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• How to remove an observer for NSNotification in a UIView?

  - by sudo rm -rf

  Hello! I've added an observer in a custom UIView I've created under initWithFrame:. [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(updateZipFromLocation:) name:@"zipFoundFromLocation" object:nil]; The problem is, this view is a subview. When the view is loaded again, it calls the initWithFrame message again, thus adding two observers and so on. How can I remove the observer when the view is going to disappear? Since it is a UIView, it says that viewWillDisappear:(BOOL)animated is not a valid method. Any ideas?

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• Improve this snippet from a prototype class

  - by seengee

  This is a snippet from a prototype class i am putting together. The scoping workaround feels a little hacky to me, can it be improved or done differently? var myClass = Class.create({ initialize: function() { $('formid').getElements().each(function(el){ $(el).observe("blur", function(){ this.validateEl(el); }.bind(this,el)); },this); }, validateEl: function(el){ // validate $(el) in here... } }); Also, it seems to me that i could be doing something like this for the event observers: $('formid').getElements().invoke("observe","blur" ... Not sure how i would pass the element references in though?

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• why Observable snapshot observer vector

  - by han14466

  In Observable's notifyObservers method, why does the coder use arrLocal = obs.toArray();? Why does not coder iterate vector directly? Thanks public void notifyObservers(Object arg) { Object[] arrLocal; synchronized (this) { /* We don't want the Observer doing callbacks into * arbitrary code while holding its own Monitor. * The code where we extract each Observable from * the Vector and store the state of the Observer * needs synchronization, but notifying observers * does not (should not). The worst result of any * potential race-condition here is that: * 1) a newly-added Observer will miss a * notification in progress * 2) a recently unregistered Observer will be * wrongly notified when it doesn't care */ if (!changed) return; arrLocal = obs.toArray(); clearChanged(); } for (int i = arrLocal.length-1; i>=0; i--) ((Observer)arrLocal[i]).update(this, arg); }

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• Invalidating UITableView contents

  - by Roman

  I have an application with several UITableViewControllers. Now, the user is allowed to change "Data source". In that case I need to invalidate (reset) data in the relevant UITableViews. I figured out, that I can use NSNotificationCenter and add these controllers as observers to events which will be generated when the data source changes. The question is, how do I reset the underlying tables? I can, of course, set some boolean flag, and call UITableView:reloadData in viewWillAppear or viewDidAppear, but I was wondering, if there's a cleaner way of doing it. Or perhaps I'm completely missing the point, and I don't need NSNotificationCenter altogether. Thank you very much in advance.

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• I'm very new to C# and reading about attributes, is there a keypress attribute?

  - by akevit

  I'm coming from intermediate java level and I wanted to spend some time tonight learning C#, partly because a game I used to play is now free to play (Asheron's Call) and when I used to play I had always wanted to write a plugin for Decal but 10 years ago I didn't know nearly enough to do anything. Anyways most of that won't mean much to anyone, but what I essentially want to do is something along the lines of (psuedo code): [KeyPressEvent("KeyPressed")] private void KeyPressed(object sender, KeyPressEventArgs args) { if (args.KeyPressed == VK_K) { // Do stuff } } If I'm not providing enough information or if my description of what I want to do is a little off base let me know. Most plugins for this are written in VB6, but in the past few years Decal has upgraded to .NET 3.5 support so I can use things up until there; a lot of the VB6 stuff uses event subscriptions (e.g. Core.EchoFilter.ServerDispatch += EchoFilter_ServerDispatch;) My C# vernacular is not up to part, but on that notion I haven't done a whole lot of Java projects that related to events (or Observers as I believe they're referred to as).

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• Designing for an algorithm that reports progress

  - by Stefano Borini

  I have an iterative algorithm and I want to print the progress. However, I may also want it not to print any information, or to print it in a different way, or do other logic. In an object oriented language, I would perform the following solutions: Solution 1: virtual method have the algorithm class MyAlgoClass which implements the algo. The class also implements a virtual reportIteration(iterInfo) method which is empty and can be reimplemented. Subclass the MyAlgoClass and override reportIteration so that it does what it needs to do. This solution allows you to carry additional information (for example, the file unit) in the reimplemented class. I don't like this method because it clumps together two functionalities that may be unrelated, but in GUI apps it may be ok. Solution 2: observer pattern the algorithm class has a register(Observer) method, keeps a list of the registered observers and takes care of calling notify() on each of them. Observer::notify() needs a way to get the information from the Subject, so it either has two parameters, one with the Subject and the other with the data the Subject may pass, or just the Subject and the Observer is now in charge of querying it to fetch the relevant information. Solution 3: callbacks I tend to see the callback method as a lightweight observer. Instead of passing an object, you pass a callback, which may be a plain function, but also an instance method in those languages that allow it (for example, in python you can because passing an instance method will remain bound to the instance). C++ however does not allow it, because if you pass a pointer to an instance method, this will not be defined. Please correct me on this regard, my C++ is quite old. The problem with callbacks is that generally you have to pass them together with the data you want the callback to be invoked with. Callbacks don't store state, so you have to pass both the callback and the state to the Subject in order to find it at callback execution, together with any additional data the Subject may provide about the event is reporting. Question My question is relative to the fact that I need to implement the opening problem in a language that is not object oriented, namely Fortran 95, and I am fighting with my usual reasoning which is based on python assumptions and style. I think that in Fortran the concept is similar to C, with the additional trouble that in C you can store a function pointer, while in Fortran 95 you can only pass it around. Do you have any comments, suggestions, tips, and quirks on this regard (in C, C++, Fortran and python, but also in any other language, so to have a comparison of language features that can be exploited on this regard) on how to design for an algorithm that must report progress to some external entity, using state from both the algorithm and the external entity ?

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• What is a good strategy for binding view objects to model objects in C++?

  - by B.J.

