: 5, favoriteFoods: ["Bread", "Pizza"])
2
 // Saves newContact on your Back4App Database synchronously and returns the new saved Item. It throws and error if something went wrong.
 let savedContact = try? newContact.save()
5
 // Saves newContact on your Back4App Database asynchronously, and passes a Result<Contact, ParseError> object to the completion block to handle the save process.
 newContact.save { result in
     // Handle the result to check wether the save process was successfull or not
 }
//When creating and saving a new instance of Contact we can use
 var newContact: Contact = Contact(name: "John Doe", birthday: Date(), numberOfFriends: 5, favoriteFoods: ["Bread", "Pizza"])
2
 // Saves newContact on your Back4App Database synchronously and returns the new saved Item. It throws and error if something went wrong.
 let savedContact = try? newContact.save()
5
 // Saves newContact on your Back4App Database asynchronously, and passes a Result<Contact, ParseError> object to the completion block to handle the save process.
 newContact.save { result in
     // Handle the result to check wether the save process was successfull or not
 }
﻿
- Unduh Template Aplikasi Kontak
Proyek XCode memiliki struktur berikut
﻿
Kapan saja, Anda dapat mengakses Proyek lengkap melalui repositori GitHub kami.
﻿Repositori Contoh iOS﻿
Untuk fokus pada tujuan utama panduan ini, kami hanya akan merinci bagian yang secara ketat terkait dengan kueri dan ParseSwift SDK.
- Alur CRUD Tambahan
Sebelum memulai dengan kueri, perlu untuk memiliki beberapa kontak yang sudah disimpan di Database Back4App Anda. Di dalam kelas NewContactController, kami mengimplementasikan formulir dasar untuk menambahkan sebuah Contact. Untuk menyimpan sebuah instance dari objek Contact, kami menggunakan metode handleAddContact() yang diimplementasikan di dalam kelas NewContactController.
Swift
 // NewContactController.swift file
 ...
3
 extension NewContactController {
     /// Retrieves the info the user entered for a new contact and stores it on your Back4App Database
     @objc fileprivate func handleAddContact() {
         view.endEditing(true)
      
         // Collect the contact's information from the form
        guard let name = nameTextField.text,
              let numberOfFriendsString = numberOfFriendsTextField.text,
              let numberOfFriends = Int(numberOfFriendsString),
              let favoriteFoods = favoriteFoodsTextField.text?.split(separator: ",") else {
            return showAlert(title: "Error", message: "The data you entered is con valid.")
        }
      
        // Once the contact's information is collected, instantiate a Contact object to save it on your Back4App Database
        let contact = Contact(
            name: name,
            birthday: birthdayDatePicker.date,
            numberOfFriends: numberOfFriends,
            favoriteFoods: favoriteFoods.compactMap { String($0).trimmingCharacters(in: .whitespaces) }
        )
      
        // Save the new Contact
        contact.save { [weak self] result in
            switch result {
            case .success(_):
                self?.showAlert(title: "Success", message: "Contact saved.") {
                    self?.dismiss(animated: true, completion: nil)
                }
            case .failure(let error):
                self?.showAlert(title: "Error", message: "Failed to save contact: \(error.message)")
            }
        }
    }
}
 // NewContactController.swift file
 ...
3
 extension NewContactController {
     /// Retrieves the info the user entered for a new contact and stores it on your Back4App Database
     @objc fileprivate func handleAddContact() {
         view.endEditing(true)
      
         // Collect the contact's information from the form
        guard let name = nameTextField.text,
              let numberOfFriendsString = numberOfFriendsTextField.text,
              let numberOfFriends = Int(numberOfFriendsString),
              let favoriteFoods = favoriteFoodsTextField.text?.split(separator: ",") else {
            return showAlert(title: "Error", message: "The data you entered is con valid.")
        }
      
        // Once the contact's information is collected, instantiate a Contact object to save it on your Back4App Database
        let contact = Contact(
            name: name,
            birthday: birthdayDatePicker.date,
            numberOfFriends: numberOfFriends,
            favoriteFoods: favoriteFoods.compactMap { String($0).trimmingCharacters(in: .whitespaces) }
        )
      
