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• DDD: Persisting aggregates

  - by Mosh

  Hello, Let's consider the typical Order and OrderItem example. Assuming that OrderItem is part of the Order Aggregate, it an only be added via Order. So, to add a new OrderItem to an Order, we have to load the entire Aggregate via Repository, add a new item to the Order object and persist the entire Aggregate again. This seems to have a lot of overhead. What if our Order has 10 OrderItems? This way, just to add a new OrderItem, not only do we have to read 10 OrderItems, but we should also re-insert all these 10 OrderItems again. (This is the approach that Jimmy Nillson has taken in his DDD book. Everytime he wants to persists an Aggregate, he clears all the child objects, and then re-inserts them again. This can cause other issues as the ID of the children are changed everytime because of the IDENTITY column in database.) I know some people may suggest to apply Unit of Work pattern at the Aggregate Root so it keeps track of what has been changed and only commit those changes. But this violates Persistence Ignorance (PI) principle because persistence logic is leaking into the Domain Model. Has anyone thought about this before? Mosh

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• video calling (center)

  - by rrejc

  We are starting to develop a new application and I'm searching for information/tips/guides on application architecture. Application should: read the data from an external (USB) device send the data to the remote server (through internet) receive the data from the remote server perform a video call with to the calling (support) center receive a video call call from the calling (support) center support touch screens In addition: some of the data should also be visible through the web page. So I was thinking about: On the server side: use the database (probably MS SQL) use ORM (nHibernate) to map the data from the DB to the domain objects create a layer with business logic in C# create a web (WCF) services (for client application) create an asp.net mvc application (for item 7.) to enable data view through the browser On the client side I would use WPF 4 application which will communicate with external device and the wcf services on the server. So far so good. Now the problem begins. I have no idea how to create a video call (outgoing or incoming) part of the application. I believe that there is no problem to communicate with microphone, speaker, camera with WPF/C#. But how to communicate with the call center? What protocol and encoding should be used? I think that I will need to create some kind of server which will: have a list of operators in the calling center and track which operator is occupied and which operator is free have a list of connected end users receive incoming calls from end users and delegate call to free operator delegate calls from calling center to the end user Any info, link, anything on where to start would be much appreciated. Many thanks!

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• Problem Displaying XML in Grid View-newbie

  - by Dean

  I am trying to do something in VisualWebDev 2008 Express that I thought would be simple, but it is not working. I want to display data from an XML file so I added the XMLDataSource to my page, pointed it to the XML file, and then added the GridView and connected it to the datasource. I am getting the following error: GridView - GridView1There was an error rendering the control. The data source for GridView with id 'GridView1' did not have any properties or attributes from which to generate columns. Ensure that your data source has content. Could someone please tell me what I might be doing wrong, TIA Dean A smippet from my XML is as follows: 6019 - Renaissance MS - New School Renaissance MS 7155 Hall Road Fairburn, GA 30213 NS-6019200-LA-01 New School Close-out NS-6019200 0.000000000000000e+000 The construction of the new Renaissance MS will be at the intersection of Jones/Hall Road, in the districts 7th & 9F and Land Lots 117, 143 & 146 of Fulton County, GA. The work includes the construction of the 180,500 square foot building that will house 34 standard classrooms, 12 standard science labs, 20 special purpose classrooms, cafeteria and litchen, gymnasium, media center and administrative offices. The site will also have multi-purpose playfields with track, softball field, tennis courts and basketball/volleyball court. Terry O'Brien Parsons Stevens Wilkinson Stang Newdow Barton Malow -84.62242 33.61497

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• How to stop ejabberd from using mnesia

