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• Should a C++ constructor do real work?

  - by Wade Williams

  I'm strugging with some advice I have in the back of my mind but for which I can't remember the reasoning. I seem to remember at some point reading some advice (can't remember the source) that C++ constructors should not do real work. Rather, they should initialize variables only. The advice when on to explain that real work should be done in some sort of init() method, to be called separately after the instance was created. The situation is I have a class that represents a hardware device. It makes logical sense to me for the constructor to call the routines that query the device in order to build up the instance variables that describe the device. In other words, once new instantiates the object, the developer receives an object which is ready to be used, no separate call to object-init() required. Is there a good reason why constructors shouldn't do real work? Obviously it could slow allocation time, but that wouldn't be any different if calling a separate method immediately after allocation. Just trying to figure out what gotchas I not currently considering that might have lead to such advice.

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• Online job-searching is tedious. Help me automate it.

  - by ehsanul

  Many job sites have broken searches that don't let you narrow down jobs by experience level. Even when they do, it's usually wrong. This requires you to wade through hundreds of postings that you can't apply for before finding a relevant one, quite tedious. Since I'd rather focus on writing cover letters etc., I want to write a program to look through a large number of postings, and save the URLs of just those jobs that don't require years of experience. I don't require help writing the scraper to get the html bodies of possibly relevant job posts. The issue is accurately detecting the level of experience required for the job. This should not be too difficult as job posts are usually very explicit about this ("must have 5 years experience in..."), but there may be some issues with overly simple solutions. In my case, I'm looking for entry-level positions. Often they don't say "entry-level", but inclusion of the words probably means the job should be saved. Next, I can safely exclude a job the says it requires "5 years" of experience in whatever, so a regex like /\d\syears/ seems reasonable to exclude jobs. But then, I realized some jobs say they'll take 0-2 years of experience, matches the exclusion regex but is clearly a job I want to take a look at. Hmmm, I can handle that with another regex. But some say "less than 2 years" or "fewer than 2 years". Can handle that too, but it makes me wonder what other patterns I'm not thinking of, and possibly excluding many jobs. That's what brings me here, to find a better way to do this than regexes, if there is one. I'd like to minimize the false negative rate and save all the jobs that seem like they might not require many years of experience. Does excluding anything that matches /[3-9]\syears|1\d\syears/ seem reasonable? Or is there a better way? Training a bayesian filter maybe?

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• Pass arguments to a parameter class object

  - by David R

  This is undoubtedly a simple question. I used to do this before, but it's been around 10 years since I worked in C++ so I can't remember properly and I can't get a simple constructor call working. The idea is that instead of parsing the args in main, main would create an object specifically designed to parse the arguments and return them as required. So: Parameters params = new Parameters(argc, argv) then I can call things like params.getfile() Only problem is I'm getting a complier error in Visual Studio 2008 and I'm sure this is simple, but I think my mind is just too rusty. What I've got so far is really basic: In the main: #include "stdafx.h" #include "Parameters.h" int _tmain(int argc, _TCHAR* argv[]) { Parameters params = new Parameters(argc, argv); return 0; } Then in the Parameters header: #pragma once class Parameters { public: Parameters(int, _TCHAR*[]); ~Parameters(void); }; Finally in the Parameters class: include "Stdafx.h" #include "Parameters.h" Parameters::Parameters(int argc, _TCHAR* argv[]) { } Parameters::~Parameters(void) { } I would appreciate if anyone could see where my ageing mind has missed the really obvious. Thanks in advance.

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• How do I set up the python/c library correctly?

  - by Bartvbl

  I have been trying to get the python/c library to like my mingW compiler. The python online doncumentation; http://docs.python.org/c-api/intro.html#include-files only mentions that I need to import the python.h file. I grabbed it from the installation directory (as is required on the windows platform), and tested it by compiling the script: #include "Python.h". This compiled fine. Next, I tried out the snippet of code shown a bit lower on the python/c API page: PyObject *t; t = PyTuple_New(3); PyTuple_SetItem(t, 0, PyInt_FromLong(1L)); PyTuple_SetItem(t, 1, PyInt_FromLong(2L)); PyTuple_SetItem(t, 2, PyString_FromString("three")); For some reason, the compiler would compile the code if I'd remove the last 4 lines (so that only the pyObject variable definition would be left), yet calling the actual constructor of the tuple returned errors. I am probably missing something completely obvious here, given I am very new to C, but does anyone know what it is?

