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  • Of transactions and Mongo

    - by Nuri Halperin
    Originally posted on: http://geekswithblogs.net/nuri/archive/2014/05/20/of-transactions-and-mongo-again.aspxWhat's the first thing you hear about NoSQL databases? That they lose your data? That there's no transactions? No joins? No hope for "real" applications? Well, you *should* be wondering whether a certain of database is the right one for your job. But if you do so, you should be wondering that about "traditional" databases as well! In the spirit of exploration let's take a look at a common challenge: You are a bank. You have customers with accounts. Customer A wants to pay B. You want to allow that only if A can cover the amount being transferred. Let's looks at the problem without any context of any database engine in mind. What would you do? How would you ensure that the amount transfer is done "properly"? Would you prevent a "transaction" from taking place unless A can cover the amount? There are several options: Prevent any change to A's account while the transfer is taking place. That boils down to locking. Apply the change, and allow A's balance to go below zero. Charge person A some interest on the negative balance. Not friendly, but certainly a choice. Don't do either. Options 1 and 2 are difficult to attain in the NoSQL world. Mongo won't save you headaches here either. Option 3 looks a bit harsh. But here's where this can go: ledger. See, and account doesn't need to be represented by a single row in a table of all accounts with only the current balance on it. More often than not, accounting systems use ledgers. And entries in ledgers - as it turns out – don't actually get updated. Once a ledger entry is written, it is not removed or altered. A transaction is represented by an entry in the ledger stating and amount withdrawn from A's account and an entry in the ledger stating an addition of said amount to B's account. For sake of space-saving, that entry in the ledger can happen using one entry. Think {Timestamp, FromAccountId, ToAccountId, Amount}. The implication of the original question – "how do you enforce non-negative balance rule" then boils down to: Insert entry in ledger Run validation of recent entries Insert reverse entry to roll back transaction if validation failed. What is validation? Sum up the transactions that A's account has (all deposits and debits), and ensure the balance is positive. For sake of efficiency, one can roll up transactions and "close the book" on transactions with a pseudo entry stating balance as of midnight or something. This lets you avoid doing math on the fly on too many transactions. You simply run from the latest "approved balance" marker to date. But that's an optimization, and premature optimizations are the root of (some? most?) evil.. Back to some nagging questions though: "But mongo is only eventually consistent!" Well, yes, kind of. It's not actually true that Mongo has not transactions. It would be more descriptive to say that Mongo's transaction scope is a single document in a single collection. A write to a Mongo document happens completely or not at all. So although it is true that you can't update more than one documents "at the same time" under a "transaction" umbrella as an atomic update, it is NOT true that there' is no isolation. So a competition between two concurrent updates is completely coherent and the writes will be serialized. They will not scribble on the same document at the same time. In our case - in choosing a ledger approach - we're not even trying to "update" a document, we're simply adding a document to a collection. So there goes the "no transaction" issue. Now let's turn our attention to consistency. What you should know about mongo is that at any given moment, only on member of a replica set is writable. This means that the writable instance in a set of replicated instances always has "the truth". There could be a replication lag such that a reader going to one of the replicas still sees "old" state of a collection or document. But in our ledger case, things fall nicely into place: Run your validation against the writable instance. It is guaranteed to have a ledger either with (after) or without (before) the ledger entry got written. No funky states. Again, the ledger writing *adds* a document, so there's no inconsistent document state to be had either way. Next, we might worry about data loss. Here, mongo offers several write-concerns. Write-concern in Mongo is a mode that marshals how uptight you want the db engine to be about actually persisting a document write to disk before it reports to the application that it is "done". The most volatile, is to say you don't care. In that case, mongo would just accept your write command and say back "thanks" with no guarantee of persistence. If the server loses power at the wrong moment, it may have said "ok" but actually no written the data to disk. That's kind of bad. Don't do that with data you care about. It may be good for votes on a pole regarding how cute a furry animal is, but