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• Am I understanding premature optimization correctly?

  - by Ed Mazur

  I've been struggling with an application I'm writing and I think I'm beginning to see that my problem is premature optimization. The perfectionist side of me wants to make everything optimal and perfect the first time through, but I'm finding this is complicating the design quite a bit. Instead of writing small, testable functions that do one simple thing well, I'm leaning towards cramming in as much functionality as possible in order to be more efficient. For example, I'm avoiding multiple trips to the database for the same piece of information at the cost of my code becoming more complex. One part of me wants to just not worry about redundant database calls. It would make it easier to write correct code and the amount of data being fetched is small anyway. The other part of me feels very dirty and unclean doing this. :-) I'm leaning towards just going to the database multiple times, which I think is the right move here. It's more important that I finish the project and I feel like I'm getting hung up because of optimizations like this. My question is: is this the right strategy to be using when avoiding premature optimization?

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• java: retrieving the "canonical value" from a Set<T> where T has a custom equals()

  - by Jason S

  I have a class Foo which overrides equals() and hashCode() properly. I would like to also would like to use a HashSet<Foo> to keep track of "canonical values" e.g. I have a class that I would like to write like this, so that if I have two separate objects that are equivalent I can coalesce them into references to the same object: class Canonicalizer<T> { final private Set<T> values = new HashSet<T>(); public T findCanonicalValue(T value) { T canonical = this.values.get(value); if (canonical == null) { // not in the set, so put it there for the future this.values.add(value); return value; } else { return canonical; } } } except that Set doesn't have a "get" method that would return the actual value stored in the set, just the "contains" method that returns true or false. (I guess that it assumes that if you have an object that is equal to a separate object in the set, you don't need to retrieve the one in the set) Is there a convenient way to do this? The only other thing I can think of is to use a map and a list: class Canonicalizer<T> { // warning: neglects concurrency issues final private Map<T, Integer> valueIndex = new HashMap<T, Integer>(); final private List<T> values = new ArrayList<T>(); public T findCanonicalValue(T value) { Integer i = this.valueIndex.get(value); if (i == null) { // not in the set, so put it there for the future i = this.values.size(); this.values.add(value); this.valueIndex.put(value, i); return value; } else { // in the set return this.values.get(i); } } }

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• Connect to Facebook with Javascript Client Library using Adobe AIR

  - by Chuck Hriczko

  I'm having an issue connecting to Facebook through the Javascript Client Library in Adobe AIR. It works fine in the browser but in Adobe AIR it seems to not be able to find the Facebook functions. Here is some code I copied from the Facebook website: (Oh and I have the xd_receiver.htm file in the correct path too) <textarea style="width: 1000px; height: 300px;" id="_traceTextBox"> </textarea> <script src="http://static.ak.connect.facebook.com/js/api_lib/v0.4/FeatureLoader.js.php" type="text/javascript"></script> // var api = FB.Facebook.apiClient; // require user to login api.requireLogin(function(exception){ FB.FBDebug.logLevel=1; FB.FBDebug.dump("Current user id is " + api.get_session().uid); // Get friends list //5-14-09: this code below is broken, correct code follows //api.friends_get(null, function(result){ // Debug.dump(result, 'friendsResult from non-batch execution '); // }); api.friends_get(new Array(), function(result, exception){ FB.FBDebug.dump(result, 'friendsResult from non-batch execution '); }); }); }); //]]> </script>

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• Implementation problem. Htaccess in php

