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• Mathematics for Computer Science Students

  - by Ender

  To cut a long story short, I am a CS student that has received no formal Post-16 Maths education for years. Right now even my Algebra is extremely rusty and I have a couple of months to shape up my skills. I've got a couple of video lectures in my bookmarks, consisting of: Pre-Calculus Algebra Calculus Probability Introduction to Statistics Differential Equations Linear Algebra My aim as of today is to be able to read the CLRS book Introduction to Algorithms and be able to follow the Mathematical notation in that, as well as being able to confidently read and back-up any arguments written in Mathematical notation. Aside from these video lectures, can anyone recommend any good books to help teach someone wishing to go from a low-foundation level to a more advanced level of Mathematics? Just as a note, I've taken a first-year module in Analytical Modelling, so I understand some of the basic concepts of Discrete Mathematics. EDIT: Just a note to those that are looking to learn Linear Algebra using the Video Lectures I have posted up. Peteris Krumins' Blog contains a run-through of these lecture notes as well as his own commentary and lecture notes, an invaluable resource for those looking to follow the lectures too.

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• emacs: x-popup-menu max size constraints?

  - by Cheeso

  I'm working on an intellisense or code-completion capability for C#. So far, so good. Right now I have basic completion working. There are 2 ways to request completion. The first cycles through all the potential matches. The second presents a popup menu of the matches. It works for types: And also for local variables: I'm confronting two problems with x-popup-menu: the popup menu can expand to consume all available screen space, when the number of choices is large. Literally it can obscure the entire screen. The silly thing is, it's scrollable. First it expands to consume all available space, then it also becomes scrollable. Is there a way I can limit the maximum size of x-popup-menu? To specify the position of the popup menu, I pass in a position, and x-popup-menu uses that as the *middle*, not the left, of the top line of the menu. Why middle? who knows. What this means is, if I specify (40 . 60) for the location of the menu, and the menu happens to be 100 pixels wide, the menu will extend beyond the left border of the emacs window. You can see this in the 2nd image above. If I knew how wide the popup would be before specifying the position, I could compensate. But I don't. Is there a workaround? Is there a way to get x-popup-menu to take its position as the LEFT rather than the middle.

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• problem with RenderOuterTable property for .net 4.0 controls

  - by Mario

  According to the new 4.0 framework overview, one should be able to add the attrib RenderOuterTable="false" to a control that supports the attribute and see css friendly code be spit out - in other words no html tables. To test this, I threw a login control into a basic fresh webpage with the following code: <asp:Login ID="Login1" runat="server" RenderOuterTable="false"></asp:Login> The result? Crappy html table output, which supposedly doesn't happen with this attrib set to false. Here is the output: &lt;table cellpadding=&quot;0&quot;&gt; <tr> <td align="center" colspan="2">Log In</td> </tr><tr> <td align="right"><label for="MainContent_Login1_UserName">User Name:</label></td><td><input name="ctl00$MainContent$Login1$UserName" type="text" id="MainContent_Login1_UserName" /><span id="MainContent_Login1_UserNameRequired" title="User Name is required." style="visibility:hidden;">*</span></td>... Hopefully you get the point. Anyone know how to stop these controls from outputting tables? This is super annoying.

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• Are there any ASP.NET MVC subscription-based starter kits or examples?

  - by Wayne M

  Basically something that handles the low-level "plumbing" code for a subscription-based service. I see a lot of things dealing with basic membership, but nothing that handles the subscription aspect (recurring billing, automated jobs for setting up billing, notification for billing, etc). This might be the one thing that keeps me from using ASP.NET MVC for my SaaS idea, since it would take a fair amount of development time to write my own; if I go with my other option, Ruby on Rails, I can buy a kit that does all of this for $250. I haven't found anything even remotely close to this for .NET - all of the SaaS sample apps I've seen are more like StackOverflow et all where you have one site that multiple people log on to, not the web application model where you have subscribers who are billed monthly, each of whom has users and other entities (e.g. Customers, Tasks, etc) for their own site. Is there anything similar for ASP.NET, or some kind of guidelines for writing my own if I have to, so I don't waste too much time? As a startup that means that I'm doing all the coding myself. I've found this, but it seems to only be for billing and didn't seem to have much (any?) documentation on exactly how to set it up.

