Syncing CoreData and Web Apps with RestKit

This presentation discusses (and provides example code for) the following things you'll want to think about when integrating your iOS app with a Rails-based API:

— Rails API Versioning
— RestKit Installation
— Mapping Configuration
— Pulling and Pushing Data
— Offline Mode and Other Syncing
— User Authentication

Transcript

1. Rails + iOS with RestKit @andrewculver
2. The Evolution of iOS Tools
3. Before iCloud
4. After iCloud
5. Syncing is ... hard?
6. Keep it simple.
7. Topics • Rails API Versioning • RestKit Installation • Mapping Configuration • Pulling and Pushing Data • Offline Mode and Other Syncing • Authentication
8. Goals • Understand some basics. • Keep it as simple as possible.
9. Our Example App “ClipQueue”
10. “ClipQueue” • Helps with workflow automation. • Detects content in the clipboard. • Prompts to save it as a “Clip”, categorize it. • Server processes it. • Dispatches webhooks, sends emails, etc.
18. Rails JSON API
19. Rails JSON API • Keep your API separate from your core app. • Doing this efficiently requires thin controllers. • Creating resources to represent actions that would otherwise be custom controller actions helps, too.
20. class Clip < ActiveRecord::Base attr_accessible :content, :created_at end Clip Model
21. Clipqueue::Application.routes.draw do namespace :api do namespace :v1 do resources :clips end end end Setting up a Router
22. class Api::V1::ClipsController < ApplicationController load_and_authorize_resource :clip respond_to :json ... end API Controller
23. class Api::V1::ClipsController < ApplicationController load_and_authorize_resource :clip respond_to :json ... def index respond_with @clips end ... end API Controller Actions
24. class Api::V1::ClipsController < ApplicationController load_and_authorize_resource :clip respond_to :json ... def show respond_with @clip end ... end API Controller Actions
25. class Api::V1::ClipsController < ApplicationController load_and_authorize_resource :clip respond_to :json ... def create @clip.save redirect_to [:api, :v1, @clip] end ... end API Controller Actions
26. class Ability include CanCan::Ability // Guest users can do anything. def initialize(user) user ||= User.new can :manage, :all end end Single User System
27. RestKit Installation
28. Installation • Use CocoaPods. • This tutorial includes great installation steps for new projects. • https://github.com/RestKit/RKGist/blob/master/ TUTORIAL.md
29. Rails API Versioning
30. Rails JSON API Versioning • If your API changes, older apps will crash. • Your ranking in the App Store will crash, too. • Does anyone have a Gem they use for this? • Maintaining old versions of your API is easy: • Make a separate copy for each new version.
31. $ cp -R v1/ v2/ Setting up a Router
32. Clipqueue::Application.routes.draw do namespace :api do namespace :v1 do resources :clips end namespace :v2 do resources :clips resources :categories end end end Setting up a Router
33. Pulling Data
34. RESTKit ‘GET’ Lifecycle • Issues HTTP GET request for URL. • Receives XML/JSON response. • Converts to NSDictionary + NSArray structure. • Matches response URL to defined entity mapping. • Maps response data to entity.
35. RKEntityMapping *clipMapping = [RKEntityMapping mappingForEntityForName: @"Clip" inManagedObjectStore: managedObjectStore]; [clipMapping addAttributeMappingsFromDictionary:@{ @"id": @"clipId", @"content": @"content", @"created_at": @"createdAt"}]; A Mapping
36. RKResponseDescriptor *clipsResponseDescriptor = [RKResponseDescriptor responseDescriptorWithMapping: clipMapping pathPattern: @"/api/v1/clips" keyPath: nil statusCodes: RKStatusCodeIndexSetForClass(RKStatusCodeClassSuccessful)]; [objectManager addResponseDescriptor:clipsResponseDescriptor]; ‘Index’ Response Descriptor
37. RKResponseDescriptor *clipResponseDescriptor = [RKResponseDescriptor responseDescriptorWithMapping: clipMapping pathPattern: @"/api/v1/clips/:id" keyPath: nil statusCodes: RKStatusCodeIndexSetForClass(RKStatusCodeClassSuccessful)]; [objectManager addResponseDescriptor:clipResponseDescriptor]; ‘Show’ Response Descriptor
38. - (void)loadClips { [[RKObjectManager sharedManager] getObjectsAtPath:@"/api/v1/clips" parameters:nil success:nil failure:nil]; } Fetching Objects (UITableViewController)
39. - (void)loadClips { [[RKObjectManager sharedManager] getObjectsAtPath:@"/api/v1/clips" parameters:nil success: ^(RKObjectRequestOperation *operation, RKMappingResult *mappingResult) {} failure: ^(RKObjectRequestOperation *operation, NSError *error) {} ]; } Fetching Objects (UITableViewController)
