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• Database structure for ecommerce site

  - by imanc

  Hey Guys, I have been tasked with designing an ecommerce solution. The aspect that is causing me the most problems is the database. Currently the site consists of 10+ country based shops each with their own database (all residing on the same mysql instance). For the new site I'd rather all these shop databases be merged into one database so that all tables (products, orders, customers etc.) have a shop_id field. From a programming perspective this seems to make the most sense as we won't have to manage data across multiple databases. Currently the entire site generates about 120k orders a year, but is experiencing fairly heavy growth and we need to design a solution that will scale. In 5 years there may be more than a million orders per year and a database that contains 5 years order history (archiving maybe a solution here). The question is - do we use a single database, or do we keep the database-per-shop structure? I am currently trying to find supporting evidence for either avenue. The company I am designing the solution for prefer the per-shop database structure because they believe it will allow the sites to scale. But my argument is that the shop's database probably won't get that busy over the next few years that they exceed the capacity of a mysql database and a "no expenses spared" hardware set-up. I am wondering if anyone has any advice either way? Does anyone have experience with websites / ecommerce sites that have tables containing millions of records? I know there is probably not a clear answer here, but at what stage do we have too many records or too large table files to have a fast loading site? Also, if anyone has any advice on sources of information - books, websites, etc. where I can do further research, it would be highly appreciated! Cheers, imanc

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• Strange results from OdbcDataReader reading Sqlite DB

  - by stout

  This method returns some strange results, and was wondering if someone could explain why this is happening, and possibly a solution to get my desired results. Results: FileName = what I'd expect FileSize = what I'd expect Buffer = all bytes = 0 BytesRead = 0 BlobString = string of binary data FieldType = BLOB (what I'd expect) ColumnType = System.String Furthermore, if the file is greater than a few KB, the reader throws an exception stating the StringBuilder capacity argument must be greater than zero (presummably because the size is greater than Int32.MaxValue). I guess my question is how does one properly read large BLOBs from an OdbcDataReader? public static String SaveBinaryFile(String Key) { try { Connect(); OdbcCommand Command = new OdbcCommand("SELECT [_filename_],[_filesize_],[_content_] FROM [_sys_content] WHERE [_key_] = '" + Key + "';", Connection); OdbcDataReader Reader = Command.ExecuteReader(CommandBehavior.SequentialAccess); if (Reader.HasRows == false) return null; String FileName = Reader.GetString(0); int FileSize = int.Parse(Reader.GetString(1)); byte[] Buffer = new byte[FileSize]; long BytesRead = Reader.GetBytes(2, 0, Buffer, 0, FileSize); String BlobString = (String)Reader["_content_"]; String FieldType = Reader.GetDataTypeName(2); Type ColumnType = Reader.GetFieldType(2); return null; } catch (Exception ex) { Tools.ErrorHandler.Catch(ex); return null; } }

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• Python : How to close a UDP socket while is waiting for data in recv ?

  - by alexroat

  Hello, let's consider this code in python: import socket import threading import sys import select class UDPServer: def __init__(self): self.s=None self.t=None def start(self,port=8888): if not self.s: self.s=socket.socket(socket.AF_INET, socket.SOCK_DGRAM) self.s.bind(("",port)) self.t=threading.Thread(target=self.run) self.t.start() def stop(self): if self.s: self.s.close() self.t.join() self.t=None def run(self): while True: try: #receive data data,addr=self.s.recvfrom(1024) self.onPacket(addr,data) except: break self.s=None def onPacket(self,addr,data): print addr,data us=UDPServer() while True: sys.stdout.write("UDP server> ") cmd=sys.stdin.readline() if cmd=="start\n": print "starting server..." us.start(8888) print "done" elif cmd=="stop\n": print "stopping server..." us.stop() print "done" elif cmd=="quit\n": print "Quitting ..." us.stop() break; print "bye bye" It runs an interactive shell with which I can start and stop an UDP server. The server is implemented through a class which launches a thread in which there's a infinite loop of recv/*onPacket* callback inside a try/except block which should detect the error and the exits from the loop. What I expect is that when I type "stop" on the shell the socket is closed and an exception is raised by the recvfrom function because of the invalidation of the file descriptor. Instead, it seems that recvfrom still to block the thread waiting for data even after the close call. Why this strange behavior ? I've always used this patter to implements an UDP server in C++ and JAVA and it always worked. I've tried also with a "select" passing a list with the socket to the xread argument, in order to get an event of file descriptor disruption from select instead that from recvfrom, but select seems to be "insensible" to the close too. I need to have a unique code which maintain the same behavior on Linux and Windows with python 2.5 - 2.6. Thanks.

