Synchronizing Core Data With Rails

Synchronizing Core Data With Rails

Ken Collinsmetaskills.net

Wednesday, July 14, 2010



Why Write Web Applications For The

Web Only?


Why Write Web Applications For The Web <html> Only?



THE BACK-END (server)

Rails Web Application



THE FRONT-END (clients)

Browser - JavaScriptiPhone - Objective-C










The "AJAX Head" Design Pattern





“e AJAX head design pattern forces the view and controller to work in isolation with the most minimal

coupling possible. Kind of like a web service.”

“...an implementation pattern that drastically modi"es common web client-server interactions in

order to bring them more closely in line with enterprise client-server interactions...”



http://voodootikigod.com/ajax-head-design-patternhttp://metaskills.net/2008/5/24/the-ajax-head-br-design-pattern

http://metaskills.net/2008/6/18/restful-ajax-with-forgery-protection

“e AJAX head design pattern forces the view and controller to work in isolation with the most minimal

coupling possible. Kind of like a web service.”

“...an implementation pattern that drastically modi"es common web client-server interactions in

order to bring them more closely in line with enterprise client-server interactions...”


http://voodootikigod.com/ajax-head-design-pattern

http://voodootikigod.com/ajax-head-design-pattern

http://metaskills.net/2008/5/24/the-ajax-head-br-design-pattern

http://metaskills.net/2008/5/24/the-ajax-head-br-design-pattern














1) AR Model2) Controller







1) AR Model2) Controller

1) CoreData Models2) External API


The Backend( part 1 - web app model )



3.0.0.beta4


3.0.0.beta4


3.0.0.beta4


Data-Interchange... JSON


Data-Interchange... JSONJSON (JavaScript Object Notation) is a lightweight format. It is easy for humans to read and write. It is easy for machines to parse and generate. JSON is a text format that is completely language independent but uses conventions that are familiar to programmers of the C-family

of languages, including C, C++, C#, Java, JavaScript, Perl, Python, and many others.


Data-Interchange... JSONJSON (JavaScript Object Notation) is a lightweight format. It is easy for humans to read and write. It is easy for machines to parse and generate. JSON is a text format that is completely language independent but uses conventions that are familiar to programmers of the C-family

of languages, including C, C++, C#, Java, JavaScript, Perl, Python, and many others.

http://www.json.org/


http://www.json.org

http://www.json.org

JSON in Ruby/Railsclass Object def to_json(options = nil) ActiveSupport::JSON.encode( self,options) end def as_json(options = nil) instance_values endend

class Foo attr_accessor :barend

f = Foo.newf.bar = 'batz'puts f.to_json # => {"bar":"batz"}


JSON in Ruby/RailsSpecifically in ActiveSupportrequire 'active_support/json' class Object

def to_json(options = nil) ActiveSupport::JSON.encode( self,options) end def as_json(options = nil) instance_values endend




JSON in Ruby/RailsSpecifically in ActiveSupportrequire 'active_support/json'

Object#to_json calls #as_json to coerce itself into something natively encodable like Hash, Integer, or String. Override #as_json instead of #to_json so you're JSON library agnostic.

class Object def to_json(options = nil) ActiveSupport::JSON.encode( self,options) end def as_json(options = nil) instance_values endend






ActiveSupport::JSON does all the work of defining #as_json on all core ruby objects. It also abstracts out decoding with hot swappable backends using ActiveSupport::JSON.backend = 'JSONGem'.







ActiveSupport::JSON does all the work of defining #as_json on all core ruby objects. It also abstracts out decoding with hot swappable backends using ActiveSupport::JSON.backend = 'JSONGem'.