40. The View • How does this information get to the user? • A NSFetchedResultsController is handling the heavy lifting.
41. Pull to Refresh
42. // In your UITableViewController. UIRefreshControl *refreshControl = [UIRefreshControl new]; [refreshControl addTarget:self action:@selector(loadClips) forControlEvents:UIControlEventValueChanged]; self.refreshControl = refreshControl; Adding Pull to Refresh (UITableViewController)
43. Pushing Data
44. RESTKit ‘POST’ Lifecycle • Issues HTTP POST request to URL. • Rails creates the object and redirects to it. • From here it’s the same as before: • Receives XML/JSON response. • Converts to NSDictionary + NSArray structure. • Matches redirected URL to defined entity mapping. • Maps response data to entity.
45. Clip *clip = (Clip *)[NSEntityDescription insertNewObjectForEntityForName:@"Clip" inManagedObjectContext:self.managedObjectContext]; clip.content = [[UIPasteboard generalPasteboard] string]; Creating a New Clip
46. [[RKObjectManager sharedManager] postObject:clip path:@"/api/v1/clips" parameters:nil success:nil failure:nil]; Posting a New Clip
47. [[RKObjectManager sharedManager] postObject:clip path:@"/api/v1/clips" parameters:nil success: ^(RKObjectRequestOperation *operation, RKMappingResult *mappingResult) {} failure: ^(RKObjectRequestOperation *operation, NSError *error) {} ]; Posting a New Clip
48. RKRequestDescriptor *newClipRequestDescriptor = [RKRequestDescriptor requestDescriptorWithMapping:[clipMapping inverseMapping] objectClass:[Clip class] rootKeyPath:@"clip"]; [objectManager addRequestDescriptor:newClipRequestDescriptor]; A Request Descriptor
49. Mass-Assignment • Rails’ new mass-assignment defaults are good, but they cause issues for us here. • RESTKit sends the ‘id’ and ‘created_at’ attributes across in the request. • This triggers an exception in development by default, because of this: config.active_record.mass_assignment_sanitizer = :strict
50. Offline Mode
51. Offline Mode • The server is the authority, but is not always available. • We want to be able to work and save data locally even in the absence of an Internet connection. • We don’t want to lose our work. • When a connection is available, we’d like our local work to be pushed up to the server.
52. A Very Simple Example • In this app, “Clips” are read-only. • Don’t have to worry about resolving conflicting changes from two sources. • How simple a solution can you get away with?
53. A Very Simple Solution • Try saving to the server. • If that doesn’t work, just save it locally. • It won’t have a “Clip ID”, but that doesn’t matter for CoreData, even with relationships. • When a connection becomes available, push it up.
54. A Very Simple Solution • Try saving to the server. • If that doesn’t work, just save it locally. • It won’t have a “Clip ID”, but that doesn’t matter for CoreData, even with relationships. • When a connection becomes available: • Push it up to the server. • Claim our shiny new “Clip ID”.
55. A Very Simple Solution • The only question is, how will the new ID get mapped to the locally stored object? • It can’t be matched by primary key ID, because it didn’t have one locally. • We’ll use a globally unique ID.
