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  • Modified map2 (without truncation of lists) in F# - how to do it idiomatically?

    - by Maciej Piechotka
    I'd like to rewrite such function into F#: zipWith' :: (a -> b -> c) -> (a -> c) -> (b -> c) -> [a] -> [b] -> [c] zipWith' _ _ h [] bs = h `map` bs zipWith' _ g _ as [] = g `map` as zipWith' f g h (a:as) (b:bs) = f a b:zipWith f g h as bs My first attempt was: let inline private map2' (xs : seq<'T>) (ys : seq<'U>) (f : 'T -> 'U -> 'S) (g : 'T -> 'S) (h : 'U -> 'S) = let xenum = xs.GetEnumerator() let yenum = ys.GetEnumerator() seq { let rec rest (zenum : IEnumerator<'A>) (i : 'A -> 'S) = seq { yield i(zenum.Current) if zenum.MoveNext() then yield! (rest zenum i) else zenum.Dispose() } let rec merge () = seq { if xenum.MoveNext() then if yenum.MoveNext() then yield (f xenum.Current yenum.Current); yield! (merge ()) else yenum.Dispose(); yield! (rest xenum g) else xenum.Dispose() if yenum.MoveNext() then yield! (rest yenum h) else yenum.Dispose() } yield! (merge ()) } However it can hardly be considered idiomatic. I heard about LazyList but I cannot find it anywhere.

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  • Does "Value Restriction" practically mean that there is no higher order functional programming?

    - by Sadache
    Does "Value Restriction" practically mean that there is no higher order functional programming? I have a problem that each time I try to do a bit of HOP I get caught by a VR error. Example: let simple (s:string)= fun rq->1 let oops= simple "" type 'a SimpleType= F of (int ->'a-> 'a) let get a = F(fun req -> id) let oops2= get "" and I would like to know whether it is a problem of a prticular implementation of VR or it is a general problem that has no solution in a mutable type-infered language that doesn't include mutation in the type system.

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  • F# ref-mutable vars vs object fields

    - by rwallace
    I'm writing a parser in F#, and it needs to be as fast as possible (I'm hoping to parse a 100 MB file in less than a minute). As normal, it uses mutable variables to store the next available character and the next available token (i.e. both the lexer and the parser proper use one unit of lookahead). My current partial implementation uses local variables for these. Since closure variables can't be mutable (anyone know the reason for this?) I've declared them as ref: let rec read file includepath = let c = ref ' ' let k = ref NONE let sb = new StringBuilder() use stream = File.OpenText file let readc() = c := stream.Read() |> char // etc I assume this has some overhead (not much, I know, but I'm trying for maximum speed here), and it's a little inelegant. The most obvious alternative would be to create a parser class object and have the mutable variables be fields in it. Does anyone know which is likely to be faster? Is there any consensus on which is considered better/more idiomatic style? Is there another option I'm missing?

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  • A good way to look back arbitrary number of items in the Array.Fold in F#

    - by tk
    In the folder function of the Array.Fold operation, i want to look back arbitrary number of items. The only way i can figure out is like this. let aFolder (dataArray, curIdx, result) (dataItem) = let N = numItemsToLookBack(result, dataItem) let recentNitems = dataArray.[curIdx - n .. curIdx - 1] let result = aCalc(result, dataItem, recentNitems ) dataArray, curIdx + 1, result myDataArray | Array.fold aFolder (myDataArray, 0, initResult) As you can see, I passed the whole dataArray and index to the folder function to get the "recentNitems". But this way allows the folder function to access not only preceding data, but also the following data. Is there a better (or more functional) way?

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  • creating an object within a function of a program

    - by user1066524
    could someone please tell me what I need to do in order to create an object in a function. I will try to explain by making up some sort of example... Let's say I have a program named TimeScheduler.cpp that implements the class Schedule.h (and I have the implementation in a separate file Schedule.cpp where we define the methods). In the declaration file we have declared two constructors Schedule(); //the default and Schedule(int, int, int);//accepts three arguments to get to the point--let's say in the main program file TimeScheduler.cpp we created our own functions in this program apart from the functions inherited from the class Schedule. so we have our prototypes listed at the top. /*prototypes*/ void makeSomeTime(); etc..... we have main(){ //etc etc... } we then define these program functions void makeSomeTime(){ //process } let's say that inside the function makeSomeTime(), we would like to create an array of Schedule objects like this Schedule ob[]={ summer(5,14, 49), fall(9,25,50) }; what do I have to do to the function makeSomeTime() in order for it to allow me to create this array of objects. The reason I ask is currently i'm having difficulty with my own program in that it WILL allow me to create this array of objects in main()....but NOT in a function like I just gave an example of. The strange thing is it will allow me to create a dynamic array of objects in the function..... like Schedule *ob = new Schedule[n+1]; ob[2]= Schedule(x,y,z); Why would it let me assign to a non-dynamic array in main(), but not let me do that in the function?

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  • Build model with nested model in rspec integration test

    - by user1116573
    I understand that I can do something like in rspec: let(:project) { Project.new } but in my app a project accepts_nested_attributes_for tasks and when I generate the Project form I build a task along with it using: @project = Project.new @project.tasks.build I need something like: let(:project) { Project.new.tasks.build } but that doesn't seem to work. How can I do this as a let in my rspec test?

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  • Identity operators in Swift

    - by Tao
    If a is identical to c, b is identical to c, why a is not identical to b? var a = [1, 2, 3] var b = a var c = a[0...2] a === c // true b === c // true a === b // false If a, b, c are constants: let a = [1, 2, 3] let b = a let c = a[0...2] a === c // true b === c // true a === b // true

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  • F# equivalent of the C# typeof(IEnumerable<>)

    - by Rune FS
    I have a piece of code where I need to figure out if a given type implements IEnumerable (I don't care about the T) I've tried (t:System.Type in case you wonder) let interfaces = t.GetInterfaces() let enumerbale = interfaces.Any( fun t -> (t.GetGenericTypeDefinition() = typeof<IEnumerable<>>) however that wont compile (the compile don't like the <). I then tried let interfaces = t.GetInterfaces() let enumerbale = interfaces.Any( fun t -> (t.GetGenericTypeDefinition() = typeof<IEnumerable<'a>>) but get's a warning that 'a is constraint to obj. I Don't want to figure out if IEnumerable is implemented but IEnumerabl<. Any one know's the solution and btw feel free to comment on the code above as well. It's my first non-trivial F# program

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  • Where should I handle the exceptions, in the BLL, DAL or PL ?

    - by Puneet Dudeja
    Which is the best place to handle the exceptions ? BLL, DAL or PL ? Should I allow the methods in the DAL and BLL to throw the exceptions up the chain and let the PL handle them? or should I handle them at the BLL ? e.g If I have a method in my DAL that issues "ExecuteNonQuery" and updates some records, and due to one or more reason, 0 rows are affected. Now, how should I let my PL know that whether an exception happened or there really was no rows matched to the condition. Should I use "try catch" in my PL code and let it know through an exception, or should I handle the exception at DAL and return some special code like (-1) to let the PL differentiate between the (exception) and (no rows matched condition i.e. zero rows affected) ?

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  • Haskell graph data type representation

    - by John Retallack
    I want to represent a graph in Haskell in the following manner: For each node I want to store it's value and a list of adjacent nodes,the problem which i'm having difficulties with is that I want the adjacent nodes to be stored as references to other nodes. For example: I want node ny to be stored as („NY“ (l p)) where l and p are adjacent nodes,and not as („NY“ („London“ „Paris“)). I tried something like this : data Node a = Node { value :: a , neighbors :: [Node a] }deriving (Show) let n1 = Node {value=1, neighbors=[n2]} let n2 = Node {value=1, neighbors=[n1 n3]} let n3 = Node {value=1, neighbors=[n2]} But i get en error in let,What am I doing wrong ?

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  • Using the West Wind Web Toolkit to set up AJAX and REST Services

