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  • Unique constraint on more than 10 columns

    - by tk
    I have a time-series simulation model which has more than 10 input variables. The number of distinct simulation instances would be more than 1 million, and each simulation instance generates a few output rows every day. To save the simulation result in a relational database, i designed tables like this. Table SimulationModel { simul_id : integer (primary key), input0 : string or numeric, input1 : string or numeric, ...} Table SimulationOutput { dt : DateTime (primary key), simul_id : integer (primary key), output0 : numeric, ...} My question is, is it fine to put an unique constraint on all of the input columns of SimulationModel table? If it is not a good idea, then what kind of other options do i have to make sure each model is unique?

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  • Why in Objective-C, we use self = [super init] instead of just [super init]?

    - by ????
    In a book, I saw that if a subclass is overriding a superclass's method, we may have self = [super init]; First, is this supposed to be done in the subclass's init method? Second, I wonder why the call is not just [super init]; ? I mean, at the time of calling init, the memory is allocated by alloc already (I think by [Foobar alloc] where Foobar is the subclass's name. So can't we just call [super init] to initialize the member variables? Why do we have to get the return value of init and assign to self? I mean, before calling [super init], self should be pointing to a valid memory allocation chuck... so why assigning something to self again? (if assigning, won't [super init] just return self's existing value?)

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  • How to tell a UITableView to preload all Rows?

    - by Infinite
    Is there a way to tell a UITableView to preload all rows? The tableView is supposed to show several comments (up to 80 comments). So my CommentCell uses a Setter to adapt the cell to a specific comment. -(void)setComment:(Comment *)newComment { if (newComment != comment) { [comment release]; comment = [newComment retain]; /* * set the cells view variables here */ } } This specific setter takes quite a bunch of processing resources and scrolling gets kinda laggy. I am using a comment-specific reuseIdentifier instead of a static cellIdentifier when calling dequeueReusableCellWithIdentifier: in order to assure, that "newComment" equals the old "comment". And in fact this does work great when scrolling over cells which have already been loaded. But when scrolling through the comments for the first time, it still lags like hell. Which leads me to my question: Is there a way to tell the tableview to preload all cells? (which I doubt) or Do I have to implement my own cache instead of relying on "dequeueReusableCellWithIdentifier:"?

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  • Is it inefficient to access a python class member container in a loop statement?

    - by Dave
    Hi there. I'm trying to adopt some best practices to keep my python code efficient. I've heard that accessing a member variable inside of a loop can incur a dictionary lookup for every iteration of the loop, so I cache these in local variables to use inside the loop. My question is about the loop statement itself... if I have the following class: class A(object): def init(self) self.myList = [ 'a','b','c', 'd', 'e' ] Does the following code in a member function incur one, or one-per-loop-iteration (5) dictionary lookups? for letter in self.myList: print letter IE, should I adopt the following pattern, if I am concerned about efficiency... localList = self.myList for letter in localList: print letter or is that actually LESS efficient due to the local variable assign? Note, I am aware that early optimization is a dangerous pitfall if I'm concerned about the overall efficiency of code development. Here I am specifically asking about the efficiency of the code, not the coding. Thanks in advance! D

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  • Retrieve a static variable using its name dynamically using reflection

    - by user2538438
    How to retrieve a static variable using its name dynamically using Java reflection? If I have class containing some variables: public class myClass { string [][] cfg1= {{"01"},{"02"},{"81"},{"82"}}; string [][]cfg2= {{"c01"},{"c02"},{"c81"},{"c82"}}; string [][] cfg3= {{"d01"},{"d02"},{"d81"}{"d82"}}; int cfg11 = 5; int cfg22 = 10; int cfg33 = 15; } And in another class I want variable name is input from user: class test { Scanner in = new Scanner(System.in); String userInput = in.nextLine(); // get variable from class myClass that has the same name as userInput System.out.println("variable name " + // correct variable from class) } Using reflection. Any help please?