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• ASP.NET Event delegation between user controls

  - by Ishan

  Give the following control hierarchy on a ASP.NET page: Page HeaderControl       (User Control) TitleControl       (Server Control) TabsControl       (User Control) other controls I'm trying to raise an event (or some notification) in the TitleControl that bubbles to the Page level. Then, I'd like to (optionally) register an event handler at the Page codebehind that will take the EventArgs and modify the TabsControl in the example above. The important thing to note is that this design will allow me to drop these controls into any Page and make the entire system work seamlessly if the event handler is wired up. The solution should not involve a call to FindControl() since that becomes a strong association. If no handler is defined in the containing Page, the event is still raised by TitleControl but is not handled. My basic goal is to use event-based programming so that I can decouple the user controls from each other. The event from TitleControl is only raised in some instances, and this seemed to be (in my head) the preferred approach. However, I can't seem to find a way to cleanly achieve this. Here are my (poor) attempts: Using HttpContext.Current.Items Add the EventArgs to the Items collection on TitleControl and pick it up on the TabsControl. This works but it's fundamentally hard to decipher since the connection between the two controls is not obvious. Using Reflection Instead of passing events, look for a function on the container Page directly within TitleControl as in: Page.GetType().GetMethod("TabControlHandler").Invoke(Page, EventArgs); This will work, but the method name will have to be a constant that all Page instances will have to defined verbatim. I'm sure that I'm over-thinking this and there must be a prettier solution using delegation, but I can't seem to think of it. Any thoughts?

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• Uncompress OpenOffice files for better storage in version control

  - by Craig McQueen

  I've heard discussion about how OpenOffice (ODF) files are compressed zip files of XML and other data. So making a tiny change to the file can potentially totally change the data, so delta compression doesn't work well in version control systems. I've done basic testing on an OpenOffice file, unzipping it and then rezipping it with zero compression. I used the Linux zip utility for my testing. OpenOffice will still happily open it. So I'm wondering if it's worth developing a small utility to run on ODF files each time just before I commit to version control. Any thoughts on this idea? Possible better alternatives? Secondly, what would be a good and robust way to implement this little utility? Bash shell that calls zip (probably Linux only)? Python? Any gotchas you can think of? Obviously I don't want to accidentally mangle a file, and there are several ways that could happen. Possible gotchas I can think of: Insufficient disk space Some other permissions issue that prevents writing the file or temporary files ODF document is encrypted (probably should just leave these alone; the encryption probably also causes large file changes and thus prevents efficient delta compression)

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• Unable to display Google Map through API in Flex SDK

  - by Spero.ShiroPetto

  Hello, I am using the mxmlc to compile the examples from google to get started in using Google Maps API in Flex 4. But after compiling the swf file the map does not load. I've registered for an API key Downloaded and included the Maps SDK in the xml config file used at compile time C:\sdk\flex4\frameworks\flex-config.xml <external-library-path> <path-element>libs/google/maps/lib/map_flex_1_18.swc</path-element> </external-library-path> Foo.mxml <?xml version="1.0" encoding="utf-8"?> <mx:Application xmlns:mx="http://www.adobe.com/2006/mxml" layout="absolute"> <maps:Map xmlns:maps="com.google.maps.*" id="map" mapevent_mapready="onMapReady(event)" width="100%" height="100%" key="{KEY}"/> <mx:Script> <![CDATA[ import com.google.maps.LatLng; import com.google.maps.Map; import com.google.maps.MapEvent; import com.google.maps.MapType; private function onMapReady(event:Event):void { this.map.setCenter(new LatLng(40.736072,-73.992062), 14, MapType.NORMAL_MAP_TYPE); } ]]> </mx:Script> </mx:Application> Any tips on where to go from here? I can compile a basic flex project without problem and displays the components I put in so i'd imagine it's something to do with the API Key? Thanks for the help

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• What is your preferred tool stack for PHP development in the Windows Environment?