In rails, with ActiveSupport, primitive ruby objects serialize their instance variables using another core extension Object#instance_values which returns a Hash of said ivars.





class Bookmark < ActiveRecord::Base JSON_ATTRS = ['id','owner_id','owner_type','url','name','position'] def as_json(options=nil) attributes.slice(*JSON_ATTRS) end end

JSON in ActiveRecord


JSON in ActiveRecordclass Bookmark < ActiveRecord::Base JSON_ATTRS = ['id','owner_id','owner_type','url','name','position'] def as_json(options=nil) attributes.slice(*JSON_ATTRS) end end

class Box < ActiveRecord::Base JSON_ATTRS = ['id','column_id','title','style','collapsed','position'] belongs_to :column has_many :bookmarks, :as => :owner, :order => 'position' acts_as_list :scope => :column_id def as_json(options=nil) attributes.slice(*JSON_ATTRS).merge(:bookmarks => bookmarks) end end


JSON in ActiveRecordclass User < ActiveRecord::Base JSON_ATTRS = ['id','email','uuid'].freeze has_one :inbox has_one :trashbox has_many :columns, :order => 'position' has_many :boxes, :through => :columns :order => 'columns.position, boxes.position' def as_json(options={}) attributes.slice(*JSON_ATTRS).merge( :inbox => inbox, :trashbox => trashbox, :columns => columns ) end end

>> Bookmark.find(27726).to_json=> "{\"position\":1,\"name\":\"Prototype Framework\",\"url\":\"http://prototypejs.org/\",\"owner_id\":7181,\"id\":27726,\"owner_type\":\"Box\"}"

>> Box.find(7181).to_json=> "{\"position\":4,\"title\":\"JavaScript Refs\",\"collapsed\":true,\"id\":7181,\"bookmarks\":[{\"position\":1,\"name\":\"Prototype Framework\",\"url\":\"http://prototypejs.org/\",\"owner_id\":7181,\"id\":27726,\"owner_type\":\"Box\"},{\"position\":2,\"name\":\"Scriptaclous Framework\",\"url\":\"http://script.aculo.us/\",\"owner_id\":7181,\"id\":27725,\"owner_type\":\"Box\"},{\"position\":3,\"name\":\"DevGuru (JavaScript)\",\"url\":\"http://www.devguru.com/technologies/javascript/home.asp\",\"owner_id\":7181,\"id\":27724,\"owner_type\":\"Box\"},{\"position\":4,\"name\":\"Dean Edwards Base.js\",\"url\":\"http://dean.edwards.name/weblog/2006/03/base/\",\"owner_id\":7181,\"id\":27723,\"owner_type\":\"Box\"}],\"column_id\":3538,\"style\":\"yellow_green\"}"


http://prototypejs.org




http://script.aculo.us

http://script.aculo.us

http://www.devguru.com/technologies/javascript/home.asp






http://dean.edwards.name/weblog/2006/03/base/




JSON in ActiveRecordDon’t Over think!

There Are Tools For Everything

Use Them


JSON in ActiveRecorddata = "{\"position\":1,\"name\":\"Prototype Framework\",\"url\":\"http://prototypejs.org/\",\"owner_id\":7181,\"id\":27726,\"owner_type\":\"Box\"}"

Bookmark.new.from_json(data)# => #<Bookmark id: nil, owner_id: nil, url: "http://prototypejs.org/", name: "Prototype Framework", created_at: nil, position: 0, owner_type: nil, updated_at: nil>

Don’t Over think!

There Are Tools For Everything

Use Them








The Backend( part 2 - web app controller )


Changing State


Changing State

CREATE READ UPDATE DELETE

DB

HTTP

INSERT SELECT UPDATE DELETE

POST GET PUT DELETE


Changing State


DB

HTTP


POST GET PUT DELETE


Changing State


DB

HTTP


POST GET PUT DELETE


Changing State


DB

HTTP


POST GET PUT DELETE

Representational State Transfer (REST)


ResourceRoutes


ResourceRoutes Homemarks::Application.routes.draw do |map|

resources :users resource :session resources :columns do collection { put :sort } member { delete :destroy_boxes } end resources :boxes do collection { put :sort } member do put :toggle_collapse put :colorize put :change_title end end end