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• Oracle Forms on-button-pressed trigger to solve three scenarios

  - by DBase486

  Hello, I'm writing a when-button-pressed trigger on a save button for an Oracle Forms 6i form, and it has to fulfill a couple of scenarios. Here's some background information: the fields we're primarily concerned with are: n_number, alert_id, end_date For all three scenarios we are comparing candidate records against the following records in the database (for the sake of argument, let's assume they're the only records in the database so far): alert_id|| n_number|| end_date ------------------------------------- 1|| 5|| _______ 2|| 6|| 10/25/2009 Scenario 1: The user enters a new record: alert_id 1 n_number 5 end_date NULL Objective: prevent the user from committing duplicate rows Scenario 2: The user enters a new record: alert_id 1 n_number 10 end_date NULL Objective: Notify the user that this alert_id already exists, but allow the user the ability to commit the row, if desired. Scenario 3: The user enters a new record: alert_id 2 n_number 6 end_date NULL Objective: Notify the user that this alert_id has occurred in the past (i.e. it has a not-null end_date), but allow the user to commit the row, if desired. I've written the code, which seems to comply with the first two scenarios, but prevents me from fulfilling the third. Issues: When I enter the third scenario case, I am prompted to commit the record, but when I attempt this, the "duplicate_stop" alert pops up, preventing me. Issues: I'm getting the following error: ORA-01843: not a valid month. While testing the code for the third scenario in Toad (hard-coding the values, etc) things seemed to be fine. Why would I encounter these problems at run-time? Help is very much appreciated. Thank you

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• JVM to ignore certificate name mismatch

  - by Heavy Bytes

  I know there were a lot of questions/answers about how to ignore SSL error in the code. On our dev region dev.domain.tld we have configured a app server over SSL. The certificate that is displayed is for somedev.domain.tld. There is no way to change the certificate, it will always be a domain mismatch. So when I deploy a web-service to https://dev.domain.tld and try to connect/call my webservice I get an exception: Caused by: java.security.cert.CertificateException: No name matching dev.domain.tld found And I have the somedev.domain.tld CERT in my trust store. Now, I saw a lot of samples how to change that in the code (using a Trust Manager that accepts all domains), but how do I specify to the JVM to ignore the domain mismatch when connecting to the server? Is there a -Djavax.net.ssl argument or something? Thank you! UPDATE: Or, since I am using Spring-WS, is there a way to set some property in Spring for that? (WebServiceTemplate) UPDATE I guess I'll have to do use something from Spring Security: http://static.springsource.org/spring-ws/sites/1.5/reference/html/security.html

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• Project euler problem 3 in haskell

  - by shk

  I'm new in Haskell and try to solve 3 problem from http://projecteuler.net/. The prime factors of 13195 are 5, 7, 13 and 29. What is the largest prime factor of the number 600851475143 ? My solution: import Data.List getD :: Int -> Int getD x = -- find deviders let deriveList = filter (\y -> (x `mod` y) == 0) [1 .. x] filteredList = filter isSimpleNumber deriveList in maximum filteredList -- Check is nmber simple isSimpleNumber :: Int -> Bool isSimpleNumber x = let deriveList = map (\y -> (x `mod` y)) [1 .. x] filterLength = length ( filter (\z -> z == 0) deriveList) in case filterLength of 2 -> True _ -> False I try to run for example: getD 13195 > 29 But when i try: getD 600851475143 I get error Exception: Prelude.maximum: empty list Why? Thank you @Barry Brown, I think i must use: getD :: Integer -> Integer But i get error: Couldn't match expected type `Int' with actual type `Integer' Expected type: [Int] Actual type: [Integer] In the second argument of `filter', namely `deriveList' In the expression: filter isSimpleNumber deriveList Thank you.