    - by Rick Strahl
    I frequently get questions about which option to use for creating AJAX and REST backends for ASP.NET applications. There are many solutions out there to do this actually, but when I have a choice - not surprisingly - I fall back to my own tools in the West Wind West Wind Web Toolkit. I've talked a bunch about the 'in-the-box' solutions in the past so for a change in this post I'll talk about the tools that I use in my own and customer applications to handle AJAX and REST based access to service resources using the West Wind West Wind Web Toolkit. Let me preface this by saying that I like things to be easy. Yes flexible is very important as well but not at the expense of over-complexity. The goal I've had with my tools is make it drop dead easy, with good performance while providing the core features that I'm after, which are: Easy AJAX/JSON Callbacks Ability to return any kind of non JSON content (string, stream, byte[], images) Ability to work with both XML and JSON interchangeably for input/output Access endpoints via POST data, RPC JSON calls, GET QueryString values or Routing interface Easy to use generic JavaScript client to make RPC calls (same syntax, just what you need) Ability to create clean URLS with Routing Ability to use standard ASP.NET HTTP Stack for HTTP semantics It's all about options! In this post I'll demonstrate most of these features (except XML) in a few simple and short samples which you can download. So let's take a look and see how you can build an AJAX callback solution with the West Wind Web Toolkit. Installing the Toolkit Assemblies The easiest and leanest way of using the Toolkit in your Web project is to grab it via NuGet: West Wind Web and AJAX Utilities (Westwind.Web) and drop it into the project by right clicking in your Project and choosing Manage NuGet Packages from anywhere in the Project.   When done you end up with your project looking like this: What just happened? Nuget added two assemblies - Westwind.Web and Westwind.Utilities and the client ww.jquery.js library. It also added a couple of references into web.config: The default namespaces so they can be accessed in pages/views and a ScriptCompressionModule that the toolkit optionally uses to compress script resources served from within the assembly (namely ww.jquery.js and optionally jquery.js). Creating a new Service The West Wind Web Toolkit supports several ways of creating and accessing AJAX services, but for this post I'll stick to the lower level approach that works from any plain HTML page or of course MVC, WebForms, WebPages. There's also a WebForms specific control that makes this even easier but I'll leave that for another post. So, to create a new standalone AJAX/REST service we can create a new HttpHandler in the new project either as a pure class based handler or as a generic .ASHX handler. Both work equally well, but generic handlers don't require any web.config configuration so I'll use that here. In the root of the project add a Generic Handler. I'm going to call this one StockService.ashx. Once the handler has been created, edit the code and remove all of the handler body code. Then change the base class to CallbackHandler and add methods that have a [CallbackMethod] attribute. Here's the modified base handler implementation now looks like with an added HelloWorld method: using System; using Westwind.Web; namespace WestWindWebAjax { /// <summary> /// Handler implements CallbackHandler to provide REST/AJAX services /// </summary> public class SampleService : CallbackHandler { [CallbackMethod] public string HelloWorld(string name) { return "Hello " + name + ". Time is: " + DateTime.Now.ToString(); } } } Notice that the class inherits from CallbackHandler and that the HelloWorld service method is marked up with [CallbackMethod]. We're done here. Services Urlbased Syntax Once you compile, the 'service' is live can respond to requests. All CallbackHandlers support input in GET and POST formats, and can return results as JSON or XML. To check our fancy HelloWorld method we can now access the service like this: http://localhost/WestWindWebAjax/StockService.ashx?Method=HelloWorld&name=Rick which produces a default JSON response - in this case a string (wrapped in quotes as it's JSON): (note by default JSON will be downloaded by most browsers not displayed - various options are available to view JSON right in the browser) If I want to return the same data as XML I can tack on a &format=xml at the end of the querystring which produces: <string>Hello Rick. Time is: 11/1/2011 12:11:13 PM</string> Cleaner URLs with Routing Syntax If you want cleaner URLs for each operation you can also configure custom routes on a per URL basis similar to the way that WCF REST does. To do this you need to add a new RouteHandler to your application's startup code in global.asax.cs one for each CallbackHandler based service you create: protected void Application_Start(object sender, EventArgs e) { CallbackHandlerRouteHandler.RegisterRoutes<StockService>(RouteTable.Routes); } With this code in place you can now add RouteUrl properties to any of your service methods. For the HelloWorld method that doesn't make a ton of sense but here is what a routed clean URL might look like in definition: [CallbackMethod(RouteUrl="stocks/HelloWorld/{name}")] public string HelloWorld(string name) { return "Hello " + name + ". Time is: " + DateTime.Now.ToString(); } The same URL I previously used now becomes a bit shorter and more readable with: http://localhost/WestWindWebAjax/HelloWorld/Rick It's an easy way to create cleaner URLs and still get the same functionality. Calling the Service with $.getJSON() Since the result produced is JSON you can now easily consume this data using jQuery's getJSON method. First we need a couple of scripts - jquery.js and ww.jquery.js in the page: <!DOCTYPE html> <html> <head> <link href="Css/Westwind.css" rel="stylesheet" type="text/css" /> <script src="scripts/jquery.min.js" type="text/javascript"></script> <script src="scripts/ww.jquery.min.js" type="text/javascript"></script> </head> <body> Next let's add a small HelloWorld example form (what else) that has a single textbox to type a name, a button and a div tag to receive the result: <fieldset> <legend>Hello World</legend> Please enter a name: <input type="text" name="txtHello" id="txtHello" value="" /> <input type="button" id="btnSayHello" value="Say Hello (POST)" /> <input type="button" id="btnSayHelloGet" value="Say Hello (GET)" /> <div id="divHelloMessage" class="errordisplay" style="display:none;width: 450px;" > </div> </fieldset> Then to call the HelloWorld method a little jQuery is used to hook the document startup and the button click followed by the $.getJSON call to retrieve the data from the server. <script type="text/javascript"> $(document).ready(function () { $("#btnSayHelloGet").click(function () { $.getJSON("SampleService.ashx", { Method: "HelloWorld", name: $("#txtHello").val() }, function (result) { $("#divHelloMessage") .text(result) .fadeIn(1000); }); });</script> .getJSON() expects a full URL to the endpoint of our service, which is the ASHX file. We can either provide a full URL (SampleService.ashx?Method=HelloWorld&name=Rick) or we can just provide the base URL and an object that encodes the query string parameters for us using an object map that has a property that matches each parameter for the server method. We can also use the clean URL routing syntax, but using the object parameter encoding actually is safer as the parameters will get properly encoded by jQuery. The result returned is whatever the result on the server method is - in this case a string. The string is applied to the divHelloMessage element and we're done. Obviously this is a trivial example, but it demonstrates the basics of getting a JSON response back to the browser. AJAX Post Syntax - using ajaxCallMethod() The previous example allows you basic control over the data that you send to the server via querystring parameters. This works OK for simple values like short strings, numbers and boolean values, but doesn't really work if you need to pass something more complex like an object or an array back up to the server. To handle traditional RPC type messaging where the idea is to map server side functions and results to a client side invokation, POST operations can be used. The easiest way to use this functionality is to use ww.jquery.js and the ajaxCallMethod() function. ww.jquery wraps jQuery's AJAX functions and knows implicitly how to call a CallbackServer method with parameters and parse the result. Let's look at another simple example that posts a simple value but returns something more interesting. Let's start with the service method: [CallbackMethod(RouteUrl="stocks/{symbol}")] public StockQuote GetStockQuote(string symbol) { Response.Cache.SetExpires(DateTime.UtcNow.Add(new TimeSpan(0, 2, 0))); StockServer server = new StockServer(); var quote = server.GetStockQuote(symbol); if (quote == null) throw new ApplicationException("Invalid Symbol passed."); return quote; } This sample utilizes a small StockServer helper class (included in the sample) that downloads a stock quote from Yahoo's financial site via plain HTTP GET requests and formats it into a StockQuote object. Lets create a small HTML block that lets us query for the quote and display it: <fieldset> <legend>Single Stock Quote</legend> Please enter a stock symbol: <input type="text" name="txtSymbol" id="txtSymbol" value="msft" /> <input type="button" id="btnStockQuote" value="Get Quote" /> <div id="divStockDisplay" class="errordisplay" style="display:none; width: 450px;"> <div class="label-left">Company:</div> <div id="stockCompany"></div> <div class="label-left">Last Price:</div> <div id="stockLastPrice"></div> <div class="label-left">Quote Time:</div> <div id="stockQuoteTime"></div> </div> </fieldset> The final result looks something like this:   Let's hook up the button handler to fire the request and fill in the data as shown: $("#btnStockQuote").click(function () { ajaxCallMethod("SampleService.ashx", "GetStockQuote", [$("#txtSymbol").val()], function (quote) { $("#divStockDisplay").show().fadeIn(1000); $("#stockCompany").text(quote.Company + " (" + quote.Symbol + ")"); $("#stockLastPrice").text(quote.LastPrice); $("#stockQuoteTime").text(quote.LastQuoteTime.formatDate("MMM dd, HH:mm EST")); }, onPageError); }); So we point at SampleService.ashx and the GetStockQuote method, passing a single parameter of the input symbol value. Then there are two handlers for success and failure callbacks.  The success handler is the interesting part - it receives the stock quote as a result and assigns its values to various 'holes' in the stock display elements. The data that comes back over the wire is JSON and it looks like this: { "Symbol":"MSFT", "Company":"Microsoft Corpora", "OpenPrice":26.11, "LastPrice":26.01, "NetChange":0.02, "LastQuoteTime":"2011-11-03T02:00:00Z", "LastQuoteTimeString":"Nov. 11, 2011 4:20pm" } which is an object representation of the data. JavaScript can evaluate this JSON string back into an object easily and that's the reslut that gets passed to the success function. The quote data is then applied to existing page content by manually selecting items and applying them. There are other ways to do this more elegantly like using templates, but here we're only interested in seeing how the data is returned. The data in the object is typed - LastPrice is a number and QuoteTime is a date. Note about the date value: JavaScript doesn't have a date literal although the JSON embedded ISO string format used above  ("2011-11-03T02:00:00Z") is becoming fairly standard for JSON serializers. However, JSON parsers don't deserialize dates by default and return them by string. This is why the StockQuote actually returns a string value of LastQuoteTimeString for the same date. ajaxMethodCallback always converts dates properly into 'real' dates and the example above uses the real date value along with a .formatDate() data extension (also in ww.jquery.js) to display the raw date properly. Errors and Exceptions So what happens if your code fails? For example if I pass an invalid stock symbol to the GetStockQuote() method you notice that the code does this: if (quote == null) throw new ApplicationException("Invalid Symbol passed."); CallbackHandler automatically pushes the exception message back to the client so it's easy to pick up the error message. Regardless of what kind of error occurs: Server side, client side, protocol errors - any error will fire the failure handler with an error object parameter. The error is returned to the client via a JSON response in the error callback. In the previous examples I called onPageError which is a generic routine in ww.jquery that displays a status message on the bottom of the