  - by Irwan

  I have a problem to fix the URL on my website at http://www.abelputra.com I need a solution: I want to change www.abelputra.com/software.php into www.abelputra.com/software I have read a tutorial like this: For .htaccess: RewriteEngine On RewriteRule ^ ([a-zA-Z0-9_-] +) $ index.php? Key = $ 1 RewriteRule ^ ([a-zA-Z0-9_-]+)/$ index.php? Key = $ 1 Then in php: index.php --- $Key=$ _GET ['key']; if ($key == 'home') { include ('index.php'); // Home page } else if ($ key == 'software') { include ('software.php'); // } else if ($ key == 'webdesign') { include ('webdesign.php'); // } The problem is: When I implemented the menu software.php index.php to call the page: www.abelputra.com/index.php?key=software what happens is the page that is shown is two pages later software.php index.php page underneath. Is it because calling functions "include ()"? index.php structures: Header Content - contains the opening words Footer software.php structure: Header Content - contains an explanation of my software Footer Sorry my english bad. im from Indonesia. Please solution .. thanks

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• What's the best way to store Logon User information for Web Application?

  - by Morgan Cheng

  I was once in a project of web application developed on ASP.NET. For each logon user, there is an object (let's call it UserSessionObject here) created and stored in RAM. For each HTTP request of given user, matching UserSessoinObject instance is used to visit user state information and connection to database. So, this UserSessionObject is pretty important. This design brings several problems found later: 1) Since this UserSessionObject is cached in ASP.NET memory space, we have to config load balancer to be sticky connection. That is, HTTP request in single session would always be sent to one web server behind. This limit scalability and maintainability. 2) This UserSessionObject is accessed in every HTTP request. To keep the consistency, there is a exclusive lock for the UserSessionObject. Only one HTTP request can be processed at any given time because it must to obtain the lock first. The performance and response time is affected. Now, I'm wondering whether there is better design to handle such logon user case. It seems Sharing-Nothing-Architecture helps. That means long user info is retrieved from database each time. I'm afraid that would hurt performance. Is there any design pattern for long user web app? Thanks.

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• Which function pair in QString to use for converting to/from std::string?

  - by Noah Roberts

  I'm working on a project that we want to use Unicode and could end up in countries like Japan, etc... We want to use std::string for the underlying type that holds string data in the data layer (see Qt, MSVC, and /Zc:wchar_t- == I want to blow up the world as to why). The problem is that I'm not completely sure which function pair (to/from) to use for this and be sure we're 100% compatible with anything the user might enter in the Qt layer. A look at to/fromStdString indicates that I'd have to use setCodecForCStrings. The documentation for that function though indicates that I wouldn't want to do this for things like Japanese. This is the set that I'd LIKE to use though. Does someone know enough to explain how I'd set this up if it's possible? The other option that looks like I could be pretty sure of it working is the to/fromUTF8 functions. Those would require a two step approach though so I'd prefer the other if possible. Is there anything I've missed?

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• How do I return the value of the owner and id attributes respectively from an XML result set using P

  - by pharma_joe

  I am using PHP to iterate over the following result set, the aim is to build a hyperlink for each result using a foreach loop. I have stored the XML result in $images, and have constructed this loop: foreach ($images as $image) { //Build link to each photo returned //base URL $flickrPhotoUrl = 'http://www.flickr.com/photos/'; //Append user ID $flickrPhotoUrl .= ""; echo $flickrPhotoUrl; } Here is a sample result from Flickr: <photos page="1" pages="10982" perpage="10" total="109813"> <photo id="4616840471" owner="47823583@N03" secret="1b83173bc0" server="4013" farm="5" title="Strawberry Bears" ispublic="1" isfriend="0" isfamily="0"></photo> <photo id="4616612597" owner="12658756@N08" secret="f626214382" server="4059" farm="5" title="Yarn Chef Minestrone - Grickle Grass" ispublic="1" isfriend="0" isfamily="0"></photo> <photo id="4616469567" owner="26284268@N00" secret="6911a66838" server="4022" farm="5" title="P5130121.JPG" ispublic="1" isfriend="0" isfamily="0"></photo> <photo id="4617076736" owner="26284268@N00" secret="8b990acba4" server="4047" farm="5" title="P5130106.JPG" ispublic="1" isfriend="0" isfamily="0"></photo> <photo id="4616470013" owner="26284268@N00" secret="44600b3836" server="4036" farm="5" title="P5130125.JPG" ispublic="1" isfriend="0" isfamily="0"></photo> <photo id="4616466147" owner="26284268@N00" secret="554eab8667" server="4052" farm="5" title="P5130116.JPG" ispublic="1" isfriend="0" isfamily="0"></photo> <photo id="4617082398" owner="26284268@N00" secret="4a2b663442" server="3350" farm="4" title="P5130118.JPG" ispublic="1" isfriend="0" isfamily="0"></photo> <photo id="4617078272" owner="26284268@N00" secret="357737017b" server="4013" farm="5" title="P5130109.JPG" ispublic="1" isfriend="0" isfamily="0"></photo> <photo id="4617081446" owner="26284268@N00" secret="1f87726497" server="4048" farm="5" title="P5130117.JPG" ispublic="1" isfriend="0" isfamily="0"></photo> <photo id="4617077676" owner="26284268@N00" secret="77ca9f754a" server="3330" farm="4" title="P5130108.JPG" ispublic="1" isfriend="0" isfamily="0"></photo>