  Imagine I have a rich data model that is represented by a hierarchy of objects. I also have a view hierarchy with views that can extract required data from model objects and display the data (and allow the user to manipulate the data). Actually, there could be multiple view hierarchies that can represent and manipulate the model (e.g. an overview-detail view and a direct manipulation view). My current approach for this is for the controller layer to store a reference to the underlying model object in the View object. The view object can then get the current data from the model for display, and can send the model object messages to update the data. View objects are effectively observers of the model objects and the model objects broadcast notifications when properties change. This approach allows all the views to update simultaneously when any view changes the model. Implemented carefully, this all works. However, it does require a lot of work to ensure that no view or model objects hold any stale references to model objects. The user can delete model objects or sub-hierarchies of the model at any time. Ensuring that all the view objects that hold references to the model objects that have been deleted is time-consuming and difficult. It feels like the approach I have been taking is not especially clean; while I don't want to have to have explicit code in the controller layer for mediating the communication between the views and the model, it seems like there must be a better (implicit) approach for establishing bindings between the view and the model and between related model objects. In particular, I am looking for an approach (in C++) that understands two key points: There is a many to one relationship between view and model objects If the underlying model object is destroyed, all the dependent view objects must be cleaned up so that no stale references exist While shared_ptr and weak_ptr can be used to manage the lifetimes of the underlying model objects and allows for weak references from the view to the model, they don't provide for notification of the destruction of the underlying object (they do in the sense that the use of a stale weak_ptr allows for notification), but I need an approach that notifies the dependent objects that their weak reference is going away. Can anyone suggest a good strategy to manage this?

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• Beware when using .NET's named pipes in a windows forms application

  - by FransBouma

  Yesterday a user of our .net ORM Profiler tool reported that he couldn't get the snapshot recording from code feature working in a windows forms application. Snapshot recording in code means you start recording profile data from within the profiled application, and after you're done you save the snapshot as a file which you can open in the profiler UI. When using a console application it worked, but when a windows forms application was used, the snapshot was always empty: nothing was recorded. Obviously, I wondered why that was, and debugged a little. Here's an example piece of code to record the snapshot. This piece of code works OK in a console application, but results in an empty snapshot in a windows forms application: var snapshot = new Snapshot(); snapshot.Record(); using(var ctx = new ORMProfilerTestDataContext()) { var customers = ctx.Customers.Where(c => c.Country == "USA").ToList(); } InterceptorCore.Flush(); snapshot.Stop(); string error=string.Empty; if(!snapshot.IsEmpty) { snapshot.SaveToFile(@"c:\temp\generatortest\test2\blaat.opsnapshot", out error); } if(!string.IsNullOrEmpty(error)) { Console.WriteLine("Save error: {0}", error); } (the Console.WriteLine doesn't do anything in a windows forms application, but you get the idea). ORM Profiler uses named pipes: the interceptor (referenced and initialized in your application, the application to profile) sends data over the named pipe to a listener, which when receiving a piece of data begins reading it, asynchronically, and when properly read, it will signal observers that new data has arrived so they can store it in a repository. In this case, the snapshot will be the observer and will store the data in its own repository. The reason the above code doesn't work in windows forms is because windows forms is a wrapper around Win32 and its WM_* message based system. Named pipes in .NET are wrappers around Windows named pipes which also work with WM_* messages. Even though we use BeginRead() on the named pipe (which spawns a thread to read the data from the named pipe), nothing is received by the named pipe in the windows forms application, because it doesn't handle the WM_* messages in its message queue till after the method is over, as the message pump of a windows forms application is handled by the only thread of the windows forms application, so it will handle WM_* messages when the application idles. The fix is easy though: add Application.DoEvents(); right before snapshot.Stop(). Application.DoEvents() forces the windows forms application to process all WM_* messages in its message queue at that moment: all messages for the named pipe are then handled, the .NET code of the named pipe wrapper will react on that and the whole process will complete as if nothing happened. It's not that simple to just say 'why didn't you use a worker thread to create the snapshot here?', because a thread doesn't get its own message pump: the messages would still be posted to the window's message pump. A hidden form would create its own message pump, so the additional thread should also create a window to get the WM_* messages of the named pipe posted to a different message pump than the one of the main window. This WM_* messages pain is not something you want to be confronted with when using .NET and its libraries. Unfortunately, the way they're implemented, a lot of APIs are leaky abstractions, they bleed the characteristics of the OS objects they hide away through to the .NET code. Be aware of that fact when using them :)

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• SQL – Business Intelligence: Derive Data or Information?

  - by Pinal Dave

  We all know the value of information in our lives. Whether it’s a personal decision or a business initiated one, people need it. But the question is: who is to make the distinction between data and information? We all come across a whole lot of data daily, that may be significant or not. We filter what’s required and forget about the rest. Information is filtered and distilled data. Filtering and distillation can also alter its actual meaning and natural state. Therefore, in this blog we discover some ways to ensure that we’re using business intelligence derived from the right information for making critical management decisions. Four key questions managers must ask themselves before making a decision: 1. Am I working with data or information? 2. What is it’s context? 3. How recent is it? 4. How was it derived or what is the source? The first question is probably the most important. You must know what you’re dealing with here. If you see use of adjectives and conclusions drawn, it’s information. Not raw data. You very next concern must be whether this is guised to present a particular viewpoint or perspective. It makes a lot of difference if you take a decision based on someone’s propaganda to distort real facts. Therefore, the context and the intentions of the distillation process must be clear to you. The next consideration is whether data is recent enough to hold any value. Since it has a very short shelf life, you must ensure that its context and value is not lost out of time. The last and the most important consideration is how was it derived in the first place. The observer effect is what calls the shots here. The source can change the context to a great extent if the collection methodology  and purpose is not clear. Gathering intelligence for decision making requires users to be keen observers and not take the information provided on its face value alone. These probing questions will allow you to make sure that you’re working with clean and accurate data devoid of any influence or manipulations. Only then can you be sure of deriving true business intelligence for your organization. BI technology is also a great way to ensure accuracy of reports. SQL BI Platform  provides advanced tools and techniques for all your BI needs and concerns. Koenig Solutions offers this course along with a host of other Business Intelligence and IT courses on all latest technologies available in the market today. Reference: Pinal Dave (http://blog.sqlauthority.com) Filed under: PostADay, SQL, SQL Authority, SQL Query, SQL Server, SQL Tips and Tricks, T SQL