not so good for business. There are several other write-concerns varying from flushing the write to the disk of the writable instance, flushing to disk on several members of the replica set, a majority of the replica set or all of the members of a replica set. The former choice is the quickest, as no network coordination is required besides the main writable instance. The others impose extra network and time cost. Depending on your tolerance for latency and read-lag, you will face a choice of what works for you. It's really important to understand that no data loss occurs once a document is flushed to an instance. The record is on disk at that point. From that point on, backup strategies and disaster recovery are your worry, not loss of power to the writable machine. This scenario is not different from a relational database at that point. Where does this leave us? Oh, yes. Eventual consistency. By now, we ensured that the "source of truth" instance has the correct data, persisted and coherent. But because of lag, the app may have gone to the writable instance, performed the update and then gone to a replica and looked at the ledger there before the transaction replicated. Here are 2 options to deal with this. Similar to write concerns, mongo support read preferences. An app may choose to read only from the writable instance. This is not an awesome choice to make for every ready, because it just burdens the one instance, and doesn't make use of the other read-only servers. But this choice can be made on a query by query basis. So for the app that our person A is using, we can have person A issue the transfer command to B, and then if that same app is going to immediately as "are we there yet?" we'll query that same writable instance. But B and anyone else in the world can just chill and read from the read-only instance. They have no basis to expect that the ledger has just been written to. So as far as they know, the transaction hasn't happened until they see it appear later. We can further relax the demand by creating application UI that reacts to a write command with "thank you, we will post it shortly" instead of "thank you, we just did everything and here's the new balance". This is a very powerful thing. UI design for highly scalable systems can't insist that the all databases be locked just to paint an "all done" on screen. People understand. They were trained by many online businesses already that your placing of an order does not mean that your product is already outside your door waiting (yes, I know, large retailers are working on it... but were' not there yet). The second thing we can do, is add some artificial delay to a transaction's visibility on the ledger. The way that works is simply adding some logic such that the query against the ledger never nets a transaction for customers newer than say 15 minutes and who's validation flag is not set. This buys us time 2 ways: Replication can catch up to all instances by then, and validation rules can run and determine if this transaction should be "negated" with a compensating transaction. In case we do need to "roll back" the transaction, the backend system can place the timestamp of the compensating transaction at the exact same time or 1ms after the original one. Effectively, once A or B visits their ledger, both transactions would be visible and the overall balance "as of now" would reflect no change.  The 2 transactions (attempted/ reverted) would be visible , since we do actually account for the attempt. Hold on a second. There's a hole in the story: what if several transfers from A to some accounts are registered, and 2 independent validators attempt to compute the balance concurrently? Is there a chance that both would conclude non-sufficient-funds even though rolling back transaction 100 would free up enough for transaction 117 (some random later transaction)? Yes. there is that chance. But the integrity of the business rule is not compromised, since the prime rule is don't dispense money you don't have. To minimize or eliminate this scenario, we can also assign a single validation process per origin account. This may seem non-scalable, but it can easily be done as a "sharded" distribution. Say we have 11 validation threads (or processing nodes etc.). We divide the account number space such that each validator is exclusively responsible for a certain range of account numbers. Sounds cunningly similar to Mongo's sharding strategy, doesn't it? Each validator then works in isolation. More capacity needed? Chop the account space into more chunks. So where  are we now with the nagging questions? "No joins": Huh? What are those for? "No transactions": You mean no cross-collection and no cross-document transactions? Granted - but don't always need them either. "No hope for real applications": well... There are more issues and edge cases to slog through, I'm sure. But hopefully this gives you some ideas of how to solve common problems without distributed locking and relational databases. But then again, you can choose relational databases if they suit your problem.