  - by Eldad Mor

  I'm trying to establish a procedure for restoring my database from a crashed server to a new server. My server is running Ejabberd as an XMPP server, and I configured it to use postgresql instead of mnesia - or so I thought. My procedure goes something like "dump the contents of the original DB, run the new server, restore the contents of the DBs using psql, then run the system". However, when I try running Ejabberd again I get a crash: =CRASH REPORT==== 3-Dec-2010::22:05:00 === crasher: pid: <0.36.0> registered_name: [] exception exit: {bad_return,{{ejabberd_app,start,[normal,[]]}, {'EXIT',"Error reading Mnesia database"}}} in function application_master:init/4 Here I was thinking that my system is running on PostgreSQL, while it seems I was still using Mnesia. I have several questions: How can I make sure mnesia is not being used? How can I divert all the ejabberd activities to PGSQL? This is the modules part in my ejabberd.cfg file: {modules, [ {mod_adhoc, []}, {mod_announce, [{access, announce}]}, % requires mod_adhoc {mod_caps, []}, {mod_configure,[]}, % requires mod_adhoc {mod_ctlextra, []}, {mod_disco, []}, {mod_irc, []}, {mod_last_odbc, []}, {mod_muc, [ {access, muc}, {access_create, muc}, {access_persistent, muc}, {access_admin, muc_admin}, {max_users, 500} ]}, {mod_offline_odbc, []}, {mod_privacy_odbc, []}, {mod_private_odbc, []}, {mod_pubsub, [ % requires mod_caps {access_createnode, pubsub_createnode}, {plugins, ["default", "pep"]} ]}, {mod_register, [ {welcome_message, none}, {access, register} ]}, {mod_roster_odbc, []}, {mod_stats, []}, {mod_time, []}, {mod_vcard_odbc, []}, {mod_version, []} ]}. What am I missing? I am assuming the crash is due to the mnesia DB being used by Ejabberd, and since it's out of sync with the PGSQL DB, it cannot operate correctly - but maybe I'm totally off track here, and would love some direction. EDIT: One problem solved. Since I'm using amazon cloud, I needed to hardcode the ERLANG_NODE so it won't be defined by the hostname (which changes on reboot). This got my ejabberd running, but still I wish to stop using mnesia, and I wonder what part of ejabberd is still using it and how can I found it.

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• Object oriented design of game in Java: How to handle a party of NPCs?

  - by Arvanem

  Hi folks, I'm making a very simple 2D RPG in Java. My goal is to do this in as simple code as possible. Stripped down to basics, my class structure at the moment is like this: Physical objects have an x and y dimension. Roaming objects are physical objects that can move(). Humanoid objects are roaming objects that have inventories of GameItems. The Player is a singleton humanoid object that can hire up to 4 NPC Humanoids to join his or her party, and do other actions, such as fight non-humanoid objects. NPC Humanoids can be hired by the Player object to join his or her party, and once hired can fight for the Player. So far I have given the Player class a "party" ArrayList of NPC Humanoids, and the NPC Humanoids class a "hired" Boolean. However, my fight method is clunky, using an if to check the party size before implementing combat, e.g. public class Player extends Humanoids { private ArrayList<Humanoids> party; // GETTERS AND SETTERS for party here //... public void fightEnemy(Enemy eneObj) { if (this.getParty().size() == 0) // Do combat without party issues else if (this.getParty().size() == 1) // Do combat with party of 1 else if (this.getParty().size() == 2) // Do combat with party of 2 // etc. My question is, thinking in object oriented design, am I on the right track to do this in as simple code as possible? Is there a better way?

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• Using TaskDialogIndirect in C#

  - by Dennis Delimarsky

  I've been working for a while with the regular Windows Vista/7 TaskDialog for a while, and I wanted to add some additional functionality (like custom buttons and a footer), so I need to use TaskDialogIndirect. Following the MSDN documentation for TaskDialogIndirect, I got this signature: [DllImport("comctl32.dll",CharSet = CharSet.Unicode,EntryPoint="TaskDialogIndirect")] static extern int TaskDialogIndirect (TASKDIALOGCONFIG pTaskConfig, out int pnButton, out int pnRadioButton, out bool pfVerificationFlagChecked); The TASKDIALOGCONFIG class is shown below: public class TASKDIALOGCONFIG { public UInt16 cbSize; public IntPtr hwndParent; public IntPtr hInstance; public String dwFlags; public String dwCommonButtons; public IntPtr hMainIcon; public String pszMainIcon; public String pszMainInstruction; public String pszContent; public UInt16 cButtons; public TASKDIALOG_BUTTON pButtons; public int nDefaultButton; public UInt16 cRadioButtons; public TASKDIALOG_BUTTON pRadioButtons; public int nDefaultRadioButton; public String pszVerificationText; public String pszExpandedInformation; public String pszExpandedControlText; public String pszCollapsedControlText; public IntPtr hFooterIcon; public IntPtr pszFooterText; public String pszFooter; // pfCallback; // lpCallbackData; public UInt16 cxWidth; } The TASKDIALOG_BUTTON implementation: public class TASKDIALOG_BUTTON { public int nButtonID; public String pszButtonText; } I am not entirely sure if I am on the right track here. Did anyone use TaskDialogIndirect from managed code directly through WinAPI (without VistaBridge or Windows API Code Pack)? I am curious about the possible implementations, as well as the callback declarations (I am not entirely sure how to implement TaskDialogCallbackProc). PS: I am looking for a direct WinAPI implementation, not one through a wrapper.