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• On The Road with the HR Community

  - by Kathryn Perry

  A guest post by Steve Boese, Director, Talent Strategy, Oracle One of the best ways to connect with and to get a feel for what is on the minds of Human Resources leaders is to get out of the office and hit the road. I’ve had the great honor to attend and/or present at a number of events recently, including the massive SHRM Annual Conference, the HR Florida Conference, and Taleo World in Chicago. These events, and many others, offer solution providers, talent management professionals, business leaders, and even more casual observers of the Human Resources field with tremendous opportunities to connect, to share information, and to learn from each other. Attending the conferences also give people a sense of how they can improve and enhance their skills and knowledge, learn about the latest workforce technologies, and bring new and innovative ideas back to their organizations. And sure, the parties and conference swag can be pretty nice as well! If you attend a few of these industry events, one of the most beneficial by-products that you can emerge with -- whether you are on the front lines in HR at your organization, or as we are at Oracle, in the business of developing and delivering innovative and impactful technology solutions to our customers -- is to get a larger sense of the big ideas and major trends, concerns, and challenges facing organizations all across the landscape, and to be able to better understand how your strategies and solutions can be improved with this greater perspective. So what are HR folks discussing and debating? What questions and problems keep them up at night? What are the bloggers and large community of HR social media enthusiasts buzzing about? From my perspective some of the common themes you see over and again across the HR community break down (broadly), into three main areas: Talent attraction - How can we locate, attract, recruit, and hire the best talent possible? What new strategies, approaches, and technologies can help us in this critically important area? What role do external social networks like LinkedIn, Facebook, and Twitter play in the increasingly competitive search for talent? Talent Retention - How can we make sure to keep that talent on our team? What engagement, development, recognition, and compensation tools can help us in this regard? How can we continue, (or become), an employer of choice? What is our unique and compelling employer value proposition? Talent Empowerment - How can we put our employees in the best position to succeed? What can we do to better align our talent with the organization’s mission and goals, while simultaneously providing the best and most driven to succeed individuals a clear path to achieve their career goals and aspirations? How can new technologies, particularly social and collaboration tools help in this area? While these are the ‘big themes’ that I know I have seen this year, certainly they are not really new, nor are they likely to fundamentally change in the next year or two. I think the reason is that at the core of any successful enterprise is a collection of smart, interested, engaged, challenged, and empowered group of people. And that was likely the case 10 or 20 years ago, and will probably be the case 10 or 20 years into the future. But what has changed, and what you can see -- evidenced by simply following the Twitter backchannel for an event and by reading some of the many fantastic HR blogs out there -- is that the HR professional's ability, along with technology solution providers like Oracle, to connect, to more openly share information with each other, and to make each other better in the process, (and to create new, improved, and more innovative solutions), has never been greater. And I think it is with this heretofore unprecedented level of opportunity to connect with other members of the community that HR professionals will be better equipped to help their organizations attract, retain, and empower their teams. We at Oracle HCM look forward to continuing to meet, engage, and connect with the HR community in the coming months. Until then -- follow us on Twitter and Facebook.

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• What is the equivalent of .NET events in Ruby?

  - by Gishu

  The problem is very simple. An object needs to notify some events that might be of interest to observers. When I sat to validate a design that I cooked up now in Ruby just to validate it.. I find myself stumped as to how to implement the object events. In .Net this would be a one-liner.. .Net also does handler method signature verification,etc. e.g. // Object with events public delegate void HandlerSignature(int a); public event HandlerSignature MyEvent; public event HandlerSignature AnotherCriticalEvent; // Client MyObject.MyEvent += new HandlerSignature(MyHandlerMethod); // MyHandlerMethod has same signature as delegate Is there an EventDispatcher module or something that I am missing that I can strap on to a Ruby class ? Hoping for an answer that plays along with Ruby's principle of least surprise. An event would be the name of the event plus a queue of [observer, methodName] objects that need to be invoked when the event takes place.

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• How do I start up an NSRunLoop, and ensure that it has an NSAutoreleasePool that gets emptied?

  - by Nick Forge

  I have a "sync" task that relies on several "sub-tasks", which include asynchronous network operations, but which all require access to a single NSManagedObjectContext. Due to the threading requirements of NSManagedObjectContexts, I need every one of these sub-tasks to execute on the same thread. Due to the amount of processing being done in some of these tasks, I need them to be on a background thread. At the moment, I'm launching a new thread by doing this in my singleton SyncEngine object's -init method: [self performSelectorInBackground:@selector(initializeSyncThread) withObject:nil]; The -initializeSyncThread method looks like this: - (void)initializeSyncThread { self.syncThread = [NSThread currentThread]; self.managedObjectContext = [(MyAppDelegate *)[UIApplication sharedApplication].delegate createManagedObjectContext]; NSRunLoop *runLoop = [NSRunLoop currentRunLoop]; [runLoop run]; } Is this the correct way to start up the NSRunLoop for this thread? Is there a better way to do it? The run loop only needs to handle 'performSelector' sources, and it (and its thread) should be around for the lifetime of the process. When it comes to setting up an NSAutoreleasePool, should I do this by using Run Loop Observers to create the autorelease pool and drain it after every run-through?

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• Oracle syntax - should we have to choose between the old and the new?