screen. But of course you can also take over the error handling yourself: $("#btnStockQuote").click(function () { ajaxCallMethod("SampleService.ashx", "GetStockQuote", [$("#txtSymbol").val()], function (quote) { $("#divStockDisplay").fadeIn(1000); $("#stockCompany").text(quote.Company + " (" + quote.Symbol + ")"); $("#stockLastPrice").text(quote.LastPrice); $("#stockQuoteTime").text(quote.LastQuoteTime.formatDate("MMM dd, hh:mmt")); }, function (error, xhr) { $("#divErrorDisplay").text(error.message).fadeIn(1000); }); }); The error object has a isCallbackError, message and  stackTrace properties, the latter of which is only populated when running in Debug mode, and this object is returned for all errors: Client side, transport and server side errors. Regardless of which type of error you get the same object passed (as well as the XHR instance optionally) which makes for a consistent error retrieval mechanism. Specifying HttpVerbs You can also specify HTTP Verbs that are allowed using the AllowedHttpVerbs option on the CallbackMethod attribute: [CallbackMethod(AllowedHttpVerbs=HttpVerbs.GET | HttpVerbs.POST)] public string HelloWorld(string name) { … } If you're building REST style API's this might be useful to force certain request semantics onto the client calling. For the above if call with a non-allowed HttpVerb the request returns a 405 error response along with a JSON (or XML) error object result. The default behavior is to allow all verbs access (HttpVerbs.All). Passing in object Parameters Up to now the parameters I passed were very simple. But what if you need to send something more complex like an object or an array? Let's look at another example now that passes an object from the client to the server. Keeping with the Stock theme here lets add a method called BuyOrder that lets us buy some shares for a stock. Consider the following service method that receives an StockBuyOrder object as a parameter: [CallbackMethod] public string BuyStock(StockBuyOrder buyOrder) { var server = new StockServer(); var quote = server.GetStockQuote(buyOrder.Symbol); if (quote == null) throw new ApplicationException("Invalid or missing stock symbol."); return string.Format("You're buying {0} shares of {1} ({2}) stock at {3} for a total of {4} on {5}.", buyOrder.Quantity, quote.Company, quote.Symbol, quote.LastPrice.ToString("c"), (quote.LastPrice * buyOrder.Quantity).ToString("c"), buyOrder.BuyOn.ToString("MMM d")); } public class StockBuyOrder { public string Symbol { get; set; } public int Quantity { get; set; } public DateTime BuyOn { get; set; } public StockBuyOrder() { BuyOn = DateTime.Now; } } This is a contrived do-nothing example that simply echoes back what was passed in, but it demonstrates how you can pass complex data to a callback method. On the client side we now have a very simple form that captures the three values on a form: <fieldset> <legend>Post a Stock Buy Order</legend> Enter a symbol: <input type="text" name="txtBuySymbol" id="txtBuySymbol" value="GLD" />&nbsp;&nbsp; Qty: <input type="text" name="txtBuyQty" id="txtBuyQty" value="10" style="width: 50px" />&nbsp;&nbsp; Buy on: <input type="text" name="txtBuyOn" id="txtBuyOn" value="<%= DateTime.Now.ToString("d") %>" style="width: 70px;" /> <input type="button" id="btnBuyStock" value="Buy Stock" /> <div id="divStockBuyMessage" class="errordisplay" style="display:none"></div> </fieldset> The completed form and demo then looks something like this:   The client side code that picks up the input values and assigns them to object properties and sends the AJAX request looks like this: $("#btnBuyStock").click(function () { // create an object map that matches StockBuyOrder signature var buyOrder = { Symbol: $("#txtBuySymbol").val(), Quantity: $("#txtBuyQty").val() * 1, // number Entered: new Date() } ajaxCallMethod("SampleService.ashx", "BuyStock", [buyOrder], function (result) { $("#divStockBuyMessage").text(result).fadeIn(1000); }, onPageError); }); The code creates an object and attaches the properties that match the server side object passed to the BuyStock method. Each property that you want to update needs to be included and the type must match (ie. string, number, date in this case). Any missing properties will not be set but also not cause any errors. Pass POST data instead of Objects In the last example I collected a bunch of values from form variables and stuffed them into object variables in JavaScript code. While that works, often times this isn't really helping - I end up converting my types on the client and then doing another conversion on the server. If lots of input controls are on a page and you just want to pick up the values on the server via plain POST variables - that can be done too - and it makes sense especially if you're creating and filling the client side object only to push data to the server. Let's add another method to the server that once again lets us buy a stock. But this time let's not accept a parameter but rather send POST data to the server. Here's the server method receiving POST data: [CallbackMethod] public string BuyStockPost() { StockBuyOrder buyOrder = new StockBuyOrder(); buyOrder.Symbol = Request.Form["txtBuySymbol"]; ; int qty; int.TryParse(Request.Form["txtBuyQuantity"], out qty); buyOrder.Quantity = qty; DateTime time; DateTime.TryParse(Request.Form["txtBuyBuyOn"], out time); buyOrder.BuyOn = time; // Or easier way yet //FormVariableBinder.Unbind(buyOrder,null,"txtBuy"); var server = new StockServer(); var quote = server.GetStockQuote(buyOrder.Symbol); if (quote == null) throw new ApplicationException("Invalid or missing stock symbol."); return string.Format("You're buying {0} shares of {1} ({2}) stock at {3} for a total of {4} on {5}.", buyOrder.Quantity, quote.Company, quote.Symbol, quote.LastPrice.ToString("c"), (quote.LastPrice * buyOrder.Quantity).ToString("c"), buyOrder.BuyOn.ToString("MMM d")); } Clearly we've made this server method take more code than it did with the object parameter. We've basically moved the parameter assignment logic from the client to the server. As a result the client code to call this method is now a bit shorter since there's no client side shuffling of values from the controls to an object. $("#btnBuyStockPost").click(function () { ajaxCallMethod("SampleService.ashx", "BuyStockPost", [], // Note: No parameters - function (result) { $("#divStockBuyMessage").text(result).fadeIn(1000); }, onPageError, // Force all page Form Variables to be posted { postbackMode: "Post" }); }); The client simply calls the BuyStockQuote method and pushes all the form variables from the page up to the server which parses them instead. The feature that makes this work is one of the options you can pass to the ajaxCallMethod() function: { postbackMode: "Post" }); which directs the function to include form variable POST data when making the service call. Other options include PostNoViewState (for WebForms to strip out WebForms crap vars), PostParametersOnly (default), None. If you pass parameters those are always posted to the server except when None is set. The above code can be simplified a bit by using the FormVariableBinder helper, which can unbind form variables directly into an object: FormVariableBinder.Unbind(buyOrder,null,"txtBuy"); which replaces the manual Request.Form[] reading code. It receives the object to unbind into, a string of properties to skip, and an optional prefix which is stripped off form variables to match property names. The component is similar to the MVC model binder but it's independent of MVC. Returning non-JSON Data CallbackHandler also supports returning non-JSON/XML data via special return types. You can return raw non-JSON encoded strings like this: [CallbackMethod(ReturnAsRawString=true,ContentType="text/plain")] public string HelloWorldNoJSON(string name) { return "Hello " + name + ". Time is: " + DateTime.Now.ToString(); } Calling this method results in just a plain string - no JSON encoding with quotes around the result. This can be useful if your server handling code needs to return a string or HTML result that doesn't fit well for a page or other UI component. Any string output can be returned. You can also return binary data. Stream, byte[] and Bitmap/Image results are automatically streamed back to the client. Notice that you should set the ContentType of the request either on the CallbackMethod attribute or using Response.ContentType. This ensures the Web Server knows how to display your binary response. Using a stream response makes it possible to return any of data. Streamed data can be pretty handy to return bitmap data from a method. The following is a method that returns a stock history graph for a particular stock over a provided number of years: [CallbackMethod(ContentType="image/png",RouteUrl="stocks/history/graph/{symbol}/{years}")] public Stream GetStockHistoryGraph(string symbol, int years = 2,int width = 500, int height=350) { if (width == 0) width = 500; if (height == 0) height = 350; StockServer server = new StockServer(); return server.GetStockHistoryGraph(symbol,"Stock History for " + symbol,width,height,years); } I can now hook this up into the JavaScript code when I get a stock quote. At the end of the process I can assign the URL to the service that returns the image into the src property and so force the image to display. Here's the changed code: $("#btnStockQuote").click(function () { var symbol = $("#txtSymbol").val(); ajaxCallMethod("SampleService.ashx", "GetStockQuote", [symbol], function (quote) { $("#divStockDisplay").fadeIn(1000); $("#stockCompany").text(quote.Company + " (" + quote.Symbol + ")"); $("#stockLastPrice").text(quote.LastPrice); $("#stockQuoteTime").text(quote.LastQuoteTime.formatDate("MMM dd, hh:mmt")); // display a stock chart $("#imgStockHistory").attr("src", "stocks/history/graph/" + symbol + "/2"); },onPageError); }); The resulting output then looks like this: The charting code uses the new ASP.NET 4.0 Chart components via code to display a bar chart of the 2 year stock data as part of the StockServer class which you can find in the sample download. The ability to return arbitrary data from a service is useful as you can see - in this case the chart is clearly associated with the service and it's nice that the graph generation can happen off a handler rather than through a page. Images are common resources, but output can also be PDF reports, zip files for downloads etc. which is becoming increasingly more common to be returned from REST endpoints and other applications. Why reinvent? Obviously the examples I've shown here are pretty basic in terms of functionality. But I hope they demonstrate the core features of AJAX callbacks that you need to work through in most applications which is simple: return data, send back data and potentially retrieve data in various formats. While there are other solutions when it comes down to making AJAX callbacks and servicing REST like requests, I like the flexibility my home grown solution provides. Simply put it's still the easiest solution that I've found that addresses my common use cases: AJAX JSON RPC style callbacks Url based access XML and JSON Output from single method endpoint XML and JSON POST support, querystring input, routing parameter mapping UrlEncoded POST data support on callbacks Ability to return stream/raw string data Essentially ability to return ANYTHING from Service and pass anything All these features are available in various solutions but not together in one place. I've been using this code base for over 4 years now in a number of projects both for myself and commercial work and it's served me extremely well. Besides the AJAX functionality CallbackHandler provides, it's also an easy way to create any kind of output endpoint I need to create. Need to create a few simple routines that spit back some data, but don't want to create a Page or View or full blown handler for it? Create a CallbackHandler and add a method or multiple methods and you have your generic endpoints.  It's a quick and easy way to add small code pieces that are pretty efficient as they're running through a pretty small handler implementation. I can have this up and running in a couple of minutes literally without any setup and returning just about any kind of data. Resources Download the Sample NuGet: Westwind Web and AJAX Utilities (Westwind.Web) ajaxCallMethod() Documentation Using the AjaxMethodCallback WebForms Control West Wind Web Toolkit Home Page West Wind Web Toolkit Source Code © Rick Strahl, West Wind Technologies, 2005-2011Posted in ASP.NET  jQuery  AJAX   Tweet (function() { var po = document.createElement('script'); po.type = 'text/javascript'; po.async = true; po.src = 'https://apis.google.com/js/plusone.js'; var s = document.getElementsByTagName('script')[0]; s.parentNode.insertBefore(po, s); })();