  - by Tim Visher

  I have been developing basic web sites for awhile now with some PHP thrown in for getting dynamic stuff done. However, I recently decided that it was time I got my hands a little dirtier so I wanted to start to play with the underpinnings of Wordpress and other such apps. I work on a Mac at home and have been using Coda for most of my editing needs and I love it. Also, to manage the services stack I use MAMP at home. However, I've begun to realize that for heavy PHP and Web work (AJAX, etc.), more is needed. I'm very interested to hear the kinds of tools more experienced web developers use on a day to day basis to manage the entire work flow. I found this article over on developer tutorials and decided to go with XAMPP (for the moment) for managing the services. However, IDE, Source Control, Debugger, etc. are all up for grabs. Anyway, your thoughts are much appreciated. And, if at all possible, try to describe your entire stack with what each tool fulfills for your development process.

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• Architecture with NHibernate and Repositories

  - by Matthew

  I've been reading up on MVC 2 and the recommended patterns, so far I've come to the conclusion (amongst much hair pulling and total confusion) that: Model - Is just a basic data container Repository - Provides data access Service - Provides business logic and acts as an API to the Controller The Controller talks to the Service, the Service talks to the Repository and Model. So for example, if I wanted to display a blog post page with its comments, I might do: post = PostService.Get(id); comments = PostService.GetComments(post); Or, would I do: post = PostService.Get(id); comments = post.Comments; If so, where is this being set, from the repository? the problem there being its not lazy loaded.. that's not a huge problem but then say I wanted to list 10 posts with the first 2 comments for each, id have to load the posts then loop and load the comments which becomes messy. All of the example's use "InMemory" repository's for testing and say that including db stuff would be out of scope. But this leaves me with many blanks, so for a start can anyone comment on the above?

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• ASP.NET MVC 2 DisplayFor()

  - by ZombieSheep

  I'm looking at the new version of ASP.NET MVC (see here for more details if you haven't seen it already) and I'm having some pretty basic trouble displaying the content of an object. In my control I have an object of type "Person", which I am passing to the view in ViewData.Model. All is well so far, and I can extact the object in the view ready for display. What I don't get, though, is how I need to call the Html.DisplayFor() method in order to get the data to screen. I've tried the following... <% MVC2test.Models.Person p = ViewData.Model as MVC2test.Models.Person; %> // snip <%= Html.DisplayFor(p => p) %> but I get the following message: CS0136: A local variable named 'p' cannot be declared in this scope because it would give a different meaning to 'p', which is already used in a 'parent or current' scope to denote something else I know this is not what I should be doing - I know that redefining a variable will producte this error, but I don't know how to access the object from the controller. So my question is, how do I pass the object to the view in order to display its properties? (I should add that I am reading up on this in my limited spare time, so it is entirely possible I have missed something fundamental) TIA

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• Looking for recommnedation on JavaScript libraries in the leage of ExtJS and Qooxdoo for serious web

  - by Kabeer

  Hello. I'm looking for a JavaScript library for my web application. The application is very data intensive and has rich form controls (almost windows like). AJAX will be used liberally. The development platform is ASP.Net (mostly ASP.Net MVC will be used). I cannot pursue with ExtJs due to the price/license factor. I checked Qooxdoo but it is very windows-unfriendly. YIU fell short of my needs w.r.t. form controls it offers. Other libraries like jQuery do not offer rich form controls. So I am looking recommendations for a library that satisfies most of following needs: Rich UI controls Solid API for AJAX handling Employs good programming practices for scripting in frontend (preferably OO but not mandatory) Free. Else has only development cost and not production Windows friendly (or at least not unfriendly) Not monolithic. Should be independent (Not have development & production dependencies) Theme'ing should be easy (preferably wrapped by the library) I am not mentioning other basic needs (like browser compatibility). I hope any popular library will honor those.