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• How to architect Rails site that can be edited while running?

  - by Chris Kimpton

  Hi, I am writing a Rails app that "scrapes/navigates" some other websites and webservices for content. I am using Mechanize and Savon to do the heavylifting. But given the dynamic nature of the web, I'd like to make my calls to these editable by the admin users of the site - rather than requiring me to release a new version of the site. The actual scraping thread happens async to the website, using the daemons gem. My requirements are: Thinking that the scraping/webservice calling code is quite simple, the easiest route is to make the whole class editable by the admins. Keep a history of the scraping code - so that we can fairly easily revert if we introduce a problem. Initially use the code from the file system, but as soon as thats been edited and stored somewhere, to use that code instead. I am thinking my options are: Store the code in the db (with a history table for the old versions) Store the code in a private git repo somewhere and access that for the history/latest versions. I am thinking the git route might be easiest, given its raison d'etre is to track file history... But perhaps there is a gem/plugin that does all this for me, out of the box? Thanks in advance for any tips/advice. ~chris

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• grep 5 seconds of input from the serial port inside a shell-script

  - by pica

  I've got a device that I'm operating next to my PC and as it runs it's spitting log lines out it's serial port. I have this wired to my PC and I can see the log lines fine if I'm using either minicom or something like: ttylog -b 115200 -d /dev/ttyS0 I want to write 5 seconds of the device serial output to a temp file (or assign it to a variable) and then later grep that file for keywords that will let me know how the device is operating. I've already tried redirecting the output to a file while running the command in the background, and then sleeping 5 seconds and killing the process, but the log lines never get written to my temp file. Example: touch tempFile ttylog -b 115200 -d /dev/ttyS0 >> tempFile & serialPID=$! sleep 5 #kill ${serialPID} #does not work, gets wrong PID killall ttylog cat tempFile The file gets created but never filled with any data. I can also replace the ttylog line with: ttylog -b 115200 -d /dev/ttyS0 |tee -a tempFile & In neither case do I ever see any log lines logged to stdout or the log file unless I have multiple versions of ttylog running by mistake (see commented out line, D'oh). I have no idea what's going on here. It seems to be a failure of redirection within my script. Am I on the right track? Is there a better way to sample 5 seconds of the serial port?

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• radgrid insert using radwinow

  - by Hamza

  Hello Everybody, The company details page in my system has a user control to show the founders of the company, that user control represents the founders by using a Rad Grid and three buttons for insert/edit/delete founders, the founders grid is being bind by using a WCF service. the insert button calls a javascript method that opens a Rad Window in which the user can insert the data for a new founder my problem is: in the Add Founder Rad Window I shouldn't save the new founder in the database, when I press Add the Rad Grid should be closed and the new founder should be added to the founders Grid's datasource, and then the grid should be bind again the questions is: what is the best way to do that, I don't want to use sessions nor json, I tried to use another wcf service which takes two parameters: reference to the grid and the new founder, and in this wcf service I get the old datasource then add the new founder to it and finally rebind the grid again, but I have faced some problems like how can I send the reference to the grid from javascript method to a WCF service, also if I add more than one founder how can keep track of the new founders and the original datasource if any of you can lead me to an example similar to my case this would be very much appreciated, also any comments and feedback are most welcomed

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• What is the best way to get an audio file duration in Android?

