Kuery Data Relasional dengan ParseSwift di iOS

13min
Kueri Relasional
Pendahuluan
Dalam panduan sebelumnya kami menjelaskan bagaimana kami dapat melakukan berbagai kueri pada Database Back4App. Dalam panduan ini, kami fokus pada jenis kueri tertentu yang melibatkan objek dengan relasi.
Prasyarat
Untuk menyelesaikan tutorial ini, Anda akan membutuhkan:
Sebuah Aplikasi dibuat di Back4App.
Aplikasi iOS dasar untuk menguji kueri
Tujuan
Kueri data relasional yang disimpan di Database Back4App menggunakan ParseSwift SDK.
- Tinjauan cepat tentang kelas Query<U>
Setiap kueri yang dilakukan pada Database Back4App dilakukan melalui kelas generik Query<U>. Parameter generik U (yang sesuai dengan protokol ParseObject) adalah tipe data dari objek yang ingin kita ambil dari database.
Diberikan tipe data seperti MyObject, kita mengambil objek-objek ini dari Database Back4App dengan cara berikut
Swift
 import ParseSwift
2
 struct MyObject: ParseObject {
   ...
 }
6
 let query = MyObject.query()
8
 // Executes the query asynchronously
query.find { result in
  // Handle the result (of type Result<[MyObject], ParseError>)
}
 import ParseSwift
2
 struct MyObject: ParseObject {
   ...
 }
6
 let query = MyObject.query()
8
 // Executes the query asynchronously
query.find { result in
  // Handle the result (of type Result<[MyObject], ParseError>)
}
﻿
Anda dapat membaca lebih lanjut tentang Query<U> kelas di sini pada dokumentasi resmi. 
- Simpan beberapa data di Database Back4App
Sebelum kita mulai mengeksekusi kueri, perlu untuk menyiapkan beberapa data di Database Back4App. Kita akan menyimpan lima jenis objek:
Author
Book
ISBD
Publisher
BookStore
 struct Author: ParseObject {
   ...
   var name: String?
 }
 struct Author: ParseObject {
   ...
   var name: String?
 }
﻿
Selain itu, untuk membangun kueri untuk data relasional, kita akan menerapkan hubungan berikut
1 hubungan antara Buku dan ISBD.
N hubungan antara Buku dan Penerbit.
M:N hubungan antara Buku dan Penulis.
M:N hubungan antara Toko Buku dan Buku.
Kami sekarang melanjutkan untuk menyimpan beberapa data di Database Back4App. Langkah ini dapat diimplementasikan menggunakan Swift atau langsung dari konsol aplikasi Anda di platform Back4App.
Swift
Back4App's console
//A quick way to insert elements on your Back4App Database is via the console located in your App’s API section. Once you are there, you can start running Javascript code to save the sample data
 // Authors
 const aaronWriter = new Parse.Object('Author');
 aaronWriter.set('name', 'Aaron Writer');
 await aaronWriter.save();
5
 const beatriceNovelist = new Parse.Object('Author');
 beatriceNovelist.set('name', 'Beatrice Novelist');
 await beatriceNovelist.save();
9
const caseyColumnist = new Parse.Object('Author');
caseyColumnist.set('name', 'Casey Columnist');
await caseyColumnist.save();
13
// Publishers
const acaciaPublishings = new Parse.Object('Publisher');
acaciaPublishings.set('name', 'Acacia Publishings');
await acaciaPublishings.save();
18
const birchDistributions = new Parse.Object('Publisher');
birchDistributions.set('name', 'Birch Distributions');
await birchDistributions.save();
22
// Books with their corresponding ISBD
const aLoveStoryISBD = new Parse.Object('ISBD');
aLoveStoryISBD.set('isbn', '9781401211868');
await aLoveStoryISBD.save();
27
const aLoveStoryBook = new Parse.Object('Book');
aLoveStoryBook.set('title', 'A Love Story');
aLoveStoryBook.set('publisher', acaciaPublishings);
aLoveStoryBook.set('publishingDate', new Date('05/07/1998'));
aLoveStoryBook.set('isbd', aLoveStoryISBD);
const bookARelation = aLoveStoryBook.relation("authors");
bookARelation.add(aaronWriter);
await aLoveStoryBook.save();
aLoveStoryISBD.set('book', aLoveStoryBook.toPointer());
await aLoveStoryISBD.save();
38
const benevolentElvesISBD = new Parse.Object('ISBD');
benevolentElvesISBD.set('isbn', '9781401211868');
await benevolentElvesISBD.save();
42
const benevolentElvesBook = new Parse.Object('Book');
benevolentElvesBook.set('title', 'Benevolent Elves');
benevolentElvesBook.set('publisher', birchDistributions);
benevolentElvesBook.set('publishingDate', new Date('11/31/2008'));
benevolentElvesBook.set('isbd', benevolentElvesISBD);
const bookBRelation = benevolentElvesBook.relation("authors");
bookBRelation.add(beatriceNovelist);
await benevolentElvesBook.save();
benevolentElvesISBD.set('book', benevolentElvesBook.toPointer());
await benevolentElvesISBD.save();