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• RMagick transparent_color deprecated? What's the alternative?

  - by user315975

  I'm developing an app that does a fair amount of generating transparent pngs on the fly. These are used as overlays, to show areas of interest in a graphic, so they have to have transparent backgrounds. I am developing in Ruby on Rails, deploying on Heroku. What works fine in development is not working in production. I get this error when I call a drawing routine using RMagick: NotImplementedError (the `transparent_color=' method is not supported by ImageMagick 6.2.4): /usr/local/lib/ruby/gems/1.8/gems/rmagick-1.15.17/lib/RMagick.rb:1691:in `transparent_color=' I'm using RMagick version 2.12.1 on the development machine, but I'm not exactly certain how to discover the version of ImageMagick that it's running, so I'm not sure if this is a case of my local code being behind or ahead. I'm hoping behind, because perhaps then there'll be a replacement for this call. Does anyone know what the fix is here? What's required to generate a transparent background, if not the call I'm using? I can't find this in the documentation: in fact, it was on a third-party site that I found mention of this capability.

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• How is the C++ synthesized move constructor affected by volatile and virtual members?

  - by user1827766

  Look at the following code: struct node { node(); //node(const node&); //#1 //node(node&&); //#2 virtual //#3 ~node (); node* volatile //#4 next; }; main() { node m(node()); //#5 node n=node(); //#6 } When compiled with gcc-4.6.1 it produces the following error: g++ -g --std=c++0x -c -o node.o node.cc node.cc: In constructor node::node(node&&): node.cc:3:8: error: expression node::next has side-effects node.cc: In function int main(): node.cc:18:14: note: synthesized method node::node(node&&) first required here As I understand the compiler fails to create default move or copy constructor on line #6, if I uncomment either line #1 or #2 it compiles fine, that is clear. The code compiles fine without c++0x option, so the error is related to default move constructor. However, what in the node class prevents default move constructor to be created? If I comment any of the lines #3 or #4 (i.e. make the destructor non-virtual or make data member non-volatile) it compiles again, so is it the combination of these two makes it not to compile? Another puzzle, line #5 does not cause an compilation error, what is different from line #6? Is it all specific for gcc? or gcc-4.6.1?

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• What library can I use to do simple, lightweight message passing?

  - by Mike

  I will be starting a project which requires communication between distributed nodes(the project is in C++). I need a lightweight message passing library to pass very simple messages(basically just strings of text) between nodes. The library must have the following characteristics: No external setup required. I need to be able to get everything up-and-running in my code - I don't want to require the user to install any packages or edit any configuration files(other than a list of IP addresses and ports to connect to). The underlying protocol which the library uses must be TCP(or if it is UDP, the library must guarantee the eventual receipt of the message). The library must be able to send and receive arbitrarily large strings(think up to 3GB+). The library needn't support any security mechanisms, fault tolerance, or encryption - I just need it to be fast, simple, and easy to use. I've considered MPI, but concluded it would require too much setup on the user's machine for my project. What library would you recommend for such a project? I would roll my own, but due to time constraints, I don't think that will be feasible.

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• Cache layer for MVC - Model or controller?

  - by Industrial

  Hi everyone, I am having some second thoughts about where to implement the caching part. Where is the most appropriate place to implement it, you think? Inside every model, or in the controller? Approach 1 (psuedo-code): // mycontroller.php MyController extends Controller_class { function index () { $data = $this->model->getData(); echo $data; } } // myModel.php MyModel extends Model_Class{ function getData() { $data = memcached->get('data'); if (!$data) { $query->SQL_QUERY("Do query!"); } return $data; } } Approach 2: // mycontroller.php MyController extends Controller_class { function index () { $dataArray = $this->memcached->getMulti('data','data2'); foreach ($dataArray as $key) { if (!$key) { $data = $this->model->getData(); $this->memcached->set($key, $data); } } echo $data; } } // myModel.php MyModel extends Model_Class{ function getData() { $query->SQL_QUERY("Do query!"); return $data; } } Thoughts: Approach 1: No multiget/multi-set. If a high number of keys would be returned, overhead would be caused. Easier to maintain, all database/cache handling is in each model Approach 2: Better performancewise - multiset/multiget is used More code required Harder to maintain Tell me what you think!

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• Is there programming language with better approach for switch's break statements ?