  - by Gilead

  Hi! I'm using a SoundPool [ 1 ] to play audio clips in my app. All is fine but I need to know when the clip playback has finished. At the moment I track it in my app by obtaining the duration of each clip using a MediaPlayer [ 2 ] instance. That works fine but it looks wasteful to load each file twice, just to get the duration. I could roughly calculate the duration myself knowing the length of the file (available from the AssetFileDescriptor [ 3 ]) but I'd still need to know the sample rate and the number of channels. I see two potential solutions to that problem: Figuring out when a clip has finished playing (doesn't seem to be possible with SoundClip). Having a class which could load just the header of an audio file and give me the sample rate/number of channels (and, ideally, the sample count to get the exact duration). Any suggestions? Thanks, Max The code I'm using at the moment (works fine but is rather heavy for the purpose): String[] fileNames = ... MediaPlayer mp = new MediaPlayer(); for (String fileName : fileNames) { AssetFileDescriptor d = context.getAssets().openFd(fileName); mp.reset(); mp.setDataSource(d.getFileDescriptor(), d.getStartOffset(), d.getLength()); mp.prepare(); int duration = mp.getDuration(); // ... } On a side note, this question has already been asked [ 4 ] but got no answers.

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• How to download .exe file with progress bar - VB 2012

  - by user2839828

  I am trying to create an updater for my program which automatically download's the latest version of my program from the web. Now I want this process to be done using a progress bar (so when the download progress is at 50% the progress bar is half-way through). This is my code: Private Sub client_ProgressChanged(ByVal sender As Object, ByVal e As DownloadProgressChangedEventArgs) Dim bytesIn As Double = Double.Parse(e.BytesReceived.ToString()) Dim totalBytes As Double = Double.Parse(e.TotalBytesToReceive.ToString()) Dim percentage As Double = bytesIn / totalBytes * 100 client.Value = Int32.Parse(Math.Truncate(percentage).ToString()) End Sub Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click Dim url As String = "MY DOWNLOAD LINK" 'Download Dim client As WebClient = New WebClient AddHandler client.DownloadProgressChanged, AddressOf client_ProgressChanged AddHandler client.DownloadFileCompleted, AddressOf client_DownloadCompleted client.DownloadFileAsync(New Uri(url), "C:\Users\User\Desktop\BACKUP\TESTING\New folder\1.exe") End Sub End Class Now I know that the place where the file is saved has been inputed manually by me , but I will change that later. My problem currently is that the file is not being downloaded. However when I change the DownloadFileAsync method to DownloadFile , my program downloads the file. However with the DownloadFile method I will not be able to use the progress bar to track the download progress. Any help is much appreciated :-)

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• Technically why is processes in Erlang more efficient than OS threads?

  - by Jonas

  Spawning processes seam to be much more efficient in Erlang than starting new threads using the OS (i.e. by using Java or C). Erlang spawns thousands and millions of processes in a short period of time. I know that they are different since Erlang do per process GC and processes in Erlang are implemented the same way on all platforms which isn't the case with OS threads. But I don't fully understand technically why Erlang processes are so much more efficient and has much smaller memory footprint per process. Both the OS and Erlang VM has to do scheduling, context switches and keep track of the values in the registers and so on... Simply why isn't OS threads implemented in the same way as processes in Erlang? Does it have to support something more? and why does it need a bigger memory footprint? Technically why is processes in Erlang more efficient than OS threads? And why can't threads in the OS be implemented and managed in the same efficient way?

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• Number Algorithm

  - by James

  I've been struggling to wrap my head around this for some reason. I have 15 bits that represent a number. The bits must match a pattern. The pattern is defined in the way the bits start out: they are in the most flush-right representation of that pattern. So say the pattern is 1 4 1. The bits will be: 000000010111101 So the general rule is, take each number in the pattern, create that many bits (1, 4 or 1 in this case) and then have at least one space separating them. So if it's 1 2 6 1 (it will be random): 001011011111101 Starting with the flush-right version, I want to generate every single possible number that meets that pattern. The # of bits will be stored in a variable. So for a simple case, assume it's 5 bits and the initial bit pattern is: 00101. I want to generate: 00101 01001 01010 10001 10010 10100 I'm trying to do this in Objective-C, but anything resembling C would be fine. I just can't seem to come up with a good recursive algorithm for this. It makes sense in the above example, but when I start getting into 12431 and having to keep track of everything it breaks down.

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• Tips on managing dependencies for a release?