const canYouBelieveItISBD = new Parse.Object('ISBD');
canYouBelieveItISBD.set('isbn', '9781401211868');
await canYouBelieveItISBD.save();
57
const canYouBelieveItBook = new Parse.Object('Book');
canYouBelieveItBook.set('title', 'Can You Believe It?');
canYouBelieveItBook.set('publisher', birchDistributions);
canYouBelieveItBook.set('publishingDate', new Date('08/21/2018'));
canYouBelieveItBook.set('isbd', canYouBelieveItISBD);
const bookCRelation = canYouBelieveItBook.relation("authors");
bookCRelation.add(aaronWriter);
bookCRelation.add(caseyColumnist);
await canYouBelieveItBook.save();
canYouBelieveItISBD.set('book', canYouBelieveItBook.toPointer());
await canYouBelieveItISBD.save();
69
// Book store
const booksOfLoveStore = new Parse.Object('BookStore');
booksOfLoveStore.set('name', 'Books of Love');
const bookStoreARelation = booksOfLoveStore.relation("books");
bookStoreARelation.add(aLoveStoryBook);
await booksOfLoveStore.save();
76
const fantasyBooksStore = new Parse.Object('BookStore');
fantasyBooksStore.set('name', 'Fantasy Books');
const bookStoreBRelation = fantasyBooksStore.relation("books");
bookStoreBRelation.add(benevolentElvesBook);
await fantasyBooksStore.save();
82
const generalBooksStore = new Parse.Object('BookStore');
generalBooksStore.set('name', 'General Books');
const bookStoreCRelation = generalBooksStore.relation("books");
bookStoreCRelation.add(aLoveStoryBook);
bookStoreCRelation.add(canYouBelieveItBook);
await generalBooksStore.save();
//A quick way to insert elements on your Back4App Database is via the console located in your App’s API section. Once you are there, you can start running Javascript code to save the sample data
 // Authors
 const aaronWriter = new Parse.Object('Author');
 aaronWriter.set('name', 'Aaron Writer');
 await aaronWriter.save();
5
 const beatriceNovelist = new Parse.Object('Author');
 beatriceNovelist.set('name', 'Beatrice Novelist');
 await beatriceNovelist.save();
9
const caseyColumnist = new Parse.Object('Author');
caseyColumnist.set('name', 'Casey Columnist');
await caseyColumnist.save();
13
// Publishers
const acaciaPublishings = new Parse.Object('Publisher');
acaciaPublishings.set('name', 'Acacia Publishings');
await acaciaPublishings.save();
18
const birchDistributions = new Parse.Object('Publisher');
birchDistributions.set('name', 'Birch Distributions');
await birchDistributions.save();
22
// Books with their corresponding ISBD
const aLoveStoryISBD = new Parse.Object('ISBD');
aLoveStoryISBD.set('isbn', '9781401211868');
await aLoveStoryISBD.save();
27
const aLoveStoryBook = new Parse.Object('Book');
aLoveStoryBook.set('title', 'A Love Story');
aLoveStoryBook.set('publisher', acaciaPublishings);
aLoveStoryBook.set('publishingDate', new Date('05/07/1998'));
aLoveStoryBook.set('isbd', aLoveStoryISBD);
const bookARelation = aLoveStoryBook.relation("authors");
bookARelation.add(aaronWriter);
await aLoveStoryBook.save();
aLoveStoryISBD.set('book', aLoveStoryBook.toPointer());
await aLoveStoryISBD.save();
38
const benevolentElvesISBD = new Parse.Object('ISBD');
benevolentElvesISBD.set('isbn', '9781401211868');
await benevolentElvesISBD.save();
42
const benevolentElvesBook = new Parse.Object('Book');
benevolentElvesBook.set('title', 'Benevolent Elves');
benevolentElvesBook.set('publisher', birchDistributions);
benevolentElvesBook.set('publishingDate', new Date('11/31/2008'));
benevolentElvesBook.set('isbd', benevolentElvesISBD);
const bookBRelation = benevolentElvesBook.relation("authors");
bookBRelation.add(beatriceNovelist);
await benevolentElvesBook.save();
benevolentElvesISBD.set('book', benevolentElvesBook.toPointer());
await benevolentElvesISBD.save();