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  • vim-powerline colors are out of whack in urxvt

    - by komidore64
    I have attached two images showing what my vim-powerline looks like. As you can see, something has happened to the colors and I cannot figure out how to fix it. I'm running Fedora 17 on a clean install with i3 (default config) and urxvt. Here is my bashrc: # .bashrc if [[ "$(uname)" != "Darwin" ]]; then # non mac os x # source global bashrc if [[ -f "/etc/bashrc" ]]; then . /etc/bashrc fi export TERM='xterm-256color' # probably shouldn't do this fi # bash prompt with colors # [ <user>@<hostname> <working directory> {current git branch (if you're in a repo)} ] # ==> PS1="\[\e[1;33m\][ \u\[\e[1;37m\]@\[\e[1;32m\]\h\[\e[1;33m\] \W\$(git branch 2> /dev/null | grep -e '\* ' | sed 's/^..\(.*\)/ {\[\e[1;36m\]\1\[\e[1;33m\]}/') ]\[\e[0m\]\n==> " # execute only in Mac OS X if [[ "$(uname)" == 'Darwin' ]]; then # if OS X has a $HOME/bin folder, then add it to PATH if [[ -d "$HOME/bin" ]]; then export PATH="$PATH:$HOME/bin" fi alias ls='ls -G' # ls with colors fi alias ll='ls -lah' # long listing of all files with human readable file sizes alias tree='tree -C' # turns on coloring for tree command alias mkdir='mkdir -p' # create parent directories as needed alias vim='vim -p' # if more than one file, open files in tabs export EDITOR='vim' # super-secret work stuff if [[ -f "$HOME/.workbashrc" ]]; then . $HOME/.workbashrc fi # Add RVM to PATH for scripting if [[ -d "$HOME/.rvm/bin" ]]; then # if installed PATH=$PATH:$HOME/.rvm/bin fi and my Xdefaults: ! URxvt config ! colors! URxvt.background: #101010 URxvt.foreground: #ededed URxvt.cursorColor: #666666 URxvt.color0: #2E3436 URxvt.color8: #555753 URxvt.color1: #993C3C URxvt.color9: #BF4141 URxvt.color2: #3C993C URxvt.color10: #41BF41 URxvt.color3: #99993C URxvt.color11: #BFBF41 URxvt.color4: #3C6199 URxvt.color12: #4174FB URxvt.color5: #993C99 URxvt.color13: #BF41BF URxvt.color6: #3C9999 URxvt.color14: #41BFBF URxvt.color7: #D3D7CF URxvt.color15: #E3E3E3 ! options URxvt*loginShell: true URxvt*font: xft:DejaVu Sans Mono for Powerline:antialias=true:size=12 URxvt*saveLines: 8192 URxvt*scrollstyle: plain URxvt*scrollBar_right: true URxvt*scrollTtyOutput: true URxvt*scrollTtyKeypress: true URxvt*urlLauncher: google-chrome and finally my vimrc set nocompatible set dir=~/.vim/ " set one place for vim swap files " vundler for vim plugins ---- filetype off set rtp+=~/.vim/bundle/vundle call vundle#rc() Bundle 'gmarik/vundle' Bundle 'tpope/vim-surround' Bundle 'greyblake/vim-preview' Bundle 'Lokaltog/vim-powerline' Bundle 'tpope/vim-endwise' Bundle 'kien/ctrlp.vim' " ---------------------------- syntax enable filetype plugin indent on " Powerline ------------------ set noshowmode set laststatus=2 let g:Powerline_symbols = 'fancy' " show fancy symbols (requires patched font) set encoding=utf-8 " ---------------------------- " ctrlp ---------------------- let g:ctrlp_open_multiple_files = 'tj' " open multiple files in additional tabs let g:ctrlp_show_hidden = 1 " include dotfiles and dotdirs in ctrlp indexing let g:ctrlp_prompt_mappings = { \ 'AcceptSelection("e")': ['<c-t>'], \ 'AcceptSelection("t")': ['<cr>', '<2-LeftMouse>'], \ } " remap <cr> to open file in a new tab " ---------------------------- set showcmd set tabpagemax=100 set hlsearch set incsearch set nowrapscan set ignorecase set smartcase set ruler set tabstop=4 set shiftwidth=4 set expandtab set wildmode=list:longest autocmd BufWritePre * :%s/\s\+$//e "remove trailing whitespace " :REV to "revert" file to state of the most recent save command REV earlier 1f " disable netrw -------------- let g:loaded_netrw = 1 let g:loaded_netrwPlugin = 1 " ---------------------------- Any guidance as to fixing the statusline would be fantastic. I've found a github issue outlining almost the exact same problem, but the solution was never posted. Thank you.

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  • Remote Desktop to Your Azure Virtual Machine

    - by Shaun
    The Windows Azure Team had just published their new development portal this week and the SDK 1.3. Within this new release there are a lot of cool feature available. The one I’m looking forward to is Remote Desktop Access to your running Windows Azure Virtual Machine.   Configuration Remote Desktop Access It would be very simple to make the azure service enable the remote desktop access. First of all let’s create a new windows azure project from the Visual Studio. In this example I just created a normal MVC 2 web role without any modifications. Then we right-click the azure project node in the solution explorer window and select “Publish”. Then let’s select the “Deploy your Windows Azure project to Windows Azure” on the top radio button. And then select the credential, deployment service/slot, storage and label as susal. You must have the Management API Certificates uploaded to your Windows Azure account, and install the certification on you machine before in order to use this one-click deployment feature. If you are familiar with this dialog you will notice that there’s a linkage named “Configure Remote Desktop connections”. Here is where you need to make this service enable the remote desktop feature. After clicked this link we will set the configuration of the remote desktop access authorization information. There are 4 steps we need to do to configure our access. Certificates: We need either create or select a certificate file in order to encypt the access cerdenticals. In this example I will use the certificate file for my Management API. Username: The remote desktop user name to access the virtual machine. Password: The password for the access. Expiration: The access cerdentals would be expired after 1 month by default but we can amend here. After that we clicked the OK button to back to the publish dialog.   The next step is to back to the new windows azure portal and navigate to the hosted services list. I created a new hosted service and upload the certificate file onto this service. The user name and password access to the azure machine must be encrypted from the local machine, and then send to the windows azure platform, then decrypted on the azure side by the same file. This is why we need to upload the certificate file onto azure. We navigated to the “Hosted Services, Storage Accounts & CDN"” from the left panel and created a new hosted service named “SDK13” and selected the “Certificates” node. Then we clicked the “Add Certificates” button. Then we select the local certificate file and the password to install it into this azure service.   The final step would be back to our Visual Studio and in the pulish dialog just click the OK button. The Visual Studio will upload our package and the configuration into our service with the remote desktop settings.   Remote Desktop Access to Azure Virtual Machine All things had been done, let’s have a look back on the Windows Azure Development Portal. If I selected the web role that I had just published we can see on the toolbar there’s a section named “Remote Access”. In this section the Enable checkbox had been checked which means this role has the Remote Desktop Access feature enabled. If we want to modify the access cerdentals we can simply click the Configure button. Then we can update the user name, password, certificates and the expiration date.   Let’s select the instance node under the web role. In this case I just created one instance for demo. We can see that when we selected the instance node, the Connect button turned enabled. After clicked this button there will be a RDP file downloaded. This is a Remote Desctop configuration file that we can use to access to our azure virtual machine. Let’s download it to our local machine and execute. We input the user name and password we specified when we published our application to azure and then click OK. There might be some certificates warning dislog appeared. This is because the certificates we use to encryption is not signed by a trusted provider. Just select OK in these cases as we know the certificate is safty to us. Finally, the virtual machine of Windows Azure appeared.   A Quick Look into the Azure Virtual Machine Let’s just have a very quick look into our virtual machine. There are 3 disks available for us: C, D and E. Disk C: Store the local resource, diagnosis information, etc. Disk D: System disk which contains the OS, IIS, .NET Frameworks, etc. Disk E: Sotre our application code. The IIS which hosting our webiste on Azure. The IP configuration of the azure virtual machine.   Summary In this post I covered one of the new feature of the Azure SDK 1.3 – Remote Desktop Access. We can set the access per service and all of the instances of this service could be accessed through the remote desktop tool. With this feature we can deep into the virtual machines of our instances to see the inner information such as the system event, IIS log, system information, etc. But we should pay attention to modify the system settings. 2 reasons from what I know for now: 1. If we have more than one instances against our service we should ensure that all system settings we modifed are applied to all instances/virtual machines. Otherwise, as the machines are under the azure load balance proxy our application process may doesn’t work due to the defferent settings between the instances. 2. When the virtual machine encounted some problem and need to be translated to another physical machine all settings we made would be disappeared.   Hope this helps, Shaun All documents and related graphics, codes are provided "AS IS" without warranty of any kind. Copyright © Shaun Ziyan Xu. This work is licensed under the Creative Commons License.

