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• How to create refresh statements for TableAdapter objects in Visual Studio?

  - by Mark Wilkins

  I am working on developing an ADO.NET data provider and an associated DDEX provider. I am unable to convince the Visual Studio TableAdapater Configuration Wizard to generate SQL statements to refresh the data table after inserts and updates. It generates the insert and delete statements but will not produce the select statements to do the refresh. The functionality referred to can be accessed by dropping a table from the Server Explorer (inside Visual Studio) onto a DataSet (e.g., DataSet1.xsd). It creates a TableAdapter object and configures SELECT, UPDATE, DELETE, and INSERT statements. If you right click on the TableAdapter object, the context menu has a “Configure” option that starts the “TableAdapter Configuration Wizard”. The first dialog of that wizard has an Advanced Options button, which leads to an option titled “Refresh the data table”. When used with SQL Server tables, that option causes a statement of the form “select field1, field2, …” to be added on to the end of the commands for the TableAdapter’s InsertCommand and UpdateCommand. Do you have any idea what type property or interface might need to be exposed from the DDEX provider (or maybe the ADO.NET data provider) in order to make Visual Studio add those refresh statements to the update/insert commands? The MSDN documentation for the Advanced SQL Generation Options Dialog Box has a note stating, “Refreshing the data table is only supported on databases that support batching of SQL statements.” This seems to imply that a .NET data provider might need to expose some property indicating such behavior is supported. But I cannot find it. Any ideas?

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• generating and unmarshalling java classes while unmarshalling input contains a DTD

  - by Hans Westerbeek

  Hi, For a Spring-based project, I have the following situation to solve: I have XML files coming in whose contents I will have to parse at runtime. Those XML files come with a DTD reference. I need to generate the classes that the unmarshaller churns out using the right at build time, using the Maven2 plugin for the unmarshalling library of choice. This is also not very hard to do, once I have generated an XSD from the DTD. I want to use spring-oxm's UnMarshaller interface to do the unmarshalling at runtime. This I understand how to do. The xml files come in with a DTD reference, and all unmarshalling libraries out there want to do unmarshalling based on an XSD. Now, as described in the castor documentation, I can convert the DTD to an XSD and keep it on the classpath. However, when an actual XML file comes into the system it will still have that DTD reference at the top, and there's nothing I can really do about that (except for string replacing which feels hacky in this case). Will this cause the unmarshaller, like Castor to fail? Am I right in suspecting that this DTD reference will cause the unmarshalling to fail? Could I do pure DTD-based unmarshalling? Or can this somehow be prevented by providing detailed configuration to the unmarshaller? Until now, I have tried castor, xmlbeans and xstream. Which would fit my purposes best? Has anyone else been in this situation? Did you also end up just doing manual DOM or SAX parsing?

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• How do I abort a socket.recv() from another thread in python?

  - by Samuel Skånberg

  I have a main thread that waits for connection. It spawns client threads that will echo the response from the client (telnet in this case). But say that I want to close down all sockets and all threads after some time, like after 1 connection. How would I do? If I do clientSocket.close() from the main thread, it won't stop doing the recv. It will only stop if I first send something through telnet, then it will fail doing further sends and recvs. My code look like this: # Echo server program import socket from threading import Thread import time class ClientThread(Thread): def __init__(self, clientSocket): Thread.__init__(self) self.clientSocket = clientSocket def run(self): while 1: try: # It will hang here, even if I do close on the socket data = self.clientSocket.recv(1024) print "Got data: ", data self.clientSocket.send(data) except: break self.clientSocket.close() HOST = '' PORT = 6000 serverSocket = socket.socket(socket.AF_INET, socket.SOCK_STREAM) serverSocket.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1) serverSocket.bind((HOST, PORT)) serverSocket.listen(1) clientSocket, addr = serverSocket.accept() print 'Got a new connection from: ', addr clientThread = ClientThread(clientSocket) clientThread.start() time.sleep(1) # This won't make the recv in the clientThread to stop immediately, # nor will it generate an exception clientSocket.close()

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• How do I sign requests reliably for the Last.fm api in C#?

  - by Arda Xi

  I'm trying to implement authorization through Last.fm. I'm submitting my arguments as a Dictionary to make the signing easier. This is the code I'm using to sign my calls: public static string SignCall(Dictionary<string, string> args) { IOrderedEnumerable<KeyValuePair<string, string>> sortedArgs = args.OrderBy(arg => arg.Key); string signature = sortedArgs.Select(pair => pair.Key + pair.Value). Aggregate((first, second) => first + second); return MD5(signature + SecretKey); } I've checked the output in the debugger, it's exactly how it should be, however, I'm still getting WebExceptions every time I try. Here's my code I use to generate the URL in case it'll help: public static string GetSignedURI(Dictionary<string, string> args, bool get) { var stringBuilder = new StringBuilder(); if (get) stringBuilder.Append("http://ws.audioscrobbler.com/2.0/?"); foreach (var kvp in args) stringBuilder.AppendFormat("{0}={1}&", kvp.Key, kvp.Value); stringBuilder.Append("api_sig="+SignCall(args)); return stringBuilder.ToString(); } And sample usage to get a SessionKey: var args = new Dictionary<string, string> { {"method", "auth.getSession"}, {"api_key", ApiKey}, {"token", token} }; string url = GetSignedURI(args, true); EDIT: Oh, and the code references an MD5 function implemented like this: public static string MD5(string toHash) { byte[] textBytes = Encoding.UTF8.GetBytes(toHash); var cryptHandler = new System.Security.Cryptography.MD5CryptoServiceProvider(); byte[] hash = cryptHandler.ComputeHash(textBytes); return hash.Aggregate("", (current, a) => current + a.ToString("x2")); }