  - by Vitaly Polonetsky

  It's the same syntax in a way too many languages: switch (someValue) { case OPTION_ONE: case OPTION_LIKE_ONE: case OPTION_ONE_SIMILAR: doSomeStuff1(); break; // EXIT the switch case OPTION_TWO_WITH_PRE_ACTION: doPreActionStuff2(); // the default is to CONTINUE to next case case OPTION_TWO: doSomeStuff2(); break; // EXIT the switch case OPTION_THREE: doSomeStuff3(); break; // EXIT the switch } Now all you know that break statements are required, because the switch will continue to the next case when break statement is missing. We have an example of that with OPTION_LIKE_ONE, OPTION_ONE_SIMILAR and OPTION_TWO_WITH_PRE_ACTION. The problem is that we only need this "skip to next case" very very very rarely. And very often we put break at the end of case. It very easy for a beginner to forget about it. And one of my C teachers even explained it to us as if it was a bug in C language (don't want to talk about it :) I would like to ask if there are any other languages that I don't know of (or forgot about) that handle switch/case like this: switch (someValue) { case OPTION_ONE: continue; // CONTINUE to next case case OPTION_LIKE_ONE: continue; // CONTINUE to next case case OPTION_ONE_SIMILAR: doSomeStuff1(); // the default is to EXIT the switch case OPTION_TWO_WITH_PRE_ACTION: doPreActionStuff2(); continue; // CONTINUE to next case case OPTION_TWO: doSomeStuff2(); // the default is to EXIT the switch case OPTION_THREE: doSomeStuff3(); // the default is to EXIT the switch } The second question: is there any historical meaning to why it is like this in C? May be continue to next case was used far more often than we use it these days ?

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• How can I test a form that requires the entry of two random characters from a security phrase?

  - by lawm

  I need to test a two-stage login system which first asks for your email address and password and then presents the user with two select lists containing [a-zA-Z0-9]. The labels beside the drop down's are of the form 'Select character X from your security phrase', where X is a random character index from a known security phrase. I'd rather not stub the code for an acceptance test, so is it possible to write a matcher in cucumber which will, given that we know the whole phrase, select the required character in each of the two lists? Here is the scenario I have so far and the steps involved: Scenario: valid login email, password and secret phrase takes me to the dashboard Given I am not logged in When I log in as "[email protected]" Then I should be on the dashboard page And I should see "Your Dashboard" When /^I log in as "([^\"]*)"$/ do |login| visit path_to('Login page') fill_in "Email", :with => login fill_in "Password", :with => "Password123" click_button "Log in" response.should contain("Please verify some characters from your security phrase") select "a", :from => "Select character X of your security phrase" select "b", :from => "Select character Y of your security phrase" click_button "Submit" end For example, if the security phrase is 'Secret123', X = 3 and Y = 8, the above would have to produce the equivalent of: select "c", :from => "Select character 3 of your security phrase" select "2", :from => "Select character 8 of your security phrase" The numbers X and Y in the actual page are inside span#svc_1 and span#svc_2 respectively. Thanks,

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• JBoss admin-console fails to load - missing Log4J jar?

  - by Jack

  I downloaded JBoss 5.1 and unzipped to ~/jboss/ such that JBoss is installed into: ~/jboss/jboss-5.1.0.GA/ I run the default deployment by using the following command found in jboss/jboss-5.1.0.GA/bin ./run.sh -c default While JBoss starts (http://127.0.0.1:8080/), admin-console is not deployed. The log file: jboss/jboss-5.1.0.GA/server/default/log shows the following information: DEPLOYMENTS IN ERROR: Deployment "vfsfile:/Users/jackwootton/jboss/jboss-5.1.0.GA/server/default/deploy/admin-console.war/" is in error due to the following reason(s): org.jboss.deployers.spi.DeploymentException: URL file:/Users/jackwootton/jboss/jboss-5.1.0.GA/server/default/tmp/az6n6v-tjilfb-h32fokxn-1-h32fosuo-v/admin-console.war/ deployment failed Deployment "vfszip:/Users/jackwootton/jboss/jboss-5.1.0.GA/server/default/deploy/quartz-ra.rar/" is in error due to the following reason(s): org.apache.commons.logging.LogConfigurationException: User-specified log class 'org.apache.commons.logging.impl.Log4JLogger' cannot be found or is not useable. The Log4J jar file exists in: jboss/jboss-5.1.0.GA/lib/jboss-logging-log4j.jar I have three questions: Have I understood the problem correctly (i.e. that admin-console cannot find the required Log4j JAR file and therefore is not deployed)? What can I do to fix this problem? Why would an out-of-the-box deployment have this problem in the first place?