const canYouBelieveItISBD = new Parse.Object('ISBD');
canYouBelieveItISBD.set('isbn', '9781401211868');
await canYouBelieveItISBD.save();
57
const canYouBelieveItBook = new Parse.Object('Book');
canYouBelieveItBook.set('title', 'Can You Believe It?');
canYouBelieveItBook.set('publisher', birchDistributions);
canYouBelieveItBook.set('publishingDate', new Date('08/21/2018'));
canYouBelieveItBook.set('isbd', canYouBelieveItISBD);
const bookCRelation = canYouBelieveItBook.relation("authors");
bookCRelation.add(aaronWriter);
bookCRelation.add(caseyColumnist);
await canYouBelieveItBook.save();
canYouBelieveItISBD.set('book', canYouBelieveItBook.toPointer());
await canYouBelieveItISBD.save();
69
// Book store
const booksOfLoveStore = new Parse.Object('BookStore');
booksOfLoveStore.set('name', 'Books of Love');
const bookStoreARelation = booksOfLoveStore.relation("books");
bookStoreARelation.add(aLoveStoryBook);
await booksOfLoveStore.save();
76
const fantasyBooksStore = new Parse.Object('BookStore');
fantasyBooksStore.set('name', 'Fantasy Books');
const bookStoreBRelation = fantasyBooksStore.relation("books");
bookStoreBRelation.add(benevolentElvesBook);
await fantasyBooksStore.save();
82
const generalBooksStore = new Parse.Object('BookStore');
generalBooksStore.set('name', 'General Books');
const bookStoreCRelation = generalBooksStore.relation("books");
bookStoreCRelation.add(aLoveStoryBook);
bookStoreCRelation.add(canYouBelieveItBook);
await generalBooksStore.save();
﻿
- Kuery data
Setelah basis data memiliki beberapa data contoh untuk dikerjakan, kita mulai mengeksekusi berbagai jenis kueri yang terkait dengan relasi yang dijelaskan sebelumnya.
Kueri yang melibatkan relasi 1:1
Diberikan dua tipe data yang berbagi relasi 1:1 (Buku dan ISBD dalam hal ini), kita dapat mengambil satu dari yang lain sebagai berikut. Cara kita mengimplementasikan relasi di Buku memungkinkan kita untuk mengambil ISBD terkait hanya dengan memanggil metode include(_:) pada kueri. Mari kita ambil ISBD dari buku A Love Story:
Swift
 let aLoveStoryBookQuery = Book.query("title" == "A Love Story").include("isbd") // Note how we include the ISBD with the include(_:) method
2
 let book = try? aLoveStoryBookQuery.first() // Retrieves synchronously the book including its ISBD
4
 aLoveStoryBookQuery.first { result in // Retrieves asynchronously the book including its ISBD
   // Handle the result (of type Result<Book, ParseError>)
 }
 let aLoveStoryBookQuery = Book.query("title" == "A Love Story").include("isbd") // Note how we include the ISBD with the include(_:) method
2
 let book = try? aLoveStoryBookQuery.first() // Retrieves synchronously the book including its ISBD
4
 aLoveStoryBookQuery.first { result in // Retrieves asynchronously the book including its ISBD
   // Handle the result (of type Result<Book, ParseError>)
 }
﻿
Di sisi lain, kueri untuk mengambil objek Buku yang terkait dengan ISBD tertentu diimplementasikan dengan cara berikut. Dengan melihat implementasi ISBD, kita mencatat bahwa relasi diwakili oleh properti buku (dari tipe Pointer<book>). Pointer ini menyediakan serangkaian metode dan properti untuk mengambil informasi tentang objek yang ditunjuknya. Secara khusus, kita memanggil metode fetch(...) pada properti buku untuk mengambil Buku﻿
Swift
 let someISBD: ISBD
2
 let book: Book? = try? someISBD.book?.fetch() // Retrieves synchronously the book asscociated to someISBD
4
 someISBD.book?.fetch { result in // Retrieves asynchronously the book asscociated to someISBD
   // Handle the result (of type Result<Book, ParseError>)
 }
 let someISBD: ISBD
2
 let book: Book? = try? someISBD.book?.fetch() // Retrieves synchronously the book asscociated to someISBD
4
 someISBD.book?.fetch { result in // Retrieves asynchronously the book asscociated to someISBD
   // Handle the result (of type Result<Book, ParseError>)
 }
﻿
Kita harus mencatat bahwa implementasi untuk 1:1 hubungan ini tidak unik. Tergantung pada kasus penggunaan Anda, Anda dapat mengimplementasikan 1:1 hubungan dengan cara yang berbeda.
Kueri yang melibatkan hubungan 1:N
Dalam skenario di mana kita perlu mengkueri semua buku yang diterbitkan oleh penerbit tertentu, kita pertama-tama perlu mengambil penerbit tersebut. Misalnya, kita pertama-tama mengambil objek data yang terkait dengan penerbit Acacia Publishings. Tergantung pada situasi, proses ini dapat bervariasi
Swift
 do {
   // Using the object's objectId
   let acaciaPublishings = try Publisher(objectId: "SOME_OBJECT_ID").fetch()
4
   // Or
   // Using a Query
   let acaciaPublishings = try Publisher.query("name" == "Acacia Publishings").first() // Returns (synchronously) the first Publisher with name 'Acacia Publishings'. The constraint is constructed using the == operator provided by the ParseSwift SDK