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• Generate jpeg compressed Tiff using RGB colorspace (using Java + JAI)

  - by nOiSe gaTe

  I'm trying to make tiled pyramidal tiffs from master tiff images using Java (JAI 1.1.3 + imageIO). The problem is: I NEED to make tiff files compressed in jpeg with RGB photometric interpretation and no matter what I try, the image still faces YCbCr photometric interpretation. Note: if I change compression type (eg. LZW or Deflate) I can get RGB colorspace but, as I said, I need jpeg compression. Except this detail the tiled PTiff I create it's ok, so I think it's better to focus the attention on simple compression step (uncompressed tiff -- jpeg tiff) this may be a basic example (removing any check to make it more readable) // reading MASTER BufferedImage img = ImageIO.read(uncompressedTiff); ImageOutputStream ios=null; ImageWriter writer=null; ios = ImageIO.createImageOutputStream(outFile); Iterator <ImageWriter> writers = ImageIO.getImageWritersByFormatName("tiff"); writer = writers.next(); // saving and compression params writer.setOutput(ios); ImageWriteParam param = writer.getDefaultWriteParam(); param.setCompressionMode(ImageWriteParam.MODE_EXPLICIT); param.setCompressionType("JPEG"); param.setCompressionQuality(0.8f); param.setTilingMode(ImageWriteParam.MODE_EXPLICIT); param.setTiling(256, 256, 0, 0); IIOMetadata metadata = getWriteMD(writer, param); // writing writer.write(metadata, new IIOImage(img, null, metadata), param); in getWriteMD method: .... TIFFTag photoInterp = base.getTag(BaselineTIFFTagSet.TAG_PHOTOMETRIC_INTERPRETATION); TIFFField fieldPhotoInter = new TIFFField(photoInterp, BaselineTIFFTagSet.PHOTOMETRIC_INTERPRETATION_RGB); .... here is the full version of getWriteMD()

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• ASP.NET MVC on GoDaddy Not Working (Not Primary Domain Deployment)

  - by JPrescottSanders

  I am trying to get ASP.NET MVC working on GoDaddy and I'm not having much luck. I have read the post on SO that covers the subject, but I must have a slightly different configuration or must be missing somehting along the way because the main MVC page comes up, but all links seem to fail and no amount of tweaking the URLs seems to get it to work. A little back ground. I have a single hosting plan with many domains pointed to sub folders of the main domain. Basic ASP.NET web forms pages work just fine, but of course I wanted to try and host a sample MVC site in one of these non-primary domains. You can go to the URL here. As you can see this first page comes up, but if you click on Home or About it doesn't work. Clicking on Home creates this link "http://www.jprescottsanders.com/jps/" and clicking on about creates this link "http://www.jprescottsanders.com/jps/Home/About". As you can see JPS sneaks in there, this of course is the sub folder that i place my web app files in. I would like to know if this is a MVC related issue or a GoDaddy issue. I suspect that MVC may want to sit in the root directory of the site, and when it puts the "jps" into the URLs it breaks the routing mechanisms (but this is conjecture). I know Dan said this was possible so I'm hoping he sees this and helps me get to the bottom of this deployment strategy for MVC.

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• making my player sprite land on top of my platform sprite

  - by Stone

  Hi, in my XNA game(im fairly new to XNA by the way) i would like to have my player sprite land on top of a platform. i have a player sprite class that inherits from my regular sprite class, and the regular sprite class for basic non playable sprite stuff such as boxes, background stuff, and platforms. However, i am unsure how to implement a way to make my player sprite land on a platform. My player Sprite can jump and move around, but i dont know where and how to check to see if it is on top of my platform sprite. My player sprites jump method is here private void Jump() { if (mCurrentState != State.Jumping) { mCurrentState = State.Jumping; mStartingPosition = Position; mDirection.Y = MOVE_UP; mSpeed = new Vector2(jumpSpeed, jumpSpeed); } } mStartingPosition is player sprites starting position of the jump, and Position is the player sprites current position. I would think that my code for checking to see whether my player sprite is on top of my platform sprite. I am unsure how to reference my platform sprite inside of the playersprite class and inside of the jump method. i think it should be something like this //platformSprite.CollisonBox would be the rectangle around the platform, but im not //sure how to check to see if player.Position is touching any point //on platformSprite.CollisionBox if(player.Position == platformSprite.CollisionBox) { player.mDirection = 0; } Again im pretty new to programming and XNA, and some of this logic i dont quite understand so any help on any of it would be greatly appreciated:D Thanks