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• Design an Application That Stores and Processes Files

  - by phasetwenty

  I'm tasked with writing an application that acts as a central storage point for files (usually document formats) as provided by other applications. It also needs to take commands like "file 395 needs a copy in X format", at which point some work is offloaded to a 3rd party application. I'm having trouble coming up with a strategy for this. I'd like to keep the design as simple as possible, so I'd like to avoid big extra frameworks or techniques like threads for as long as it makes sense. The clients are expected to be web applications (for example, one is a django application that receives files from our customers; the others are not yet implemented). The platform it will be running on is likely going to be Python on Linux, unless I have a strong argument to use something else. In the beginning I thought I could fit the information I wanted to communicate in the filenames, and let my application parse the filename to figure out what it needed to do, but this is proving too inflexible with the amount of information I'm realizing I need to make available. Another idea is to pair FTP with a database used as a communication medium (client uploads a file and updates the database with a command as a row in a table) but I don't like this idea because adding commands (a known change) looks like it will require adding code as well as changing database schemas. It will also muddy up the interface my clients will have to use. I looked into Pyro to let applications communicate more directly but I don't like the idea of running an extra nameserver for this one purpose. I also don't see a good way to do file transfer within this framework. What I'm looking for is techniques and/or technologies applicable to my problem. At the simplest level, I need the ability to accept files and messages with them.

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• Doubly Linked Lists Implementation

  - by user552127

  Hi All, I have looked at most threads here about Doubly linked lists but still unclear about the following. I am practicing the Goodrich and Tamassia book in Java. About doubly linked lists, please correct me if I am wrong, it is different from a singly linked list in that a node could be inserted anywhere, not just after the head or after the tail using both the next and prev nodes available, while in singly linked lists, this insertion anywhere in the list is not possible ? If one wants to insert a node in a doubly linked list, then the default argument should be either the node after the to-be inserted node or node before the to-be inserted node ? But if this is so, then I don't understand how to pass the node before or after. Should we be displaying all nodes that were inserted till now and ask the user to select the node before or after which some new node is to be inserted ? My doubt is how to pass this default node. Because I assume that will require the next and prev nodes of these nodes as well. For e.g, Head<-A<-B<-C<-D<-E<-tail If Z is the new node to be inserted after say D, then how should node D be passed ? I am confused with this though it seems pretty simple to most. But pl do explain. Thanks, Sanjay

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• How to associate application with existing file types using WiX installer?

  - by Marek

  related to this: http://stackoverflow.com/questions/138550/how-to-register-file-types-extensions-with-a-wix-installer but not a duplicate. I need to handle existing file types (.jpg files). I do not want to be the default handler for .jpg, I would just like to extend the "Open with" menu with a link to my app. I see HKCR\.jpg\OpenWithList\ and HKCR\.jpg\OpenWithProgIds\ in the registry but I am not sure whether to write to these and how to do it correctly with WiX. Should I use something like this? <ProgId Id='??what here?' Description='Jpeg handled by my App'> <Extension Id='jpg' ContentType='image/jpeg'> <Verb Id='openwithmyapp' Sequence='10' Command='OpenWithMyApp' Target='[!FileId]' Argument='"%1"' /> </Extension> </ProgId> There are many ways how to fail here (like Photo Mechanics did, the HKCR for image file types is a real mess after I have installed this software) How to do this correctly with WiX?