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  • SQL SERVER – CTE can be Updated

    - by Pinal Dave
    Today I have received a fantastic email from Matthew Spieth. SQL Server expert from Ohio. He recently had a great conversation with his colleagues in the office and wanted to make sure that everybody who reads this blog knows about this little feature which is commonly confused. Here is his statement and we will start our story with Matthew’s own statement: “Users often confuse CTE with Temp Table but technically they both are different, CTE are like Views and they can be updated just like views.“ Very true statement from Matthew. I totally agree with what he is saying. Just like him, I have enough, time came across a situation when developers think CTE is like temp table. When you update temp table, it remains in the scope of the temp table and it does not propagate it to the table based on which temp table is built. However, this is not the case when it is about CTE, when you update CTE, it updates underlying table just like view does. Here is the working example of the same built by Matthew to illustrate this behavior. Check the value in the base table first. USE AdventureWorks2012; -- Check - The value in the base table is updated SELECT Color FROM [Production].[Product] WHERE ProductNumber = 'CA-6738'; Now let us build CTE with the same data. ;WITH CTEUpd(ProductID, Name, ProductNumber, Color) AS( SELECT ProductID, Name, ProductNumber, Color FROM [Production].[Product] WHERE ProductNumber = 'CA-6738') Now let us update CTE with following code. -- Update CTE UPDATE CTEUpd SET Color = 'Rainbow'; Now let us check the BASE table based on which the CTE was built. -- Check - The value in the base table is updated SELECT Color FROM [Production].[Product] WHERE ProductNumber = 'CA-6738'; That’s it! You can update CTE and it will update the base table. Here is the script which you should execute all together. USE AdventureWorks2012; -- Check - The value in the base table is updated SELECT Color FROM [Production].[Product] WHERE ProductNumber = 'CA-6738'; -- Build CTE ;WITH CTEUpd(ProductID, Name, ProductNumber, Color) AS( SELECT ProductID, Name, ProductNumber, Color FROM [Production].[Product] WHERE ProductNumber = 'CA-6738') -- Update CTE UPDATE CTEUpd SET Color = 'Rainbow'; -- Check - The value in the base table is updated SELECT Color FROM [Production].[Product] WHERE ProductNumber = 'CA-6738'; If you are aware of such scenario, do let me know and I will post this on my blog with due credit to you. Reference: Pinal Dave (http://blog.sqlauthority.com)Filed under: PostADay, SQL, SQL Authority, SQL Query, SQL Server, SQL Tips and Tricks, SQL View, T SQL Tagged: CTE

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  • SQL SERVER – Extending SQL Azure with Azure worker role – Guest Post by Paras Doshi

    - by pinaldave
    This is guest post by Paras Doshi. Paras Doshi is a research Intern at SolidQ.com and a Microsoft student partner. He is currently working in the domain of SQL Azure. SQL Azure is nothing but a SQL server in the cloud. SQL Azure provides benefits such as on demand rapid provisioning, cost-effective scalability, high availability and reduced management overhead. To see an introduction on SQL Azure, check out the post by Pinal here In this article, we are going to discuss how to extend SQL Azure with the Azure worker role. In other words, we will attempt to write a custom code and host it in the Azure worker role; the aim is to add some features that are not available with SQL Azure currently or features that need to be customized for flexibility. This way we extend the SQL Azure capability by building some solutions that run on Azure as worker roles. To understand Azure worker role, think of it as a windows service in cloud. Azure worker role can perform background processes, and to handle processes such as synchronization and backup, it becomes our ideal tool. First, we will focus on writing a worker role code that synchronizes SQL Azure databases. Before we do so, let’s see some scenarios in which synchronization between SQL Azure databases is beneficial: scaling out access over multiple databases enables us to handle workload efficiently As of now, SQL Azure database can be hosted in one of any six datacenters. By synchronizing databases located in different data centers, one can extend the data by enabling access to geographically distributed data Let us see some scenarios in which SQL server to SQL Azure database synchronization is beneficial To backup SQL Azure database on local infrastructure Rather than investing in local infrastructure for increased workloads, such workloads could be handled by cloud Ability to extend data to different datacenters located across the world to enable efficient data access from remote locations Now, let us develop cloud-based app that synchronizes SQL Azure databases. For an Introduction to developing cloud based apps, click here Now, in this article, I aim to provide a bird’s eye view of how a code that synchronizes SQL Azure databases look like and then list resources that can help you develop the solution from scratch. Now, if you newly add a worker role to the cloud-based project, this is how the code will look like. (Note: I have added comments to the skeleton code to point out the modifications that will be required in the code to carry out the SQL Azure synchronization. Note the placement of Setup() and Sync() function.) Click here (http://parasdoshi1989.files.wordpress.com/2011/06/code-snippet-1-for-extending-sql-azure-with-azure-worker-role1.pdf ) Enabling SQL Azure databases synchronization through sync framework is a two-step process. In the first step, the database is provisioned and sync framework creates tracking tables, stored procedures, triggers, and tables to store metadata to enable synchronization. This is one time step. The code for the same is put in the setup() function which is called once when the worker role starts. Now, the second step is continuous (or on demand) synchronization of SQL Azure databases by propagating changes between databases. This is done on a continuous basis by calling the sync() function in the while loop. The code logic to synchronize changes between SQL Azure databases should be put in the sync() function. Discussing the coding part step by step is out of the scope of this article. Therefore, let me suggest you a resource, which is given here. Also, note that before you start developing the code, you will need to install SYNC framework 2.1 SDK (download here). Further, you will reference some libraries before you start coding. Details regarding the same are available in the article that I just pointed to. You will be charged for data transfers if the databases are not in the same datacenter. For pricing information, go here Currently, a tool named DATA SYNC, which is built on top of sync framework, is available in CTP that allows SQL Azure <-> SQL server and SQL Azure <-> SQL Azure synchronization (without writing single line of code); however, in some cases, the custom code shown in this blogpost provides flexibility that is not available with Data SYNC. For instance, filtering is not supported in the SQL Azure DATA SYNC CTP2; if you wish to have such a functionality now, then you have the option of developing a custom code using SYNC Framework. Now, this code can be easily extended to synchronize at some schedule. Let us say we want the databases to get synchronized every day at 10:00 pm. This is what the code will look like now: (http://parasdoshi1989.files.wordpress.com/2011/06/code-snippet-2-for-extending-sql-azure-with-azure-worker-role.pdf) Don’t you think that by writing such a code, we are imitating the functionality provided by the SQL server agent for a SQL server? Think about it. We are scheduling our administrative task by writing custom code – in other words, we have developed a “Light weight SQL server agent for SQL Azure!” Since the SQL server agent is not currently available in cloud, we have developed a solution that enables us to schedule tasks, and thus we have extended SQL Azure with the Azure worker role! Now if you wish to track jobs, you can do so by storing this data in SQL Azure (or Azure tables). The reason is that Windows Azure is a stateless platform, and we will need to store the state of the job ourselves and the choice that you have is SQL Azure or Azure tables. Note that this solution requires custom code and also it is not UI driven; however, for now, it can act as a temporary solution until SQL server agent is made available in the cloud. Moreover, this solution does not encompass functionalities that a SQL server agent provides, but it does open up an interesting avenue to schedule some of the tasks such as backup and synchronization of SQL Azure databases by writing some custom code in the Azure worker role. Now, let us see one more possibility – i.e., running BCP through a worker role in Azure-hosted services and then uploading the backup files either locally or on blobs. If you upload it locally, then consider the data transfer cost. If you upload it to blobs residing in the same datacenter, then no transfer cost applies but the cost on blob size applies. So, before choosing the option, you need to evaluate your preferences keeping the cost associated with each option in mind. In this article, I have shown that Azure worker role solution could be developed to synchronize SQL Azure databases. Moreover, a light-weight SQL server agent for SQL Azure can be developed. Also we discussed the possibility of running BCP through a worker role in Azure-hosted services for backing up our precious SQL Azure data. Thus, we can extend SQL Azure with the Azure worker role. But remember: you will be charged for running Azure worker roles. So at the end of the day, you need to ask – am I willing to build a custom code and pay money to achieve this functionality? I hope you found this blog post interesting. If you have any questions/feedback, you can comment below or you can mail me at Paras[at]student-partners[dot]com Reference: Pinal Dave (http://blog.SQLAuthority.com) Filed under: Pinal Dave, PostADay, SQL, SQL Authority, SQL Azure, SQL Query, SQL Server, SQL Tips and Tricks, T SQL, Technology

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  • Fragmented Log files could be slowing down your database