  - by Andrew Murray

  Our system comprises many .NET websites, class libraries, and a MSSQL database. We use SVN for source control and TeamCity to automatically build to a Test server. Our team is normally working on 4 or 5 projects at a time. We try to lump many changes into a largish rollout every 2-4 weeks. My problem is with keeping track of all the dependencies for a rollout. Example: Website A cannot go live until we've rolled out Branch X of Class library B, built in turn against the Trunk of Class library C, which needs Config Updates Y and Z and Database Update D, which needs Migration Script E... It gets even more complex - like making sure each developer's project is actually compatible with the others and are building against the same versions. Yes, this is a management issue as much as a technical issue. Currently our non-optimal solution is: a whiteboard listing features that haven't gone live yet relying on our memory and intuition when planning the rollout, until we're pretty sure we've thought of everything... a dry-run on our Staging environment. It's a good indication but we're often not sure if Staging is 100% in sync with Live - part of the problem I'm hoping to solve. some amount of winging it on rollout day. So far so good, minus a few close calls. But as our system grows, I'd like a more scientific release management system allowing for more flexibility, like being able to roll out a single change or bugfix on it's own, safe in the knowledge that it won't break anything else. I'm guessing the best solution involves some sort of version numbering system, and perhaps using a project management tool. We're a start-up, so we're not too hot on religiously sticking to rigid processes, but we're happy to start, providing it doesn't add more overhead than it's worth. I'd love to hear advice from other teams who have solved this problem.

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• Optimize GROUP BY&ORDER BY query

  - by Jan Hancic

  I have a web page where users upload&watch videos. Last week I asked what is the best way to track video views so that I could display the most viewed videos this week (videos from all dates). Now I need some help optimizing a query with which I get the videos from the database. The relevant tables are this: video (~239371 rows) VID(int), UID(int), title(varchar), status(enum), type(varchar), is_duplicate(enum), is_adult(enum), channel_id(tinyint) signup (~115440 rows) UID(int), username(varchar) videos_views (~359202 rows after 6 days of collecting data, so this table will grow rapidly) videos_id(int), views_date(date), num_of_views(int) The table video holds the videos, signup hodls users and videos_views holds data about video views (each video can have one row per day in that table). I have this query that does the trick, but takes ~10s to execute, and I imagine this will only get worse over time as the videos_views table grows in size. SELECT v.VID, v.title, v.vkey, v.duration, v.addtime, v.UID, v.viewnumber, v.com_num, v.rate, v.THB, s.username, SUM(vvt.num_of_views) AS tmp_num FROM video v LEFT JOIN videos_views vvt ON v.VID = vvt.videos_id LEFT JOIN signup s on v.UID = s.UID WHERE v.status = 'Converted' AND v.type = 'public' AND v.is_duplicate = '0' AND v.is_adult = '0' AND v.channel_id <> 10 AND vvt.views_date >= '2001-05-11' GROUP BY vvt.videos_id ORDER BY tmp_num DESC LIMIT 8 And here is a screenshot of the EXPLAIN result: So, how can I optimize this?

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• Can I recover lost commits in a SVN repository using a local tracking git-svn branch?

  - by Ian Stevens

  A SVN repo I use git-svn to track was recently corrupted and a backup was recovered. However, a week's worth of commits were lost in the recovery. Is it possible to recover those lost commits using git-svn dcommit on my local git repo? Is it sufficient to run git-svn dcommit with the SHA1 of the last recovered commit in SVN? eg. > svn info http://tracked-svn/trunk | sed -n "s/Revision: //p" 252 > git log --grep="git-svn-id:.*@252" --format=oneline | cut -f1 -d" " 55bb5c9cbb5fe11a90ec2e9e1e0c7c502908cf9a > git svn dcommit 55bb5c9cbb5fe11a90ec2e9e1e0c7c502908cf9a Or will the git-svn-id need to be stripped from the intended commits? I tried this using --dry-run but couldn't tell whether it would try to submit all commits: > git svn dcommit --verbose --dry-run 55bb5c9cbb5fe11a90ec2e9e1e0c7c502908cf9a Committing to http://tracked-svn/trunk ... dcommitted on a detached HEAD because you gave a revision argument. The rewritten commit is: 55bb5c9cbb5fe11a90ec2e9e1e0c7c502908cf9a Thanks for your help.