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• Avoiding seasonality assumption for stl() or decompose() in R

  - by user303922

  Hello everybody, I have high frequency commodity price data that I need to analyze. My objective is to not assume any seasonal component and just identify a trend. Here is where I run into problems with R. There are two main functions that I know of to analyze this time series: decompose() and stl(). The problem is that they both take a ts object type with a frequency parameter greater than or equal to 2. Is there some way I can assume a frequency of 1 per unit time and still analyze this time series using R? I'm afraid that if I assume frequency greater than 1 per unit time, and seasonality is calculated using the frequency parameter, then my forecasts are going to depend on that assumption. names(crude.data)=c('Date','Time','Price') names(crude.data) freq = 2 win.graph() plot(crude.data$Time,crude.data$Price, type="l") crude.data$Price = ts(crude.data$Price,frequency=freq) I want frequency to be 1 per unit time but then decompose() and stl() don't work! dim(crude.data$Price) decom = decompose(crude.data$Price) win.graph() plot(decom$random[2:200],type="line") acf(decom$random[freq:length(decom$random-freq)]) Thank you.

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• Create a multicolor selectbox on Symfony2

  - by Ninsuo

  I try to create the following field : <select name="test"> <option value="1">a</option> <option value="2">b</option> <option value="3" style="font-weight: bold; color: red;">c</option> <option value="4">d</option> <option value="5">e</option> </select> This creates a 2-color selectbox : But in Symfony2, I do not know how to apply a class to a single option. If in my view I do : {{ form_widget(myForm.test, { 'attr': { 'class': 'red', } }) }} Or if in my form I do : $builder->add('test', 'choice', array( 'required' => true, 'choices' => array('a', 'b', 'c', 'd', 'e'), 'attr' => array('class' => 'red'), )); The attribute is stored into the <select> tag and apply to the whole selectable values. How do I apply a class to an <option> in Symfony2 ?

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• How to determine which inheriting class is using an abstract class's methods.

  - by Kin

  In my console application have an abstract Factory class "Listener" which contains code for listening and accepting connections, and spawning client classes. This class is inherited by two more classes (WorldListener, and MasterListener) that contain more protocol specific overrides and functions. I also have a helper class (ConsoleWrapper) which encapsulates and extends System.Console, containing methods for writing to console info on what is happening to instances of the WorldListener and MasterListener. I need a way to determine in the abstract ListenerClass which Inheriting class is calling its methods. Any help with this problem would be greatly appreciated! I am stumped :X Simplified example of what I am trying to do. abstract class Listener { public void DoSomething() { if(inheriting class == WorldListener) ConsoleWrapper.WorldWrite("Did something!"); if(inheriting class == MasterListener) ConsoleWrapper.MasterWrite("Did something!"); } } public static ConsoleWrapper { public void WorldWrite(string input) { System.Console.WriteLine("[World] {0}", input); } } public class WorldListener : Listener { public void DoSomethingSpecific() { ConsoleWrapper.WorldWrite("I did something specific!"); } } public void Main() { new WorldListener(); new MasterListener(); } Expected output [World] Did something! [World] I did something specific! [Master] Did something! [World] I did something specific!