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• jQuery: Using autocomplete to add values to two fields instead of one

  - by rayne

  I want to use the autocomplete plugin for jQuery to populate not one, but two fields when selecting one of the autocomplete values - the name of a band is entered in the #band input field, but the band url (if exists) should also automatically be added to the #url input field when selecting the band name. Right now I simply have an un-pretty list in an external php file from which the autocompleter takes it's values: $bands_sql = "SELECT bands.name, bands.url FROM bands ORDER BY name"; $bands_result = mysql_query($bands_sql) or print (mysql_error()); while ($bands_row = mysql_fetch_array($bands_result)) { $band_name = $bands_row['name']; $band_url = $bands_row['url']; echo $band_name."\n"; #needs to be replaced with an array that holds name and url } My autocomplete function looks very basic atm, but as I'm an absolute beginner when it comes to jQuery (and also clueless when it comes to PHP arrays), I have no idea how to tell it to populate two fields and not one. $(document).ready(function() { $("#band").autocomplete('/autocomplete-bands.php'); }); Is that even possible?!

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• Issue with Facebook JS API, revokeAuthorization

  - by BBonifield

  I am trying to integrate FB connect into our user profile screen. Although, I'm having an issue with FB.ApiClient.revokeAuthorization. http://pastie.org/921942 The basic problem is that I revoke the auth at line 44 after the user clicks the disconnect button. After that, all subsequent API calls don't have a valid session to even check user status. I've tried wrapping blocks in a FB.Connect.forceSessionRefresh block, but then the code will never be called at all. I'm not sure what the proper workflow should be for this purpose. Right now it's basically... User arrives at profile NOT connected to the application. User clicks on the connect button. Once connected, DOM manipulation occurs to hide the connect button and add in a disconnect button. User clicks on the disconnect button. User's authorization to the application is revoked and (it seems) the API session to the FB server is invalidated. DOM manipulation occurs to hide the disconnect button and readd the connect button. User clicks on the connect button. Once connected, the FB.Connect.get_loggedInUser() don't return the actual user.

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• RSA example that do not use NoPadding

  - by Tom Brito

  Where can I find a RSA encrypt example that does not use "NoPadding"? --update Better: how to make this code run correctly without throw the "too much data for RSA block" exception? import java.math.BigInteger; import java.security.KeyFactory; import java.security.interfaces.RSAPrivateKey; import java.security.interfaces.RSAPublicKey; import java.security.spec.RSAPrivateKeySpec; import java.security.spec.RSAPublicKeySpec; import javax.crypto.Cipher; /** * Basic RSA example. */ public class TestRSA { public static void main(String[] args) throws Exception { byte[] input = new byte[100]; Cipher cipher = Cipher.getInstance("RSA/None/NoPadding", "BC"); KeyFactory keyFactory = KeyFactory.getInstance("RSA", "BC"); // create the keys RSAPublicKeySpec pubKeySpec = new RSAPublicKeySpec(new BigInteger("d46f473a2d746537de2056ae3092c451", 16), new BigInteger("11", 16)); RSAPrivateKeySpec privKeySpec = new RSAPrivateKeySpec(new BigInteger( "d46f473a2d746537de2056ae3092c451", 16), new BigInteger("57791d5430d593164082036ad8b29fb1", 16)); RSAPublicKey pubKey = (RSAPublicKey) keyFactory.generatePublic(pubKeySpec); RSAPrivateKey privKey = (RSAPrivateKey) keyFactory.generatePrivate(privKeySpec); // encryption step cipher.init(Cipher.ENCRYPT_MODE, pubKey); byte[] cipherText = cipher.doFinal(input); // decryption step cipher.init(Cipher.DECRYPT_MODE, privKey); byte[] plainText = cipher.doFinal(cipherText); } }