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• strange redefined symbols

  - by Chris H

  I included this header into one of my own: http://codepad.org/lgJ6KM6b When I compiled I started getting errors like this: CMakeFiles/bin.dir/SoundProjection.cc.o: In function `Gnuplot::reset_plot()': /usr/lib/gcc/x86_64-pc-linux-gnu/4.3.4/include/g++-v4/new:105: multiple definition of `Gnuplot::reset_plot()' CMakeFiles/bin.dir/main.cc.o:project/gnuplot-cpp/gnuplot_i.hpp:962: first defined here CMakeFiles/bin.dir/SoundProjection.cc.o: In function `Gnuplot::set_smooth(std::basic_string, std::allocator const&)': project/gnuplot-cpp/gnuplot_i.hpp:1041: multiple definition of `Gnuplot::set_smooth(std::basic_string, std::allocator const&)' CMakeFiles/bin.dir/main.cc.o:project/gnuplot-cpp/gnuplot_i.hpp:1041: first defined here CMakeFiles/bin.dir/SoundProjection.cc.o:/usr/include/eigen2/Eigen/src/Core/arch/SSE/PacketMath.h:41: multiple definition of `Gnuplot::m_sGNUPlotFileName' I know it's hard to see in this mess, but look at where the redefinitions are taking place. They take place in files like /usr/lib/gcc/x86_64-pc-linux-gnu/4.3.4/include/g++-v4/new:105. How is the new operator getting information about a gnuplot header? I can't even edit that file. How could that ever even be possible? I'm not even sure how to start debugging this. I hope I've provided enough information. I wasn't able to reproduce this in a small project. I mostly just looking for tips on how to find out why this is happening, and how to track it down. Thanks.

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• OutOfMemoryException

  - by Andrew

  I have an application that is pretty memory hungry. It holds a large amount of data in some big arrays. I have recently been noticing the occasional OutOfMemoryException. These OutOfMemoryExceptions are occurring long before my application (ASP.Net) has used up the 800mb available to it. I have track the issue down to the area of code where the array is resized. The array contains a structure that is 74bytes in size. (I know that you shouldn't create struct's that are bigger than 16bytes), but this application is a port from a Vb6 application). I have tried changing the struct to a class and this appears to have fixed the problem for now. I think the reason that changing to a class solves the problem has to do with the fact that when using a struct and the array is resized, a segment of memory that is large enough to store the new array needs to be reserved (e.g. (currentArraySize + increaseBySize)*74) cannot be found. This leads to the OutOfMemoryException. This isn't the case with a class as each element of the array only needs 8bytes to store a pointer to the new object. Is my thinking correct here?

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• How can a program be detected as running?

  - by ryeguy

  I have written a program that is sort of an unofficial, standalone plugin for an application. It allows customers to get a service that is a lower priced alternative then the vendor-owned one. My program is not illegal, against any kind of TOS, and is certainly not a virus, adware, or anything like that. That being said, the vendor of course is not happy about me taking his competition, and is trying to block my application from running. He has already tried some tactics to stop people from running my app alongside his. He makes it so if it is detected, his app throws a fake error. First, he checked to see if my program was running by looking for an open window with the right title. I countered this by randomizing the program title at startup. Next, he looked for the running process name. I countered this by making the app copy itself when it is started as [random string].exe and then running that. Anyways, my question is this: what else can he do to detect if my program running? I know that you can read window text (ie status bar, labels). I'm prepared to counter this by replacing the labels with images (ugh, any other way?). But what else is there? Can you detect what .dlls a program has loaded? If so, could this be solved by randomizing the dll names before loading them? I know that it's possible to get a program's signature in memory and track it that way (like a virus scanner), but the chances of him doing that probably aren't good because that sounds pretty advanced. Even though this is kinda crappy of him to be doing, its kind of fun. It's like a nerdy fist fight. EDIT: When I said it's a plugin, that is just the (incorrect) term I used. It's a standalone EXE. The "API" between my program and the other is mine is simply entering data into the controls (like textboxes, etc).

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• Complex derived attributes in Django models