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• I am using a regex snippet query string path

  - by Shelby Poston

  Using the following to load images base on two ids one is the and bookid and the out is the client. My folder structures is this. root path = flipbooks subfolders under flipbooks are books and clients in subfolder books I have and .net page title tablet. the tablet code behind checks the bookid of client and render a the tablet page with images in a flipbook fashion. because we have over 15000 records and flipbooks already created and stored in the database. I don't move the client folder under the books subfolders. I need the code below to get to the client subfolder in the query string and help to change this would be helpful. The result now is http://www.somewebsite.com/books/client/images/someimage1.jpg[^] I need the results to be http://www.somewebsite.com/client/images/someimage1.jpg[^]. I tried moving the tablet.aspx file to the root flipbooks and it works but i have provide a user name and password each time. This need to be access by the public and my root is protected. Don't want to have to change permission. I am trying to remove the /books function getParameterByName(name) { var results = RegExp('[?&]' + name + '=([^&]*)').exec(window.location.search); return results ? decodeURIComponent(results[1].replace(/\+/g, ' ')) : null; } Thanks Mission Critical

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• How to store a linked list in a struct in C

  - by LuckySlevin

  typedef struct child_list {int count; char vo[100]; child_list*next;} child_list; typedef struct parent_list { char vo[100]; child_list * head; int count; parent_list * next; } parent_list; As you can see there are two structures. child_list is used to create a linked list. And this list will be stored in a linked list of parent list. My problem is to display the child list which in the parent_list. My desire to get while displaying the linked list of parent_list: This lists work with this logic. I already made append and other stuff. For example if i enter ab cd ab ja cd ab Word Count List ab 3 cd->ja cd 2 ab->ab ja 1 cd The problematic part is displaying child_list which is in the parent_list nodes(List column of output). I don't know my question is clear please ask for further info.

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• virtual methods and template classes

  - by soxs060389

  Hi I got over a problem, I think a very specific one. I've got 2 classes, a B aseclass and a D erived class (from B aseclass). B is a template class ( or class template) and has a pure virtual method virutal void work(const T &dummy) = 0; The D erived class is supposed to reimplement this, but as D is Derived from B rather than D being another template class, the compiler spits at me that virtual functions and templates don't work at once. Any ideas how to acomplish what I want? I am thankfull for any thoughts and Ideas, especially if you allready worked out that problem this class is fixed aka AS IS, I can not edit this without breaking existing code base template <typename T> class B { public: ... virtual void work(const T &dummy) = 0; .. }; take int* as an example class D : public B<int*>{ ... virtual void work(const int* &dummy){ /* put work code here */ } .. }; Edit: The compiler tells me, that void B<T>::work(const T&) [with T = int*] is pure virtual within D

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• Const_cast on a this pointer - would I get told off by other C++ coders for doing this?

  - by BeeBand

  I have a class Game e.g. class Game { public: InitObjects(); ... }; And I have another class Grid, that needs to be initialised with a non-const reference to that Game object. ( A Grid object needs to call functions that can update a Game object ). class Grid { public: Grid(Game & g): game(g){} ... private: Game & game; ... }; The Game object is responsible for initialising the Grid. I did this: void Game::InitObjects() { grid = new Grid(*(const_cast<Game*>(this)) ); } grid is not a member of a Game - it's a global ( argh - i know... I don't mind making it a member, but I have the same problem right? ). Can some seasoned C++ folk tell me if this odd looking const_cast is acceptable?