  - by Martin Milan

  Hi, I work on a code base in the region of about 1'000'000 lines of source, in a team of around eight developers. Our code is basically an application using an Oracle database, but the code has evolved over time (we have plenty of source code from the mid nineties in there!). A dispute has arisen amongst the team over the syntax that we are using for querying the Oracle database. At the moment, the overwhelming majority of our queries use the "old" Oracle Syntax for joins, meaning we have code that looks like this... Example of Inner Join select customers.*, orders.date, orders.value from customers, orders where customers.custid = orders.custid Example of Outer Join select customers.custid, contacts.ContactName, contacts.ContactTelNo from customers, contacts where customers.custid = contacts.custid(+) As new developers have joined the team, we have noticed that some of them seem to prefer using SQL-92 queries, like this: Example of Inner Join select customers.*, orders.date, orders.value from customers inner join orders on (customers.custid = orders.custid) Example of Outer Join select customers.custid, contacts.ContactName, contacts.ContactTelNo from customers left join contacts on (customers.custid = contacts.custid) Group A say that everyone should be using the the "old" syntax - we have lots of code in this format, and we ought to value consistency. We don't have time to go all the way through the code now rewriting database queries, and it wouldn't pay us if we had. They also point out that "this is the way we've always done it, and we're comfortable with it..." Group B however say that they agree that we don't have the time to go back and change existing queries, we really ought to be adopting the "new" syntax on code that we write from here on in. They say that developers only really look at a single query at a time, and that so long as developers know both syntax there is nothing to be gained from rigidly sticking to the old syntax, which might be deprecated at some point in the future. Without declaring with which group my loyalties lie, I am interested in hearing the opinions of impartial observers - so let the games commence! Martin. Ps. I've made this a community wiki so as not to be seen as just blatantly chasing after question points...

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• Cocoa document-based app: Notification not always received by observer

  - by roysolay

  Hi, I hope somebody can help with my notification problem. I have a notification which looks to be set up correctly but it isn’t delivered as expected. I am developing a document based app. The delegate/ document class posts the notification when it reads from a saved file: [[NSNotificationCenter defaultCenter] postNotificationName:notifyBsplinePolyOpened object:self]; Logging tells me that this line is reached whenever I open a saved document. In the DrawView class, I have observers for the windowOpen notification and the bsplinePoly file open notification: [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(mainWindowOpen:) name:NSWindowDidBecomeMainNotification object:nil]; [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(savedBspline:) name:notifyBsplinePolyOpened object:nil]; - (void) mainWindowOpen:(NSNotification*) note { NSLog(@"Window opened"); _mainWindow = [note object]; } - (void) savedBspline:(NSNotification*) note { NSLog(@"savedBspline called"); NSLog(@"note is %@", [note name]); } The behavior is odd. When I save and close the main window and reopen it, I get the “Window opened” message but not the “savedBspline called” message. If I leave a main window open and open a previously saved session, I get the “Window opened” message and the “savedBspline called” message. I have searched online discussion and Apple DevCenter documentation but I have not seen this problem.

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• Implementation of MVC with SQLite and NSURLConnection, use cases?

  - by user324723

  I'm interested in knowing how others have implemented/designed database & web services in their iphone app and how they simplified it for the entire application. My application is dependent on these services and I can't figure out a efficient way to use them together due to the (semi)complexity of my requirements. My past attempts on combining them haven't been completely successful or at least optimal in my mind. I'm building a database driven iphone app that uses a relational database in sqlite and consumes web services based on missing content or user interaction. Like this hasn't been done before...right? Since I am using a relational database - any web services consumed requires normalization, parsing the result and persisting it to the database before it can be displayed in a table view controller. The applications UI consists of nested(nav controller) table views where a user can select a cell and be taken to the next table view where it attempts to populate the table views data source from the database. If nothing exists in the database then it will send a request via web services to download its content, thus download - parse - persist - query - display. Since the user has the ability to request a refresh of this data it still requires the same process. Quickly describing what I've implemented and tried to run with - 1st attempt - Used a singleton web service class that handled sending web service requests, parsing the result and returning it to the table view controller via delegate protocols. Once the controller received that data it would then be responsible for persisting it to the database and re-returning the result. I didn't like the idea of only preventing the case where the app delegate selector doesn't exists(released) causing the app to crash. 2nd attempt - Used NSNotificationCenter for easy access to both database and web services but later realized it was more complex due to adding and removing observers per view(which isn't advised anyways).

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• Observer Design Pattern - multiple event types

  - by David

  I'm currently implementing the Observer design pattern and using it to handle adding items to the session, create error logs and write messages out to the user giving feedback on their actions (e.g. You've just logged out!). I began with a single method on the subject called addEvent() but as I added more Observers I found that the parameters required to detail all the information I needed for each listener began to grow. I now have 3 methods called addMessage(), addStorage() and addLog(). These add data into an events array that has a key related to the event type (e.g. log, message, storage) but I'm starting to feel that now the subject needs to know too much about the listeners that are attached. My alternative thought is to go back to addEvent() and pass an event type (e.g. USER_LOGOUT) along with the data associated and each Observer maintains it's own list of event handles it is looking for (possibly in a switch statement), but this feels cumbersome. Also, I'd need to check that sufficient data had also been passed along with the event type. What is the correct way of doing this? Please let me know if I can explain any parts of this further. I hope you can help and see the problem I'm battling with.

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• In Rails, a Sweeper isn't getting called in a Model-only setup

  - by charliepark

  I'm working on a Rails app, where I'm using page caching to store static html output. The caching works fine. I'm having trouble expiring the caches, though. I believe my problem is, in part, because I'm not expiring the cache from my controller. All of the actions necessary for this are being handled within the model. This seems like it should be doable, but all of the references to Model-based cache expiration that I'm finding seem to be out of date, or are otherwise not working. In my environment.rb file, I'm calling config.load_paths += %W( #{RAILS_ROOT}/app/sweepers ) And I have, in the /sweepers folder, a LinkSweeper file: class LinkSweeper < ActionController::Caching::Sweeper observe Link def after_update(link) clear_links_cache(link) end def clear_links_cache(link) # expire_page :controller => 'links', :action => 'show', :md5 => link.md5 expire_page '/l/'+ link.md5 + '.html' end end So ... why isn't it deleting the cached page when I update the model? (Process: using script/console, I'm selecting items from the database and saving them, but their corresponding pages aren't deleting from the cache), and I'm also calling the specific method in the Link model that would normally invoke the sweeper. Neither works. If it matters, the cached file is an md5 hash off a key value in the Links table. The cached page is getting stored as something like /l/45ed4aade64d427...99919cba2bd90f.html. Essentially, it seems as though the Sweeper isn't actually observing the Link. I also read (here) that it might be possible to simply add the sweeper to config.active_record.observers in environment.rb, but that didn't seem to do it (and I wasn't sure if the load_path of app/sweepers in environment.rb obviated that).