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  • Phase REST XML into variable

    - by 001
    I want to get a response from the REST XML web service, and phase it into variables so I can use them in my program. 1) How come this code does not work? I get an empty string... // Get response string ws_response=""; using (HttpWebResponse response = request.GetResponse() as HttpWebResponse) { // Get the response stream StreamReader reader = new StreamReader(response.GetResponseStream()); // web service response string ws_response = reader.ReadToEnd; // <---???? I get an empty string // do phasing here (ie XML element into variable) etc.. // }

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  • Inheritance - initialization problem

    - by dumbquestion
    I have a c++ class derived from a base class in a framework. The derived class doesn't have any data members because I need it to be freely convertible into a base class and back - the framework is responsible for loading and saving the objects and I can't change it. My derived class just has functions for accessing the data. But there are a couple of places where I need to store some temporary local variables to speed up access to data in the base class. mydata* MyClass::getData() { if ( !m_mydata ) { // set to NULL in the constructor m_mydata = some_long_and complex_operation_to_get_the_data_in_the_base() } return m_mydata; } The problem is if I just access the object by casting the base class pointer returned from the framework to MyClass* the ctor for MyClass is never called and m_mydata is junk. Is there a way of only initializing the m_mydata pointer once?

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  • Sorting a value pair in Javascript

    - by Bradley M. Davis
    I must be missing the proper term or else I'm sure I could find the answer by searching... in any case, here's what I want to do. Through javascript, I get four variables (A, B, C, and D) that I would like to sort, and still keep track of the variable name (since it's encoded with meaning information). Sample Data: A = 2; B = 1; C = 4; D = 3; What I need to do now is sort them in value order (4,3,2,1) such that I can actually know the variable name ordering (C,D,A,B).

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  • Nested loop with dependent bounds trip count

    - by aaa
    hello. just out of curiosity I tried to do the following, which turned out to be not so obvious to me; Suppose I have nested loops with runtime bounds, for example: t = 0 // trip count for l in 0:N for k in 0:N for j in max(l,k):N for i in k:j+1 t += 1 t is loop trip count is there a general algorithm/way (better than N^4 obviously) to calculate loop trip count? I am working on the assumption that the iteration bounds depend only on constant or previous loop variables.

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  • Keeping Computer Science Writing Accessible and Eloquent

    - by Federer
    This question is particularly aimed at descriptions and explanations of what is happening in a computer program, as well as any general advice or approaches for undertaking technical reports in Computer Science at both undergraduate and graduate levels. You see, I am having particular difficulty in the best way to explain what is happening. As in, given any given program from a multi-agent system to a standard webservice, the best and most eloquent way to say exactly what is going on, the logic behind it and it's respective justifications. Should I avoid saying class names? Avoid specifying methods? Keep referring to class variables and any particular references? I'm banging my head against the wall at trying to keep a solid technical foundation and making it accessible to people of all backgrounds. Apologies for the rather vague question. Cheers.

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  • I don't get this C/C++ Joke

    - by Buttercup
    After reading this article on thedailywtf.com, I'm not sure that I really got the joke. It says there that some guy changed the code from int function() { int x; char data_string[15]; ... x = 2; strcpy(data_string,"data data data"); ... } to int function() { int x = 2; char data_string[15] = "data data data"; ... } everywhere in the code and that for some reason did inflate the size of the executable from 1 to 2 CDs (or maybe it didn't do that?). Obviously I'm not familiar enough with C/C++ to get this joke, but what seems strangest is that the 2nd code listing seems "cleaner"—at least from what I've been told in school (that is that initializing variables is a good thing, not a bad one).

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  • How much memory is reserved when i declare a string?

    - by Bhagya
    What exactly happens, in terms of memory, when i declare something like: char arr[4]; How many bytes are reserved for arr? How is null string accommodated when I 'strcpy' a string of length 4 in arr? I was writing a socket program, and when I tried to suffix NULL at arr[4] (i.e. the 5th memory location), I ended up replacing the values of some other variables of the program (overflow) and got into a big time mess. Any descriptions of how compilers (gcc is what I used) manage memory?