ResourceRoutes

1 line 7 actions

Homemarks::Application.routes.draw do |map|



ResourceRoutes

1 line 7 actions

Collections & Members




ResourceRoutes

1 line 7 actions


Current User Scope Implied




ResourceRoutes

1 line 7 actions


Current User Scope Implied

You will PUT




Generated URLs$ rake routes CONTROLLER=users

GET /users(.:format) {:controller=>"users", :action=>"index"} POST /users(.:format) {:controller=>"users", :action=>"create"} GET /users/new(.:format) {:controller=>"users", :action=>"new"} GET /users/:id(.:format) {:controller=>"users", :action=>"show"} PUT /users/:id(.:format) {:controller=>"users", :action=>"update"} DELETE /users/:id(.:format) {:controller=>"users", :action=>"destroy"} GET /users/:id/edit(.:format) {:controller=>"users", :action=>"edit"}


class BoxesController < ApplicationController def create @box = current_user.columns.find(params[:column_id]).boxes.create! render :json => @box.id end def sort @box.insert_at params[:position] ; head :ok end def toggle_collapse @box.toggle(:collapsed).save! ; head :ok end end

class SessionsController < ApplicationController

def create self.current_user = User.authenticate params[:email], params[:password] logged_in? ? head(:ok) : render(:json => login_failures, :status => :unauthorized) end

end

RESTful Actions


Configure Mime TypesMime::Type.register_alias "text/html", :iphoneMime::Type.register_alias "text/html", :myiphoneapp_htmlMime::Type.register_alias "application/json", :myiphoneapp_json


class ApplicationController < ActionController::Base protect_from_forgery before_filter :set_myiphone_app_request after_filter :brand_response_headers protected

def myiphone_app_request? request.env["HTTP_USER_AGENT"] && request.env["HTTP_USER_AGENT"][/HomeMarks iPhone\/\d\.\d/] end def set_myiphone_app_request if myiphone_app_request? case request.format.symbol when :json then request.format = :myiphoneapp_json when :html then request.format = :myiphoneapp_html end end end

def brand_response_headers response.headers['X-Homemarks'] = '3.0' end

def set_iphone_request request.format = :iphone if iphone_request? end

def iphone_request? !myiphone_app_request? && request.env["HTTP_USER_AGENT"] && request.env["HTTP_USER_AGENT"][/(iPhone|iPod)/] end

def protect_against_forgery? myiphone_app_request? ? false : super end end

CriticalSupport


The Frontend( part 1 - core data model )


ObjC RESTful Resource











http://code.google.com/p/json-framework/http://allseeing-i.com/ASIHTTPRequest/


http://code.google.com/p/json-framework/




MyApp Singletons// Hard core singleton pattern.

[[UIApplication sharedApplication] openURL:...][[NSURLCredentialStorage sharedCredentialStorage] allCredentials]

// Simple class method singleton pattern.

[MyApp mom] // NSManagedObjectModel[MyApp moc] // NSManagedObjectContext[MyApp mocImport] // NSManagedObjectContext[MyApp psc] // NSPersistentStoreCoordinator

[MyApp userAgent] // NSString

[MyApp queue] // ASINetworkQueue[MyApp myUrlFor:action] // NSURL


@implementation MyApp

+ (NSManagedObjectModel *)mom { static NSManagedObjectModel *mom; if (mom == nil) { mom = [[NSManagedObjectModel mergedModelFromBundles:nil] retain]; } return mom;}

+ (NSManagedObjectContext *)moc { static NSManagedObjectContext *moc; if (moc == nil) { NSPersistentStoreCoordinator *psc = [self psc]; if (psc != nil) { moc = [[NSManagedObjectContext alloc] init]; [moc setPersistentStoreCoordinator:psc]; [moc setUndoManager:nil]; [moc setStalenessInterval:3.0]; } } return moc;}

+ (NSManagedObjectContext *)mocImport { // Do same thing above, make sure undo mgr is nil.}

+ (NSPersistentStoreCoordinator *)psc { static NSPersistentStoreCoordinator *psc; if (psc == nil) // Normal PSC code here. return psc;}