   ... // To be completed below
} catch {
// Hanlde the error (of type ParseError)
}
 do {
   // Using the object's objectId
   let acaciaPublishings = try Publisher(objectId: "SOME_OBJECT_ID").fetch()
4
   // Or
   // Using a Query
   let acaciaPublishings = try Publisher.query("name" == "Acacia Publishings").first() // Returns (synchronously) the first Publisher with name 'Acacia Publishings'. The constraint is constructed using the == operator provided by the ParseSwift SDK

   ... // To be completed below
} catch {
// Hanlde the error (of type ParseError)
}
﻿
Sekarang kita memiliki akses ke acaciaPublishings, kita dapat membangun kueri untuk mengambil buku-buku terkaitnya. Kita melanjutkan untuk membuat kueri dengan menginstansiasi kelas Query<Book> . Dalam hal ini, kelas ini diinstansiasi menggunakan metode statis query(...) yang disediakan oleh objek Book. Argumen (variadic) untuk metode ini adalah objek QueryConstraint standar. Oleh karena itu, buku-buku yang kita cari diambil dengan cuplikan berikut
Swift
 do {
   let acaciaPublishings = try Publisher.query("name" == "Acacia Publishings").first() // Returns the first Publisher with name 'Acacia Publishings'
3
   let constraint: QueryConstraint = try "publisher" == publisher
   let query = Book.query(constraint) // Creates the query to retrieve all Book objects where its publisher field equalt to 'acaciaPublishings'
6
   let books: [Book] = try query.find() // Executes the query synchronously
8
   // books should contain only one element: the book 'A Love Story'
} catch {
  // Hanlde the error (of type ParseError)
}
 do {
   let acaciaPublishings = try Publisher.query("name" == "Acacia Publishings").first() // Returns the first Publisher with name 'Acacia Publishings'
3
   let constraint: QueryConstraint = try "publisher" == publisher
   let query = Book.query(constraint) // Creates the query to retrieve all Book objects where its publisher field equalt to 'acaciaPublishings'
6
   let books: [Book] = try query.find() // Executes the query synchronously
8
   // books should contain only one element: the book 'A Love Story'
} catch {
  // Hanlde the error (of type ParseError)
}
﻿
Implementasi asinkron untuk cuplikan di atas dapat ditulis dengan cara berikut
Swift
 // We retrieve the Publisher with name 'Acacia Publishings'
 Publisher.query("name" == "Acacia Publishings").first { result in
   switch result {
   case .success(let publisher):
     guard let constraint: QueryConstraint = try? "publisher" == publisher else { fatalError() }
6
     // Then, we retrieve the books with the corresponding constraint          
     Book.query(constraint).find { result in
       switch result {
      case .success(let books):
        // books should contain only one element: the book 'A Love Story'
        break
      case .failure(let error):
        // handle the error (of type ParseError)
        break
      }
    }
18
  case .failure(let error):
    // handle the error (of type ParseError)
    break
  }
}
 // We retrieve the Publisher with name 'Acacia Publishings'