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• Using an element against an entire list in Haskell

  - by Snick

  I have an assignment and am currently caught in one section of what I'm trying to do. Without going in to specific detail here is the basic layout: I'm given a data element, f, that holds four different types inside (each with their own purpose): data F = F Float Int, Int a function: func :: F -> F-> Q Which takes two data elements and (by simple calculations) returns a type that is now an updated version of one of the types in the first f. I now have an entire list of these elements and need to run the given function using one data element and return the type's value (not the data element). My first analysis was to use a foldl function: myfunc :: F -> [F] -> Q myfunc y [] = func y y -- func deals with the same data element calls myfunc y (x:xs) = foldl func y (x:xs) however I keep getting the same error: "Couldn't match expected type 'F' against inferred type 'Q'. In the first argument of 'foldl', namely 'myfunc' In the expression: foldl func y (x:xs) I apologise for such an abstract analysis on my problem but could anyone give me an idea as to what I should do? Should I even use a fold function or is there recursion I'm not thinking about?

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• DOMAIN REDIRECT PROBLEM WITH JQUERY / JAVASCRIPT

  - by GiovanniDema

  Hi guys, first time here. I got a strange problem. I have a fullscreen image scaler javascript (as GOTOCHINA website) that works very well on my website. Then, I purchased a domain redirect pointing on my website and when redirecting suddenly internet explorer 7 and internet explorer 8 give me this error Messagge: is not a valid argument. Line: 34 Char: 17 URI: http://*****/scaler.js The script is var db=document.body; var imag=document.getElementById('wallpaper'); var dbsize={}; var imgsrc=imag.src; var keyStop=function(e){ var e=window.event||e||{}; var tag=e.target.tagName.toLowerCase(); if(tag!='textarea'&&!(tag=='input'&&(e.target.type=='text'||e.target.type=='password'))){ if(e.keyCode==32||e.keyCode==39||e.keyCode==40){ if(e.preventDefault)e.preventDefault(); else e.returnValue=false; } } } if(this.addEventListener)window.addEventListener('keydown',keyStop,false); else window.attachEvent('onkeydown',keyStop); setInterval(function(){ window.scrollTo(0,0); if(imag.complete){ if(db.clientWidth!=dbsize.w||db.clientHeight!=dbsize.h||imag.src!=imgsrc){ imgsrc=imag.src; var dbsizew=db.clientWidth; var dbsizeh=db.clientHeight; var newwidth=Math.round(dbsizeh*(imag.offsetWidth/imag.offsetHeight)); var nextvar=dbsizewnewwidth?dbsizew:newwidth; imag.style.width=nextvar+'px'; } } },300); In other words when i open the official website everything's working correctly. When i open redirect domain pointing on official website... the previous error appears. The line is exactly this - imag.style.width=nextvar+'px'; Thanks in advance Giovanni

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• no instance of overloaded function getline c++

  - by Dave

  I'm a bit confused as to what i have incorrect with my script that is causing this error. I have a function which calls a fill for game settings but it doesn't like my getline. Also i should mention these are the files i have included for it: #include <fstream> #include <cctype> #include <map> #include <iostream> #include <string> #include <algorithm> #include <vector> using namespace std;' This is what i have: std::map<string, string> loadSettings(std::string file){ ifstream file(file); string line; std::map<string, string> config; while(std::getline(file, line)) { int pos = line.find('='); if(pos != string::npos) { string key = line.substr(0, pos); string value = line.substr(pos + 1); config[trim(key)] = trim(value); } } return (config); } The function is called like this from my main.cpp //load settings for game std::map<string, string> config = loadSettings("settings.txt"); //load theme for game std::map<string, string> theme = loadSettings("theme.txt"); Where did i go wrong ? Please help! The error: settings.h(61): error C2784: 'std::basic_istream<_Elem,_Traits> &std::getline(std::basic_istream<_Elem,_Traits> &&,std::basic_string<_Elem,_Traits,_Alloc> &)' : could not deduce template argument for 'std::basic_istream<_Elem,_Traits> &&' from 'std::string'

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• Calling a WPF Application and modify exposed properties?

