Read application data
Query by Id
Now that you were able to make a mutation, take the Id that was printed out and use it in your query to retrieve data.
func getTodo() { Amplify.API.query(request: .get(Todo.self, byId: "9FCF5DD5-1D65-4A82-BE76-42CB438607A0")) { event in switch event { case .success(let result): switch result { case .success(let todo): guard let todo = todo else { print("Could not find todo") return } print("Successfully retrieved todo: \(todo)") case .failure(let error): print("Got failed result with \(error.errorDescription)") } case .failure(let error): print("Got failed event with error \(error)") } }}func getTodo() -> AnyCancellable { Amplify.API .query(request: .get(Todo.self, byId: "9FCF5DD5-1D65-4A82-BE76-42CB438607A0")) .resultPublisher .sink { if case let .failure(error) = $0 { print("Got failed event with error \(error)") } } receiveValue: { result in switch result { case .success(let todo): guard let todo = todo else { print("Could not find todo") return } print("Successfully retrieved todo: \(todo)") case .failure(let error): print("Got failed result with \(error.errorDescription)") } }}List Query
You can get the list of items using .paginatedList with optional parameters limit and where to specify the page size and condition. By default, the page size is 1000.
func listTodos() { let todo = Todo.keys let predicate = todo.name == "my first todo" && todo.description == "todo description" Amplify.API.query(request: .paginatedList(Todo.self, where: predicate, limit: 1000)) { event in switch event { case .success(let result): switch result { case .success(let todos): print("Successfully retrieved list of todos: \(todos)") case .failure(let error): print("Got failed result with \(error.errorDescription)") } case .failure(let error): print("Got failed event with error \(error)") } }}func listTodos() -> AnyCancellable { let todo = Todo.keys let predicate = todo.name == "my first todo" && todo.description == "todo description" let sink = Amplify.API.query(request: .paginatedList(Todo.self, where: predicate, limit: 1000)) .resultPublisher .sink { if case let .failure(error) = $0 { print("Got failed event with error \(error)") } } receiveValue: { result in switch result { case .success(let todos): print("Successfully retrieved list of todos: \(todos)") case .failure(let error): print("Got failed result with \(error.errorDescription)") } } return sink}List subsequent pages of items
If you are using SwiftUI and have SwiftUI imported in the same code file, you will need to import the class Amplify.List to resolve name collision with SwiftUI.List:
import SwiftUIimport Amplifyimport class Amplify.ListFor large data sets, you'll need to paginate through the results. After receiving the first page of results, you can check if there is a subsequent page and obtain the next page.
var todos: [Todo] = []var currentPage: List<Todo>?
func listFirstPage() { let todo = Todo.keys let predicate = todo.name == "my first todo" && todo.description == "todo description" Amplify.API.query(request: .paginatedList(Todo.self, where: predicate, limit: 1000)) { event in switch event { case .success(let result): switch result { case .success(let todos): print("Successfully retrieved list of todos: \(todos)") self.currentPage = todos self.todos.append(contentsOf: todos) case .failure(let error): print("Got failed result with \(error.errorDescription)") } case .failure(let error): print("Got failed event with error \(error)") } }}
func listNextPage() { if let current = currentPage, current.hasNextPage() { current.getNextPage { result in switch result { case .success(let todos): self.todos.append(contentsOf: todos) self.currentPage = todos case .failure(let coreError): print("Failed to get next page \(coreError)") } } }}List all pages
If you want to get all pages, retrieve the subsequent page when you have successfully retrieved the first or next page.
- Update the above method
listFirstPage()tolistAllPages() - Call
listNextPageRecursively()in the success block of the query inlistAllPages() - Update the
listNextPage()tolistNextPageRecursively() - Call
listNextPageRecursively()in the success block of the query inlistNextPageRecursively()
The completed changes should look like this
var todos: [Todo] = []var currentPage: List<Todo>?
func listAllPages() { // 1. Updated from `listFirstPage()` let todo = Todo.keys let predicate = todo.name == "my first todo" && todo.description == "todo description" Amplify.API.query(request: .paginatedList(Todo.self, where: predicate, limit: 1000)) { event in switch event { case .success(let result): switch result { case .success(let todos): print("Successfully retrieved list of todos: \(todos)") self.currentPage = todos self.todos.append(contentsOf: todos) self.listNextPageRecursively() // 2. Added case .failure(let error): print("Got failed result with \(error.errorDescription)") } case .failure(let error): print("Got failed event with error \(error)") } }}
func listNextPageRecursively() { // 3. Updated from `listNextPage()` if let current = currentPage, current.hasNextPage() { current.getNextPage { result in switch result { case .success(let todos): self.todos.append(contentsOf: todos) self.currentPage = todos self.listNextPageRecursively() // 4. Added case .failure(let coreError): print("Failed to get next page \(coreError)") } } }}