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• Sending data back to Controller Spring-MVC

  - by Umesh Awasthi

  I am not sure if this is a complex problem but as a starting person this seems a bit complex to me. I have an object based on which i need to show some values on the UI and let user select some of them, i need to send data back to another controller when user click on the submit button.Here is the structure of my data object public class PrsData{ private Map<String, List<PrsCDData>> prsCDData; } public class PrsCDData{ private Map<String, Collection<ConfiguredDesignData>> configuredDesignData; } public ConfiguredDesignData{ // simple fields } I have set the object in model before showing the view like model.addAttribute("prsData", productData.getPrData()); In the form i have following settings <form:form method="post" commandName="prsData" action="${addProductToCartAction}" > <form:hidden path="prsCDData['${prsCDDataMap.key}'] [${status.index}].configuredDesignData['${configuredDesignDataMap.key}'] [${configuredDesignDataStatus.index}].code"/> <form:hidden path="prsCDData['${prsCDDataMap.key}'] [${status.index}].configuredDesignData['${configuredDesignDataMap.key}'] [${configuredDesignDataStatus.index}].description"/> </form:form> This is what i have at AddProductToCartController public String addToCart(@RequestParam("productCodePost") final String code, @ModelAttribute("prsData") final PrsData prsData, final Model model, @RequestParam(value = "qty", required = false, defaultValue = "1") final long qty) On submitting the form i am getting following exception org.springframework.beans.NullValueInNestedPathException: Invalid property 'prsCDData[Forced][0]' of bean class [com.product.data.PrsData]: Cannot access indexed value of property referenced in indexed property path 'prsCDData[Forced][0]': returned null It seems like its trying to access the values on this controller while i am trying to send value to that controller and trying to create same object with selected values Can any one tell me where i am doing wrong and what i need to take care of

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• Populating PDF Fields using FDFACX

  - by NWilliams

  I was recently asked to preform some updates to an existing PDF document. The changes required were completed using Adobe Designer (the only tool I have available to me). These changes included alignment, and new text. Note that there were fillable form fields on the forms, and they were left untouched. The saved version of the form was then put into our ASP.NET application, which pre-populates the form fields were applicable (things like name, address etc... things we have in our database). For some reason, the new form does not populate. I've confirmed that the form fields have the correct names, that the actual file (the pdf) that is being pre-populated has the same permissions as others that are working. There are no errors thrown, and no difference in a step through with a working form and a non-working form. This is a legacy project and I have no real experience with the PDF populator they are using ... FDFACX .NET? And can't find a lot of info on it online. Any ideas?

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• How does a java compiler resolve a non-imported name

  - by gexicide

  Consider I use a type X in my java compilation unit from package foo.bar and X is not defined in the compilation unit itself nor is it directly imported. How does a java compiler resolve X now efficiently? There are a few possibilities where X could reside: X might be imported via a star import a.b.* X might reside in the same package as the compilation unit X might be a language type, i.e. reside in java.lang The problem I see is especially (2.). Since X might be a package-private type, it is not even required that X resides in a compilation unit that is named X.java. Thus, the compiler must look into all entries of the class path and search for any classes in a package foo.bar, it then must read every class that is in package foo.bar to check whether X is included. That sounds very expensive. Especially when I compile only a single file, the compiler has to read dozens of class files only to find a type X. If I use a lot of star imports, this procedure has to be repeated for a lot of types (although class files won't be read twice, of course). So is it advisable to import also types from the same package to speed up the compilation process? Or is there a faster method for resolving an unimported type X which I was not able to find?