 Publisher.query("name" == "Acacia Publishings").first { result in
   switch result {
   case .success(let publisher):
     guard let constraint: QueryConstraint = try? "publisher" == publisher else { fatalError() }
6
     // Then, we retrieve the books with the corresponding constraint          
     Book.query(constraint).find { result in
       switch result {
      case .success(let books):
        // books should contain only one element: the book 'A Love Story'
        break
      case .failure(let error):
        // handle the error (of type ParseError)
        break
      }
    }
18
  case .failure(let error):
    // handle the error (of type ParseError)
    break
  }
}
﻿
Query yang melibatkan hubungan M:N (Kasus 1)
Untuk menggambarkan kasus ini, kita mempertimbangkan skenario berikut; kita ingin mencantumkan semua toko yang memiliki buku yang diterbitkan setelah tanggal tertentu (misalnya, 01/01/2010). Pertama, kita memerlukan query perantara untuk memilih buku-buku tersebut. Selanjutnya, kita membangun query utama untuk mencantumkan toko-toko.
Oleh karena itu, kita menyiapkan query pertama untuk buku-buku
Swift
 let booksQuery = Book.query("publishingDate" > Date(string: "01/01/2010")) // We construct the date constraint using the > operator provided by the ParseSwift SDK
      
 do {
   let books = try booksQuery.find()
   ... // To be completed below
 } catch let error as ParseError {
   // Handle any potential error
 } catch {
   // Handle any potential error
}
 let booksQuery = Book.query("publishingDate" > Date(string: "01/01/2010")) // We construct the date constraint using the > operator provided by the ParseSwift SDK
      
 do {
   let books = try booksQuery.find()
   ... // To be completed below
 } catch let error as ParseError {
   // Handle any potential error
 } catch {
   // Handle any potential error
}
﻿
Kami kemudian membangun kueri toko menggunakan booksQuery’s results. Metode containedIn(_:array:) mengembalikan batasan yang kami butuhkan untuk kasus ini
Swift
 let booksQuery = Book.query("publishingDate" > Date(string: "01/01/2010")) // We construct the date constraint using the > operator provided by the ParseSwift SDK
      
 do {
   let books = try booksQuery.find()

   // Here is where we construct the stores' query with the corresponding constraint
   let storesQuery = BookStore.query(try containedIn(key: "books", array: books))
  
   let stores = try storesQuery.find()
  
  // stores should containt only one element: the 'General Books' BookStore 
} catch let error as ParseError {
  // Handle any potential error
} catch {
  // Handle any potential error
}
 let booksQuery = Book.query("publishingDate" > Date(string: "01/01/2010")) // We construct the date constraint using the > operator provided by the ParseSwift SDK
      
 do {
   let books = try booksQuery.find()

   // Here is where we construct the stores' query with the corresponding constraint
   let storesQuery = BookStore.query(try containedIn(key: "books", array: books))
  
   let stores = try storesQuery.find()
  