@end

CoreData


#pragma mark Network

+ (ASINetworkQueue *)queue { static ASINetworkQueue *queue; if (queue == nil) { queue = [[ASINetworkQueue queue] retain]; [queue go]; } return queue;}

+ (NSURL *)myUrlFor:(NSString *)action { return [NSURL URLWithString:[NSString stringWithFormat:@"http://%@/%@", [self siteHost], action]];}

#pragma mark Device/Bundle

// http://www.drobnik.com/touch/2009/07/determining-the-hardware-model/

+ (NSString *)userAgent { static NSString *ua; if (ua == nil) { NSString *appVersion = [self appVersion]; NSString *platformString = [[UIDevice currentDevice] platformString]; NSString *systemVersion = [UIDevice currentDevice].systemVersion; ua = [[NSString stringWithFormat:@"HomeMarks iPhone/%@ (%@; %@)", appVersion,platformString,systemVersion] retain]; } return ua;}

Misc


http://www.drobnik.com/touch/2009/07/determining-the-hardware-model/

http://www.drobnik.com/touch/2009/07/determining-the-hardware-model/

Taming Core Data


Taming Core DataSet the class for all your models and generate classes!



Subclass NSManagedObject to your name space.



Subclass NSManagedObject to your name space.

Make all your generated model classes subclass from above.


Less Wizardry@implementation MyManagedObject

#pragma mark Reflection

+ (NSEntityDescription *)entity { return [[[MyApp mom] entitiesByName] objectForKey:NSStringFromClass(self)];}

+ (NSFetchRequest *)fetchRequestForEntity { NSFetchRequest *fetchRequest = [[[NSFetchRequest alloc] init] autorelease]; [fetchRequest setEntity:[self entity]]; return fetchRequest;}

@end


Less Wizardry@implementation MyManagedObject

#pragma mark Finders

+ (MyManagedObject *)objectWithID:(NSString *)anId { if (anId == nil) return nil; NSURL *myURL = [NSURL URLWithString:anId]; NSManagedObjectID *myId = [[MyApp psc] managedObjectIDForURIRepresentation:myURL]; return (MyManagedObject *)[[MyApp moc] objectWithID:myId];}

- (NSString *)objectIDURLString { return [[[self objectID] URIRepresentation] absoluteString];}

@end

x-coredata://EB8922D9- DC06-4256-A21B-DFFD47D7E6DA/MyEntity/p3


Create/Import Helpers@implementation MyManagedObject

#pragma mark Creators

+ (id)newObject:(NSDictionary *)attributes { return [self newObject:attributes inContext:nil];}

+ (id)newObject:(NSDictionary *)attributes inContext:(NSManagedObjectContext *)context { NSManagedObjectContext *moc = context ? context : [MyApp moc]; id mobj = [[self alloc] initWithEntity:[self entity] insertIntoManagedObjectContext:moc]; if (attributes != nil) { for (id key in attributes) { [mobj setValue:[attributes valueForKey:key] forKey:key]; } } return mobj;}

@end


The Frontend( part 2 - external api )


// Assumes MyRequest & MyFormRequest subclasses of // ASIHTTPRequest and ASIFormDataRequest (minimal use).

@implementation ASIHTTPRequest (MyAdditions)

#pragma mark Designated Initializer

- (id)initWithMyURL:(NSURL *)newURL { self = [self initWithURL:newURL]; self.username = [MyApp userEmail]; self.password = [MyApp userPass]; self.useCookiePersistance = NO; self.useSessionPersistance = NO; self.useKeychainPersistance = NO; self.allowCompressedResponse = YES; self.shouldRedirect = NO; self.requestMethod = @"GET"; self.delegate = [MyApp appDelegate]; self.didFinishSelector = @selector(globalRequestFinished:); self.didFailSelector = @selector(globalRequestFailed:); [self addRequestHeader:@"HTTP_ACCEPT" value:@"application/json"]; [self addRequestHeader:@"User-Agent" value:[MyApp userAgent]]; return self;}

#pragma mark Utility

+ (NSURL *)urlFor:(NSString *)action { NSURL *url = [NSURL URLWithString:[NSString stringWithFormat:@"http://%@/%@",[MyApp siteHost],action]]; return url;}