        // Save the new Contact
        contact.save { [weak self] result in
            switch result {
            case .success(_):
                self?.showAlert(title: "Success", message: "Contact saved.") {
                    self?.dismiss(animated: true, completion: nil)
                }
            case .failure(let error):
                self?.showAlert(title: "Error", message: "Failed to save contact: \(error.message)")
            }
        }
    }
}
﻿
Untuk detail lebih lanjut tentang langkah ini, Anda dapat pergi ke panduan operasi dasar.
- Melakukan kueri dasar
- Berdasarkan nama
Contoh pertama yang kita lihat adalah kueri yang memungkinkan kita untuk mengambil kontak yang memiliki substring tertentu di nama field. Untuk melakukan ini, kita pertama-tama membuat sebuah QueryConstraint objek. Objek ini akan berisi batasan yang kita inginkan. ParseSwift SDK menyediakan metode berikut untuk (secara tidak langsung) membuat sebuah QueryConstraint﻿
Swift
 // QueryConstraint.swift file
2
 /**
   Add a constraint for finding string values that contain a provided substring.
   - warning: This will be slow for large datasets.
   - parameter key: The key that the string to match is stored in.
   - parameter substring: The substring that the value must contain.
   - parameter modifiers: Any of the following supported PCRE modifiers (defaults to nil):
     - `i` - Case insensitive search
    - `m` - Search across multiple lines of input
  - returns: The resulting `QueryConstraint`.
 */
public func containsString(key: String, substring: String, modifiers: String? = nil) -> QueryConstraint
14
/**
 Add a constraint that requires that a key is equal to a value.
 - parameter key: The key that the value is stored in.
 - parameter value: The value to compare.
 - returns: The same instance of `QueryConstraint` as the receiver.
 - warning: See `equalTo` for more information.
 Behavior changes based on `ParseSwift.configuration.isUsingEqualQueryConstraint`
 where isUsingEqualQueryConstraint == true is known not to work for LiveQuery on
 Parse Servers  <= 5.0.0.
 */
public func == <T>(key: String, value: T) -> QueryConstraint where T: Encodable
 // QueryConstraint.swift file
2
 /**
   Add a constraint for finding string values that contain a provided substring.
   - warning: This will be slow for large datasets.
   - parameter key: The key that the string to match is stored in.
   - parameter substring: The substring that the value must contain.
   - parameter modifiers: Any of the following supported PCRE modifiers (defaults to nil):
     - `i` - Case insensitive search
    - `m` - Search across multiple lines of input
  - returns: The resulting `QueryConstraint`.
 */
public func containsString(key: String, substring: String, modifiers: String? = nil) -> QueryConstraint
14
/**
 Add a constraint that requires that a key is equal to a value.
 - parameter key: The key that the value is stored in.
 - parameter value: The value to compare.
 - returns: The same instance of `QueryConstraint` as the receiver.
 - warning: See `equalTo` for more information.
 Behavior changes based on `ParseSwift.configuration.isUsingEqualQueryConstraint`
 where isUsingEqualQueryConstraint == true is known not to work for LiveQuery on
 Parse Servers  <= 5.0.0.
 */
public func == <T>(key: String, value: T) -> QueryConstraint where T: Encodable
﻿
Sebagai contoh, kueri yang memungkinkan kita untuk mengambil semua Kontak yang memiliki John di nama mereka dapat dibuat dengan
Swift
 // Create the query sending the constraint as parameter
 let constraint: QueryConstraint = containsString(key: "name", substring: "John") // The first parameter (key) referres to the name of the field
 let query = Contact.query(constrain)
4
 // Retrieve the contacts asynchronously (or sinchronously if needed)
 query.find() { result in
     // Handle the result and do the corresponding UI update
 }
 // Create the query sending the constraint as parameter
 let constraint: QueryConstraint = containsString(key: "name", substring: "John") // The first parameter (key) referres to the name of the field
 let query = Contact.query(constrain)
4
 // Retrieve the contacts asynchronously (or sinchronously if needed)
 query.find() { result in
     // Handle the result and do the corresponding UI update
 }
﻿
Jika batasan mengharuskan nama field untuk cocok dengan tepat string yang diberikan, kita bisa menggunakan
Swift
 // Create the query sending the constraint as parameter
 let value = "John"
 let constraint: QueryConstraint = "name" == value
 let query = Contact.query(constrain)
 // Create the query sending the constraint as parameter
 let value = "John"
 let constraint: QueryConstraint = "name" == value
 let query = Contact.query(constrain)
﻿
- Berdasarkan jumlah teman
Sebuah kueri dengan batasan yang melibatkan perbandingan numerik dapat dibangun dengan membuat sebuahQueryConstraint dengan
Swift
 /**
  Add a constraint that requires that a key is greater than a value.
  - parameter key: The key that the value is stored in.
  - parameter value: The value to compare.
  - returns: The same instance of `QueryConstraint` as the receiver.
  */
 public func > <T>(key: String, value: T) -> QueryConstraint where T: Encodable
8
 /**
 Add a constraint that requires that a key is greater than or equal to a value.
 - parameter key: The key that the value is stored in.
 - parameter value: The value to compare.
 - returns: The same instance of `QueryConstraint` as the receiver.
 */
public func >= <T>(key: String, value: T) -> QueryConstraint where T: Encodable
16
/**
 Add a constraint that requires that a key is less than a value.
 - parameter key: The key that the value is stored in.
 - parameter value: The value to compare.
 - returns: The same instance of `QueryConstraint` as the receiver.
 */
public func < <T>(key: String, value: T) -> QueryConstraint where T: Encodable
24
/**
 Add a constraint that requires that a key is less than or equal to a value.
 - parameter key: The key that the value is stored in.
 - parameter value: The value to compare.
 - returns: The same instance of `QueryConstraint` as the receiver.
 */
public func <= <T>(key: String, value: T) -> QueryConstraint where T: Encodable