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  • Any FACEBOX altenatives?

    - by Nuri Akman
    Dear All, I'm using facebox ( http://famspam.com/facebox ) for calling web pages in modal window. Is there any RECOMMENDED alternatives to do this? I prefer jQuery releated solutions. Regards, Nuri Akman

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  • The last MVVM you'll ever need?

    - by Nuri Halperin
    As my MVC projects mature and grow, the need to have some omnipresent, ambient model properties quickly emerge. The application no longer has only one dynamic pieced of data on the page: A sidebar with a shopping cart, some news flash on the side – pretty common stuff. The rub is that a controller is invoked in context of a single intended request. The rest of the data, even though it could be just as dynamic, is expected to appear on it's own. There are many solutions to this scenario. MVVM prescribes creating elaborate objects which expose your new data as a property on some uber-object with more properties exposing the "side show" ambient data. The reason I don't love this approach is because it forces fairly acute awareness of the view, and soon enough you have many MVVM objects laying around, and views have to start doing null-checks in order to ensure you really supplied all the values before binding to them. Ick. Just as unattractive is the ViewData dictionary. It's not strongly typed, and in both this and the MVVM approach someone has to populate these properties – n'est pas? Where does that live? With MVC2, we get the formerly-futures  feature Html.RenderAction(). The feature allows you plant a line in a view, of the format: <% Html.RenderAction("SessionInterest", "Session"); %> While this syntax looks very clean, I can't help being bothered by it. MVC was touting a very strong separation of concerns, the Model taking on the role of the business logic, the controller handling route and performing minimal view-choosing operations and the views strictly focused on rendering out angled-bracket tags. The RenderAction() syntax has the view calling some controller and invoking it inline with it's runtime rendering. This – to my taste – embeds too much  knowledge of controllers into the view's code – which was allegedly forbidden.  The one way flow "Controller Receive Data –> Controller invoke Model –> Controller select view –> Controller Hand data to view" now gets a "View calls controller and gets it's own data" which is not so one-way anymore. Ick. I toyed with some other solutions a bit, including some base controllers, special view classes etc. My current favorite though is making use of the ExpandoObject and dynamic features with C# 4.0. If you follow Phil Haack or read a bit from David Heyden you can see the general picture emerging. The game changer is that using the new dynamic syntax, one can sprout properties on an object and make use of them in the view. Well that beats having a bunch of uni-purpose MVVM's any day! Rather than statically exposed properties, we'll just use the capability of adding members at runtime. Armed with new ideas and syntax, I went to work: First, I created a factory method to enrich the focuse object: public static class ModelExtension { public static dynamic Decorate(this Controller controller, object mainValue) { dynamic result = new ExpandoObject(); result.Value = mainValue; result.SessionInterest = CodeCampBL.SessoinInterest(); result.TagUsage = CodeCampBL.TagUsage(); return result; } } This gives me a nice fluent way to have the controller add the rest of the ambient "side show" items (SessionInterest, TagUsage in this demo) and expose them all as the Model: public ActionResult Index() { var data = SyndicationBL.Refresh(TWEET_SOURCE_URL); dynamic result = this.Decorate(data); return View(result); } So now what remains is that my view knows to expect a dynamic object (rather than statically typed) so that the ASP.NET page compiler won't barf: <%@ Page Language="C#" Title="Ambient Demo" MasterPageFile="~/Views/Shared/Ambient.Master" Inherits="System.Web.Mvc.ViewPage<dynamic>" %> Notice the generic ViewPage<dynamic>. It doesn't work otherwise. In the page itself, Model.Value property contains the main data returned from the controller. The nice thing about this, is that the master page (Ambient.Master) also inherits from the generic ViewMasterPage<dynamic>. So rather than the page worrying about all this ambient stuff, the side bars and panels for ambient data all reside in a master page, and can be rendered using the RenderPartial() syntax: <% Html.RenderPartial("TagCloud", Model.SessionInterest as Dictionary<string, int>); %> Note here that a cast is necessary. This is because although dynamic is magic, it can't figure out what type this property is, and wants you to give it a type so its binder can figure out the right property to bind to at runtime. I use as, you can cast if you like. So there we go – no violation of MVC, no explosion of MVVM models and voila – right? Well, I could not let this go without a tweak or two more. The first thing to improve, is that some views may not need all the properties. In that case, it would be a waste of resources to populate every property. The solution to this is simple: rather than exposing properties, I change d the factory method to expose lambdas - Func<T> really. So only if and when a view accesses a member of the dynamic object does it load the data. public static class ModelExtension { // take two.. lazy loading! public static dynamic LazyDecorate(this Controller c, object mainValue) { dynamic result = new ExpandoObject(); result.Value = mainValue; result.SessionInterest = new Func<Dictionary<string, int>>(() => CodeCampBL.SessoinInterest()); result.TagUsage = new Func<Dictionary<string, int>>(() => CodeCampBL.TagUsage()); return result; } } Now that lazy loading is in place, there's really no reason not to hook up all and any possible ambient property. Go nuts! Add them all in – they won't get invoked unless used. This now requires changing the signature of usage on the ambient properties methods –adding some parenthesis to the master view: <% Html.RenderPartial("TagCloud", Model.SessionInterest() as Dictionary<string, int>); %> And, of course, the controller needs to call LazyDecorate() rather than the old Decorate(). The final touch is to introduce a convenience method to the my Controller class , so that the tedium of calling Decorate() everywhere goes away. This is done quite simply by adding a bunch of methods, matching View(object), View(string,object) signatures of the Controller class: public ActionResult Index() { var data = SyndicationBL.Refresh(TWEET_SOURCE_URL); return AmbientView(data); } //these methods can reside in a base controller for the solution: public ViewResult AmbientView(dynamic data) { dynamic result = ModelExtension.LazyDecorate(this, data); return View(result); } public ViewResult AmbientView(string viewName, dynamic data) { dynamic result = ModelExtension.LazyDecorate(this, data); return View(viewName, result); } The call to AmbientView now replaces any call the View() that requires the ambient data. DRY sattisfied, lazy loading and no need to replace core pieces of the MVC pipeline. I call this a good MVC day. Enjoy!