  - by Justin

  I have a WPF Keyboard Application, it is developed in such a way that an application could call it and modify its properties to adapt the Keyboard to do what it needs to. Right now I have a file *.Keys.Set which tells the application (on open) to style itself according to that new style. I know this file could be passed as a command line argument into the application. That would not be a problem. My concern is, is there a way via a managed environment to change the properties of the executable as long as they are exposed properly, an example: 'Creates a new instance of the Keyboard Application Dim e_key as new WpfApplication("C:\egt\components\keyboard.exe") 'Sets the style path e_key.SetStylePath("c:\users\joe\apps\me\default.keys.set") e_key.Refresh() 'Applies the style e_key.HideMenu() 'Hides the menu e_key.ShowDeck("PIN") 'Shows the custom "deck" of keyboard keys the developer 'Created in the style application. ''work with events and response 'Clear the instance from memory e_key.close e_key.dispose e_key = nothing This would allow my application to become easily accessible to other Touch Screen Application Developers, allowing them to use my keyboard and keep the functionality they need. It seems like it might be possible because (name of executable).application shows all the exposed functions, properties, and values. I just have never done this before. Any help would be appreciated, thank you in advance.

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• Specifying character

  - by danutenshu

  So below I have a code in C++ that is supposed to invert the arguments in a vector, but not the sequence. I have listed my problems as sidenotes in the code below. The invert function is supposed to invert each argument, and then the main function just outputs the inverted words in same order For instance, program("one two three four")=ruof eerth owt eno #include <iostream> #include <string> using namespace std; int invert(string normal) { string inverted; for (int num=normal.size()-1; num>=0; num--) { inverted.append(normal[num]); //I don't know how to get each character //I need another command for append } return **inverted**; <---- } int main(int argc, char* argv[]) { string text; for (int a=1; a<argc; a++) { text.append(invert(argv[a])); //Can't run the invert function text.append(" "); } cout << text << endl; return 0; }

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• Passing in extra parameters in a URL

  - by Scott Atkinson

  I have the below column on my table what gets binded on pageload, the parameters in there work fine but i need to add an additional parameter which is the fullname which is the next column along but im having trouble figuring our the syntax, here is my ASP <asp:TemplateField HeaderText="ID"> <ItemTemplate> <asp:HyperLink ID="hyperLeadID" runat="server" NavigateUrl='<%#Eval("ID","/documents/Q-Sheet.aspx?LeadID={0}&isHappyCallReferral=yes&isHappyName={1}") %>' Text='<%#Eval("ID")%>'></asp:HyperLink> </ItemTemplate> </asp:TemplateField> <asp:TemplateField HeaderText="Referral Name"> <ItemTemplate> <asp:Label ID="lblRefName" CssClass="gvItem" runat="server" Text='<%# DataBinder.Eval(Container, "DataItem.Name") %>'></asp:Label> </ItemTemplate> </asp:TemplateField> As you can see at the end of ID column i have added isHappyName={1} which i assumed it would select the next column along as it starts at 0 but it keeps throwing an error which is "Index (zero based) must be greater than or equal to zero and less than the size of the argument list." Can someone help me to pass the usersname through the URL Thanks

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• Removing a pattern from the beggining and end of a string in ruby

  - by seaneshbaugh

  So I found myself needing to remove <br /> tags from the beginning and end of strings in a project I'm working on. I made a quick little method that does what I need it to do but I'm not convinced it's the best way to go about doing this sort of thing. I suspect there's probably a handy regular expression I can use to do it in only a couple of lines. Here's what I got: def remove_breaks(text) if text != nil and text != "" text.strip! index = text.rindex("<br />") while index != nil and index == text.length - 6 text = text[0, text.length - 6] text.strip! index = text.rindex("<br />") end text.strip! index = text.index("<br />") while index != nil and index == 0 text = test[6, text.length] text.strip! index = text.index("<br />") end end return text end Now the "<br />" could really be anything, and it'd probably be more useful to make a general use function that takes as an argument the string that needs to be stripped from the beginning and end. I'm open to any suggestions on how to make this cleaner because this just seems like it can be improved.