 /**
  Add a constraint that requires that a key is greater than a value.
  - parameter key: The key that the value is stored in.
  - parameter value: The value to compare.
  - returns: The same instance of `QueryConstraint` as the receiver.
  */
 public func > <T>(key: String, value: T) -> QueryConstraint where T: Encodable
8
 /**
 Add a constraint that requires that a key is greater than or equal to a value.
 - parameter key: The key that the value is stored in.
 - parameter value: The value to compare.
 - returns: The same instance of `QueryConstraint` as the receiver.
 */
public func >= <T>(key: String, value: T) -> QueryConstraint where T: Encodable
16
/**
 Add a constraint that requires that a key is less than a value.
 - parameter key: The key that the value is stored in.
 - parameter value: The value to compare.
 - returns: The same instance of `QueryConstraint` as the receiver.
 */
public func < <T>(key: String, value: T) -> QueryConstraint where T: Encodable
24
/**
 Add a constraint that requires that a key is less than or equal to a value.
 - parameter key: The key that the value is stored in.
 - parameter value: The value to compare.
 - returns: The same instance of `QueryConstraint` as the receiver.
 */
public func <= <T>(key: String, value: T) -> QueryConstraint where T: Encodable
﻿
Untuk mengkueri semua kontak dengan 30 atau lebih teman, kita menggunakan
Swift
 let query = Contacts.query("numberOfFriends" >= 30)
2
 // Retrieve the contacts asynchronously (or sinchronously if needed)
 query.find() { result in
     // Handle the result and do the corresponding UI update
 }
 let query = Contacts.query("numberOfFriends" >= 30)
2
 // Retrieve the contacts asynchronously (or sinchronously if needed)
 query.find() { result in
     // Handle the result and do the corresponding UI update
 }
﻿
- Mengurutkan hasil kueri
Untuk mengurutkan hasil dari sebuah kueri, objek Query<contacts> menyediakan metode order(_:) yang mengembalikan sebuah Query<contact> baru dengan mempertimbangkan opsi pengurutan yang diminta. Sebagai parameter, kita mengirimkan sebuah enumerasi (Query<contact>.Order) untuk menunjukkan pengurutan yang kita inginkan. Potongan kode berikut menerapkan urutan menurun berdasarkan bidang birthday.
Swift
 // A query without order to retrieve all the Contact items
 let unorderedQuery = Contact.query()
3
 // Sorts the contacts based on their brithday. The parameter in the enumeration is the key of the field used to order the results
 let descendingOrder = Query<Contact>.Order.descending("birthday")
6
 let orderedQuery = unorderedQuery.order([descendingOrder]) // Returns a new query with the requested (descending) ordering option
8
 // Executes que query asynchronously and returns a Result<[Contact], ParseError> object with the result
orderedContacts.find() { result in
    // Handle the result
}
 // A query without order to retrieve all the Contact items
 let unorderedQuery = Contact.query()
3
 // Sorts the contacts based on their brithday. The parameter in the enumeration is the key of the field used to order the results
 let descendingOrder = Query<Contact>.Order.descending("birthday")
6
 let orderedQuery = unorderedQuery.order([descendingOrder]) // Returns a new query with the requested (descending) ordering option
8
 // Executes que query asynchronously and returns a Result<[Contact], ParseError> object with the result
orderedContacts.find() { result in
    // Handle the result
}
﻿
Dalam contoh proyek, kami menerapkan kuery yang disebutkan di atas. Kelas ContactsController memiliki metode fetchContacts() di mana Anda akan menemukan cuplikan berikut 
Swift
 ...
2
 class ContactsController {
     let queryType: QueryType
5
     ...
7
     private func fetchContacts() {
         // We create a Query<Contact> according to the queryType enumeration
        let query: Query<Contact> = {
            switch queryType {
            case .byName(let value):
                return Contact.query(containsString(key: "name", substring: value))
            case .byNumberOfFriends(let quantity):
                return Contact.query("numberOfFriends" >= quantity)
            case .byOrdering(let order):
                let query = Contact.query()
                switch order {
                case .ascending: return query.order([.ascending("birthday")])
                case .descending: return query.order([.descending("birthday")])
                }
            case .all:
                return Contact.query()
            }
        }()
      