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• Query MySQL data from Excel (or vice-versa)

  - by Charles

  I'm trying to automate a tedious problem. I get large Excel (.xls or .csv, whatever's more convenient) files with lists of people. I want to compare these against my MySQL database.* At the moment I'm exporting MySQL tables and reading them from an Excel spreadsheet. At that point it's not difficult to use =LOOKUP() and such commands to do the work I need, and of course the various text processing I need to do is easy enough to do in Excel. But I can't help but think that this is more work than it needs to be. Is there some way to get at the MySQL data directly from Excel? Alternately, is there a way I could access a reasonably large (~10k records) csv file in a sql script? This seems to be rather basic, but I haven't managed to make it work so far. I found an ODBC connection for MySQL but that doesn't seem to do what I need. In particular, I'm testing whether the name matches or whether any of four email addresses match. I also return information on what matched for the benefit of the next person to use the data, something like "Name 'Bob Smith' not found, but 'Robert Smith' matches on email address robert.smith@foo".

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• Web-based game in Python + Django and client browser polling

  - by ty

  I am creating a text-based game that implements a basic model in which multiple (10+) players interact with data and one moderator watches them and sets certain environmental statistics that affect gameplay. Recently I have begun to familiarize myself with Django. It seems to me that it would be an excellent tool for creating a game quickly, particularly because the nature of my game depends largely on sets of data (which lends itself quite well to a database). I am wondering how to "push" changes made by the game moderator to the players (for example, the moderator can decide to display an image to all players). The game is turn-based, not real-time, but certain messages need to be pushed out in roughly real-time. My thoughts: I could have each player's browser poll a status periodically (say, every 30 seconds) to see if there is a message from a moderator. But this forces a lag and means different players might receive it at different times. And reducing this interval to <10 seems like a bad idea for the server. Is there a better way to inform clients of changes? Would you suggest something other than using a web framework like Django? Thanks!

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• How can i Execute a Controller's ActionMethod programatically?

  - by Pure.Krome

  Hi folks, I'm trying to execute a controller's Action Method programatically and I'm not sure how. Scenario: When my ControllerFactory fails to find the controller, I wish it to manually execute a single action method which i have on a simple, custom controller. I don't want to rely on using any route data to determine the controller/method .. because that route might not have been wired up. Eg. // NOTE: Error handling removed from this example. public class MyControllerFactory : DefaultControllerFactory { protected override IController GetControllerInstance(Type controllerType) { IController result = null; // Try and load the controller, based on the controllerType argument. // ... snip // Did we retrieve a controller? if (controller == null) { result = new MyCustomController(); ((MyCustomController)result).Execute404NotFound(); // <-- HERE! } return result; } } .. and that method is .. public static void Execute404NotFound(this Controller controller) { result = new 404NotFound(); // Setup any ViewData.Model stuff. result.ExecuteResult(controller.ControllerContext); // <-- RUNTIME // ERROR's HERE } Now, when I run the controller factory fails to find a controller, i then manually create my own basic controller. I then call the extension method 'Execute404NotFound' on this controller instance. That's fine .. until it runs the ExecuteResult(..) method. Why? the controller has no ControllerContext data. As such, the ExecuteResult crashes because it requires some ControllerContext. So - can someone out there help me? see what I'm doing wrong. Remember - i'm trying to get my controller factory to manually / programmatically call a method on a controller which of course would return an ActionResult. Please help!