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• strcmp() but with 0-9 AFTER A-Z? (C/C++)

  - by Aaron

  For reasons I completely disagree with but "The Powers (of Anti-Usability) That Be" continue to decree despite my objections, I have a sorting routine which does basic strcmp() compares to sort by its name. It works great; it's hard to get that one wrong. However, at the 11th hour, it's been decided that entries which begin with a number should come AFTER entries which begin with a letter, contrary to the ASCII ordering. They cite the EBCDIC standard has numbers following letters so the prior assumption isn't a universal truth, and I have no power to win this argument... but I digress. Therein lies my problem. I've replaced all appropriate references to strcmp with a new function call nonstd_strcmp, and now need to implement the modifications to accomplish the sort change. I've used a FreeBSD source as my base: http://freebsd.active-venture.com/FreeBSD-srctree/newsrc/libkern/strncmp.c.html if (n == 0) return (0); do { if (*s1 != *s2++) return (*(const unsigned char *)s1 - *(const unsigned char *)(s2 - 1)); if (*s1++ == 0) break; } while (--n != 0); return (0); I guess I might need to take some time away to really think about how it should be done, but I'm sure I'm not the only one who's experienced the brain-deadness of just-before-release spec changes.

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• Writing a plist

  - by iOS-Newbie

  I am trying to test out writing a dictionary to a plist. The following code does not report any errors, but I cannot find any trace of the file that I supposed wrote. Here is the code snippet: NSDictionary *myDictionary = [NSDictionary dictionaryWithObjectsAndKeys: @"First letter of the alphabet", @"A", @"Second letter of the alphabet", @"B", @"Third letter of the alphabet", @"C", nil ]; I can see the dictionary contents displayed properly with either method calls: NSLog(@"Here is my partial dictionary %@", myDictionary); for (NSString *key in myDictionary) NSLog(@"here it is again %@ %@", key, [myDictionary objectForKey:key]); The following code displays the "succeeded" message when the program is run repeatedly if ([myDictionary writeToFile: @"myDictionary" atomically:YES ] == NO) NSLog(@"write to file failed"); else NSLog(@"write to file succeeded"); even when changing the atomically: argument to NO to not write a temporary file. However, when I search my current directory, or even my entire Mac, I cannot find any file called "myDictionary.plist" or any file with the string "myDictionary". Isn't the path variable "@myDictionary" supposed to represent the file at the current directory, i.e. where the class executable resides?

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• Specifying different initial values for fields in inherited models (django)

  - by Shawn Chin

  Question : What is the recommended way to specify an initial value for fields if one uses model inheritance and each child model needs to have different default values when rendering a ModelForm? Take for example the following models where CompileCommand and TestCommand both need different initial values when rendered as ModelForm. # ------ models.py class ShellCommand(models.Model): command = models.Charfield(_("command"), max_length=100) arguments = models.Charfield(_("arguments"), max_length=100) class CompileCommand(ShellCommand): # ... default command should be "make" class TestCommand(ShellCommand): # ... default: command = "make", arguments = "test" I am aware that one can used the initial={...} argument when instantiating the form, however I would rather store the initial values within the context of the model (or at least within the associated ModelForm). My current approach What I'm doing at the moment is storing an initial value dict within Meta, and checking for it in my views. # ----- forms.py class CompileCommandForm(forms.ModelForm): class Meta: model = CompileCommand initial_values = {"command":"make"} class TestCommandForm(forms.ModelForm): class Meta: model = TestCommand initial_values = {"command":"make", "arguments":"test"} # ------ in views FORM_LOOKUP = { "compile": CompileCommandFomr, "test": TestCommandForm } CmdForm = FORM_LOOKUP.get(command_type, None) # ... initial = getattr(CmdForm, "initial_values", {}) form = CmdForm(initial=initial) This feels too much like a hack. I am eager for a more generic / better way to achieve this. Suggestions appreciated. Other attempts I have toyed around with overriding the constructor for the submodels: class CompileCommand(ShellCommand): def __init__(self, *args, **kwargs): kwargs.setdefault('command', "make") super(CompileCommand, self).__init__(*args, **kwargs) and this works when I try to create an object from the shell: >>> c = CompileCommand(name="xyz") >>> c.save() <CompileCommand: 123> >>> c.command 'make' However, this does not set the default value when the associated ModelForm is rendered, which unfortunately is what I'm trying to achieve. Update 2 (looks promising) I now have the following in forms.py which allow me to set Meta.default_initial_values without needing extra code in views. class ModelFormWithDefaults(forms.ModelForm): def __init__(self, *args, **kwargs): if hasattr(self.Meta, "default_initial_values"): kwargs.setdefault("initial", self.Meta.default_initial_values) super(ModelFormWithDefaults, self).__init__(*args, **kwargs) class TestCommandForm(ModelFormWithDefaults): class Meta: model = TestCommand default_initial_values = {"command":"make", "arguments":"test"}

