Paginated Watchers for GraphQL Queries #3007
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| Original file line number | Diff line number | Diff line change |
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| #if !COCOAPODS | ||
| import ApolloAPI | ||
| #endif | ||
| import Foundation | ||
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| public typealias Cursor = String | ||
| /// Pagination help information, returned by the GraphQL server. Contains info based on the requested connection parameters. | ||
| public protocol PageInfoType { | ||
| /// Whether or not there are subsequent items past this page in the connection. | ||
| var hasNextPage: Bool { get } | ||
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| /// The final cursor, marking the end of the page. | ||
| var endCursor: Cursor? { get } | ||
| } | ||
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| /// Handles pagination in the queue by managing multiple query watchers. | ||
| final class GraphQLPaginatedQueryWatcher<Query: GraphQLQuery, T>: Cancellable { | ||
| /// Given a page, create a query of the type this watcher is responsible for | ||
| public typealias CreatePageQuery = (PageInfoType) -> Query? | ||
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| private typealias ResultHandler = (Result<GraphQLResult<Query.Data>, Error>) -> Void | ||
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| private let client: any ApolloClientProtocol | ||
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| private var initialWatcher: GraphQLQueryWatcher<Query>? | ||
| private var subsequentWatchers: [GraphQLQueryWatcher<Query>] = [] | ||
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| private let createPageQuery: CreatePageQuery | ||
| private let nextPageTransform: (T?, T) -> T | ||
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| private var model: T? // 🚗 | ||
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| private var resultHandler: ResultHandler? | ||
| private var callbackQueue: DispatchQueue | ||
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| /// Designated initializer | ||
| /// | ||
| /// - Parameters: | ||
| /// - client: The client protocol to pass in | ||
| /// - inititalCachePolicy: The preferred cache policy for the initlal page. Defaults to `returnCacheDataAndFetch`. | ||
| /// - callbackQueue: The queue for response callbacks. | ||
| /// - query: The query to watch | ||
| /// - createPageQuery: A function which creates a new `Query` given some pagination information. | ||
| /// - transform: Transforms the `Query.Data` to the intended model | ||
| /// - nextPageTransform: A function which combines extant data with the new data from the next page | ||
| /// - onReceiveResults: The callback function which returns changes or an error. | ||
| public init( | ||
| client: ApolloClientProtocol, | ||
| inititalCachePolicy: CachePolicy = .returnCacheDataAndFetch, | ||
| callbackQueue: DispatchQueue = .main, | ||
| query: Query, | ||
| createPageQuery: @escaping CreatePageQuery, | ||
| transform: @escaping (Query.Data) -> T?, | ||
| nextPageTransform: @escaping (T?, T) -> T, | ||
| onReceiveResults: @escaping (Result<T, Error>) -> Void | ||
| ) { | ||
| self.callbackQueue = callbackQueue | ||
| self.client = client | ||
| self.createPageQuery = createPageQuery | ||
| self.nextPageTransform = nextPageTransform | ||
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| let resultHandler: ResultHandler = { [weak self] result in | ||
| guard let self else { return } | ||
| switch result { | ||
| case .failure(let error): | ||
| guard !error.wasCancelled else { return } | ||
| // Forward all errors aside from network cancellation errors | ||
| onReceiveResults(.failure(error)) | ||
| case .success(let graphQLResult): | ||
| guard let data = graphQLResult.data, let transformedModel = transform(data) else { return } | ||
| let model = nextPageTransform(self.model, transformedModel) | ||
| self.model = model | ||
| onReceiveResults(.success(model)) | ||
| } | ||
| } | ||
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| self.resultHandler = resultHandler | ||
| initialWatcher = client.watch( | ||
| query: query, | ||
| cachePolicy: .returnCacheDataAndFetch, | ||
| callbackQueue: callbackQueue, | ||
| resultHandler: resultHandler | ||
| ) | ||
| } | ||
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| public func fetch() { | ||
| initialWatcher?.refetch() | ||
| cancelSubsequentWatchers() | ||
| } | ||
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| @discardableResult | ||
| public func fetchNext(page: PageInfoType) -> Bool { | ||