        // Execute the query
        query.find { [weak self] result in
            switch result {
            case .success(let contacts):
                self?.contacts = contacts
              
                // Update the UI
                DispatchQueue.main.async { self?.tableView.reloadData() }
            case .failure(let error):
                // Notify the user about the error that happened during the fetching process
                self?.showAlert(title: "Error", message: "Failed to retrieve contacts: \(error.message)")
                return
            }
        }
    }
}
 ...
2
 class ContactsController {
     let queryType: QueryType
5
     ...
7
     private func fetchContacts() {
         // We create a Query<Contact> according to the queryType enumeration
        let query: Query<Contact> = {
            switch queryType {
            case .byName(let value):
                return Contact.query(containsString(key: "name", substring: value))
            case .byNumberOfFriends(let quantity):
                return Contact.query("numberOfFriends" >= quantity)
            case .byOrdering(let order):
                let query = Contact.query()
                switch order {
                case .ascending: return query.order([.ascending("birthday")])
                case .descending: return query.order([.descending("birthday")])
                }
            case .all:
                return Contact.query()
            }
        }()
      
        // Execute the query
        query.find { [weak self] result in
            switch result {
            case .success(let contacts):
                self?.contacts = contacts
              
                // Update the UI
                DispatchQueue.main.async { self?.tableView.reloadData() }
            case .failure(let error):
                // Notify the user about the error that happened during the fetching process
                self?.showAlert(title: "Error", message: "Failed to retrieve contacts: \(error.message)")
                return
            }
        }
    }
}
﻿
- Jalankan aplikasi!
Sebelum menekan tombol jalankan di XCode, jangan lupa untuk mengonfigurasi Back4App  aplikasi Anda di AppDelegate kelas!
Menggunakan tombol+ di bilah navigasi, tambahkan beberapa kontak dan uji berbagai kueri.