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• Using function arguments to dynamically generate a query

  - by Varun

  I am working on an issue management system, developed in PHP/MySQL. It requires search functionality, where the user will mention the search parameters and based on these parameters the system will return the result set. To solve this I am trying to write a function and all the user selected parameters are passed as arguments. Based on the arguments I will dynamically generate the query. Sample Query: select * from tickets inner join ticket_assigned_to on tickets.id=ticket_assigned_to.ticket_id where tickets.project_id= in ('') and tickets.status in ('') and ticket_assigned_to.user_id in ('') and tickets.reporter_user_id='' and tickets.operator_user_id in ('') and tickets.due_date between '' and '' and tickets.ts_created between '' and ''; I also need to handle cases where the arguments can be ORed or ANDed in the query. For example: select * from tickets inner join ticket_assigned_to on tickets.id=ticket_assigned_to.ticket_id where tickets.project_id= in ('') and tickets.status in ('') or tickets.due_date = '' or tickets.ts_created between '' and ''; I am also planning to use the same function at other places in the project also. Like to display all the tickets of a user or all tickets created between given dates and so on... How to handle this situation? Should I go with a single function which handles all this or numerous small functions? Need guidance here.

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• How to find which delimiter was used during string split (VB.NET)

  - by typoknig

  Hi all, lets say I have a string that I want to split based on several characters, like ".", "!", and "?". How do I figure out which one of those characters split my string so I can add that same character back on to the end of the split segments in question? Dim linePunctuation as Integer = 0 Dim myString As String = "some text. with punctuation! in it?" For i = 1 To Len(myString) If Mid$(entireFile, i, 1) = "." Then linePunctuation += 1 Next For i = 1 To Len(myString) If Mid$(entireFile, i, 1) = "!" Then linePunctuation += 1 Next For i = 1 To Len(myString) If Mid$(entireFile, i, 1) = "?" Then linePunctuation += 1 Next Dim delimiters(3) As Char delimiters(0) = "." delimiters(1) = "!" delimiters(2) = "?" currentLineSplit = myString.Split(delimiters) Dim sentenceArray(linePunctuation) As String Dim count As Integer = 0 While linePunctuation > 0 sentenceArray(count) = currentLineSplit(count)'Here I want to add what ever delimiter was used to make the split back onto the string before it is stored in the array.' count += 1 linePunctuation -= 1 End While

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• how to use iterator in c++?

  - by tsubasa

  I'm trying to calculate distance between 2 points. The 2 points I stored in a vector in c++: (0,0) and (1,1). I'm supposed to get results as 0 1.4 1.4 0 but the actual result that I got is 0 1 -1 0 I think there's something wrong with the way I use iterator in vector. Could somebody help? I posted the code below. typedef struct point { float x; float y; } point; float distance(point *p1, point *p2) { return sqrt((p1->x - p2->x)*(p1->x - p2->x) + (p1->y - p2->y)*(p1->y - p2->y)); } int main() { vector <point> po; point p1; p1.x=0; p1.y=0; point p2; p2.x=1; p2.y=1; po.push_back(p1); po.push_back(p2); vector <point>::iterator ii; vector <point>::iterator jj; for (ii=po.begin(); ii!=po.end(); ii++) { for (jj=po.begin(); jj!=po.end(); jj++) { cout<<distance(ii,jj)<<" "; } } return 0; }

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• Appengine JDO dataclasses to python model

  - by M.A. Cape

  Does anyone have tried to implement an app in GAE having both java and python? I have an existing app and my front end is in java. Now I want to use the existing datastore to be interfaced by python. My problem is i don't know how to define the relationships and model that would be equivalent to the one in java. I have tried the one-to-many relationship in python but when stored in the datastore, the fields are different than the one-to-many of java. My data classes are as follows. //one-to-many owned Parent Class public class Parent{ @PrimaryKey @Persistent private String unitID; //some other fields... @Persistent @Order(extensions = @Extension(vendorName="datanucleus", key="list-ordering", value="dateCreated desc")) private List <Child> child; //methods & constructors were omitted } Child public class Child{ @PrimaryKey @Persistent(valueStrategy = IdGeneratorStrategy.IDENTITY) private Key uId; @Persistent private String name; /* etc... */ }