+ (MyRequest *)myRequestFor:(NSString *)action { MyRequest *request = [[[MyRequest alloc] initWithMyURL:[self urlFor:action]] autorelease]; return request;}

+ (MyFormRequest *)myFormRequestFor:(NSString *)action withParams:(NSDictionary *)params { MyFormRequest *request = [[[MyFormRequest alloc] initWithMyURL:[self urlFor:action]] autorelease]; if (params != nil) { for (id key in params) { [request setPostValue:[params objectForKey:key] forKey:key]; } } request.requestMethod = @"POST"; return request;}

+ (MyFormRequest *)myPutRequestFor:(NSString *)action withParams:(NSDictionary *)params { MyFormRequest *request = [self myFormRequestFor:action withParams:params]; request.requestMethod = @"PUT"; return request;}

+ (MyRequest *)myDeleteRequestFor:(NSString *)action { MyRequest *request = [self myRequestFor:action]; request.requestMethod = @"DELETE"; return request;}

@end

Customize To Your API


// Assumes MyRequest & MyFormRequest subclasses of // ASIHTTPRequest and ASIFormDataRequest (minimal use).


#pragma mark Designated Initializer

- (id)initWithMyURL:(NSURL *)newURL { self = [self initWithURL:newURL]; self.username = [MyApp userEmail]; self.password = [MyApp userPass]; self.useCookiePersistance = NO; self.useSessionPersistance = NO; self.useKeychainPersistance = NO; self.allowCompressedResponse = YES; self.shouldRedirect = NO; self.requestMethod = @"GET"; self.delegate = [MyApp appDelegate]; self.didFinishSelector = @selector(globalRequestFinished:); self.didFailSelector = @selector(globalRequestFailed:); [self addRequestHeader:@"HTTP_ACCEPT" value:@"application/json"]; [self addRequestHeader:@"User-Agent" value:[MyApp userAgent]]; return self;}

#pragma mark Utility

+ (NSURL *)urlFor:(NSString *)action { NSURL *url = [NSURL URLWithString:[NSString stringWithFormat:@"http://%@/%@",[MyApp siteHost],action]]; return url;}

+ (MyRequest *)myRequestFor:(NSString *)action { MyRequest *request = [[[MyRequest alloc] initWithMyURL:[self urlFor:action]] autorelease]; return request;}

+ (MyFormRequest *)myFormRequestFor:(NSString *)action withParams:(NSDictionary *)params { MyFormRequest *request = [[[MyFormRequest alloc] initWithMyURL:[self urlFor:action]] autorelease]; if (params != nil) { for (id key in params) { [request setPostValue:[params objectForKey:key] forKey:key]; } } request.requestMethod = @"POST"; return request;}

+ (MyFormRequest *)myPutRequestFor:(NSString *)action withParams:(NSDictionary *)params { MyFormRequest *request = [self myFormRequestFor:action withParams:params]; request.requestMethod = @"PUT"; return request;}

+ (MyRequest *)myDeleteRequestFor:(NSString *)action { MyRequest *request = [self myRequestFor:action]; request.requestMethod = @"DELETE"; return request;}

@end


Import On Launch@implementation ASIHTTPRequest (MyAdditions)

+ (void)getUserDataFor:(id)aDelegate { MyRequest *request = [self myRequestFor:@"myhome.json"]; request.delegate = aDelegate; request.didFinishSelector = @selector(didGetUserData:); request.didFailSelector = @selector(didNotGetUserData:); if ([MyApp userEtag] != nil) { [request addRequestHeader:@"If-None-Match" value:[MyApp userEtag]]; } [[MyApp queue] addOperation:request];}

@end


Import On Launch@implementation ASIHTTPRequest (MyAdditions)