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  • Do I need to install Glassfish?

    - by Ayusman
    Hi, I am new to glassfish server. i have a question on glassfish usage: can I just use glassfish like a tomcat server without needing an installation? where in, I just take a folder containing glassfish folders, jars etc... dump it in a folder location setup a few environment variables and it runs.. just like tomcat? is it possible with glassfish? also does glassfish installation does any other background things like creating registry entries etc other than creating the glassfish folder structure? TIA Ayusman

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  • how does "recent history" work on sites for php? (PHP)

    - by ggfan
    I'm not sure if there is an explanation on SO for beginners, but if so, could you provide the links. I am interested in creating a "recent viewed" function that shows what links they clicked on before. I'm not sure if this is the 'correct' way to do it, but this is what I have so far... user clicks on a link(say ad.php?posting_id=12). if the user doesn't click on the link, no cookie or session is stored for the link if the user clicks on the link, it sets a cookie for $_cookie['ad.php?posting_id=22'] Each time the user clicks, more cookies are set In the recent viewed function, it gets all the $_cookie variables and displays them. if the user wants to clear the history, just destroy all the cookies I'm not sure if this is the way to do it, but is the viable? If not, what are the steps to create a "recent viewed" function

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  • Unable to access static var from Document Class in AS3

    - by omidomid
    I have a Document class called "CityModule", and an asset with class "City". Below is the coe for each. For some reason, I am unable to access the static variables of the City class from CityModule: CityModule.as: package { public class CityModule extends MovieClip { public function CityModule() { var buildings:Array = City.getBuildings(); } } } } City.as: package { import flash.display.MovieClip; public class City extends MovieClip { private static var _buildings:Array = [ {className:'City.Generic1', type:'generic'}, {className:'City.Generic2', type:'generic'}, {className:'City.Generic3', type:'generic'} ]; public function City(){ //empty } public static function getBuildings():Array{ return _buildings; } } } Doing this gives me a "Call to a possibly undefined method getBuildings" error. If I instantiate an instance of City, I can see any public/ getters/ setters perfectly fine. But static isn't working...

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  • Factory vs instance constructors

    - by Neil N
    I can't think of any reasons why one is better than the other. Compare these two implementations: public class MyClass { public myClass(string fileName) { // some code... } } as opposed to: public class MyClass { private myClass(){} public static Create(string fileName) { // some code... } } There are some places in the .Net framework that use the static method to create instances. At first I was thinking, it registers it's instances to keep track of them, but regular constructors could do the same thing through the use of private static variables. What is the reasoning behind this style?

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  • Should I always release self for failed init methods?

    - by leo
    Should I always release self when there is a failure inside init, or should I only do so if I have initialized instance variables first? To put it another way, is this pattern valid? Is there a time when I shouldn't release self inside an init method, or should I assume that if the control flow enters init, self has at least a retain count of 1? - (id)init { if ((self = [super init]) == nil) { [self release]; return nil; } //do some init stuff if (somethingFailed) { [self release]; return nil; } return self; }

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  • Manage bad_alloc exception in C++ construtor

    - by Jimmy zhang
    I have Java experience and recently am doing some C++ coding. My question is that if I have class A, in which I have to instantiate class B and class C as two of the member variables of A. If in the constructor of A, should I assume that allocations of class B and C never fail, and handle the bad allocation exception in the destructor of A? If I don't make that assumption, meaning that I add some try catch block to catch bad_alloc of class B and class C, then if the allocation exception occurs, should I do clean up in the constructor of A? What are the recommended practices? If "new" generates a bad allocation, what value does the pointer carry?

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  • Fully automated MS SQL Restore

    - by hasen j
    I'm not very fluent with MS-SQL commands. I need a script to restore a database from a .bak file and move the logical_data and logical_log files to a specific path. I can do: restore filelistonly from disk='D:\backups\my_backup.bak' This will give me a result set with a column LogicalName, next I need to use the logical names from the result set in the restore command: restore database my_db_name from disk='d:\backups\my_backups.bak' with file=1, move 'logical_data_file' to 'd:\data\mydb.mdf', move 'logical_log_file' to 'd:\data\mylog.ldf' How do I capture the logical names from the first result set into variables that can be supplied to the "move" command? I think the solution might be trivial, but I'm pretty new to mssql.