    - by Fatherjack
    Something that is sometimes forgotten by a lot of DBAs is the fact that database log files get fragmented in the same way that you get fragmentation in a data file. The cause is very different but the effect is the same – too much effort reading and writing data. Data files get fragmented as data is changed through normal system activity, INSERTs, UPDATEs and DELETEs cause fragmentation and most experienced DBAs are monitoring their indexes for fragmentation and dealing with it accordingly. However, you don’t hear about so many working on their log files. How can a log file get fragmented? I’m glad you asked. When you create a database there are at least two files created on the disk storage; an mdf for the data and an ldf for the log file (you can also have ndf files for extra data storage but that’s off topic for now). It is wholly possible to have more than one log file but in most cases there is little point in creating more than one as the log file is written to in a ‘wrap-around’ method (more on that later). When a log file is created at the time that a database is created the file is actually sub divided into a number of virtual log files (VLFs). The number and size of these VLFs depends on the size chosen for the log file. VLFs are also created in the space added to a log file when a log file growth event takes place. Do you have your log files set to auto grow? Then you have potentially been introducing many VLFs into your log file. Let’s get to see how many VLFs we have in a brand new database. USE master GO CREATE DATABASE VLF_Test ON ( NAME = VLF_Test, FILENAME = 'C:\Program Files\Microsoft SQL Server\MSSQL10.ROCK_2008\MSSQL\DATA\VLF_Test.mdf', SIZE = 100, MAXSIZE = 500, FILEGROWTH = 50 ) LOG ON ( NAME = VLF_Test_Log, FILENAME = 'C:\Program Files\Microsoft SQL Server\MSSQL10.ROCK_2008\MSSQL\DATA\VLF_Test_log.ldf', SIZE = 5MB, MAXSIZE = 250MB, FILEGROWTH = 5MB ); go USE VLF_Test go DBCC LOGINFO; The results of this are firstly a new database is created with specified files sizes and the the DBCC LOGINFO results are returned to the script editor. The DBCC LOGINFO results have plenty of interesting information in them but lets first note there are 4 rows of information, this relates to the fact that 4 VLFs have been created in the log file. The values in the FileSize column are the sizes of each VLF in bytes, you will see that the last one to be created is slightly larger than the others. So, a 5MB log file has 4 VLFs of roughly 1.25 MB. Lets alter the CREATE DATABASE script to create a log file that’s a bit bigger and see what happens. Alter the code above so that the log file details are replaced by LOG ON ( NAME = VLF_Test_Log, FILENAME = 'C:\Program Files\Microsoft SQL Server\MSSQL10.ROCK_2008\MSSQL\DATA\VLF_Test_log.ldf', SIZE = 1GB, MAXSIZE = 25GB, FILEGROWTH = 1GB ); With a bigger log file specified we get more VLFs What if we make it bigger again? LOG ON ( NAME = VLF_Test_Log, FILENAME = 'C:\Program Files\Microsoft SQL Server\MSSQL10.ROCK_2008\MSSQL\DATA\VLF_Test_log.ldf', SIZE = 5GB, MAXSIZE = 250GB, FILEGROWTH = 5GB ); This time we see more VLFs are created within our log file. We now have our 5GB log file comprised of 16 files of 320MB each. In fact these sizes fall into all the ranges that control the VLF creation criteria – what a coincidence! The rules that are followed when a log file is created or has it’s size increased are pretty basic. If the file growth is lower than 64MB then 4 VLFs are created If the growth is between 64MB and 1GB then 8 VLFs are created If the growth is greater than 1GB then 16 VLFs are created. Now the potential for chaos comes if the default values and settings for log file growth are used. By default a database log file gets a 1MB log file with unlimited growth in steps of 10%. The database we just created is 6 MB, let’s add some data and see what happens. USE vlf_test go -- we need somewhere to put the data so, a table is in order IF OBJECT_ID('A_Table') IS NOT NULL DROP TABLE A_Table go CREATE TABLE A_Table ( Col_A int IDENTITY, Col_B CHAR(8000) ) GO -- Let's check the state of the log file -- 4 VLFs found EXECUTE ('DBCC LOGINFO'); go -- We can go ahead and insert some data and then check the state of the log file again INSERT A_Table (col_b) SELECT TOP 500 REPLICATE('a',2000) FROM sys.columns AS sc, sys.columns AS sc2 GO -- insert 500 rows and we get 22 VLFs EXECUTE ('DBCC LOGINFO'); go -- Let's insert more rows INSERT A_Table (col_b) SELECT TOP 2000 REPLICATE('a',2000) FROM sys.columns AS sc, sys.columns AS sc2 GO 10 -- insert 2000 rows, in 10 batches and we suddenly have 107 VLFs EXECUTE ('DBCC LOGINFO'); Well, that escalated quickly! Our log file is split, internally, into 107 fragments after a few thousand inserts. The same happens with any logged transactions, I just chose to illustrate this with INSERTs. Having too many VLFs can cause performance degradation at times of database start up, log backup and log restore operations so it’s well worth keeping a check on this property. How do we prevent excessive VLF creation? Creating the database with larger files and also with larger growth steps and actively choosing to grow your databases rather than leaving it to the Auto Grow event can make sure that the growths are made with a size that is optimal. How do we resolve a situation of a database with too many VLFs? This process needs to be done when the database is under little or no stress so that you don’t affect system users. The steps are: BACKUP LOG YourDBName TO YourBackupDestinationOfChoice Shrink the log file to its smallest possible size DBCC SHRINKFILE(FileNameOfTLogHere, TRUNCATEONLY) * Re-size the log file to the size you want it to, taking in to account your expected needs for the coming months or year. ALTER DATABASE YourDBName MODIFY FILE ( NAME = FileNameOfTLogHere, SIZE = TheSizeYouWantItToBeIn_MB) * – If you don’t know the file name of your log file then run sp_helpfile while you are connected to the database that you want to work on and you will get the details you need. The resize step can take quite a while This is already detailed far better than I can explain it by Kimberley Tripp in her blog 8-Steps-to-better-Transaction-Log-throughput.aspx. The result of this will be a log file with a VLF count according to the bullet list above. Knowing when VLFs are being created By complete coincidence while I have been writing this blog (it’s been quite some time from it’s inception to going live) Jonathan Kehayias from SQLSkills.com has written a great article on how to track database file growth using Event Notifications and Service Broker. I strongly recommend taking a look at it as this is going to catch any sneaky auto grows that take place and let you know about them right away. Hassle free monitoring of VLFs If you are lucky or wise enough to be using SQL Monitor or another monitoring tool that let’s you write your own custom metrics then you can keep an eye on this very easily. There is a custom metric for VLFs (written by Stuart Ainsworth) already on the site and there are some others there are very useful so take a moment or two to look around while you are there. Resources MSDN – http://msdn.microsoft.com/en-us/library/ms179355(v=sql.105).aspx Kimberly Tripp from SQLSkills.com – http://www.sqlskills.com/BLOGS/KIMBERLY/post/8-Steps-to-better-Transaction-Log-throughput.aspx Thomas LaRock at Simple-Talk.com – http://www.simple-talk.com/sql/database-administration/monitoring-sql-server-virtual-log-file-fragmentation/ Disclosure I am a Friend of Red Gate. This means that I am more than likely to say good things about Red Gate DBA and Developer tools. No matter how awesome I make them sound, take the time to compare them with other products before you contact the Red Gate sales team to make your order.

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  • Converting a generic list into JSON string and then handling it in java script

    - by Jalpesh P. Vadgama
    We all know that JSON (JavaScript Object Notification) is very useful in case of manipulating string on client side with java script and its performance is very good over browsers so let’s create a simple example where convert a Generic List then we will convert this list into JSON string and then we will call this web service from java script and will handle in java script. To do this we need a info class(Type) and for that class we are going to create generic list. Here is code for that I have created simple class with two properties UserId and UserName public class UserInfo { public int UserId { get; set; } public string UserName { get; set; } } Now Let’s create a web service and web method will create a class and then we will convert this with in JSON string with JavaScriptSerializer class. Here is web service class. using System; using System.Collections.Generic; using System.Linq; using System.Web; using System.Web.Services; namespace Experiment.WebService { /// <summary> /// Summary description for WsApplicationUser /// </summary> [WebService(Namespace = "http://tempuri.org/")] [WebServiceBinding(ConformsTo = WsiProfiles.BasicProfile1_1)] [System.ComponentModel.ToolboxItem(false)] // To allow this Web Service to be called from script, using ASP.NET AJAX, uncomment the following line. [System.Web.Script.Services.ScriptService] public class WsApplicationUser : System.Web.Services.WebService { [WebMethod] public string GetUserList() { List<UserInfo> userList = new List<UserInfo>(); for (int i = 1; i <= 5; i++) { UserInfo userInfo = new UserInfo(); userInfo.UserId = i; userInfo.UserName = string.Format("{0}{1}", "J", i.ToString()); userList.Add(userInfo); } System.Web.Script.Serialization.JavaScriptSerializer jSearializer = new System.Web.Script.Serialization.JavaScriptSerializer(); return jSearializer.Serialize(userList); } } } Note: Here you must have this attribute here in web service class ‘[System.Web.Script.Services.ScriptService]’ as this attribute will enable web service to call from client side. Now we have created a web service class let’s create a java script function ‘GetUserList’ which will call web service from JavaScript like following function GetUserList() { Experiment.WebService.WsApplicationUser.GetUserList(ReuqestCompleteCallback, RequestFailedCallback); } After as you can see we have inserted two call back function ReuqestCompleteCallback and RequestFailedCallback which handle errors and result from web service. ReuqestCompleteCallback will handle result of web service and if and error comes then RequestFailedCallback will print the error. Following is code for both function. function ReuqestCompleteCallback(result) { result = eval(result); var divResult = document.getElementById("divUserList"); CreateUserListTable(result); } function RequestFailedCallback(error) { var stackTrace = error.get_stackTrace(); var message = error.get_message(); var statusCode = error.get_statusCode(); var exceptionType = error.get_exceptionType(); var timedout = error.get_timedOut(); // Display the error. var divResult = document.getElementById("divUserList"); divResult.innerHTML = "Stack Trace: " + stackTrace + "<br/>" + "Service Error: " + message + "<br/>" + "Status Code: " + statusCode + "<br/>" + "Exception Type: " + exceptionType + "<br/>" + "Timedout: " + timedout; } Here in above there is a function called you can see that we have use ‘eval’ function which parse string in enumerable form. Then we are calling a function call ‘CreateUserListTable’ which will create a table string and paste string in the a div. Here is code for that function. function CreateUserListTable(userList) { var tablestring = '<table ><tr><td>UsreID</td><td>UserName</td></tr>'; for (var i = 0, len = userList.length; i < len; ++i) { tablestring=tablestring + "<tr>"; tablestring=tablestring + "<td>" + userList[i].UserId + "</td>"; tablestring=tablestring + "<td>" + userList[i].UserName + "</td>"; tablestring=tablestring + "</tr>"; } tablestring = tablestring + "</table>"; var divResult = document.getElementById("divUserList"); divResult.innerHTML = tablestring; } Now let’s create div which will have all html that is generated from this function. Here is code of my web page. We also need to add a script reference to enable web service from client side. Here is all HTML code we have. <form id="form1" runat="server"> <asp:ScriptManager ID="myScirptManger" runat="Server"> <Services> <asp:ServiceReference Path="~/WebService/WsApplicationUser.asmx" /> </Services> </asp:ScriptManager> <div id="divUserList"> </div> </form> Now as we have not defined where we are going to call ‘GetUserList’ function so let’s call this function on windows onload event of javascript like following. window.onload=GetUserList(); That’s it. Now let’s run it on browser to see whether it’s work or not and here is the output in browser as expected. That’s it. This was very basic example but you can crate your own JavaScript enabled grid from this and you can see possibilities are unlimited here. Stay tuned for more.. Happy programming.. Technorati Tags: JSON,Javascript,ASP.NET,WebService

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  • Looking into ASP.Net MVC 4.0 Mobile Development - part 2

    - by nikolaosk
    In this post I will be continuing my discussion on ASP.Net MVC 4.0 mobile development. You can have a look at my first post on the subject here . Make sure you read it and understand it well before you move one reading the remaining of this post. I will not be writing any code in this post. I will try to explain a few concepts related to the MVC 4.0 mobile functionality. In this post I will be looking into the Browser Overriding feature in ASP.Net MVC 4.0. By that I mean that we override the user agent for a given user session. This is very useful feature for people who visit a site through a device and they experience the mobile version of the site, but what they really want is the option to be able to switch to the desktop view. "Why they might want to do that?", you might wonder.Well first of all the users of our ASP.Net MVC 4.0 application will appreciate that they have the option to switch views while some others will think that they will enjoy more the contents of our website with the "desktop view" since the mobile device they view our site has a quite large display.  Obviously this is only one site. These are just different views that are rendered.To put it simply, browser overriding lets our application treat requests as if they were coming from a different browser rather than the one they are actually from. In order to do that programmatically we must have a look at the System.Web.WebPages namespace and the classes in it. Most specifically the class BrowserHelpers. Have a look at the picture below   In this class we see some extension methods for HttpContext class.These methods are called extensions-helpers methods and we use them to switch to one browser from another thus overriding the current/actual browser. These APIs have effect on layout,views and partial views and will not affect any other ASP.Net Request.Browser related functionality.The overridden browser is stored in a cookie. Let me explain what some of these methods do. SetOverriddenBrowser() -  let us set the user agent string to specific value GetOverriddenBrowser() -  let us get the overridden value ClearOverriddenBrowser() -  let us remove any overridden user agent for the current request   To recap, in our ASP.Net MVC 4.0 applications when our application is viewed in our mobile devices, we can have a link like "Desktop View" for all those who desperately want to see the site with in full desktop-browser version.We then can specify a browser type override. My controller class (snippet of code) that is responsible for handling the switching could be something like that. public class SwitchViewController : Controller{ public RedirectResult SwitchView(bool mobile, string returnUrl){if (Request.Browser.IsMobileDevice == mobile)HttpContext.ClearOverriddenBrowser();elseHttpContext.SetOverriddenBrowser(mobile ? BrowserOverride.Mobile : BrowserOverride.Desktop);return Redirect(returnUrl);}} Hope it helps!!!!