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• What's the difference between DI and factory patterns?

  - by Anthony Short

  I have a class which depends on 3 classes, all 3 of which have other classes they rely on. Currently, I'm using a container class to build up all the required classes, inject them into one another and return the application. The simplified version of the container looks something like this: class Builder { private $_options; public function __construct($options) { $this->_options = $options; } public function build() { $cache = $this->getCache(); $response = $this->getResponse(); $engine = $this->getEngine(); return new Application($cache,$response,$engine); } public function getResponse() { $encoder = $this->getResponseEncoder(); $cache = $this->getResponseCache(); return new Response($encoder,$cache); } // Methods for building each object } I'm not sure if this would be classified as FactoryMethod or a DI Container. They both seem to solve the same problem in the same way - They build objects and inject dependencies. This container has some more complicated building methods, like loading observers and attaching them to observable objects. Should factories be doing all the building (loading extensions etc) and the DI container should use these factories to inject dependencies? That way the sub-packages, like Cache, Response etc, can each have their own specialised factories.

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• Callback from static library

  - by MortenHN

  I think this should be simple, but im having a real hard time finding information about this topic. I have made a static library and have no problem getting the basics to work. But im having a hard time figuring out how to make a call back from the static library to the main APP. I would like my static library to only use one header as front, this header should contain functions like: requestImage:(NSString *)path; requestLikstOfSomething:(NSSting *)guid; and so on.. These functions should do the necessary work and start a async NSURLConnection, and call back to the main application when the call have finished. How do you guys do this, what are the best ways to callback from a static library when a async method is finished? should i do this with delegates (is this possible), notifications, key/value observers. I really want to know how you guys have solved this, and what you regard as the best practices. Im going to have 20-25 different calls so i want the static library header file to be as simple as possible preferable only with a list of the 20-25 functions. UPDATE: My question is not how to use delegate pattern, but witch way is the best to do callbacks from static librarys. I would like to use delegates but i dont want to have 20-25 protocol declarations in the public header file. I would prefer to have only one function for each request. Thanks in advance. Best regards Morten

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• Algorithmia Source Code released on CodePlex

  - by FransBouma

  Following the release of our BCL Extensions Library on CodePlex, we have now released the source-code of Algorithmia on CodePlex! Algorithmia is an algorithm and data-structures library for .NET 3.5 or higher and is one of the pillars LLBLGen Pro v3's designer is built on. The library contains many data-structures and algorithms, and the source-code is well documented and commented, often with links to official descriptions and papers of the algorithms and data-structures implemented. The source-code is shared using Mercurial on CodePlex and is licensed under the friendly BSD2 license. User documentation is not available at the moment but will be added soon. One of the main design goals of Algorithmia was to create a library which contains implementations of well-known algorithms which weren't already implemented in .NET itself. This way, more developers out there can enjoy the results of many years of what the field of Computer Science research has delivered. Some algorithms and datastructures are known in .NET but are re-implemented because the implementation in .NET isn't efficient for many situations or lacks features. An example is the linked list in .NET: it doesn't have an O(1) concat operation, as every node refers to the containing LinkedList object it's stored in. This is bad for algorithms which rely on O(1) concat operations, like the Fibonacci heap implementation in Algorithmia. Algorithmia therefore contains a linked list with an O(1) concat feature. The following functionality is available in Algorithmia: Command, Command management. This system is usable to build a fully undo/redo aware system by building your object graph using command-aware classes. The Command pattern is implemented using a system which allows transparent undo-redo and command grouping so you can use it to make a class undo/redo aware and set properties, use its contents without using commands at all. The Commands namespace is the namespace to start. Classes you'd want to look at are CommandifiedMember, CommandifiedList and KeyedCommandifiedList. See the CommandQueueTests in the test project for examples. Graphs, Graph algorithms. Algorithmia contains a sophisticated graph class hierarchy and algorithms implemented onto them: non-directed and directed graphs, as well as a subgraph view class, which can be used to create a view onto an existing graph class which can be self-maintaining. Algorithms include transitive closure, topological sorting and others. A feature rich depth-first search (DFS) crawler is available so DFS based algorithms can be implemented quickly. All graph classes are undo/redo aware, as they can be set to be 'commandified'. When a graph is 'commandified' it will do its housekeeping through commands, which makes it fully undo-redo aware, so you can remove, add and manipulate the graph and undo/redo the activity automatically without any extra code. If you define the properties of the class you set as the vertex type using CommandifiedMember, you can manipulate the properties of vertices and the graph contents with full undo/redo functionality without any extra code. Heaps. Heaps are data-structures which have the largest or smallest item stored in them always as the 'root'. Extracting the root from the heap makes the heap determine the next in line to be the 'maximum' or 'minimum' (max-heap vs. min-heap, all heaps in Algorithmia can do both). Algorithmia contains various heaps, among them an implementation of the Fibonacci heap, one of the most efficient heap datastructures known today, especially when you want to merge different instances into one. Priority queues. Priority queues are specializations of heaps. Algorithmia contains a couple of them. Sorting. What's an algorithm library without sort algorithms? Algorithmia implements a couple of sort algorithms which sort the data in-place. This aspect is important in situations where you want to sort the elements in a buffer/list/ICollection in-place, so all data stays in the data-structure it already is stored in. PropertyBag. It re-implements Tony Allowatt's original idea in .NET 3.5 specific syntax, which is to have a generic property bag and to be able to build an object in code at runtime which can be bound to a property grid for editing. This is handy for when you have data / settings stored in XML or other format, and want to create an editable form of it without creating many editors. IEditableObject/IDataErrorInfo implementations. It contains default implementations for IEditableObject and IDataErrorInfo (EditableObjectDataContainer for IEditableObject and ErrorContainer for IDataErrorInfo), which make it very easy to implement these interfaces (just a few lines of code) without having to worry about bookkeeping during databinding. They work seamlessly with CommandifiedMember as well, so your undo/redo aware code can use them out of the box. EventThrottler. It contains an event throttler, which can be used to filter out duplicate events in an event stream coming into an observer from an event. This can greatly enhance performance in your UI without needing to do anything other than hooking it up so it's placed between the event source and your real handler. If your UI is flooded with events from data-structures observed by your UI or a middle tier, you can use this class to filter out duplicates to avoid redundant updates to UI elements or to avoid having observers choke on many redundant events. Small, handy stuff. A MultiValueDictionary, which can store multiple unique values per key, instead of one with the default Dictionary, and is also merge-aware so you can merge two into one. A Pair class, to quickly group two elements together. Multiple interfaces for helping with building a de-coupled, observer based system, and some utility extension methods for the defined data-structures. We regularly update the library with new code. If you have ideas for new algorithms or want to share your contribution, feel free to discuss it on the project's Discussions page or send us a pull request. Enjoy!