| guard page.hasNextPage, | ||
| let nextPageQuery = createPageQuery(page), | ||
| let resultHandler | ||
| else { return false } | ||
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| let nextPageWatcher = client.watch( | ||
| query: nextPageQuery, | ||
| cachePolicy: .fetchIgnoringCacheData, | ||
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| callbackQueue: callbackQueue | ||
| ) { result in | ||
| resultHandler(result) | ||
| } | ||
| subsequentWatchers.append(nextPageWatcher) | ||
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| return true | ||
| } | ||
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| public func cancel() { | ||
| initialWatcher?.cancel() | ||
| cancelSubsequentWatchers() | ||
| } | ||
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| private func cancelSubsequentWatchers() { | ||
| subsequentWatchers.forEach { $0.cancel() } | ||
| subsequentWatchers.removeAll() | ||
| } | ||
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| deinit { | ||
| cancel() | ||
| } | ||
| } | ||
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| private extension Error { | ||
| var wasCancelled: Bool { | ||
| if let apolloError = self as? URLSessionClient.URLSessionClientError, | ||
| case let .networkError(data: _, response: _, underlying: underlying) = apolloError { | ||
| return underlying.wasCancelled | ||
| } | ||
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| return (self as NSError).code == NSURLErrorCancelled | ||
| } | ||
| } | ||
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,206 @@ | ||
| @testable import Apollo | ||
| import ApolloAPI | ||
| import ApolloInternalTestHelpers | ||
| import Nimble | ||
| import XCTest | ||
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| class PaginatedWatchQueryTests: XCTestCase, CacheDependentTesting { | ||
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| var cacheType: TestCacheProvider.Type { | ||
| InMemoryTestCacheProvider.self | ||
| } | ||
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| var cache: NormalizedCache! | ||
| var server: MockGraphQLServer! | ||
| var client: ApolloClient! | ||
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| override func setUpWithError() throws { | ||
| try super.setUpWithError() | ||
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| cache = try makeNormalizedCache() | ||
| let store = ApolloStore(cache: cache) | ||
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| server = MockGraphQLServer() | ||
| let networkTransport = MockNetworkTransport(server: server, store: store) | ||
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| client = ApolloClient(networkTransport: networkTransport, store: store) | ||
| } | ||
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| override func tearDownWithError() throws { | ||
| cache = nil | ||
| server = nil | ||
| client = nil | ||
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| try super.tearDownWithError() | ||
| } | ||
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| private class MockPaginatedSelectionSet: MockSelectionSet { | ||
| override class var __selections: [Selection] { [ | ||
| .field("hero", Hero.self) | ||
| ]} | ||
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| var hero: Hero { __data["hero"] } | ||
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| class Hero: MockSelectionSet { | ||
| override class var __selections: [Selection] {[ | ||
| .field("name", String.self), | ||
| .field("friendsConnection", FriendsConnection.self, arguments: [ | ||
| "first": .variable("first"), | ||
| "after": .variable("after") | ||
| ]) | ||
| ]} | ||
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| var name: String { __data["name"] } | ||
| var friends: FriendsConnection { __data["friendsConnection"] } | ||
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| class FriendsConnection: MockSelectionSet { | ||
| override class var __selections: [Selection] {[ | ||
| .field("totalCount", Int.self), | ||
| .field("friends", [Character].self), | ||
| .field("pageInfo", PageInfo.self) | ||
| ]} | ||
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| var totalCount: Int { __data["totalCount"] } | ||
| var friends: [Character] { __data["friends"] } | ||
| var pageInfo: PageInfo { __data["pageInfo"] } | ||
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| class Character: MockSelectionSet { | ||
| override class var __selections: [Selection] {[ | ||
| .field("name", String.self), | ||
| ]} | ||
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| var name: String { __data["name"] } | ||
| } | ||
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| class PageInfo: MockSelectionSet { | ||