  - by rabidpebble

  What I want to do is implement submission scoring for a site with users voting on the content, much like in e.g. reddit (see the 'hot' function in http://code.reddit.com/browser/sql/functions.sql). My submission model currently keeps track of up and down vote totals. Currently, when a user votes I create and save a related Vote object and then use F() expressions to update the Submission object's voting totals. The problem is that I want to update the score for the submission at the same time, but F() expressions are limited to only simple operations (it's missing support for log(), date_part(), sign() etc.) From my limited experience with Django I can see 4 options here: extend F() somehow (haven't looked at the code yet) to support the missing SQL functions; this is my preferred option and seems to fit within the Django framework the best define a scoring function (much like reddit's 'hot' function) in my database, and have Django use the value of that function for the value of the score field; as far as I can tell, #2 is not possible wrap my two step voting process in a suitably isolated transaction so that I can calculate the voting totals in Python and then update the Submission's voting totals without fear that another vote against the submission could be added/changed in the meantime; I'm hesitant to take this route because it seems overly complex - what is a "suitably isolated transaction" in this case anyway? use raw SQL; I would prefer to avoid this entirely -- what's the point of an ORM if I have to revert to SQL for such a common use case as this! (Note that this coming from somebody who loves sprocs, but is using Django for ease of development.) Before I embark on this mission to extend F() (which I'm not sure is even possible), am I about to reinvent the wheel? Is there a more standard way to do this? It seems like such a common use case and yet in an hour of searching I have yet to find a common solution...

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• Obtaining YouTube video ID in a URL and inputting selected video ID into a URL

  - by Dave

  I've been having trouble in trying to figure this out. What I am trying to do is, obtain the ID of a video from YouTube, and input the 11 character ID into the css of a div of a specific id by using jquery. I know the URL for the thumbnail of any video, but I just need to be able to change the ID to display different video thumbnails. <script> $(document).ready(function() { function(data){ videoID = data.split('www.youtube.com/v/')[1].split('&amp')[0]; $("#304817679").append(videoID); }); $("#304817679").replaceWith("<div id=\"304817679\" style=\"background: url(http://img.youtube.com/vi/"+ $.function(data) +"/0.jpg) no-repeat middle; width: 15px; height: 150px;\"></div>"); }); }); </script> <div id="304817679"> <div style="display: none;"><object width="248" height="222"><param name="movie" value="http://www.youtube.com/v/vy90n2nNRKQ&amp;rel=0&amp;egm=0&amp;showinfo=0&amp;fs=1"></param><param name="wmode" value="transparent"></param><param name="allowFullScreen" value="true"></param><embed src="http://www.youtube.com/v/vy90n2nNRKQ&amp;rel=0&amp;egm=0&amp;showinfo=0&amp;fs=1" type="application/x-shockwave-flash" width="248" height="222" allowFullScreen="true" wmode="transparent"></embed></object></div> </div> Trying to explain this better, I want the 11 Character YouTube Video ID from the embedded code, and put it into the URL of the thumbnail (http://img.youtube.com/vi/"+ function(data) +"/0.jpg). Which, would then also replace the original div (div id="304817679"). Am I on the right track with my script? I'm entirely new to this, and I would appreciate some of the help that's offered here.

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• WCF Data Services - neither .Expand or .LoadProperty seems to do what I need

  - by TomK

  I am building a school management app where they track student tardiness and absences. I've got three entities to help me in this. A Students entity (first name, last name, ID, etc.); a SystemAbsenceTypes entity with SystemAbsenceTypeID values for Late, Absent-with-Reason, Absent-without-Reason; and a cross-reference table called StudentAbsences (matching the student IDs with the absence-type ID, plus a date, and a Notes field). What I want to do is query my entities for a given student, and then add up the number of each kind of Absence, for a given date range. I prepare my currentStudent object without a problem, then I do this... Me.Data.LoadProperty(currentStudent, "StudentAbsences") 'Loads the cross-ref data lblDaysLate.Text = (From ab In currentStudent.StudentAbsences Where ab.SystemAbsenceTypes.SystemAbsenceTypeID = Common.enuStudentAbsenceTypes.Late).Count.ToString ...and this second line fails, complaining it has no value for an object. I presume the problem is that while it DOES see that there are (let's say) four absences for the currentStudent (ie, currentStudent.StudentAbsences.Count = 4) -- it can't yet "peer into" each one of the absences to look at its type. How do I use .Expand or .LoadProperty to make this happen? I tried fiddling with .LoadProperty but it doesn't take a two-level syntax like so... Data.LoadProperty(currentStudent,"StudentAbsences.SystemAbsenceTypeID") or the like. Is there some other technique?