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• Code Contracts: Do we have to specify Contract.Requires(...) statements redundantly in delegating me

  - by herzmeister der welten

  I'm intending to use the new .NET 4 Code Contracts feature for future development. This made me wonder if we have to specify equivalent Contract.Requires(...) statements redundantly in a chain of methods. I think a code example is worth a thousand words: public bool CrushGodzilla(string weapon, int velocity) { Contract.Requires(weapon != null); // long code return false; } public bool CrushGodzilla(string weapon) { Contract.Requires(weapon != null); // specify contract requirement here // as well??? return this.CrushGodzilla(weapon, int.MaxValue); } For runtime checking it doesn't matter much, as we will eventually always hit the requirement check, and we will get an error if it fails. However, is it considered bad practice when we don't specify the contract requirement here in the second overload again? Also, there will be the feature of compile time checking, and possibly also design time checking of code contracts. It seems it's not yet available for C# in Visual Studio 2010, but I think there are some languages like Spec# that already do. These engines will probably give us hints when we write code to call such a method and our argument currently can or will be null. So I wonder if these engines will always analyze a call stack until they find a method with a contract that is currently not satisfied? Furthermore, here I learned about the difference between Contract.Requires(...) and Contract.Assume(...). I suppose that difference is also to consider in the context of this question then?

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• How to get address of va_arg?

  - by lionbest

  I hack some old C API and i got a compile error with the following code: void OP_Exec( OP* op , ... ) { int i; va_list vl; va_start(vl,op); for( i = 0; i < op->param_count; ++i ) { switch( op->param_type[i] ) { case OP_PCHAR: op->param_buffer[i] = va_arg(vl,char*); // ok it works break; case OP_INT: op->param_buffer[i] = &va_arg(vl,int); // error here break; // ... more here } } op->pexec(op); va_end(vl); } The error with gcc version 4.4.1 (Ubuntu 4.4.1-4ubuntu9) was: main.c|55|error: lvalue required as unary ‘&’ operand So why exactly it's not possible here to get a pointer to argument? How to fix it? This code is executed very often with different OP*, so i prefer to not allocate extra memory. Is it possible to iterate over va_list knowing only the size of arguments?

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• Save PowerPoint slides as images

  - by nihi_l_ist

  I want to save some presentation file as images into some directory and use the code: OpenFileDialog o = new OpenFileDialog(); o.ShowDialog(); if (o.FileName != null) { ApplicationClass pptApplication = new ApplicationClass(); Presentation pptPresentation = pptApplication.Presentations.Open(o.FileName, MsoTriState.msoFalse, MsoTriState.msoFalse, MsoTriState.msoFalse); FolderBrowserDialog fb = new FolderBrowserDialog(); fb.ShowDialog(); for (int i = 0; i < pptPresentation.Slides.Count; i++) { pptPresentation.Slides[i].Export(fb.SelectedPath + "Slide" + (i + 1) + ".jpg", "jpg", 320, 240); } } use namespaces: using Microsoft.Office.Core; using Microsoft.Office.Interop.PowerPoint; But i get the following error: 'Microsoft.Office.Interop.PowerPoint.ApplicationClass' does not contain a definition for 'Presentations' and no extension method 'Presentations' accepting a first argument of type 'Microsoft.Office.Interop.PowerPoint.ApplicationClass' could be found (are you missing a using directive or an assembly reference?) Tho it seems that it has property called Presentations.. What am i doing incorrectly?