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• Spring Security 3.0 - Intercept-URL - All pages require authentication but one

  - by gav

  Hi All, I want any user to be able to submit their name to a volunteer form but only administrators to be able to view any other URL. Unfortunately I don't seem to be able to get this correct. My resources.xml are as follows; <?xml version="1.0" encoding="UTF-8"?> <beans:beans xmlns="http://www.springframework.org/schema/security" xmlns:beans="http://www.springframework.org/schema/beans" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-3.0.xsd http://www.springframework.org/schema/security http://www.springframework.org/schema/security/spring-security-3.0.xsd"> <http realm = "BumBumTrain Personnel list requires you to login" auto-config="true" use-expressions="true"> <http-basic/> <intercept-url pattern="/person/volunteer*" access=""/> <intercept-url pattern="/**" access="isAuthenticated()" /> </http> <authentication-manager alias="authenticationManager"> <authentication-provider> <user-service> <user name="admin" password="admin" authorities="ROLE_ADMIN"/> </user-service> </authentication-provider> </authentication-manager> </beans:beans> Specifically I am trying to achieve the access settings I described via; <intercept-url pattern="/person/volunteer*" access=""/> <intercept-url pattern="/**" access="isAuthenticated()" /> Could someone please describe how to use intercept-url to achieve the outcome I've described? Thanks Gav

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• Dependency Injection and decoupling of software layers

  - by cs31415

  I am trying to implement Dependency Injection to make my app tester friendly. I have a rather basic doubt. Data layer uses SqlConnection object to connect to a SQL server database. SqlConnection object is a dependency for data access layer. In accordance with the laws of dependency injection, we must not new() dependent objects, but rather accept them through constructor arguments. Not wanting to upset the DI gods, I dutifully create a constructor in my DAL that takes in SqlConnection. Business layer calls DAL. Business layer must therefore, pass in SqlConnection. Presentation layer calls Business layer. Hence it too, must pass in SqlConnection to business layer. This is great for class isolation and testability. But didn't we just couple the UI and Business layers to a specific implementation of the data layer which happens to use a relational database? Why do the Presentation and Business layers need to know that the underlying data store is SQL? What if the app needs to support multiple data sources other than SQL server (such as XML files, Comma delimited files etc.) Furthermore, what if I add another object upon which my data layer is dependent on (say, a second database). Now, I have to modify the upper layers to pass in this new object. How can I avoid this merry-go-round and reap all the benefits of DI without the pain?

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• correct way to create a pivot table in postgresql using CASE WHEN

  - by mojones

  I am trying to create a pivot table type view in postgresql and am nearly there! Here is the basic query: select acc2tax_node.acc, tax_node.name, tax_node.rank from tax_node, acc2tax_node where tax_node.taxid=acc2tax_node.taxid and acc2tax_node.acc='AJ012531'; And the data: acc | name | rank ----------+-------------------------+-------------- AJ012531 | Paromalostomum fusculum | species AJ012531 | Paromalostomum | genus AJ012531 | Macrostomidae | family AJ012531 | Macrostomida | order AJ012531 | Macrostomorpha | no rank AJ012531 | Turbellaria | class AJ012531 | Platyhelminthes | phylum AJ012531 | Acoelomata | no rank AJ012531 | Bilateria | no rank AJ012531 | Eumetazoa | no rank AJ012531 | Metazoa | kingdom AJ012531 | Fungi/Metazoa group | no rank AJ012531 | Eukaryota | superkingdom AJ012531 | cellular organisms | no rank What I am trying to get is the following: acc | species | phylum AJ012531 | Paromalostomum fusculum | Platyhelminthes I am trying to do this with CASE WHEN, so I've got as far as the following: select acc2tax_node.acc, CASE tax_node.rank WHEN 'species' THEN tax_node.name ELSE NULL END as species, CASE tax_node.rank WHEN 'phylum' THEN tax_node.name ELSE NULL END as phylum from tax_node, acc2tax_node where tax_node.taxid=acc2tax_node.taxid and acc2tax_node.acc='AJ012531'; Which gives me the output: acc | species | phylum ----------+-------------------------+----------------- AJ012531 | Paromalostomum fusculum | AJ012531 | | AJ012531 | | AJ012531 | | AJ012531 | | AJ012531 | | AJ012531 | | Platyhelminthes AJ012531 | | AJ012531 | | AJ012531 | | AJ012531 | | AJ012531 | | AJ012531 | | AJ012531 | | Now I know that I have to group by acc at some point, so I try select acc2tax_node.acc, CASE tax_node.rank WHEN 'species' THEN tax_node.name ELSE NULL END as sp, CASE tax_node.rank WHEN 'phylum' THEN tax_node.name ELSE NULL END as ph from tax_node, acc2tax_node where tax_node.taxid=acc2tax_node.taxid and acc2tax_node.acc='AJ012531' group by acc2tax_node.acc; But I get the dreaded ERROR: column "tax_node.rank" must appear in the GROUP BY clause or be used in an aggregate function All the previous examples I've been able to find use something like SUM() around the CASE statements, so I guess that is the aggregate function. I have tried using FIRST(): select acc2tax_node.acc, FIRST(CASE tax_node.rank WHEN 'species' THEN tax_node.name ELSE NULL END) as sp, FIRST(CASE tax_node.rank WHEN 'phylum' THEN tax_node.name ELSE NULL END) as ph from tax_node, acc2tax_node where tax_node.taxid=acc2tax_node.taxid and acc2tax_node.acc='AJ012531' group by acc2tax_node.acc; but get the error: ERROR: function first(character varying) does not exist Can anyone offer any hints?