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• Delphi 6 OleServer.pas Invoke memory leak

  - by Mike Davis

  There's a bug in delphi 6 which you can find some reference online for when you import a tlb the order of the parameters in an event invocation is reversed. It is reversed once in the imported header and once in TServerEventDIspatch.Invoke. you can find more information about it here: http://cc.embarcadero.com/Item/16496 somewhat related to this issue there appears to be a memory leak in TServerEventDispatch.Invoke with a parameter of a Variant of type Var_Array (maybe others, but this is the more obvious one i could see). The invoke code copies the args into a VarArray to be passed to the event handler and then copies the VarArray back to the args after the call, relevant code pasted below: // Set our array to appropriate length SetLength(VarArray, ParamCount); // Copy over data for I := Low(VarArray) to High(VarArray) do VarArray[I] := OleVariant(TDispParams(Params).rgvarg^[I]); // Invoke Server proxy class if FServer <> nil then FServer.InvokeEvent(DispID, VarArray); // Copy data back for I := Low(VarArray) to High(VarArray) do OleVariant(TDispParams(Params).rgvarg^[I]) := VarArray[I]; // Clean array SetLength(VarArray, 0); There are some obvious work-arounds in my case: if i skip the copying back in case of a VarArray parameter it fixes the leak. to not change the functionality i thought i should copy the data in the array instead of the variant back to the params but that can get complicated since it can hold other variants and seems to me that would need to be done recursively. Since a change in OleServer will have a ripple effect i want to make sure my change here is strictly correct. can anyone shed some light on exactly why memory is being leaked here? I can't seem to look up the callstack any lower than TServerEventDIspatch.Invoke (why is that?) I imagine that in the process of copying the Variant holding the VarArray back to the param list it added a reference to the array thus not allowing it to be release as normal but that's just a rough guess and i can't track down the code to back it up. Maybe someone with a better understanding of all this could shed some light?

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• How can I make this method more Scalalicious

  - by Neil Chambers

  I have a function that calculates the left and right node values for some collection of treeNodes given a simple node.id, node.parentId association. It's very simple and works well enough...but, well, I am wondering if there is a more idiomatic approach. Specifically is there a way to track the left/right values without using some externally tracked value but still keep the tasty recursion. /* * A tree node */ case class TreeNode(val id:String, val parentId: String){ var left: Int = 0 var right: Int = 0 } /* * a method to compute the left/right node values */ def walktree(node: TreeNode) = { /* * increment state for the inner function */ var c = 0 /* * A method to set the increment state */ def increment = { c+=1; c } // poo /* * the tasty inner method * treeNodes is a List[TreeNode] */ def walk(node: TreeNode): Unit = { node.left = increment /* * recurse on all direct descendants */ treeNodes filter( _.parentId == node.id) foreach (walk(_)) node.right = increment } walk(node) } walktree(someRootNode) Edit - The list of nodes is taken from a database. Pulling the nodes into a proper tree would take too much time. I am pulling a flat list into memory and all I have is an association via node id's as pertains to parents and children. Adding left/right node values allows me to get a snapshop of all children (and childrens children) with a single SQL query. The calculation needs to run very quickly in order to maintain data integrity should parent-child associations change (which they do very frequently). In addition to using the awesome Scala collections I've also boosted speed by using parallel processing for some pre/post filtering on the tree nodes. I wanted to find a more idiomatic way of tracking the left/right node values. After looking at the answers listed I have settled on this synthesised version: def walktree(node: TreeNode) = { def walk(node: TreeNode, counter: Int): Int = { node.left = counter node.right = treeNodes .filter( _.parentId == node.id) .foldLeft(counter+1) { (counter, curnode) => walk(curnode, counter) + 1 } node.right } walk(node,1) }

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• Starting with versioning mysql schemata without overkill. Good solutions?

  - by tharkun

  I've arrived at the point where I realise that I must start versioning my database schemata and changes. I consequently read the existing posts on SO about that topic but I'm not sure how to proceed. I'm basically a one man company and not long ago I didn't even use version control for my code. I'm on a windows environment, using Aptana (IDE) and SVN (with Tortoise). I work on PHP/mysql projects. What's a efficient and sufficient (no overkill) way to version my database schemata? I do have a freelancer or two in some projects but I don't expect a lot of branching and merging going on. So basically I would like to keep track of concurrent schemata to my code revisions. [edit] Momentary solution: for the moment I decided I will just make a schema dump plus one with the necessary initial data whenever I'm going to commit a tag (stable version). That seems to be just enough for me at the current stage.[/edit] [edit2]plus I'm now also using a third file called increments.sql where I put all the changes with dates, etc. to make it easy to trace the change history in one file. from time to time I integrate the changes into the two other files and empty the increments.sql[/edit]

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