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  • MVC Automatic Menu

    - by Nuri Halperin
    An ex-colleague of mine used to call his SQL script generator "Super-Scriptmatic 2000". It impressed our then boss little, but was fun to say and use. We called every batch job and script "something 2000" from that day on. I'm tempted to call this one Menu-Matic 2000, except it's waaaay past 2000. Oh well. The problem: I'm developing a bunch of stuff in MVC. There's no PM to generate mounds of requirements and there's no Ux Architect to create wireframe. During development, things change. Specifically, actions get renamed, moved from controller x to y etc. Well, as the site grows, it becomes a major pain to keep a static menu up to date, because the links change. The HtmlHelper doesn't live up to it's name and provides little help. How do I keep this growing list of pesky little forgotten actions reigned in? The general plan is: Decorate every action you want as a menu item with a custom attribute Reflect out all menu items into a structure at load time Render the menu using as CSS  friendly <ul><li> HTML. The MvcMenuItemAttribute decorates an action, designating it to be included as a menu item: [AttributeUsage(AttributeTargets.Method, AllowMultiple = true)] public class MvcMenuItemAttribute : Attribute {   public string MenuText { get; set; }   public int Order { get; set; }   public string ParentLink { get; set; }   internal string Controller { get; set; }   internal string Action { get; set; }     #region ctor   public MvcMenuItemAttribute(string menuText) : this(menuText, 0) { } public MvcMenuItemAttribute(string menuText, int order) { MenuText = menuText; Order = order; }       internal string Link { get { return string.Format("/{0}/{1}", Controller, this.Action); } }   internal MvcMenuItemAttribute ParentItem { get; set; } #endregion } The MenuText allows overriding the text displayed on the menu. The Order allows the items to be ordered. The ParentLink allows you to make this item a child of another menu item. An example action could then be decorated thusly: [MvcMenuItem("Tracks", Order = 20, ParentLink = "/Session/Index")] . All pretty straightforward methinks. The challenge with menu hierarchy becomes fairly apparent when you try to render a menu and highlight the "current" item or render a breadcrumb control. Both encounter an  ambiguity if you allow a data source to have more than one menu item with the same URL link. The issue is that there is no great way to tell which link a person click. Using referring URL will fail if a user bookmarked the page. Using some extra query string to disambiguate duplicate URLs essentially changes the links, and also ads a chance of collision with other query parameters. Besides, that smells. The stock ASP.Net sitemap provider simply disallows duplicate URLS. I decided not to, and simply pick the first one encountered as the "current". Although it doesn't solve the issue completely – one might say they wanted the second of the 2 links to be "current"- it allows one to include a link twice (home->deals and products->deals etc), and the logic of deciding "current" is easy enough to explain to the customer. Now that we got that out of the way, let's build the menu data structure: public static List<MvcMenuItemAttribute> ListMenuItems(Assembly assembly) { var result = new List<MvcMenuItemAttribute>(); foreach (var type in assembly.GetTypes()) { if (!type.IsSubclassOf(typeof(Controller))) { continue; } foreach (var method in type.GetMethods()) { var items = method.GetCustomAttributes(typeof(MvcMenuItemAttribute), false) as MvcMenuItemAttribute[]; if (items == null) { continue; } foreach (var item in items) { if (String.IsNullOrEmpty(item.Controller)) { item.Controller = type.Name.Substring(0, type.Name.Length - "Controller".Length); } if (String.IsNullOrEmpty(item.Action)) { item.Action = method.Name; } result.Add(item); } } } return result.OrderBy(i => i.Order).ToList(); } Using reflection, the ListMenuItems method takes an assembly (you will hand it your MVC web assembly) and generates a list of menu items. It digs up all the types, and for each one that is an MVC Controller, digs up the methods. Methods decorated with the MvcMenuItemAttribute get plucked and added to the output list. Again, pretty simple. To make the structure hierarchical, a LINQ expression matches up all the items to their parent: public static void RegisterMenuItems(List<MvcMenuItemAttribute> items) { _MenuItems = items; _MenuItems.ForEach(i => i.ParentItem = items.FirstOrDefault(p => String.Equals(p.Link, i.ParentLink, StringComparison.InvariantCultureIgnoreCase))); } The _MenuItems is simply an internal list to keep things around for later rendering. Finally, to package the menu building for easy consumption: public static void RegisterMenuItems(Type mvcApplicationType) { RegisterMenuItems(ListMenuItems(Assembly.GetAssembly(mvcApplicationType))); } To bring this puppy home, a call in Global.asax.cs Application_Start() registers the menu. Notice the ugliness of reflection is tucked away from the innocent developer. All they have to do is call the RegisterMenuItems() and pass in the type of the application. When you use the new project template, global.asax declares a class public class MvcApplication : HttpApplication and that is why the Register call passes in that type. protected void Application_Start() { AreaRegistration.RegisterAllAreas(); RegisterRoutes(RouteTable.Routes);   MvcMenu.RegisterMenuItems(typeof(MvcApplication)); }   What else is left to do? Oh, right, render! public static void ShowMenu(this TextWriter output) { var writer = new HtmlTextWriter(output);   renderHierarchy(writer, _MenuItems, null); }   public static void ShowBreadCrumb(this TextWriter output, Uri currentUri) { var writer = new HtmlTextWriter(output); string currentLink = "/" + currentUri.GetComponents(UriComponents.Path, UriFormat.Unescaped);   var menuItem = _MenuItems.FirstOrDefault(m => m.Link.Equals(currentLink, StringComparison.CurrentCultureIgnoreCase)); if (menuItem != null) { renderBreadCrumb(writer, _MenuItems, menuItem); } }   private static void renderBreadCrumb(HtmlTextWriter writer, List<MvcMenuItemAttribute> menuItems, MvcMenuItemAttribute current) { if (current == null) { return; } var parent = current.ParentItem; renderBreadCrumb(writer, menuItems, parent); writer.Write(current.MenuText); writer.Write(" / ");   }     static void renderHierarchy(HtmlTextWriter writer, List<MvcMenuItemAttribute> hierarchy, MvcMenuItemAttribute root) { if (!hierarchy.Any(i => i.ParentItem == root)) return;   writer.RenderBeginTag(HtmlTextWriterTag.Ul); foreach (var current in hierarchy.Where(element => element.ParentItem == root).OrderBy(i => i.Order)) { if (ItemFilter == null || ItemFilter(current)) {   writer.RenderBeginTag(HtmlTextWriterTag.Li); writer.AddAttribute(HtmlTextWriterAttribute.Href, current.Link); writer.AddAttribute(HtmlTextWriterAttribute.Alt, current.MenuText); writer.RenderBeginTag(HtmlTextWriterTag.A); writer.WriteEncodedText(current.MenuText); writer.RenderEndTag(); // link renderHierarchy(writer, hierarchy, current); writer.RenderEndTag(); // li } } writer.RenderEndTag(); // ul } The ShowMenu method renders the menu out to the provided TextWriter. In previous posts I've discussed my partiality to using well debugged, time test HtmlTextWriter to render HTML rather than writing out angled brackets by hand. In addition, writing out using the actual writer on the actual stream rather than generating string and byte intermediaries (yes, StringBuilder being no exception) disturbs me. To carry out the rendering of an hierarchical menu, the recursive renderHierarchy() is used. You may notice that an ItemFilter is called before rendering each item. I figured that at some point one might want to exclude certain items from the menu based on security role or context or something. That delegate is the hook for such future feature. To carry out rendering of a breadcrumb recursion is used again, this time simply to unwind the parent hierarchy from the leaf node, then rendering on the return from the recursion rather than as we go along deeper. I guess I was stuck in LISP that day.. recursion is fun though.   Now all that is left is some usage! Open your Site.Master or wherever you'd like to place a menu or breadcrumb, and plant one of these calls: <% MvcMenu.ShowBreadCrumb(this.Writer, Request.Url); %> to show a breadcrumb trail (notice lack of "=" after <% and the semicolon). <% MvcMenu.ShowMenu(Writer); %> to show the menu.   As mentioned before, the HTML output is nested <UL> <LI> tags, which should make it easy to style using abundant CSS to produce anything from static horizontal or vertical to dynamic drop-downs.   This has been quite a fun little implementation and I was pleased that the code size remained low. The main crux was figuring out how to pass parent information from the attribute to the hierarchy builder because attributes have restricted parameter types. Once I settled on that implementation, the rest falls into place quite easily.