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• Updating section in ConfigParser (or an alternative)

  - by lyrae

  I am making a plugin for another program and so I am trying to make thing as lightweight as possible. What i need to do is be able to update the name of a section in the ConfigParser's config file. [project name] author:john doe email: [email protected] year: 2010 I then have text fields where user can edit project's name, author, email and year. I don't think changing [project name] is possible, so I have thought of two solutions: 1 -Have my config file like this: [0] projectname: foobar author:john doe email: [email protected] year: 2010 that way i can change project's name just like another option. But the problem is, i would need the section # to be auto incremented. And to do this i would have to get every section, sort of, and figure out what the next number should be. The other option would be to delete the entire section and its value, and re-add it with the updated values which would require a little more work as well, such as passing a variable that holds the old section name through functions, etc, but i wouldn't mind if it's faster. Which of the two is best? or is there another way? I am willing to go with the fastest/lightweight solution possible, doesn't matter if it requires more work or not.

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• A quick question on data returned by jquery.ajax() call (EDITED)

  - by recipriversexclusion

  EDIT: The original problem was due a stupid syntax mistake somewhere else, whicj I fixed. I have a new problem though, as described below I have the following jquery.ajax call: $.ajax({ type: 'GET', url: servicesUrl + "/" + ID + "/tasks", dataType: "xml", success : createTaskListTable }); The createTaskListTable function is defined as function createTaskListTable(taskListXml) { $(taskListXml).find("Task").each(function(){ alert("Found task") }); // each task } Problem is: this doesn't work, I get an error saying taskListXml is not defined. JQuery documentation states that the success functions gets passed three arguments, the first of which is the data. How can I pass the data returned by .ajax() to my function with a variable name of my own choosing. My problem now is that I'm getting the XML from a previous ajax call! How is this even possible? That previous function is defined as function convertServiceXmlDataToTable(xml), so they don't use the same variable name. Utterly confused. Is this some caching issue? If so, how can I clear the browser cache to get rid of the earlier XML? Thanks!

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• Javascript Closures, Callbacks, This and That

  - by nazbot

  I am having some trouble getting a callback function to work. Here is my code: SomeObject.prototype.refreshData = function() { var read_obj = new SomeAjaxCall("read_some_data", { }, this.readSuccess, this.readFail); } SomeObject.prototype.readSuccess = function(response) { this.data = response; this.someList = []; for (var i = 0; i < this.data.length; i++) { var systemData = this.data[i]; var system = new SomeSystem(systemData); this.someList.push(system); } this.refreshList(); } Basically SomeAjaxCall is making an ajax request for data. If it works we use the callback 'this.readSuccess' and if it fails 'this.readFail'. I have figured out that 'this' in the SomeObject.readSuccess is the global this (aka the window object) because my callbacks are being called as functions and not member methods. My understanding is that I need to use closures to keep the 'this' around, however, I have not been able to get this to work. If someone is able show me what I should be doing I would appreciate it greatly. I am still wrapping my head around how closures work and specifically how they would work in this situation. Thanks!

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• How to globalize ASP.NET MVC views (decimal separators in particular)?

  - by Pawel Krakowiak

  I'm working with the NerdDinner sample application and arrived at the section which deals with the Virtual Earth map. The application stores some values for the longitude and latitude. Unfortunately on my system floating point numbers are stored with a comma as the decimal separator, not a dot like in the US. So if I have a latitude of 47.64 it's retrieved and displayed as 47,64. Because that value is passed in a function call to the Virtual Earth API it fails at that point (e.g. JavaScript API expects 47.64, -122.13, but gets 47,64, -122,13). I need to make sure that the application always uses dots. In a WebForms app I would have a common class which overrides the System.Web.UI.Page.InitializeCulture() method and I would be inheriting my pages from that class. I am not sure about how to do the same with MVC. Do I need a customized ViewPage or something? Is there an easy way to solve this? Examples?