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• When using delegates, need better way to do sequential processing

  - by Padawan

  I have a class WebServiceCaller that uses NSURLConnection to make asynchronous calls to a web service. The class provides a delegate property and when the web service call is done, it calls a method webServiceDoneWithXXX on the delegate. There are several web service methods that can be called, two of which are say GetSummary and GetList. The classes that use WebServiceCaller initially need both the summary and list so they are written like this: -(void)getAllData { [webServiceCaller getSummary]; } -(void)webServiceDoneWithGetSummary { [webServiceCaller getList]; } -(void)webServiceDoneWithGetList { ... } This works but there are at least two problems: The calls are split across delegate methods so it's hard to see the sequence at a glance but more important it's hard to control or modify the sequence. Sometimes I want to call just GetSummary and not also GetList so I would then have to use an ugly class-level state variable that tells webServiceDoneWithGetSummary whether to call GetList or not. Assume that GetList cannot be done until GetSummary completes and returns some data which is used as input to GetList. Is there a better way to handle this and still get asynchronous calls? Update based on Matt Long's answer: Using notifications instead of a delegate, it looks like I can solve problem #2 by setting a different selector depending on whether I want the full sequence (GetSummary+GetList) or just GetSummary. Both observers would still use the same notification name when calling GetSummary. I would have to write two separate methods to handle GetSummaryDone instead of using a single delegate method (where I would have needed some class-level variable to tell whether to then call GetList). -(void)getAllData { [[NSNotificationCenter defaultCenter] addObserver:self              selector:@selector(getSummaryDoneAndCallGetList:)                  name:kGetSummaryDidFinish object:nil];     [webServiceCaller getSummary]; } -(void)getSummaryDoneAndCallGetList { [NSNotificationCenter removeObserver] //process summary data [[NSNotificationCenter defaultCenter] addObserver:self              selector:@selector(getListDone:)                  name:kGetListDidFinish object:nil];     [webServiceCaller getList]; } -(void)getListDone { [NSNotificationCenter removeObserver] //process list data } -(void)getJustSummaryData { [[NSNotificationCenter defaultCenter] addObserver:self              selector:@selector(getJustSummaryDone:) //different selector but                  name:kGetSummaryDidFinish object:nil]; //same notification name     [webServiceCaller getSummary]; } -(void)getJustSummaryDone { [NSNotificationCenter removeObserver] //process summary data } I haven't actually tried this yet. It seems better than having state variables and if-then statements but you have to write more methods. I still don't see a solution for problem 1.

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• Setting up a "to-many" relationship value dependency for a transient Core Data attribute

  - by Greg Combs

  I've got a relatively complicated Core Data relationship structure and I'm trying to figure out how to set up value dependencies (or observations) across various to-many relationships. Let me start out with some basic info. I've got a classroom with students, assignments, and grades (students X assignments). For simplicity's sake, we don't really have to focus much on the assignments yet. StudentObj <--->> ScoreObj <<---> AssignmentObj Each ScoreObj has a to-one relation with the StudentObj and the AssignmentObj. ScoreObj has real attributes for the numerical grade, the turnInDate, and notes. AssignmentObj.scores is the set of Score objects for that assignment (N = all students). AssignmentObj has real attributes for name, dueDate, curveFunction, gradeWeight, and maxPoints. StudentObj.scores is the set of Score objects for that student (N = all assignments). StudentObj also has real attributes like name, studentID, email, etc. StudentObj has a transient (calculated, not stored) attribute called gradeTotal. This last item, gradeTotal, is the real pickle. it calculates the student's overall semester grade using the scores (ScoreObj) from all their assignments, their associated assignment gradeWeights, curves, and maxPoints, and various other things. This gradeTotal value is displayed in a table column, along with all the students and their individual assignment grades. Determining the value of gradeTotal is a relatively expensive operation, particularly with a large class, therefore I want to run it only when necessary. For simplicity's sake, I'm not storing that gradeTotal value in the core data model. I don't mind caching it somewhere, but I'm having a bitch of a time determining where and how to best update that cache. I need to run that calculation for each student whenever any value changes that affects their gradeTotal. If this were a simple to-one relationship, I know I could use something like keyPathsForValuesAffectingGradeTotal ... but it's more like a many-to-one-to-many relationship. Does anyone know of an elegant (and KVC correct) solution? I guess I could tear through all those score and assignment objects and tell them to register their students as observers. But this seems like a blunt force approach.