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  • DotNetNuke + PayPal

    - by Nuri Halperin
    A DotNetNuke i'm supporting has had a paypal "buy now" button and other variations with custom fields for a while now. About 2 weeks ago (somewhere in March 2010) they all stopped working. The problem manifested such that once you clicked the "buy now" button, Paypal site would throw a scary error page to the effect of: "Internal Server Error The server encountered an internal error or misconfiguration and was unable to complete your request. Please contact the server administrator, [email protected] and inform them of the time the error occurred, and anything you might have done that may have caused the error. More information about this error may be available in the server error log" Once I verified no cheeky content editor changed the page, I went digging for answers. The main source incompatibility of PayPal's simple HTML forms is that DNN includes a form on every page, and nested forms are not really supported. As blogged here and lamented here, the solution I came up with is simply to modify the form enctype to 'application/x-www-form-urlencoded' as illustrated below: 1: <input type="image" border="0" 2: src="https://www.paypal.com/en_US/i/btn/btn_buynowCC_LG.gif" 3: name="submit" 4: alt="PayPal - The safer, easier way to pay online!" 5: onClick="this.form.action='https://www.paypal.com/cgi-bin/webscr'; this.form.enctype='application/x-www-form-urlencoded';this.form.submit();" /> One would think that PayPal would want the masses submitting HTML in all manners of "enctype", but I guess every company has it's quirks. At least my favorite non-profit can now continue and accept payments. Sigh.

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  • How can I enable http auth in lighttpd for all directories except one?

    - by Nuri Hodges
    I am trying to authenticate access to everything in webroot (/) except anything that resides in a particular directory (/directory/) and I've tried both of these options to no avail: $HTTP["url"] =~ "^(?!(/directory))" { auth.require = ( "" => ( "method" => "basic", "realm" => "auth to this area", "require" => "user=username" ) ) } $HTTP["url"] != "/directory" { auth.require = ( "" => ( "method" => "basic", "realm" => "auth to this area", "require" => "user=username" ) ) }

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  • What am I doing wrong with this cat 6 patch panel wiring?

    - by Max Hodges
    top number is transmitter bottom number is remote terminator 12345678 36145278 is this because I could be mixing T568A and T568B wiring? how do I know if my patch cord is A or B? Do I just look at the plug and match it up with the diagram on the back of the panel somehow? EDIT I read that 36145278 indicates a cross over cable, but I'm not trying to make a cross over. Where did I go wrong? I'm guessing the cable plug is T568A but I wired it to the panel using T568B. So I need to redo it as T568A. But in the future how do I know if I cable is A or B? Cheers!

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  • Mercurial hook fails on Windows

    - by Nick Hodges
    I am trying to use the headcount hook (https://bitbucket.org/dgc/headcount/overview) with my main develop repository. I pulled the code and placed it in C:\Python26\Lib\site-packages. I made the following entries into my hgrc file: [hooks] pretxnchangegroup.headcount = python:headcount.headcount.hook [headcount] push_ok = * commit_ok = * warnmsg = %(headcount)d new heads detected. You may not push new heads to this repository. debug = False All this is as per the install instructions. I then cloned the repository, created a branch, committed a change to that branch, and then issued: hg push -f as a test. However, this fails with: C:\junk\htmlwriter>hg push -f pushing to c:\code\htmlwriter searching for changes adding changesets adding manifests adding file changes added 1 changesets with 1 changes to 1 files transaction abort! rollback completed abort: pretxnchangegroup.headcount hook is invalid (import of "headcount.headcou nt" failed) I then ran this: C:\Python26>python c:\Python26\Lib\site-packages\headcount\headcount.py Traceback (most recent call last): File "c:\Python26\Lib\site-packages\headcount\headcount.py", line 2, in <modul e> import mercurial.node ImportError: No module named mercurial.node I'm far from a python expert, so can someone help me figure out how to get the headcount hook to run inside my mercurial environment? Details: Windows 7, Mercurial 1.7.2, TortoiseHg 1.1.7