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• Windows Live Messenger Activity SDK: Is it possible to use jQuery?

  - by Cheeso

  There's an SDK that lets developers build "activities" and games for use in Windows Live Messenger. The basic approach is to build a web app, that gets approved and hosted by Microsoft. questions Anyone done this? Can you use jQuery in that web app? how do you debug the thing, running within Windows Live Messenger? EDIT: I tried using jQuery, but couldn't get it to do much of anything. I also couldn't debug it at all, when running within the IM client. The IE8 F12 debug tools are not available in that context. I believe the embedded browser was silently not loading external script, and then silently throwing exceptions. So I backed off to use only script in the .HTM file. Since it is Windows Live Messenger, the embedded browser is IE, so the generality made possible in jQuery isn't strictly necessary. I was able to use old-skool DHTML interfaces to get done, what I needed. I'm still interested in seeing examples of what other people have produced in the way of WLM Activities or games, using the Messenger Activity SDK. I think Flash is possible, and I think XAML is also possible, but I haven't seen source code examples for any of those.

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• Updating extra attributes in a has_many, :through relationship using Rails

  - by Robbie

  I've managed to set up a many-to-many relationship between the following models Characters Skills PlayerSkills PlayerSkills, right now, has an attribute that Skills don't normally have: a level. The models look something like this (edited for conciseness): class PlayerSkill < ActiveRecord::Base belongs_to :character belongs_to :skill end class Skill < ActiveRecord::Base has_many :player_skills has_many :characters, :through => :player_skills attr_accessible :name, :description end class Character < ActiveRecord::Base belongs_to :user has_many :player_skills has_many :skills, :through => :player_skills end So nothing too fancy in the models... The controller is also very basic at this point... it's pretty much a stock update action. The form I'm looking to modify is characters#edit. Right now it renders a series of checkboxes which add/remove skills from the characters. This is great, but the whole point of using has_many :through was to track a "level" as well. Here is what I have so far: - form_for @character do |f| = f.error_messages %p = f.label :name %br = f.text_field :name %p = f.label :race %br = f.text_field :race %p = f.label :char_class %br = f.text_field :char_class %p - @skills.each do |skill| = check_box_tag "character[skill_ids][]", skill.id, @character.skills.include?(skill) =h skill.name %br %p = f.submit After it renders "skill.name", I need it to print a text_field that updates player_skill. The problem, of course, is that player_skill may or may not exist! (Depending on if the box was already ticked when you loaded the form!) From everything I've read, has_many :through is great because it allows you to treat the relationship itself as an entity... but I'm completely at a loss as to how to handle the entity in this form. As always, thanks in advance for any and all help you can give me!

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