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• Rails send mail with GMail

  - by Danny McClelland

  Hi Everyone, I am on rails 2.3.5 and have the latest Ruby installed and my application is running well, except, GMail emails. I am trying to setup my gmail imap connection which has worked previously but now doesnt want to know. This is my code: # Be sure to restart your server when you modify this file # Uncomment below to force Rails into production mode when # you don't control web/app server and can't set it the proper way # ENV['RAILS_ENV'] ||= 'production' # Specifies gem version of Rails to use when vendor/rails is not present RAILS_GEM_VERSION = '2.3.5' unless defined? RAILS_GEM_VERSION # Bootstrap the Rails environment, frameworks, and default configuration require File.join(File.dirname(__FILE__), 'boot') Rails::Initializer.run do |config| # Gems config.gem "capistrano-ext", :lib => "capistrano" config.gem "configatron" # Make Time.zone default to the specified zone, and make Active Record store time values # in the database in UTC, and return them converted to the specified local zone. config.time_zone = "London" # The internationalization framework can be changed to have another default locale (standard is :en) or more load paths. # All files from config/locales/*.rb,yml are added automatically. # config.i18n.load_path << Dir[File.join(RAILS_ROOT, 'my', 'locales', '*.{rb,yml}')] #config.i18n.default_locale = :de # Your secret key for verifying cookie session data integrity. # If you change this key, all old sessions will become invalid! # Make sure the secret is at least 30 characters and all random, # no regular words or you'll be exposed to dictionary attacks. config.action_controller.session = { :session_key => '_base_session', :secret => '7389ea9180b15f1495a5e73a69a893311f859ccff1ffd0fa2d7ea25fdf1fa324f280e6ba06e3e5ba612e71298d8fbe7f15fd7da2929c45a9c87fe226d2f77347' } config.active_record.observers = :user_observer end ActiveSupport::CoreExtensions::Date::Conversions::DATE_FORMATS.merge!(:default => '%d/%m/%Y') ActiveSupport::CoreExtensions::Time::Conversions::DATE_FORMATS.merge!(:default => '%d/%m/%Y') require "will_paginate" ActionMailer::Base.delivery_method = :smtp ActionMailer::Base.smtp_settings = { :enable_starttls_auto => true, :address => "smtp.gmail.com", :port => 587, :domain => "XXXXXXXX.XXX", :authentication => :plain, :user_name => "XXXXXXXXXX.XXXXXXXXXX.XXX", :password => "XXXXX" } But the above just results in an SMTP auth error in the production log. I have read varied reports of this not working in Rails 2.2.2 but nothing for 2.3.5, anyone got any ideas? Thanks, Danny

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• routing specific IP to ppp0 tunnel

  - by gompertz

  Hi All, I feel I've struggled with this long enough and need some help. I have a pptp tunnel and am trying to route destination traffic from 208.85.40.20 to the pptp tunnel (ppp0). (Keen observers may recognize the ip as being that of pandora.com). I am doing all this configuration on a router... and I know it's not working successfully as traceroute yields nothing but astericks. I've pasted relevant outputs below: (with some "security" editing to the addresses) root@OpenWrt:~# ifconfig br0 Link encap:Ethernet HWaddr 00:1A:92:BC:XX:XX inet addr:192.168.1.1 Bcast:192.168.1.255 Mask:255.255.255.0 UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1 RX packets:28185 errors:0 dropped:0 overruns:0 frame:0 TX packets:24936 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:0 RX bytes:4894242 (4.6 MiB) TX bytes:5941902 (5.6 MiB) eth0 Link encap:Ethernet HWaddr 00:1A:92:BC:XX:XX UP BROADCAST RUNNING PROMISC MULTICAST MTU:1500 Metric:1 RX packets:51829 errors:0 dropped:0 overruns:0 frame:0 TX packets:56824 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:1000 RX bytes:11490288 (10.9 MiB) TX bytes:11857913 (11.3 MiB) Interrupt:4 eth2 Link encap:Ethernet HWaddr 00:1A:92:BC:XX:XX UP BROADCAST RUNNING ALLMULTI MULTICAST MTU:1500 Metric:1 RX packets:4 errors:0 dropped:0 overruns:0 frame:15426 TX packets:9529 errors:21 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:1000 RX bytes:423 (423.0 B) TX bytes:596036 (582.0 KiB) Interrupt:2 Base address:0x2000 lo Link encap:Local Loopback inet addr:127.0.0.1 Mask:255.0.0.0 UP LOOPBACK RUNNING MTU:16436 Metric:1 RX packets:30 errors:0 dropped:0 overruns:0 frame:0 TX packets:30 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:0 RX bytes:2300 (2.2 KiB) TX bytes:2300 (2.2 KiB) ppp0 Link encap:Point-Point Protocol inet addr:68.68.39.250 P-t-P:172.16.20.1 Mask:255.255.255.255 UP POINTOPOINT RUNNING NOARP MULTICAST MTU:1400 Metric:1 RX packets:165 errors:2 dropped:0 overruns:0 frame:0 TX packets:68 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:3 RX bytes:7006 (6.8 KiB) TX bytes:3462 (3.3 KiB) vlan0 Link encap:Ethernet HWaddr 00:1A:92:BC:XX:XX UP BROADCAST RUNNING ALLMULTI MULTICAST MTU:1500 Metric:1 RX packets:28182 errors:0 dropped:0 overruns:0 frame:0 TX packets:33813 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:0 RX bytes:5006544 (4.7 MiB) TX bytes:6609774 (6.3 MiB) vlan1 Link encap:Ethernet HWaddr 00:1A:92:BC:XX:XX inet addr:173.183.111.3 Bcast:173.183.111.255 Mask:255.255.224.0 UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1 RX packets:23653 errors:0 dropped:0 overruns:0 frame:0 TX packets:23012 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:0 RX bytes:5522012 (5.2 MiB) TX bytes:4982944 (4.7 MiB) wds0.4915 Link encap:Ethernet HWaddr 00:1A:92:BC:XX:XX UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1 RX packets:0 errors:0 dropped:0 overruns:0 frame:0 TX packets:0 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:1000 RX bytes:0 (0.0 B) TX bytes:0 (0.0 B) wds0.4915 Link encap:Ethernet HWaddr 00:1A:92:BC:XX:XX UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1 RX packets:0 errors:0 dropped:0 overruns:0 frame:0 TX packets:0 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:1000 RX bytes:0 (0.0 B) TX bytes:0 (0.0 B) root@OpenWrt:~# cat /etc/ppp/ip-up iptables -A FORWARD -t filter -i br0 -m state --state NEW,ESTABLISHED,RELATED -j ACCEPT iptables -A FORWARD -t filter -i ppp0 -m state --state ESTABLISHED,RELATED -j ACCEPT iptables -t nat -A POSTROUTING -o ppp0 -s 192.168.1.1/24 -d 0/0 -j MASQUERADE iptables -A forwarding_rule -o ppp0 -j ACCEPT iptables -A forwarding_rule -i ppp0 -j ACCEPT iptables -t nat -A postrouting_rule -o ppp0 -j MASQUERADE root@OpenWrt:~# route Kernel IP routing table Destination Gateway Genmask Flags Metric Ref Use Iface 172.16.20.1 * 255.255.255.255 UH 0 0 0 ppp0 208.85.40.20 * 255.255.255.255 UH 0 0 0 ppp0 192.168.1.0 * 255.255.255.0 U 0 0 0 br0 173.183.192.0 * 255.255.224.0 U 0 0 0 vlan1 default d173-183-192-1. 0.0.0.0 UG 0 0 0 vlan1 default 192.168.1.1 0.0.0.0 UG 0 0 0 br0 Any advice is greatly appreciated, I'm not too great with network but am pretty astute at learning ;-)

