Synchronizing Core Data With Rails

Synchronizing Core
Data With Rails
Ken Collins
metaskills.net

Wednesday, July 14, 2010

Why Write Web
Applications For The
Web Only?


Why Write Web
Web <html> Only?


Why Write Web
Web <html> Only?
THE BACK-END (server)

Rails Web Application


Why Write Web
Web <html> Only?
THE BACK-END (server) THE FRONT-END (clients)

Rails Web Application Browser - JavaScript
iPhone - Objective-C


The "AJAX Head"
Design Pattern


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...”


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-pattern
http://metaskills.net/2008/5/24/the-ajax-head-br-design-pattern
http://metaskills.net/2008/6/18/restful-ajax-with-forgery-protection


Why Write Web
Web <html> Only?

1) AR Model
2) Controller


Why Write Web
Web <html> Only?

1) AR Model 1) CoreData Models
2) Controller 2) External API


The Backend
( part 1 - web app model )


.0.b e t a4
3.0


Data-Interchange... JSON


JSON (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.


JSON (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/


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

class Foo
attr_accessor :bar
end

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


JSON in Ruby/Rails
Specifically in ActiveSupport
require 'active_support/json' class Object
ActiveSupport::JSON.encode(
self,options)
end
def as_json(options = nil)
instance_values
end
end

class Foo
attr_accessor :bar
end

f = Foo.new
f.bar = 'batz'


JSON in Ruby/Rails
Object#to_json calls #as_json to ActiveSupport::JSON.encode(
coerce itself into something natively self,options)
encodable like Hash, Integer, or String. end
Override #as_json instead of #to_json def as_json(options = nil)
so you're JSON library agnostic. instance_values
end
end

class Foo
attr_accessor :bar
end

f = Foo.new
f.bar = 'batz'


JSON in Ruby/Rails
end
ActiveSupport::JSON does all the work end
of defining #as_json on all core ruby
objects. It also abstracts out decoding class Foo
with hot swappable backends using attr_accessor :bar
ActiveSupport::JSON.backend = end
JSONGem'.
'
f = Foo.new
f.bar = 'batz'


JSON in Ruby/Rails
end
ActiveSupport::JSON does all the work end
of defining #as_json on all core ruby
objects. It also abstracts out decoding class Foo
with hot swappable backends using attr_accessor :bar
ActiveSupport::JSON.backend = end
JSONGem'.
'
f = Foo.new
In rails, with ActiveSupport, primitive f.bar = 'batz'
ruby objects serialize their instance puts f.to_json # => {"bar":"batz"}
variables using another core extension
Object#instance_values which returns
a Hash of said ivars.


JSON in ActiveRecord
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


class Bookmark < ActiveRecord::Base

JSON_ATTRS = ['id','owner_id','owner_type','url','name','position']

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

attributes.slice(*JSON_ATTRS).merge(:bookmarks => bookmarks)
end

end


>> Bookmark.find(27726).to_json
=> "{"position 1,
": "name "Prototype
": class User < ActiveRecord::Base
Framework ", "url "http:/
": /prototypejs.org/",
"owner_id ":7181, ":27726,
"id "owner_type": JSON_ATTRS = ['id','email','uuid'].freeze
"Box "}"
has_one :inbox
>> Box.find(7181).to_json has_one :trashbox
=> "{ "position ":4, "title "JavaScript Refs
": ", has_many :columns, :order => 'position'
"collapsed ":true, ":7181,
"id "bookmarks ": has_many :boxes, :through => :columns
[{ "position 1,": "name "Prototype Framework
": :order => 'columns.position,

", "url "http:/
": /prototypejs.org/ ", "owner_id ":
boxes.position'
7181, ":27726,
"id "owner_type "Box ": "},
{ "position ":2, "name "Scriptaclous
":
Framework ", "url "http:/
": /script.aculo.us/ ", def as_json(options={})
"owner_id ":7181, ":27725,
"id "owner_type ": attributes.slice(*JSON_ATTRS).merge(
"Box "position
"},{ ":3, "name "DevGuru
": :inbox => inbox,
(JavaScript) ", "url "http:/
": / :trashbox => trashbox,
www.devguru.com/technologies/javascript/ :columns => columns
home.asp ", "owner_id ":7181, ":
"id )
27724, "owner_type "Box "position
": "},{ ": end
4, "name "Dean Edwards Base.js
": ", "url ":
"http:/ /dean.edwards.name/weblog/ end
2006/03/base/ ", "owner_id ":7181, ": "id
27723, "owner_type "Box ": "}], "column_id ":
3538, "style "yellow_green
": "}"


Don’t Over think!

There Are Tools For
Everything

Use Them


Don’t Over think! data = "{"position":
1,"name":"Prototype
Framework","url":
There Are Tools For "http://prototypejs.org/",
"owner_id":7181,"id":
Everything 27726,"owner_type":"Box
"}"

Use Them 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>


The Backend
( part 2 - web app controller )


Changing State


Changing State

CREATE READ UPDATE DELETE

DB INSERT SELECT UPDATE DELETE

HTTP POST GET PUT DELETE


Changing State

CREATE READ UPDATE DELETE

DB INSERT SELECT UPDATE DELETE

HTTP POST GET PUT DELETE

Representational State Transfer (REST)


Resource
Routes


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

resources :users
resource :session

resources :columns do
collection { put :sort }
member { delete :destroy_boxes }
end

resources :boxes do
member do
put :toggle_collapse
put :colorize
put :change_title
end
end

end


Resource

resources :users
resource :session

1 line 7 actions resources :columns do
end

resources :boxes do
member do
put :colorize
put :change_title
end
end

end


Resource

resources :users
resource :session

Collections & end
Members resources :boxes do
member do
put :colorize
put :change_title
end
end

end


Resource

resources :users
resource :session

Collections & end
member do
Current User put :toggle_collapse
put :colorize
Scope Implied put :change_title
end
end

end


Resource

resources :users
resource :session

Collections & end
member do
Current User put :toggle_collapse
put :colorize
Scope Implied put :change_title
end
end
You will PUT
end


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"}


RESTful Actions
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


Configure Mime Types
Mime::Type.register_alias "text/html", :iphone
Mime::Type.register_alias "text/html", :myiphoneapp_html
Mime::Type.register_alias "application/json", :myiphoneapp_json


class ApplicationController < ActionController::Base

Critical
protect_from_forgery
before_filter :set_myiphone_app_request
after_filter :brand_response_headers

protected

Support def myiphone_app_request?
request.env["HTTP_USER_AGENT"] &&

end
request.env["HTTP_USER_AGENT"][/HomeMarks iPhone/d.d/]

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


The Frontend
( part 1 - core data model )


ObjC RESTful Resource


ObjC RESTful Resource

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


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


Core
@implementation MyApp

+ (NSManagedObjectModel *)mom {
static NSManagedObjectModel *mom;
if (mom == nil) {

Data
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


#pragma mark Network

+ (ASINetworkQueue *)queue {

Misc
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;
}


Taming Core Data


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


Taming Core Data
your models and
generate classes!

Subclass
NSManagedObject
to your name space.


Taming Core Data
your models and
generate classes!

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

#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

#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 )


Customize To Your 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 {

}

#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

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


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

Apache Logs
"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)"


Import On Launch


Import On Launch
class 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 Launch
class 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


Models Drive

#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


Models Drive

#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 HMColumn

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

@end


@implementation HMColumn

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

@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 (box example)
@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


The End
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Synchronizing Core Data With Rails

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