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  • Do you use Phing?

    - by Sam McAfee
    Does anyone use Phing to deploy PHP applications, and if so how do you use it? We currently have a hand-written "setup" script that we run whenever we deploy a new instance of our project. We just checkout from SVN and run it. It sets some basic configuration variables, installs or reloads the database, and generates a v-host for the site instance. I have often thought that maybe we should be using Phing. I haven't used ant much, so I don't have a real sense of what Phing is supposed to do other than script the copying of files from one place to another much as our setup script does. What are some more advanced uses that you can give examples of to help me understand why we would or would not want to integrate Phing into our process.

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  • How to pass a value between Silverlight pages for WP7?

    - by Sebastian Gray
    I've got a MainPage.xaml page a Detail.xaml page. I've passed variables to the Detail.xaml from MainPage.xaml by using a static variable and referencing it in Detail.xaml (the detail page is acting like a dialog). However once I've updated the content of another object, I want to call a method in MainPage.xaml to refresh the content of that page using the updated object from the Detail.xaml page. I assume I am not using the correct paradigm for this and should probably be using MVVM or something but I'm not familiar with the implementation and was hoping there was a simple way to do this?

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  • Display calculating result in the same page

    - by garcon1986
    Hello, I have a table in my php code. In the second column of the table, normally it displays "---", and after i click the submit button, it will display the calculating result in the same page. For example, <table> <tr><td>1</td><td>---</td></tr> <tr><td>2</td><td>---</td></tr> <tr><td>3</td><td>---</td></tr> </table> And in the same page, it should receive the variables $var1 = $_POST['variable1']; I'm not sure which way to use, ajax or javascript or just css? Do you have any ideas? Thanks

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  • Rails Variable across all controller actions

    - by bob
    Hello, This should be a very simple rails question. I have a variable like the following. @administration = Administration.first I want this variable to be accessible through every controller action across all my controllers so for example if I have a Product controller and inside of it I have the usual CRUD actions, I want the @administration variable as defined above to be put into all the CRUD actions. (It would not be needed in destroy or create or update). I have many controllers throughout my project and I was wondering if there is an easier way than adding it manually through all of the actions that I want it in. I tried a global variable $administration = Administration.first but I run into an issue where it is not updated when I update the actual content of the Administration.first table. Also, I would like to avoid global variables. Any help would be much appreciated. Thanks! :)

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  • How to refresh site if $_SESSION variable has changed

    - by 4ndro1d
    I'm writing in my $_SESSION variable from a database, when i clicked a link. public function getProjectById($id){ $query="SELECT * FROM projects WHERE id=\"$id\""; $result=mysql_query($query); $num=mysql_numrows($result); while ($row = mysql_fetch_object($result)) { $_SESSION['projectid'] = $row->id; $_SESSION['projecttitle'] = $row->title; $_SESSION['projectinfo'] = $row->info; $_SESSION['projecttext'] = $row->text; $_SESSION['projectcategory'] = $row->category; } } Now my variable is overwritten and I want to show these variables in my index.php like this: <div id="textContent"> <?php if(isset($_SESSION['projecttext']) && !empty($_SESSION['projecttext'])) { echo $_SESSION['projecttext']; }else { echo 'No text'; } ?></div> But of course, my page will not refresh automatically. How can I do that?

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  • User Controls Importing Problem (asp.net)(vb)

    - by Phil
    I have this class that contains vars for db connection; Public Shared s As String Public Shared con As String = WebConfigurationManager.ConnectionStrings("foo").ToString() Public Shared c As New SqlConnection(con) Public Shared x As New SqlCommand(s, c) I import this to my page like this; Imports DBVars I'm then able to access these vars from my page. But if I try to import them into a user control the variables are not available. Am I making an error or is this expected? Thanks.

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