  // stores should containt only one element: the 'General Books' BookStore 
} catch let error as ParseError {
  // Handle any potential error
} catch {
  // Handle any potential error
}
﻿
Demikian pula, kami dapat menerapkan proses ini secara asinkron
Swift
 let booksQuery = Book.query("publishingDate" > Date(string: "01/01/2010")) // We construct the date constraint using the > operator provided by the ParseSwift SDK
2
 booksQuery.find { result in
   switch result {
   case .success(let books):
     guard let constraint = try? containedIn(key: "books", array: books) else { fatalError() }
     let storesQuery = BookStore.query(constraint)
              
     storesQuery.find { result in
      switch result {
      case .success(let stores):
      
      case .failure(let error):
        // Handle the error (of type ParseError)
      }
    }
  case .failure(let error):
    // Handle the error (of type ParseError)
  }
}
 let booksQuery = Book.query("publishingDate" > Date(string: "01/01/2010")) // We construct the date constraint using the > operator provided by the ParseSwift SDK
2
 booksQuery.find { result in
   switch result {
   case .success(let books):
     guard let constraint = try? containedIn(key: "books", array: books) else { fatalError() }
     let storesQuery = BookStore.query(constraint)
              
     storesQuery.find { result in
      switch result {
      case .success(let stores):
      
      case .failure(let error):
        // Handle the error (of type ParseError)
      }
    }
  case .failure(let error):
    // Handle the error (of type ParseError)
  }
}
﻿
Kueri yang melibatkan hubungan M:N (Kasus 2)
Misalkan kita perlu memilih semua toko yang memiliki buku yang ditulis oleh seorang penulis tertentu, katakanlah, Aaron Writer. Untuk mencapai ini, kita memerlukan dua kueri tambahan:
Sebuah kueri (Query<Author>) untuk mendapatkan objek yang terkait dengan penulis Aaron Writer.
Sebuah kueri (Query<Book>) untuk memilih semua buku yang ditulis oleh Aaron Writer.
Kueri utama (Query<BookStore>) untuk memilih toko yang kita cari.
Prosedur untuk menerapkan kueri ini sangat mirip dengan yang sebelumnya:
Swift
 let authorQuery = Author.query("name" == "Aaron Writer") // The first query to retrieve the data object associated to 'Aaron Writer'
2
 do {
   let aaronWriter = try authorQuery.first()
          
   let booksQuery = Book.query(try containedIn(key: "authors", array: [aaronWriter])) // The second query to retrieve the books written by 'Aaron Writer'
          
   let books = try booksQuery.find()
          
  let storesQuery = BookStore.query(try containedIn(key: "books", array: books)) // The main query to select the stores where the author ('Aaron Writer') has his books available

  let stores = try storesQuery.find()
          
  // stores should contain two items: 'Books of Love' and 'General Books'
} catch let error as ParseError {
  // Handle the error
} catch {
  // Handle the error
}
 let authorQuery = Author.query("name" == "Aaron Writer") // The first query to retrieve the data object associated to 'Aaron Writer'
2
 do {
   let aaronWriter = try authorQuery.first()
          
   let booksQuery = Book.query(try containedIn(key: "authors", array: [aaronWriter])) // The second query to retrieve the books written by 'Aaron Writer'
          
   let books = try booksQuery.find()
          
  let storesQuery = BookStore.query(try containedIn(key: "books", array: books)) // The main query to select the stores where the author ('Aaron Writer') has his books available

  let stores = try storesQuery.find()
          
  // stores should contain two items: 'Books of Love' and 'General Books'
} catch let error as ParseError {
  // Handle the error
} catch {
  // Handle the error
}
﻿
Kesimpulan
Dengan ParseSwift SDK, kami dapat membangun kueri relasional yang memungkinkan kami untuk memilih item berdasarkan jenis hubungan yang mereka miliki dengan tipe data lainnya.
Diperbarui 27 Jan 2025
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Kueri Relasional

Pendahuluan

Prasyarat

Tujuan

1 - Tinjauan cepat tentang kelas Query<U>

2 - Simpan beberapa data di Database Back4App

3 - Kuery data

Kesimpulan