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• Loading a view routed by a URL parameter (e.g., /users/:id) in MEAN stack

  - by Matt Rowles

  I am having difficulties with trying to load a user by their id, for some reason my http.get call isn't hitting my controller. I get the following error in the browser console: TypeError: undefined is not a function at new <anonymous> (http://localhost:9000/scripts/controllers/users.js:10:8) Update I've fixed my code up as per comments below, but now my code just enters an infinite loop in the angular users controllers (see code below). I am using the Angular Express Generator for reference Backend - nodejs, express, mongo routes.js: // not sure if this is required, but have used it before? app.param('username', users.show); app.route('/api/users/:username') .get(users.show); controller.js: // This never gets hit exports.show = function (req, res, next, username) { User.findOne({ username: username }) .exec(function (err, user) { req.user = user; res.json(req.user || null); }); }; Frontend - angular app.js: $routeProvider .when('/users/:username', { templateUrl: function( params ){ return 'users/view/' + params.username; }, controller: 'UsersCtrl' }) services/user.js: angular.module('app') .factory('User', function ($resource) { return $resource('/api/users/:username', { username: '@username' }, { update: { method: 'PUT', params: {} }, get: { method: 'GET', params: { username:'username' } } }); }); controllers/users.js: angular.module('app') .controller('UsersCtrl', ['$scope', '$http', '$routeParams', '$route', 'User', function ($scope, $http, $routeParams, $route, User) { // this returns the error above $http.get( '/api/users/' + $routeParams.username ) .success(function( user ) { $scope.user = user; }) .error(function( err) { console.log( err ); }); }]); If it helps, I'm using this setup

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• Having to insert a record, then update the same record warrants 1:1 relationship design?

  - by dianovich

  Let's say an Order has many Line items and we're storing the total cost of an order (based on the sum of prices on order lines) in the orders table. -------------- orders -------------- id ref total_cost -------------- -------------- lines -------------- id order_id price -------------- In a simple application, the order and line are created during the same step of the checkout process. So this means INSERT INTO orders .... -- Get ID of inserted order record INSERT into lines VALUES(null, order_id, ...), ... where we get the order ID after creating the order record. The problem I'm having is trying to figure out the best way to store the total cost of an order. I don't want to have to create an order create lines on an order calculate cost on order based on lines then update record created in 1. in orders table This would mean a nullable total_cost field on orders for starters... My solution thus far is to have an order_totals table with a 1:1 relationship to the orders table. But I think it's redundant. Ideally, since everything required to calculate total costs (lines on an order) is in the database, I would work out the value every time I need it, but this is very expensive. What are your thoughts?

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• Is it okay to rely on javascript for menu layout?

  - by Ryan

  I have a website template where I do not know the number of menu items or the size of the menu items that will be required. The js below works exactly the way I want it to, however this is the most js I've every written. Are there any disadvantages or potential problems with this method that I'm not aware of because I'm a js beginner? I'm currently manually setting the padding for each site. Thank you! var width_of_text = 0; var number_of_li = 0; // measure the width of each <li> and add it to the total with, increment li counter $('li').each(function() { width_of_text += $(this).width(); number_of_li++; }); // calculate the space between <li>'s so the space is equal var padding = Math.floor((900 - width_of_text)/(number_of_li - 1)); // add the padding the all but the first <li> $('li').each(function(index) { if (index !== 0) { $(this).css("padding-left", padding); } });

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• POST method getting converted to GET in IE-9

  - by Sri127

  I have this line of code in my JSP. (I'm using struts 1.3) <html:form action="screening/mine.do" method="post"> . . . </html:form When the action corresponding to mine.do is invoked (using struts-config.xml), the page is getting submitted as GET instead of POST. All the request parameters including the required ones are getting lost due to this. This issue occcurs only in IE-9. The response remains as POST when I use other versions of IE or any other browsers. How do I make the response to remain as POST in IE-9 ? EDIT : I observed one more issue in this. Whenever the page is rendered in a new window, this issue occurs. Other places, the POST works fine in IE-9. Also, this issue occurs in Win7/IE-8, but works absolutely fine in XP/IE-8. Is there something to do with the OS as well??? Any solutions would be useful. Thanks!!

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• Hopping from a C++ to a Perl Unix profile?

  - by rocknroll

  Hi all, I have been a C++,Linux Developer till now and I am adept in this stack. Off late I have been getting opportunities that require Perl,Unix (with knowledge of C++,shell scripting) expertise. Organisations are showing interest even thought I don't have much scripting experience to boast off. The roll is more in a Support,maintenance project involving SQL as well. Off late I am in a fix whether to forgo these offers or not. I don't know the dynamics of an IT organisation and thus on one hand I fear that my C++ experience will be nullified and on the positive side I am getting to work on a new technology stack which will only add to my skill set. I am sure, most of you at some point of time have encountered such dilemmas and would have taken some decision. I want you to share your perspectives on such a scenario where a person is required to change his/her technology stack when changing his/her job. What are the merits and demerits in going with either of the choices? Also I know that C++ isn't going anywhere in the near future. What about perl? I have no clue as to what the future holds for perl developer? Whether there are enough opportunities for a perl developer? I am asking this question here because most of my fellow programmers face this career choice dilemma. Thanks.