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• How to compare two structure strings in C++

  - by Arvandor

  Ok, so this week in class we're working with arrays. I've got an assignment that wanted me to create a structure for an employee containing an employee ID, first name, last name, and wages. Then it has me ask users for input for 5 different employees all stored in an array of this structure, then ask them for a search field type, then a search value. Lastly, display all the information for all positive search results. I'm still new, so I'm sure it isn't a terribly elegant program, but what I'm trying to do now is figure out how to compare a user entered string with the string stored in the structure... I'll try to give all the pertinent code below. struct employee { int empid, string firstname, string lastname, float wage }; employee emparray[] = {}; employee value[] = {}; //Code for populating emparray and structure, then determine search field etc. cout << "Enter a search value: "; cin >> value.lastname; for(i = 0; i < 5; i++) { if(strcmp(value.lastname.c_str, emparray[i].lastname.c_str) == 0) { output(); } } Which... I thought would work, but it's giving me the following error.. Error 1 error C3867: 'std::basic_string<_Elem,_Traits,_Alloc>::c_str': function call missing argument list; use '&std::basic_string<_Elem,_Traits,_Alloc>::c_str' to create a pointer to member d:\myfile Any thoughts on what's going on? Is there a way to compare two .name notated strings without totally revamping the program? IF you want to drill me on best practices, please feel free, but also please try to solve my particular problem.

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• Memory management of objects returned by methods (iOS / Objective-C)

  - by iOSNewb

  I am learning Objective-C and iOS programming through the terrific iTunesU course posted by Stanford (http://www.stanford.edu/class/cs193p/cgi-bin/drupal/) Assignment 2 is to create a calculator with variable buttons. The chain of commands (e.g. 3+x-y) is stored in a NSMutableArray as "anExpression", and then we sub in random values for x and y based on an NSDictionary to get a solution. This part of the assignment is tripping me up: The final two [methods] “convert” anExpression to/from a property list: + (id)propertyListForExpression:(id)anExpression; + (id)expressionForPropertyList:(id)propertyList; You’ll remember from lecture that a property list is just any combination of NSArray, NSDictionary, NSString, NSNumber, etc., so why do we even need this method since anExpression is already a property list? (Since the expressions we build are NSMutableArrays that contain only NSString and NSNumber objects, they are, indeed, already property lists.) Well, because the caller of our API has no idea that anExpression is a property list. That’s an internal implementation detail we have chosen not to expose to callers. Even so, you may think, the implementation of these two methods is easy because anExpression is already a property list so we can just return the argument right back, right? Well, yes and no. The memory management on this one is a bit tricky. We’ll leave it up to you to figure out. Give it your best shot. Obviously, I am missing something with respect to memory management because I don't see why I can't just return the passed arguments right back. Thanks in advance for any answers!

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• Would an immutable keyword in Java be a good idea?

  - by berry120

  Generally speaking, the more I use immutable objects in Java the more I'm thinking they're a great idea. They've got lots of advantages from automatically being thread-safe to not needing to worry about cloning or copy constructors. This has got me thinking, would an "immutable" keyword go amiss? Obviously there's the disadvantages with adding another reserved word to the language, and I doubt it will actually happen primarily for the above reason - but ignoring that I can't really see many disadvantages. At present great care has to be taken to make sure objects are immutable, and even then a dodgy javadoc comment claiming a component object is immutable when it's in fact not can wreck the whole thing. There's also the argument that even basic objects like string aren't truly immutable because they're easily vunerable to reflection attacks. If we had an immutable keyword the compiler could surely recursively check and give an iron clad guarantee that all instances of a class were immutable, something that can't presently be done. Especially with concurrency becoming more and more used, I personally think it'd be good to add a keyword to this effect. But are there any disadvantages or implementation details I'm missing that makes this a bad idea?

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