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• jquery draggable/droppable issue

  - by Scarface

  Hey guys I have a drag and drop function that does not fully work. What I want to do is be able to drag and drop a picture into a div and have that picture pop up in the div. I have a list of 2 pictures right now, so I have the following function echoed for each picture. Both pictures are draggable and droppable, but the first one is the only one that appears in the div, regardless of which picture gets dragged in. I am not sure what is wrong because the jquery function seems to be unique to each picture. If any one has any suggestions I would appreciate it greatly. while ($row = mysql_fetch_assoc($query)) { $image=htmlentities($row['image']); //image name $uniqid=uniqid(); //unique id for jquery functions $dirname = "usercontent/$user/images/$image"; echo "<img id=\"$uniqid\" src=\"$dirname\" width=\"75\" height=\"75\"/>"; echo "<script> $(function() { $(\"#$uniqid\").draggable({ scroll: true, scrollSensitivity: 10, scrollSpeed: 10, revert: true, helper: 'clone', cursorAt: { cursor: 'move', top: 27, left: 27 } }); $(\"#droppable2, #droppable-background , #droppable2-innerer\").droppable({ greedy: true, activeClass: 'ui-state-hover', hoverClass: 'ui-state-active', drop: function(event, ui) { $(this).addClass('ui-state-highlight').find('> p').html('Dropped!'); $('#droppable-background').css(\"background-image\",\"url($dirname)\"); } }); }); </script>"; }

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• How do actually castings work at the CLR level?

  - by devoured elysium

  When doing an upcast or downcast, what does really happen behind the scenes? I had the idea that when doing something as: string myString = "abc"; object myObject = myString; string myStringBack = (string)myObject; the cast in the last line would have as only purpose tell the compiler we are safe we are not doing anything wrong. So, I had the idea that actually no casting code would be embedded in the code itself. It seems I was wrong: .maxstack 1 .locals init ( [0] string myString, [1] object myObject, [2] string myStringBack) L_0000: nop L_0001: ldstr "abc" L_0006: stloc.0 L_0007: ldloc.0 L_0008: stloc.1 L_0009: ldloc.1 L_000a: castclass string L_000f: stloc.2 L_0010: ret Why does the CLR need something like castclass string? There are two possible implementations for a downcast: You require a castclass something. When you get to the line of code that does an castclass, the CLR tries to make the cast. But then, what would happen had I ommited the castclass string line and tried to run the code? You don't require a castclass. As all reference types have a similar internal structure, if you try to use a string on an Form instance, it will throw an exception of wrong usage (because it detects a Form is not a string or any of its subtypes). Also, is the following statamente from C# 4.0 in a Nutshell correct? Upcasting and downcasting between compatible reference types performs reference conversions: a new reference is created that points to the same object. Does it really create a new reference? I thought it'd be the same reference, only stored in a different type of variable. Thanks

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• Is it a good idea to use MySQL and Neo4j together?

  - by Sanoj

  I will make an application with a lot of similar items (millions), and I would like to store them in a MySQL database, because I would like to do a lot of statistics and search on specific values for specific columns. But at the same time, I will store relations between all the items, that are related in many connected binary-tree-like structures (transitive closure), and relation databases are not good at that kind of structures, so I would like to store all relations in Neo4j which have good performance for this kind of data. My plan is to have all data except the relations in the MySQL database and all relations with item_id stored in the Neo4j database. When I want to lookup a tree, I first search the Neo4j for all the item_id:s in the tree, then I search the MySQL-database for all the specified items in a query that would look like: SELECT * FROM items WHERE item_id = 45 OR item_id = 345435 OR item_id = 343 OR item_id = 78 OR item_id = 4522 OR item_id = 676 OR item_id = 443 OR item_id = 4255 OR item_id = 4345 Is this a good idea, or am I very wrong? I haven't used graph-databases before. Are there any better approaches to my problem? How would the MySQL-query perform in this case?

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