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• JSP getParameter problem

  - by user236501

  I have a form, if the timer reach the form will auto redirect to the Servlet to update database. My problem now is if javascript redirect the window to servlet my request.getParameter is null. function verify(f,whichCase){ if(whichCase == "Submit"){ msg = "Are you sure that you want to submit this test?"; var i = confirm(msg) if(i){ parent.window.location = "sindex.jsp" } return i; } } I doing this because i got a iframe in my jsp. Timer update problem have to use iframe. So, when time up or user click submit parent.window.location can let me refresh parent window <form method="POST" action="${pageContext.request.contextPath}/TestServlet" onSubmit="return verify(this,whichPressed)"> My form when user click submit button within the timing, it will trigger the verify function to let user confirm submit. So inside my TestServlet i got this, because using javascript redirect request.getParameter("answer") this keep return me null. protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { if (request.getParameter("Submit") != null) { String ans = request.getParameter("answer"); Answer a = new Answer(ans, no); aa.CreateAnswer(an,t.getTestCode(),username); RequestDispatcher rd = request.getRequestDispatcher("/sindex.jsp"); rd.forward(request, response); } } Below are my timer when time up redirect to TestServlet trigger the doGet method if((mins == 0) && (secs == 0)) { window.alert("Time is up. Press OK to submit the test."); // change timeout message as required var sUrl = "TestServlet"; parent.window.location = sUrl // redirects to specified page once timer ends and ok button is pressed } else { cd = setTimeout("redo()",1000); }

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• jQuery Suspected Naming Convention Problem

  - by donfigga

  Hi all, I'm having a problem with this jQuery function, the portion of the function that renames the id, class and name of the dropdown only works for the first dropdown, subsequent ones do not work, any ideas? I suspect it may have something to do with naming convention as in cat.parent_id but it is required for asp.net mvc model binding. $(document).ready(function () { $("table select").live("change", function () { var id = $(this).attr('id'); if ($(this).attr('classname') != "selected") { var rowIndex = $(this).closest('tr').prevAll().length; $.getJSON("/Category/GetSubCategories/" + $(this).val(), function (data) { if (data.length > 0) { //problematic portion $("#" + id).attr('classname', 'selected'); $("#" + id).attr('name', 'sel' + rowIndex); $("#" + id).attr('id', 'sel' + rowIndex); var position = ($('table').get(0)); var tr = position.insertRow(rowIndex + 1); var td1 = tr.insertCell(-1); var td2 = tr.insertCell(-1); td1.appendChild(document.createTextNode('SubCategory')); var sel = document.createElement("select"); sel.name = 'parent_id'; sel.id = 'parent_id'; sel.setAttribute('class', 'unselected'); td2.appendChild(sel); $('#parent_id').append($("<option></option>").attr("value", "-1").text("-please select item-")); $.each(data, function (GetSubCatergories, Category) { $('#parent_id').append($("<option></option>"). attr("value", Category.category_id). text(Category.name)); }); sel.name = 'cat.parent_id'; sel.id = 'cat.parent_id'; } }); } }); });

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• Django Many-to-Many Question

  - by DZ

  My questions seems like a common problem that when I have seen any questions on it is never really asked right or not answered. So Im going to try to get the question right, and maybe someone knows how to resolve the issue, or correct my understanding. The problem: When you have a many-to-many relation ship (related_name not through) and you are trying to use the admin interface you are required to input one of the rleationships even though it does not have to exsist for you to create the first entry. Meaning you have to assign a group to an event to create the group. Wow that sounds complicated. So I can see why the question is not getting answered. Lets try the non code explanation example... First and important versions: Django 1.1.1 Phython 2.6 So I have a model where I created a many-to-many realtionship and Im using the related_name Im creating an app that is an event organizer, for simplicty lets say events although they could be anytype). For this first post Im going to stay away from the code and just try to explain. A few keys: (explaining comment) ** - many-to-many So in the model we have 1) The Main Event (this is main model) 2) Groups (link to events and their can be many events for a group) a) Events** I have simplified this example a little becuase I recognize that what does it matter. Just create the event first... But there are specific varations where that will not work. What the many-to-many related_name does it created another table with the indecies of the two other tables. Nothing says that this extra table HAS to be populated. Becuase if I look in the database and work within myPHPadmin I can create a group with out registering an event, since the connection between the two is a seperate table the DB does not care. How do I make the admin interface this realize it? Ok I know thats a lot so I hope I have explained it clearly. Thank you anyone for your comments/thoughts/advice

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• Extending a form field to add new validations.