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  • New way of creating web applications on Visual Studio 2013

    - by DigiMortal
    Yesterday Visual Studio 2013 Preview was released and now it’s time to play with it. First thing I noticed was the new way how to create web applications. For all web applications there is generic dialog where you can set all important options for your new web application before it is created. Let’s see how it works. Also let’s take a look at new blue theme of Visual Studio 2013. Read more from my new blog @ gunnarpeipman.com

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  • Feedback Filtration&ndash;Processing Negative Comments for Positive Gains

    - by D'Arcy Lussier
    After doing 7 conferences, 5 code camps, and countless user group events, I feel that this is a post I need to write. I actually toyed with other names for this post, however those names would just lend itself to the type of behaviour I want people to avoid – the reactionary, emotional response that speaks to some deeper issue beyond immediate facts and context. Humans are incredibly complex creatures. We’re also emotional, which serves us well in certain situations but can hinder us in others. Those of us in leadership build up a thick skin because we tend to encounter those reactionary, emotional responses more often, and we’re held to a higher standard because of our positions. While we could react with emotion ourselves, as the saying goes – fighting fire with fire just makes a bigger fire. So in this post I’ll share my thought process for dealing with negative feedback/comments and how you can still get value from them. The Thought Process Let’s take a real-world example. This week I held the Prairie IT Pro & Dev Con event. We’ve gotten a lot of session feedback already, most of it overwhelmingly positive. But some not so much – and some to an extreme I rarely see but isn’t entirely surprising to me. So here’s the example from a person we’ll refer to as Mr. Horrible: How was the speaker? Horrible! Worst speaker ever! Did the session meet your expectations? Hard to tell, speaker ruined it. Other Comments: DO NOT bring this speaker back! He was at this conference last year and I hoped enough negative feedback would have taught you to not bring him back...obviously not...I will not return to this conference next year if this speaker is brought back. Now those are very strong words. “Worst speaker ever!” “Speaker ruined it” “I will not return to this conference next year if the speaker is brought back”. The speakers I invite to speak at my conference are not just presenters but friends and colleagues. When I see this, my initial reaction is of course very emotional: I get defensive, I get angry, I get offended. So that’s where the process kicks in. Step 1 – Take a Deep Breath Take a deep breath, calm down, and walk away from the keyboard. I didn’t do that recently during an email convo between some colleagues and it ended up in my reacting emotionally on Twitter – did I mention those colleagues follow my Twitter feed? Yes, I ate some crow. Ok, now that we’re calm, let’s move on to step 2. Step 2 – Strip off the Emotion We need to take off the emotion that people wrap their words in and identify the root issues. For instance, if I see: “I hated this session, the presenter was horrible! He spoke so fast I couldn’t make out what he was saying!” then I drop off the personal emoting (“I hated…”) and the personal attack (“the presenter was horrible”) and focus on the real issue this person had – that the speaker was talking too fast. Now we have a root cause of the displeasure. However, we’re also dealing with humans who are all very different. Before I call up the speaker to talk about his speaking pace, I need to do some other things first. Back to our Mr. Horrible example, I don’t really have much to go on. There’s no details of how the speaker “ruined” the session or why he’s the “worst speaker ever”. In this case, the next step is crucial. Step 3 – Validate the Feedback When I tell people that we really like getting feedback for the sessions, I really really mean it. Not just because we want to hear what individuals have to say but also because we want to know what the group thought. When a piece of negative feedback comes in, I validate it against the group. So with the speaker Mr. Horrible commented on, I go to the feedback and look at other people’s responses: 2 x Excellent 1 x Alright 1 x Not Great 1 x Horrible (our feedback guy) That’s interesting, it’s a bit all over the board. If we look at the comments more we find that the people who rated the speaker excellent liked the presentation style and found the content valuable. The one guy who said “Not Great” even commented that there wasn’t anything really wrong with the presentation, he just wasn’t excited about it. In that light, I can try to make a few assumptions: - Mr. Horrible didn’t like the speakers presentation style - Mr. Horrible was expecting something else that wasn’t communicated properly in the session description - Mr. Horrible, for whatever reason, just didn’t like this presenter Now if the feedback was overwhelmingly negative, there’s a different pattern – one that validates the negative feedback. Regardless, I never take something at face value. Even if I see really good feedback, I never get too happy until I see that there’s a group trend towards the positive. Step 4 – Action Plan Once I’ve validated the feedback, then I need to come up with an action plan around it. Let’s go back to the other example I gave – the one with the speaker going too fast. I went and looked at the feedback and sure enough, other people commented that the speaker had spoken too quickly. Now I can go back to the speaker and let him know so he can get better. But what if nobody else complained about it? I’d still mention it to the speaker, but obviously one person’s opinion needs to be weighed as such. When we did PrDC Winnipeg in 2011, I surveyed the attendees about the food. Everyone raved about it…except one person. Am I going to change the menu next time for that one person while everyone else loved it? Of course not. There’s a saying – A sure way to fail is to try to please everyone. Let’s look at the Mr. Horrible example. What can I communicate to the speaker with such limited information provided in the feedback from Mr. Horrible? Well looking at the groups feedback, I can make a few suggestions: - Ensure that people understand in the session description the style of the talk - Ensure that people understand the level of detail/complexity of the talk and what prerequisite knowledge they should have I’m looking at it as possibly Mr. Horrible assumed a much more advanced talk and was disappointed, while the positive feedback by people who – from their comments – suggested this was all new to them, were thrilled with the session level. Step 5 – Follow Up For some feedback, I follow up personally. Especially with negative or constructive feedback, its important to let the person know you heard them and are making changes because of their comments. Even if their comments were emotionally charged and overtly negative, it’s still important to reach out personally and professionally. When you remove the emotion, negative comments can be the best feedback you get. Also, people have bad days. We’ve all had one of “those days” where we talked more sternly than normal to someone, or got angry at something we’d normally shrug off. We have various stresses in our lives and sometimes they seep out in odd ways. I always try to give some benefit of the doubt, and re-evaluate my view of the person after they’ve responded to my communication. But, there is such a thing as garbage feedback. What Mr. Horrible wrote is garbage. It’s mean spirited. It’s hateful. It provides nothing constructive at all. And a tell-tale sign that feedback is garbage – the person didn’t leave their name even though there was a field for it. Step 6 – Delete It Feedback must be processed in its raw form, and the end products should drive improvements. But once you’ve figured out what those things are, you shouldn’t leave raw feedback lying around. They are snapshots in time that taken alone can be damaging. Also, you should never rest on past praise. In a future blog post, I’m going to talk about how we can provide great feedback that, even when its critical, can still be constructive.

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  • SQL SERVER – Introduction to FIRST _VALUE and LAST_VALUE – Analytic Functions Introduced in SQL Server 2012

    - by pinaldave
    SQL Server 2012 introduces new analytical functions FIRST_VALUE() and LAST_VALUE(). This function returns first and last value from the list. It will be very difficult to explain this in words so I’d like to attempt to explain its function through a brief example. Instead of creating a new table, I will be using the AdventureWorks sample database as most developers use that for experiment purposes. Now let’s have fun following query: USE AdventureWorks GO SELECT s.SalesOrderID,s.SalesOrderDetailID,s.OrderQty, FIRST_VALUE(SalesOrderDetailID) OVER (ORDER BY SalesOrderDetailID) FstValue, LAST_VALUE(SalesOrderDetailID) OVER (ORDER BY SalesOrderDetailID) LstValue FROM Sales.SalesOrderDetail s WHERE SalesOrderID IN (43670, 43669, 43667, 43663) ORDER BY s.SalesOrderID,s.SalesOrderDetailID,s.OrderQty GO The above query will give us the following result: What’s the most interesting thing here is that as we go from row 1 to row 10, the value of the FIRST_VALUE() remains the same but the value of the LAST_VALUE is increasing. The reason behind this is that as we progress in every line – considering that line and all the other lines before it, the last value will be of the row where we are currently looking at. To fully understand this statement, see the following figure: This may be useful in some cases; but not always. However, when we use the same thing with PARTITION BY, the same query starts showing the result which can be easily used in analytical algorithms and needs. Let us have fun through the following query: Let us fun following query. USE AdventureWorks GO SELECT s.SalesOrderID,s.SalesOrderDetailID,s.OrderQty, FIRST_VALUE(SalesOrderDetailID) OVER (PARTITION BY SalesOrderID ORDER BY SalesOrderDetailID) FstValue, LAST_VALUE(SalesOrderDetailID) OVER (PARTITION BY SalesOrderID ORDER BY SalesOrderDetailID) LstValue FROM Sales.SalesOrderDetail s WHERE SalesOrderID IN (43670, 43669, 43667, 43663) ORDER BY s.SalesOrderID,s.SalesOrderDetailID,s.OrderQty GO The above query will give us the following result: Let us understand how PARTITION BY windows the resultset. I have used PARTITION BY SalesOrderID in my query. This will create small windows of the resultset from the original resultset and will follow the logic or FIRST_VALUE and LAST_VALUE in this resultset. Well, this is just an introduction to these functions. In the future blog posts we will go deeper to discuss the usage of these two functions. By the way, these functions can be applied over VARCHAR fields as well and are not limited to the numeric field only. Reference: Pinal Dave (http://blog.SQLAuthority.com) Filed under: Pinal Dave, PostADay, SQL, SQL Authority, SQL Function, SQL Query, SQL Scripts, SQL Server, SQL Tips and Tricks, T SQL, Technology