| override class var __selections: [Selection] {[ | ||
| .field("endCursor", Optional<String>.self), | ||
| .field("hasNextPage", Bool.self) | ||
| ]} | ||
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| var endCursor: String? { __data["endCursor"] } | ||
| var hasNextPage: Bool { __data["hasNextPage"] } | ||
| } | ||
| } | ||
| } | ||
| } | ||
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| struct HeroViewModel: Equatable { | ||
| struct Friend: Equatable { | ||
| let name: String | ||
| } | ||
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| let name: String | ||
| let friends: [Friend] | ||
| } | ||
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| struct Page: PageInfoType { | ||
| var endCursor: Cursor? | ||
| var hasNextPage: Bool | ||
| } | ||
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| // MARK: - Tests | ||
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| func testMultiPageResults() { | ||
| let query = MockQuery<MockPaginatedSelectionSet>() | ||
| query.__variables = ["first": 2, "after": GraphQLNullable<String>.null] | ||
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| var results: [HeroViewModel] = [] | ||
| var watcher: GraphQLPaginatedQueryWatcher<MockQuery<MockPaginatedSelectionSet>, HeroViewModel>? | ||
| addTeardownBlock { watcher?.cancel() } | ||
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| runActivity("Initial fetch from server") { _ in | ||
| let serverExpectation = server.expect(MockQuery<MockPaginatedSelectionSet>.self) { _ in | ||
| [ | ||
| "data": [ | ||
| "hero": [ | ||
| "name": "R2-D2", | ||
| "friendsConnection": [ | ||
| "totalCount": 3, | ||
| "friends": [ | ||
| [ | ||
| "name": "Luke Skywalker" | ||
| ], | ||
| [ | ||
| "name": "Han Solo" | ||
| ] | ||
| ], | ||
| "pageInfo": [ | ||
| "endCursor": "Y3Vyc29yMg==", | ||
| "hasNextPage": true | ||
| ] | ||
| ] | ||
| ], | ||
| ] | ||
| ] | ||
| } | ||
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| watcher = GraphQLPaginatedQueryWatcher( | ||
| client: client, | ||
| query: query | ||
| ) { pageInfo in | ||
| let query = MockQuery<MockPaginatedSelectionSet>() | ||
| query.__variables = ["first": 2, "after": "1"] | ||
| return query | ||
| } transform: { data in | ||
| HeroViewModel( | ||
| name: data.hero.name, | ||
| friends: data.hero.friends.friends.map { | ||
| HeroViewModel.Friend(name: $0.name) | ||
| } | ||
| ) | ||
| } nextPageTransform: { oldData, newData in | ||
| guard let oldData else { return newData } | ||
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| return HeroViewModel( | ||
| name: newData.name, | ||
| friends: oldData.friends + newData.friends | ||
| ) | ||
| } onReceiveResults: { result in | ||
| guard case let .success(value) = result else { return XCTFail() } | ||
| results.append(value) | ||
| } | ||
| guard let watcher else { return XCTFail() } | ||
| wait(for: [serverExpectation], timeout: 1.0) | ||
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| let secondPageExpectation = server.expect(MockQuery<MockPaginatedSelectionSet>.self) { _ in | ||
| [ | ||
| "data": [ | ||
| "hero": [ | ||
| "name": "R2-D2", | ||
| "friendsConnection": [ | ||
| "totalCount": 3, | ||
| "friends": [ | ||
| [ | ||
| "name": "Leia Organa" | ||
| ] | ||
| ], | ||
| "pageInfo": [ | ||
| "endCursor": "Y3Vyc29yMw==", | ||
| "hasNextPage": false | ||
| ] | ||
| ] | ||
| ], | ||
| ] | ||
| ] | ||
| } | ||
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| _ = watcher.fetchNext(page: Page(endCursor: "Y3Vyc29yMg==", hasNextPage: true)) | ||
| wait(for: [secondPageExpectation], timeout: 1.0) | ||
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| XCTAssertEqual(results.count, 2) | ||
| XCTAssertEqual(results, [ | ||
| HeroViewModel(name: "R2-D2", friends: [ | ||
| HeroViewModel.Friend(name: "Luke Skywalker"), | ||
| HeroViewModel.Friend(name: "Han Solo"), | ||
| ]), | ||
| HeroViewModel(name: "R2-D2", friends: [ | ||
| HeroViewModel.Friend(name: "Luke Skywalker"), | ||
| HeroViewModel.Friend(name: "Han Solo"), | ||
| HeroViewModel.Friend(name: "Leia Organa"), | ||
| ]) | ||
| ]) | ||
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| } | ||
| } | ||
| } |
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GraphQLQueryWatcherhas always held aweakreference to the client. I'm wondering if this should do the same. I don't imagine that this would create a retain cycle, as the retain cycle would be broken as soon as you callcancel().Any thoughts on this? @Iron-Ham @calvincestari @BobaFetters
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I think this sounds reasonable