  - by duallain

  I've written an app that uses forms to collect information that is then sent in an email. Many of these forms have a filefield used to attach files to the email. I'd like to validate two things, the size of the file (to ensure the emails are accepted by our mail server. I'd also like to check the file extension, to discourage attaching file types not useable for our users. (This is the python class I'm trying to extend) class FileField(Field): widget = FileInput default_error_messages = { 'invalid': _(u"No file was submitted. Check the encoding type on the form."), 'missing': _(u"No file was submitted."), 'empty': _(u"The submitted file is empty."), 'max_length': _(u'Ensure this filename has at most %(max)d characters (it has %(length)d).'), } def __init__(self, *args, **kwargs): self.max_length = kwargs.pop('max_length', None) super(FileField, self).__init__(*args, **kwargs) def clean(self, data, initial=None): super(FileField, self).clean(initial or data) if not self.required and data in EMPTY_VALUES: return None elif not data and initial: return initial # UploadedFile objects should have name and size attributes. try: file_name = data.name file_size = data.size except AttributeError: raise ValidationError(self.error_messages['invalid']) if self.max_length is not None and len(file_name) > self.max_length: error_values = {'max': self.max_length, 'length': len(file_name)} raise ValidationError(self.error_messages['max_length'] % error_values) if not file_name: raise ValidationError(self.error_messages['invalid']) if not file_size: raise ValidationError(self.error_messages['empty']) return data

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• Tired of Exploring

  - by Abhi

  Dear All I am tired of my work. I am exploring all day and at the end of the day i feel that i have not gain anything. Its been 1 year & 3 month working in Wince 6.0 r3 but i feel that i have gained nothing. I feel like that i have wasted these month without doing anything. At fast i worked in GUI application in which i was gaining confidence but then i was shifted from that domain to something for which lot of knowledge is required i.e writing or adjusting BSP. Now at present i have shifted to work on silverlight which is again a new domain for me. My day starts from 10am and ends at 7pm @ office by doing nothing. I am tired completely. Can anyone help me what shall i do in this situation? How shall i start to achieve the target? Where should i stick "deadline" or "learning the target first" as deadline is also important? I am completely depressed.

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• Why can't we just use a hash of passphrase as the encryption key (and IV) with symmetric encryption algorithms?

  - by TX_

  Inspired by my previous question, now I have a very interesting idea: Do you really ever need to use Rfc2898DeriveBytes or similar classes to "securely derive" the encryption key and initialization vector from the passphrase string, or will just a simple hash of that string work equally well as a key/IV, when encrypting the data with symmetric algorithm (e.g. AES, DES, etc.)? I see tons of AES encryption code snippets, where Rfc2898DeriveBytes class is used to derive the encryption key and initialization vector (IV) from the password string. It is assumed that one should use a random salt and a shitload of iterations to derive secure enough key/IV for the encryption. While deriving bytes from password string using this method is quite useful in some scenarios, I think that's not applicable when encrypting data with symmetric algorithms! Here is why: using salt makes sense when there is a possibility to build precalculated rainbow tables, and when attacker gets his hands on hash he looks up the original password as a result. But... with symmetric data encryption, I think this is not required, as the hash of password string, or the encryption key, is never stored anywhere. So, if we just get the SHA1 hash of password, and use it as the encryption key/IV, isn't that going to be equally secure? What is the purpose of using Rfc2898DeriveBytes class to generate key/IV from password string (which is a very very performance-intensive operation), when we could just use a SHA1 (or any other) hash of that password? Hash would result in random bit distribution in a key (as opposed to using string bytes directly). And attacker would have to brute-force the whole range of key (e.g. if key length is 256bit he would have to try 2^256 combinations) anyway. So either I'm wrong in a dangerous way, or all those samples of AES encryption (including many upvoted answers here at SO), etc. that use Rfc2898DeriveBytes method to generate encryption key and IV are just wrong.

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