+ (void)getUserDataFor:(id)aDelegate { MyRequest *request = [self myRequestFor:@"myhome.json"]; request.delegate = aDelegate; request.didFinishSelector = @selector(didGetUserData:); request.didFailSelector = @selector(didNotGetUserData:); if ([MyApp userEtag] != nil) { [request addRequestHeader:@"If-None-Match" value:[MyApp userEtag]]; } [[MyApp queue] addOperation:request];}

@end


Import On Launch

- (void)didGetUserData:(MyRequest *)request { if ([request isNotModified]) { [[MyApp appDelegate] didGetUserData]; return; } else { [MyApp setUserEtag:[[request responseHeaders] objectForKey:@"Etag"]]; [self importUserData:[request responseJSON]]; [[MyApp appDelegate] didGetUserData]; }}

The Controller (request delegate)


Import On Launch




Import On Launch



"GET /myhome.json HTTP/1.1" 200 5115 "-" "MyApp iPhone/1.0 (iPhone 3GS; 3.1.3)""GET /myhome.json HTTP/1.1" 304 - "-" "MyApp iPhone/1.0 (iPhone 3GS; 3.1.3)"

Apache Logs


Import On Launch



"GET /myhome.json HTTP/1.1" 200 5115 "-" "MyApp iPhone/1.0 (iPhone 3GS; 3.1.3)""GET /myhome.json HTTP/1.1" 304 - "-" "MyApp iPhone/1.0 (iPhone 3GS; 3.1.3)"

Apache Logs


Import On Launch


Import On Launchclass UsersController < ApplicationController

def home if stale?(:etag => current_user) respond_to do |format| format.html { render :layout => 'application' } format.hmiphoneapp_json { render :json => current_user } end end end end


Import On Launchclass UsersController < ApplicationController

def home if stale?(:etag => current_user) respond_to do |format| format.html { render :layout => 'application' } format.hmiphoneapp_json { render :json => current_user } end end end end

@implementation MyAppDelegate

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions { [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(clearEtag:) name:NSManagedObjectContextDidSaveNotification object:[HMApp moc]]; //...}

- (void)clearEtag:(NSNotification *)notification { [MyApp removeUserEtag];}

@end


@implementation MyManagedObject

#pragma mark MyRequest Handling

- (void)createRemoteFinished:(MyRequest *)request { if ([request isSuccessfulMyAppText]) { NSInteger *remoteInt = [[request responseString] integerValue]; NSNumber *remoteId = [NSNumber numberWithInteger:remoteInt]; [self setValue:remoteId forKey:@"remoteId"]; [self save]; }}

@end

@implementation MyRequest

+ (void)columnCreate:(HMColumn *)column { MyFormRequest *request = [self myFormRequestFor:@"columns" withParams:nil]; request.delegate = column; request.didFinishSelector = @selector(createRemoteFinished:); request.didFailSelector = @selector(createRemoteFailed:); [[HMApp queue] addOperation:request];}

@end

Models Drive





@end

@implementation HMColumn

+ (void)createRemote { HMColumn *newColumn = [[self class] newObject:nil]; //... [newColumn save]; [MyRequest columnCreate:newColumn]; [newColumn release];}

@end



@end

Models Drive





@end

@implementation HMColumn

+ (void)createRemote { HMColumn *newColumn = [[self class] newObject:nil]; //... [newColumn save]; [MyRequest columnCreate:newColumn]; [newColumn release];}

@end



@end


@implementation HMBox

- (void)colorize { if ([[self changedValues] hasKey:@"style"] && [self save]) [HMRequest boxColorize:self];}

@end


+ (NSString *)box:(HMBox *)box action:(NSString *)action { return [NSString stringWithFormat:@"boxes/%@/%@",[[box remoteId] stringValue],action];}

+ (void)boxColorize:(HMBox *)box { NSString *action = [self box:box action:@"colorize"]; NSDictionary *params = [NSDictionary dictionaryWithObjectsAndKeys:box.style,@"color",nil]; MyFormRequest *request = [self myPutRequestFor:action withParams:params]; [[MyApp queue] addOperation:request];}

@end

Models Drive (box example)


The End( liked my talk – buy my app - write a review )


Technology

Synchronizing Core Data With Rails