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  • SQL SERVER – Saturday Fun Puzzle with SQL Server DATETIME2 and CAST

    - by pinaldave
    Note: I have used SQL Server 2012 for this small fun experiment. Here is what we are going to do. We will run the script one at time instead of running them all together and try to guess the answer. I am confident that many will get it correct but if you do not get correct, you learn something new. Let us create database and sample table. CREATE DATABASE DB2012 GO USE DB2012 GO CREATE TABLE TableDT (DT1 VARCHAR(100), DT2 DATETIME2, DT1C AS DT1, DT2C AS DT2); INSERT INTO TableDT (DT1, DT2) SELECT GETDATE(), GETDATE() GO There are four columns in the table. The first column DT1 is regular VARCHAR and second DT2 is DATETIME2. Both of the column are been populated with the same data as I have used the function GETDATE(). Now let us do the SELECT statement and get the result from both the columns. Before running the query please guess the answer and write it down on the paper or notepad. Question 1: Guess the resultset SELECT DT1, DT2 FROM TableDT GO Now once again run the select statement on the same table but this time retrieve the computed columns only. Once again I suggest you write down the result on the notepad. Question 2: Guess the resultset SELECT DT1C, DT2C FROM TableDT GO Now here is the best part. Let us use the CAST function over the computed columns. Here I do want you to stop and guess the answer for sure. If you have not done it so far, stop do it, believe me you will like it. Question 3: Guess the resultset SELECT CAST(DT1C AS DATETIME2) CDT1C, CAST(DT2C AS DATETIME2) CDT1C FROM TableDT GO Now let us inspect all the answers together and see how many of you got it correct. Answer 1: Answer 2: Answer 3:  If you have not tried to run the script so far, you can execute all the three of the above script together over here and see the result together. SELECT CAST(DT1C AS DATETIME2) CDT1C, CAST(DT2C AS DATETIME2) CDT1C FROM TableDT GO Here is the Saturday Fun question to you – why do we get same result from both of the expressions in Question 3, where as in question 2 both the expression have different answer. I will publish the valid answer with explanation in future blog posts. Reference: Pinal Dave (http://blog.sqlauthority.com) Filed under: PostADay, SQL, SQL Authority, SQL DateTime, SQL Puzzle, SQL Query, SQL Server, SQL Tips and Tricks, T SQL, Technology

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  • C# Extension Methods - To Extend or Not To Extend...

    - by James Michael Hare
    I've been thinking a lot about extension methods lately, and I must admit I both love them and hate them. They are a lot like sugar, they taste so nice and sweet, but they'll rot your teeth if you eat them too much.   I can't deny that they aren't useful and very handy. One of the major components of the Shared Component library where I work is a set of useful extension methods. But, I also can't deny that they tend to be overused and abused to willy-nilly extend every living type.   So what constitutes a good extension method? Obviously, you can write an extension method for nearly anything whether it is a good idea or not. Many times, in fact, an idea seems like a good extension method but in retrospect really doesn't fit.   So what's the litmus test? To me, an extension method should be like in the movies when a person runs into their twin, separated at birth. You just know you're related. Obviously, that's hard to quantify, so let's try to put a few rules-of-thumb around them.   A good extension method should:     Apply to any possible instance of the type it extends.     Simplify logic and improve readability/maintainability.     Apply to the most specific type or interface applicable.     Be isolated in a namespace so that it does not pollute IntelliSense.     So let's look at a few examples in relation to these rules.   The first rule, to me, is the most important of all. Once again, it bears repeating, a good extension method should apply to all possible instances of the type it extends. It should feel like the long lost relative that should have been included in the original class but somehow was missing from the family tree.    Take this nifty little int extension, I saw this once in a blog and at first I really thought it was pretty cool, but then I started noticing a code smell I couldn't quite put my finger on. So let's look:       public static class IntExtensinos     {         public static int Seconds(int num)         {             return num * 1000;         }           public static int Minutes(int num)         {             return num * 60000;         }     }     This is so you could do things like:       ...     Thread.Sleep(5.Seconds());     ...     proxy.Timeout = 1.Minutes();     ...     Awww, you say, that's cute! Well, that's the problem, it's kitschy and it doesn't always apply (and incidentally you could achieve the same thing with TimeStamp.FromSeconds(5)). It's syntactical candy that looks cool, but tends to rot and pollute the code. It would allow things like:       total += numberOfTodaysOrders.Seconds();     which makes no sense and should never be allowed. The problem is you're applying an extension method to a logical domain, not a type domain. That is, the extension method Seconds() doesn't really apply to ALL ints, it applies to ints that are representative of time that you want to convert to milliseconds.    Do you see what I mean? The two problems, in a nutshell, are that a) Seconds() called off a non-time value makes no sense and b) calling Seconds() off something to pass to something that does not take milliseconds will be off by a factor of 1000 or worse.   Thus, in my mind, you should only ever have an extension method that applies to the whole domain of that type.   For example, this is one of my personal favorites:       public static bool IsBetween<T>(this T value, T low, T high)         where T : IComparable<T>     {         return value.CompareTo(low) >= 0 && value.CompareTo(high) <= 0;     }   This allows you to check if any IComparable<T> is within an upper and lower bound. Think of how many times you type something like:       if (response.Employee.Address.YearsAt >= 2         && response.Employee.Address.YearsAt <= 10)     {     ...     }     Now, you can instead type:       if(response.Employee.Address.YearsAt.IsBetween(2, 10))     {     ...     }     Note that this applies to all IComparable<T> -- that's ints, chars, strings, DateTime, etc -- and does not depend on any logical domain. In addition, it satisfies the second point and actually makes the code more readable and maintainable.   Let's look at the third point. In it we said that an extension method should fit the most specific interface or type possible. Now, I'm not saying if you have something that applies to enumerables, you create an extension for List, Array, Dictionary, etc (though you may have reasons for doing so), but that you should beware of making things TOO general.   For example, let's say we had an extension method like this:       public static T ConvertTo<T>(this object value)     {         return (T)Convert.ChangeType(value, typeof(T));     }         This lets you do more fluent conversions like:       double d = "5.0".ConvertTo<double>();     However, if you dig into Reflector (LOVE that tool) you will see that if the type you are calling on does not implement IConvertible, what you convert to MUST be the exact type or it will throw an InvalidCastException. Now this may or may not be what you want in this situation, and I leave that up to you. Things like this would fail:       object value = new Employee();     ...     // class cast exception because typeof(IEmployee) != typeof(Employee)     IEmployee emp = value.ConvertTo<IEmployee>();       Yes, that's a downfall of working with Convertible in general, but if you wanted your fluent interface to be more type-safe so that ConvertTo were only callable on IConvertibles (and let casting be a manual task), you could easily make it:         public static T ConvertTo<T>(this IConvertible value)     {         return (T)Convert.ChangeType(value, typeof(T));     }         This is what I mean by choosing the best type to extend. Consider that if we used the previous (object) version, every time we typed a dot ('.') on an instance we'd pull up ConvertTo() whether it was applicable or not. By filtering our extension method down to only valid types (those that implement IConvertible) we greatly reduce our IntelliSense pollution and apply a good level of compile-time correctness.   Now my fourth rule is just my general rule-of-thumb. Obviously, you can make extension methods as in-your-face as you want. I included all mine in my work libraries in its own sub-namespace, something akin to:       namespace Shared.Core.Extensions { ... }     This is in a library called Shared.Core, so just referencing the Core library doesn't pollute your IntelliSense, you have to actually do a using on Shared.Core.Extensions to bring the methods in. This is very similar to the way Microsoft puts its extension methods in System.Linq. This way, if you want 'em, you use the appropriate namespace. If you don't want 'em, they won't pollute your namespace.   To really make this work, however, that namespace should only include extension methods and subordinate types those extensions themselves may use. If you plant other useful classes in those namespaces, once a user includes it, they get all the extensions too.   Also, just as a personal preference, extension methods that aren't simply syntactical shortcuts, I like to put in a static utility class and then have extension methods for syntactical candy. For instance, I think it imaginable that any object could be converted to XML:       namespace Shared.Core     {         // A collection of XML Utility classes         public static class XmlUtility         {             ...             // Serialize an object into an xml string             public static string ToXml(object input)             {                 var xs = new XmlSerializer(input.GetType());                   // use new UTF8Encoding here, not Encoding.UTF8. The later includes                 // the BOM which screws up subsequent reads, the former does not.                 using (var memoryStream = new MemoryStream())                 using (var xmlTextWriter = new XmlTextWriter(memoryStream, new UTF8Encoding()))                 {                     xs.Serialize(xmlTextWriter, input);                     return Encoding.UTF8.GetString(memoryStream.ToArray());                 }             }             ...         }     }   I also wanted to be able to call this from an object like:       value.ToXml();     But here's the problem, if i made this an extension method from the start with that one little keyword "this", it would pop into IntelliSense for all objects which could be very polluting. Instead, I put the logic into a utility class so that users have the choice of whether or not they want to use it as just a class and not pollute IntelliSense, then in my extensions namespace, I add the syntactical candy:       namespace Shared.Core.Extensions     {         public static class XmlExtensions         {             public static string ToXml(this object value)             {                 return XmlUtility.ToXml(value);             }         }     }   So now it's the best of both worlds. On one hand, they can use the utility class if they don't want to pollute IntelliSense, and on the other hand they can include the Extensions namespace and use as an extension if they want. The neat thing is it also adheres to the Single Responsibility Principle. The XmlUtility is responsible for converting objects to XML, and the XmlExtensions is responsible for extending object's interface for ToXml().

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