REST Services with Sinatra and iOS

What is REST?

Wikipedia: "Representational state transfer (REST) is a style of software architecture for distributed hypermedia systems such as the World Wide Web."

Represenational State Transfer (Roy Felding): "REST is a coordinated set of architectural constraints that attempts to minimize latency and network communication, while at the same time maximizing the independence and scalability of component implementations."

REST is a set of Constraints

• Client-Server - data stays on server
• Stateless
  • no client context on the server
  • don't set 'current' anything
• Cacheable
• Layered system
• Code on demand
• Uniform Interface (through URIs)

REST Uses Universal Resource Indicators

• Client uses URI to request a representation of a resource
• The exact resource is indicated by the URI itself, not the request body
• If you are building a REST service, your URLs are your user interface.
• Good
  • GET /tasks/1
  • POST /projects/1/tasks
• Bad
  • POST /getTask/
  • GET /addTask?title=5

REST Communicates With Resources

• POST (create)
  • 201 (Created)
  • 422 (Unprocessable Entity)
• GET, PUT, DELETE, PATCH
  • 200 (OK)
  • 404 (NOT FOUND)

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The App

• Todos application
• Manage tasks

The URIs (The UI)

get '/tasks' do
  Task.to_json
end 

post '/tasks' do
  pp @data
  @task = Task.new @data 
  if @task.valid?
    @task.save
    @task.to_json
  else
    status 422 
    @task.errors_hash.to_json
  end 
end 

get '/tasks/:id' do
  @task = Task.find(params)
  raise Sinatra::NotFound unless @task
  @task.to_json
end 

put '/tasks/:id' do
  @task = Task.find :id => params[:id]
  raise Sinatra::NotFound unless @task
  @task.update @data
  @task.to_json
end 

delete '/tasks/:id' do
  @task = Task.find :id => params[:id]
  raise Sinatra::NotFound unless @task
  @task.destroy
  @task.to_json
end

The Client

• RestKit
• Task
• Manager

Services

  -(void)createObject:(NSObject *)theObject withMapping:(RKObjectMapping *)mapping{
    self.target = theObject;
    [[LBDataManager sharedManager].rkObjectManager 
     postObject:theObject mapResponseWith:mapping delegate:self];
  }

  -(void)objectLoader:(RKObjectLoader *)objectLoader didFailWithError:(NSError *)error{
    [self.delegate objectDidFailCreation:error];
    [super objectLoader:objectLoader didFailWithError:error];
  }

  -(void)objectLoader:(RKObjectLoader *)objectLoader didLoadObjects:(NSArray *)loadedObjects{
    [self.delegate didCreateObject:[loadedObjects objectAtIndex:0]];
    [super objectLoader:objectLoader didLoadObjects:loadedObjects];
  }

Create a task

-(void)saveTask{
  [[LBCreateObjectService serviceWithDelegate:self] 
   createObject:self.task 
   withMapping:[Task serializationMapping]];
}

-(void)didCreateObject:(NSObject *)theObject{
  [self.delegate taskFormView:self didSaveTask:self.task];
}

-(void)objectDidFailCreation:(NSError *)error{
  [[[UIAlertView alloc] initWithTitle:@"Error" 
                              message:error.localizedDescription 
                             delegate:self 
                    cancelButtonTitle:@"Ok" 
                    otherButtonTitles: nil] show];
}

Read tasks

-(void)loadData{
  [[LBReadObjectService serviceWithDelegate:self] readObjectsForMapping:[Task mapping] atPath:@"tasks"];
}

-(void)readObjectService:(LBReadObjectService *)service didReadObjects:(NSArray *)objects{
  self.tasks = objects; 
  [self.tableView reloadData];
}

Update a task

-(void)updateTask{
  [[LBUpdateObjectService serviceWithDelegate:self] 
   updateObject:self.task
   withMapping:[Task serializationMapping]];
}

-(void)didUpdateObject:(NSObject *)target{
  [self.delegate taskFormView:self didSaveTask:self.task];
}

Destroy a task

-(void)deleteTask{
  [[LBDeleteObjectService serviceWithDelegate:self] deleteObject:self.task];
}
-(void)didDeleteObject:(NSObject *)target{
  [self.navigationController popViewControllerAnimated:YES];
}

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Questions/Discussion

Handling relationships