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Page updated May 8, 2024

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() async {
do {
let result = try await Amplify.API.query(
request: .get(Todo.self, byId: "9FCF5DD5-1D65-4A82-BE76-42CB438607A0")
)
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)")
}
} catch let error as APIError {
print("Failed to query todo: ", error)
} catch {
print("Unexpected error: \(error)")
}
}
func getTodo() -> AnyCancellable {
let sink = Amplify.Publisher.create {
try await Amplify.API.query(
request: .get(Todo.self, byId: "9FCF5DD5-1D65-4A82-BE76-42CB438607A0")
)
}
.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)")
}
}
return sink
}

List Query

You can get the list of items using .list with optional parameters limit and where to specify the page size and condition. By default, the page size is 1000.

func listTodos() async {
let todo = Todo.keys
let predicate = todo.name == "my first todo" && todo.description == "todo description"
let request = GraphQLRequest<Todo>.list(Todo.self, where: predicate, limit: 1000)
do {
let result = try await Amplify.API.query(request: request)
switch result {
case .success(let todos):
print("Successfully retrieved list of todos: \(todos)")
case .failure(let error):
print("Got failed result with \(error.errorDescription)")
}
} catch let error as APIError {
print("Failed to query list of todos: ", error)
} catch {
print("Unexpected error: \(error)")
}
}
func listTodos() -> AnyCancellable {
let todo = Todo.keys
let predicate = todo.name == "my first todo" && todo.description == "todo description"
let request = GraphQLRequest<Todo>.list(Todo.self, where: predicate, limit: 1000)
let sink = Amplify.Publisher.create {
try await Amplify.API.query(request: request)
}
.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 SwiftUI
import Amplify
import class Amplify.List

For 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() async {
let todo = Todo.keys
let predicate = todo.name == "my first todo" && todo.description == "todo description"
let request = GraphQLRequest<Todo>.list(Todo.self, where: predicate, limit: 1000)
do {
let result = try await Amplify.API.query(request: request)
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)")
}
} catch let error as APIError {
print("Failed to query list of todos: ", error)
} catch {
print("Unexpected error: \(error)")
}
}
func listNextPage() async {
if let current = self.currentPage, current.hasNextPage() {
do {
let todos = try await current.getNextPage()
self.todos.append(contentsOf: todos)
self.currentPage = todos
} catch {
print("Failed to get next page \(error)")
}
}
}

List all pages

If you want to get all pages, retrieve the subsequent page when you have successfully retrieved the first or next page.

  1. Update the above method listFirstPage() to listAllPages()
  2. Call listNextPageRecursively() in the success block of the query in listAllPages()
  3. Update the listNextPage() to listNextPageRecursively()
  4. Call listNextPageRecursively() in the success block of the query in listNextPageRecursively()

The completed changes should look like this:

var todos: [Todo] = []
var currentPage: List<Todo>?
func listAllPages() async { // 1. Updated from `listFirstPage()`
let todo = Todo.keys
let predicate = todo.name == "my first todo" && todo.description == "todo description"
let request = GraphQLRequest<Todo>.list(Todo.self, where: predicate, limit: 1000)
do {
let result = try await Amplify.API.query(request: request)
switch result {
case .success(let todos):
print("Successfully retrieved list of todos: \(todos)")
self.currentPage = todos
self.todos.append(contentsOf: todos)
await self.listNextPageRecursively() // 2. Added
case .failure(let error):
print("Got failed result with \(error.errorDescription)")
}
} catch let error as APIError {
print("Failed to query list of todos: ", error)
} catch {
print("Unexpected error: \(error)")
}
}
func listNextPageRecursively() async { // 3. Updated from `listNextPage()`
if let current = currentPage, current.hasNextPage() {
do {
let todos = try await current.getNextPage()
self.todos.append(contentsOf: todos)
self.currentPage = todos
await self.listNextPageRecursively() // 4. Added
} catch {
print("Failed to get next page \(error)")
}
}
}