56. NSString *dataBaseString = [RKApplicationDataDirectory() stringByAppendingPathComponent:@"ClipQueue.sqlite"]; NSPersistentStore __unused *persistentStore = [managedObjectStore addSQLitePersistentStoreAtPath:dataBaseString fromSeedDatabaseAtPath:nil withConfiguration:nil options:nil error:nil]; Adding Local Storage
57. RKEntityMapping *clipMapping = [RKEntityMapping mappingForEntityForName: @"Clip" inManagedObjectStore: managedObjectStore]; [clipMapping addAttributeMappingsFromDictionary:@{ @"id": @"clipId", @"content": @"content", @"uuid": @"uuid", @"created_at": @"createdAt", @"deleted_at": @"deletedAt"}]; clipMapping.identificationAttributes = @[ @"uuid" ]; An Improved Mapping
58. clip.uuid = [self getUUID]; [[RKObjectManager sharedManager] postObject:clip path:@"/api/v1/clips" parameters:nil success: ^(RKObjectRequestOperation *operation, RKMappingResult *mappingResult) {} failure: ^(RKObjectRequestOperation *operation, NSError *error) { NSError *localError = nil; if (![self.managedObjectContext save:&localError]) { // Show UIAlertView to user. [self showErrorAlert:[localError localizedDescription]]; } }]; Queuing Up Locally
59. NSFetchRequest *request = [[NSFetchRequest alloc] init]; NSEntityDescription *entity = [NSEntityDescription entityForName:@"Clip" inManagedObjectContext:self.managedObjectContext]; [request setEntity:entity]; NSPredicate *predicate = [NSPredicate predicateWithFormat:@"clipId == 0"]; [request setPredicate:predicate]; ... for (Clip *clip in mutableFetchResults) { [[RKObjectManager sharedManager] postObject:clip path:@"/api/v1/clips" parameters:nil success:nil failure: nil]; } Syncing Up
60. class Clip < ActiveRecord::Base ... before_validation do self.uuid = UUIDTools::UUID.random_create.to_s if uuid.nil? end end Updating API Logic
61. Sync Friendly Deletes
62. Sync Friendly Deletes • An object exists locally, but not on the server. • Was it created locally or deleted remotely? • An object exists remotely, but not locally. • Was it created remotely or deleted locally? • Let’s look at a really easy way to deal with this.
63. class Clip < ActiveRecord::Base ... scope :not_deleted, where('deleted_at IS NULL') def destroy self.update_column(:deleted_at, Time.zone.now) end end Soft Delete
64. - (NSFetchedResultsController *)fetchedResultsController { ... // Filter out deleted results. NSPredicate *predicate = [NSPredicate predicateWithFormat:@"deletedAt == nil"]; [fetchRequest setPredicate:predicate]; ... } Filtering Deleted Items
65. Added Bonus • NSFetchedResultsController makes this an other UI updates really pleasant to the user by default, even when they’re triggered by results from the server.
66. Authentication
67. Authentication Goals • Require username and password. • Scope all data by user.
68. Authentication • Prompt for credentials. • Store them in iOS Keychain. • Delay loading until credentials are provided. • Configure the credentials for RestKit. • Implement data scoping on the server based on the session.
69. Devise.setup do |config| ... config.http_authenticatable = true ... end HTTP Authentication
70. - (void)viewWillAppear:(BOOL)animated { [super viewWillAppear:animated]; if ([self shouldDisplayLoginModal]) { [self performSegueWithIdentifier:@"ShowLogin" sender:self]; } } Show Sign-In Modal
71. - (void)viewDidAppear:(BOOL)animated { [super viewDidAppear:animated]; if (![self shouldDisplayLoginModal]) { [self loadObjectsFromDataStore]; } } Delay Loading
72. RKObjectManager* objectManager = [RKObjectManager sharedManager]; objectManager.client.username = emailAddressField.text; objectManager.client.password = passwordField.text; Configure Credentials
73. Add User-Clips Relationship • Add “user_id” attribute to Clip. • Add “has_one :user” relationship to Clip. • Add “has_many :clips” relationship to User.
74. class Ability include CanCan::Ability def initialize(user) user ||= User.new if user.persisted? can :manage, :clip, {user_id: user.id} end end end HTTP Authentication
75. class Api::V1::ClipsController < ApplicationController before_filter :authenticate_user! load_and_authorize_resource :clip, through: current_user ... end Scoping Controller Results
76. What We’ve Covered • Rails API Versioning • RestKit Installation • Mapping Configuration • Pulling and Pushing Data • Offline Mode and Other Syncing • Authentication
77. Goals • Understand some basics. • Keep it as simple as possible.
78. Additional Resources Blake Watters’ RESTKit 0.20.0 “Gist” Tutorial https://github.com/RestKit/RKGist/blob/master/TUTORIAL.md (A work in progress.)
79. Thanks! Questions? @andrewculver