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  • Problem sending mail with simple .net application. Server refusal error.

    - by Fatih
    I have a very simple .net application for testing SMTP on .net. But i am receiving this weird error. "System.Net.Mail.SmtpException: Failure sending mail. --- System.Net.WebException: Unable to connect to the remote server --- System.Net.Sockets.SocketException: No connection could be made because the target machine actively refused it" SMTP server is remote and doesn't need any kind of authentication so i don't need credentials. But i can send mails from this computer with outlook using same smtp server and same smtp settings without any problem. Any ideas? It will be appreciated so much. Imports System.Net.Mail Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click Dim smtp As New SmtpClient smtp.Host = "10.241.128.220" smtp.Port = 25 smtp.Send("[email protected]", "[email protected]", "test", "test") End Sub

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  • Daily tech links for .net and related technologies - Mar 29-31, 2010

    - by SanjeevAgarwal
    Daily tech links for .net and related technologies - Mar 29-31, 2010 Web Development Querying the Future With Reactive Extensions - Phil Haack Creating an OData API for StackOverflow including XML and JSON in 30 minutes - Scott Hanselman MVC Automatic Menu - Nuri Halperin jqGrid for ASP.NET MVC - TriRand Team Foolproof Provides Contingent Data Annotation Validation for ASP.NET MVC 2 -Nick Riggs Using FubuMVC.UI in asp.net MVC : Getting started - Cannibal Coder Building A Custom ActionResult in MVC...(read more)

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  • Code Golf: Phone Number to Words

    - by Nick Hodges
    Guidelines for code-golf on SO We've all seen phone numbers that are put into words: 1-800-BUY-MORE, etc. What is the shortest amount of code you can write that will produce all the possible combinations of words for a 7 digit US phone number. Input will be a seven digit integer (or string, if that is simpler), and assume that the input is properly formed. Output will be a list of seven character strings that For instance, the number 428-5246 would produce GATJAGM GATJAGN GATJAGO GATJAHM GATJAHN GATJAHO and so on..... Winning criteria will be code from any language with the fewest characters that produce every possible letter combination. Additional Notes: To make it more interesting, words can be formed only by using the letters on a North American Classic Key Pad phone with three letters per number as defined here.That means that Z and Q are excluded. For the number '1', put a space. For the number '0', put a hyphen '-' Bonus points awarded for recognizing output as real English words. Okay, not really. ;-)

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  • How many developers are there in the world?

    - by Nick Hodges
    What is the total number of software developers in the world? And to respond to the inevitable "How do you define a software developer?" -- I'll answer two ways: Define it as "Anyone who writes code to make a computer do something he wants done". Define it however you like and then answer the question References to studies or more authoritative sources of information would be greatly appreciated.

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  • form not showing for empty records