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• Blogging tips for SQL Server professionals

  - by jamiet

  For some time now I have been intending to put some material together relating my blogging experiences since I began blogging in 2004 and that led to me submitting a session for SQLBits recently where I intended to do just that. That didn’t get enough votes to allow me to present however so instead I resolved to write a blog post about it and Simon Sabin’s recent post Blogging – how do you do it? has prompted me to get around to completing it. So, here I present a compendium of tips that I’ve picked up from authoring a fair few blog posts over the past 6 years. Feedburner Feedburner.com is a service that can consume your blog’s default RSS feed and provide another, replacement, feed that has exactly the same content. You can then supply that replacement feed on your blog site for other people to consume in their RSS readers. Why would you want to do this? Well, two reasons actually: It makes your blog portable. If you ever want to move your blog to a different URL you don’t have to tell your subscribers to move to a different feed. The feedburner feed is a pointer to your blog content rather than being a copy of it. Feedburner will collect stats telling you how many people are subscribed to your feed, which RSS readers they use, stuff like that. Here’s a sample screenshot for http://sqlblog.com/blogs/jamie_thomson/: It also tells you what your most viewed posts are: Web stats like these are notoriously inaccurate but then again the method of measurement here is not important, what IS important is that it gives you a trustworthy ranking of your blog posts and (in my opinion) knowing which are your most popular posts is more important than knowing exactly how many views each post has had. This is just the tip of the iceberg of what Feedburner provides and I recommend every new blogger to try it! Monitor subscribers using Google Reader If for some reason Feedburner is not to your taste or (more likely) you already have an established RSS feed that you do not want to change then Google provide another way in which you can monitor your readership in the shape of their online RSS reader, Google Reader. It provides, for every RSS feed, a collection of stats including the number of Google Reader users that have subscribed to that RSS feed. This is really valuable information and in fact I have been recording this statistic for mine and a number of other blogs for a few years now and as such I can produce the following chart that indicates how readership is trending for those blogs over time: [Good news for my fellow SQLBlog bloggers.] As Stephen Few readily points out, its not the numbers that are important but the trend. Search Engine Optimisation (SEO) SEO (or “How do I get my blog to show up in Google”) is a massive area of expertise which I don’t want (and am unable) to cover in much detail here but there are some simple rules of thumb that will help: Tags – If your blog engine offers the ability to add tags to your blog post, use them. Invariably those tags go into the meta section of the page HTML and search engines lap that stuff up. For example, from my recent post Microsoft publish Visual Studio 2010 Database Project Guidance: Title – Search engines take notice of web page titles as well so make them specific and descriptive (e.g. “Configuring dtsConfig connection strings”) rather than esoteric and meaningless in a vain attempt to be humorous (e.g. “Last night a DJ saved my ETL batch”)! Title(2) – Make your title even more search engine friendly by mentioning high level subject areas, not dissimilar to Twitter hashtags. For example, if you look at all of my posts related to SSIS you will notice that nearly all contain the word “SSIS” in the title even if I had to shoehorn it in there by putting it in square brackets or similar. Another tip, if you ARE putting words into your titles in this artificial manner then put them at the end so that they’re not that prominent in search engine results; they’re there for the search engines to consume, not for human beings. Images – Always add titles and alternate text (ALT attribute) to images in your blog post. If you use Windows 7 or Windows Vista then you can use Live Writer (which Simon recommended) makes this easy for you. Headings – If you want to highlight section headings use heading tags (e.g. <H1>, <H2>, <H3> etc…) rather than just formatting the text appropriately – again, Live makes this easy. These tags give your blog posts structure that is understood by search engines and RSS readers alike. (I believe it makes them more amenable to CSS as well – though that’s not something I know too much about). If you check the HTML source for the blog post you’re reading right now you’ll be able to scan through and see where I have used heading tags. Microsoft provide a free tool called the SEO Toolkit that will analyse your blog site (for free) and tell you what things you should change to improve SEO. Go read more and download for free at Search Engine Optimization Toolkit. Did I mention that it was free? Miscellaneous Tips If you are including code in your blog post then ensure it is formatted correctly. Use SQL Server Central’s T-SQL prettifier for formatting T-SQL code. Use images and videos. Personally speaking there’s nothing I like less when reading a blog than paragraph after paragraph of text. Images make your blog more appealing which means people are more likely to read what you have written. Be original. Don’t plagiarise other people’s content and don’t simply rewrite the contents of Books Online. Every time you publish a blog post tweet a link to it. Include hashtags in your tweet that are more likely to grab people’s attention. That’s probably enough for now - I hope this blog post proves useful to someone out there. If you would appreciate a related session at a forthcoming SQLBits conference then please let me know. This will likely be my last blog post for 2010 so I would like to take this opportunity to thank everyone that has commented on, linked to or read any of my blog posts in that time. 2011 is shaping up to be a very interesting for SQL Server observers with the impending release of SQL Server code-named Denali and I promise I’ll have lots more content on that as the year progresses. Happy New Year. @Jamiet

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