    - by Chris Hodges
    I have a relatively simple PHP page called editcustomers with 3 columns. The problem I'm having is that the form will show when there is a record in the database and the fields will be populated with that info. When no such records exists, the form is not even shown, eliminating the possibility to insert a record. My page layout is as follows: Column 1 shows a form containing customer information, allowing it to be edited. Column 2 allows ordering of products and showing how many products were ordered Column 3 shows the total paid so far, and the total owing. The code for the page I have at present: <html> <?php $id = $_GET['id']; require_once('connect.php'); $sth = $dbh->query("SELECT * FROM users where id = '$id';"); $sth->setFetchMode(PDO::FETCH_ASSOC); $eth = $dbh->query("SELECT * FROM purchases where id = '$id';"); $eth->setFetchMode(PDO::FETCH_ASSOC); ?> <div id="main"> <div id="left"> <form name="custInfo" action ="process.php" method ="post" > <input type = "hidden" name ="formType" value="custInfo"/> <?php while($row = $sth->fetch()){ ?> <p><input type = "hidden" name ="id" value="<?php echo $row["id"] ?>"/> <p><input type = "text" name ="firstName" size ="30" value=" <?php echo $row["firstName"]?>"/> <p><input type = "text" name ="lastName" size ="30" value="<?php echo $row["lastName"]?>"/> <p><input type = "text" name ="country" size ="30" value="<?php echo $row["country"]?>"/> <p></p> <input type="submit" value="Update" /> <?php }?> </div> <div id="mid"> <form name="custCosts" action ="process.php" method ="post" > <input type = "hidden" name ="formType" value="custCosts"/> <?php while($row = $eth->fetch()){ ?> <p><input type = "hidden" name ="id" value="<?php echo $row["id"] ?>"/> <p><input type = "text" name ="amountOwed" size ="30" value=" <?php echo $row["amountOwed"]?>"/> <p><input type = "text" name ="numAaa" size ="30" value="<?php echo $row["numAaa"]?>"/> <p><input type = "text" name ="numBbb" size ="30" value="<?php echo $row["numBbb"]?>"/> <p></p> <input type="submit" value="Update" /> <?php }?> </div> <div id="right"> <b>Total Balance</b> <p> Money owed: </p> <p> aaa total: </p> <p> bbb total: </p> <p> Total: </p> <input type = "text" name ="pay" size ="20" /></p> <input type="submit" value="Make Payment" /> </div> <?php $dbh =null; ?> </body> </html> And the code for all the database trickery: <?php require_once 'connect.php'; $formType = $_POST['formType']; $id = $_POST['id']; $firstName = $_POST['firstName']; $lastName = $_POST['lastName']; $country = $_POST['country']; $amountOwed = $_POST['amountOwed ']; $numAaa = $_POST['numAaa']; $numBbb = $_POST['numBbb']; if(empty($_POST['id'])) { $sth = $dbh->prepare("INSERT INTO customers (firstName, lastName, country) VALUES ('$firstName', '$lastName', '$country')"); $sth->execute(); } elseif(!empty($_POST['id']) && !isset($_POST['stayCost']) && $_POST['formType'] == 'guestInfo'){ $sth = $dbh->prepare("UPDATE customers SET firstName = '$firstName', lastName = '$lastName', country = '$country' WHERE id = '$id'"); $sth->execute(); }elseif(!empty($_POST['id']) && isset($_POST['stayCost']) && $_POST['formType'] == 'guestInfo'){ $sth = $dbh->prepare("INSERT INTO purchases (id, amountOwed, numAaa, numBbb) VALUES ('$id', '$amountOwed', '$numAaa', '$numBbb'"); $sth->execute(); }elseif(!empty($_POST['id']) && $_POST['formType'] == 'guestCosts'){ $sth = $dbh->prepare("UPDATE purchases SET amountOwed= '$amountOwed', numAaa = '$numAaa', numBbb= '$numBbb' WHERE id = '$id'"); $sth->execute(); } $dbh =null; ?> Why does the form not even display if there is no record? An error or something I might understand....but the form is still in the HTML and should still be being output, from what I can see. Why is this not the case?

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  • Speaking at SW FL Code Camp Sept 8th 2012

    - by Nikita Polyakov
    It’s always a great time when it’s a Code Camp! I will be presenting “Windows [Phone] Live Tiles & Push Notifications“ at this year’s South West Florida Code Camp 2012 on September 8th.  As with many Code Camps – it’s going to be a trick to pick which session to go to at each time slot, and that’s how you know it’s a good one – so much content – so many great speakers! Hope to see you there! Details & Registration: http://codecamp.swfldev.net Code Camp 2012 will take place at: Hodges University 2649 Professional Circle Naples, Florida 34119 Don’t forget about these two great events coming up as well: http://www.TampaCodeCamp.com and http://itprocamp.com/tampa/

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  • How to enable SmartLinking?

    - by John
    Hello, I requested a feature on Delphi's uservoice(link) ,but I didn't understood the answer of Nick Hodges. What version of Delphi supports SmartLinking? How do I enable this option in Delphi 2009/Delphi 2010? Thanks in advance.

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