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• Scaling Image to multiple sizes for Deep Zoom

  - by AnthonyWJones

  Lets assume I have a bitmap with a square aspect and width of 2048 pixels. In order to create a set of files need by Silverlight's DeepZoomImageTileSource I need to scale this bitmap to 1024 then to 512 then to 256 etc down to 1 pixel image. There are two, I suspect naive, approaches:- For each image required scale the original full size image to the required size. However it seems excessive to be scaling the full image to the very small sizes. Having scaled from one level to the next discard the original image and scale each sucessive scaled image as the source of the next smaller image. However I suspect that this would generate images in the 256-64 range with poor fidelity than using option 1. Note unlike with the Deep Zoom Composer this tool is expected to act in an on-demand fashion hence it needs to complete in a reasonable timeframe (tops 30 seconds). On the pluse side I'm only creating a single multiscale image not a pyramid of mutliple high-res images. I am outside my comfort zone here, any graphics experts got any advice? Am I wrong about point 2? Is point 1 reasonably performant and I'm worrying about nothing? Option 3?

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• How can I access mainframe data with .Net applications and SQL Queries?

  - by orandov

  We have a large amount of data stored on an IBM mainframe using VSAM files. A lot of this data is dropped on the network every night in the form of text files to be processed and dumped into FoxPro and SQL Server databases. There are also many text files produced nightly by custom applications that get uploaded to the mainframe to keep everything in sync. Keeping the everything in sync is very tricky, to say the least. We are not getting rid of the mainframe any time soon and we would like to replace all the nightly batch processing with real time access to the mainframe data. We would like to be able to: Read data directly from the mainframe and produce reports based on it. Possibly using SQL queries. Read and Write data from custom .Net applications. We are not looking for a new platform to interface with the mainframe like Information Builders offers. We don't want to build application modules or reports with new "Business Intelligence" tools. We already know how to generate reports and write custom applications using SQL,.Net, Visual Studio, etc. All we are looking for is some sort of adapter to connect to our mainframe data. Any ideas are appreciated.

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• Problems setting up AuthLogic

  - by sscirrus

  Hi all, I'm trying to set up a simple login using AuthLogic into my User table. Every time I try, the login fails and I don't know why. I'm sure this is a simple error but I've been hitting a brick wall with it for a while. #user_sessions_controller def create @user_session = UserSession.new(params[:user_session]) if @user_session.save flash[:notice] = "Login successful!" else flash[:notice] = "We couldn't log you in. Please try again!" redirect_to :controller => "index", :action => "index" end end #_user_login.html.erb (this is the partial from my index page where Users log in) <% form_tag user_session_path do %> <p><label for="login">Login:</label> <%= text_field_tag "login", nil, :class => "inputBox", :id => "login", </p> <p><label for="password">Password: </label> <%= password_field_tag "password", nil, :class => "inputBox", :id => "password", </p> <p><%= submit_tag "submit", :class => "submit" %></p> <% end %> I had Faker generate some data for my user table but I cannot log in! Every time I try it just redirects to index. Where am I going wrong? Thanks everybody.

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• Reversible pseudo-random sequence generator

  - by user350651

  I would like some sort of method to create a fairly long sequence of random numbers that I can flip through backwards and forwards. Like a machine with "next" and "previous" buttons, that will give you random numbers. Something like 10-bit resolution (i.e. positive integers in a range from 0 to 1023) is enough, and a sequence of 100k numbers. It's for a simple game-type app, I don't need encryption-strength randomness or anything, but I want it to feel fairly random. I have a limited amount of memory available though, so I can't just generate a chunk of random data and go through it. I need to get the numbers in "interactive time" - I can easily spend a few ms thinking about the next number, but not comfortably much more than that. Eventually it will run on some sort of microcontroller, probably just an Arduino. I could do it with a simple linear congruential generator (LCG). Going forwards is simple, to go backwards I'd have to cache the most recent numbers and store some points at intervals so I can recreate the sequence from there. But maybe there IS some pseudo-random generator that allows you to go both forwards and forwards? It should be possible to hook up two linear feedback shift registers (LFSRs) to roll in different directions, no? Or maybe I can just get by with garbling the index number using a hash function of some sort? I'm going to try that first. Any other ideas?

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• How to implement custom JSF component for drawing chart?

  - by Roman

  I want to create a component which can be used like: <mc:chart data="#{bean.data}" width="200" height="300" /> where #{bean.data} returns a collection of some objects or chart model object or something else what can be represented as a chart (to put it simple, let's assume it returns a collection of integers). I want this component to generate html like this: <img src="someimg123.png" width="200" height="300"/> The problem is that I have some method which can receive data and return image, like: public RenderedImage getChartImage (Collection<Integer> data) { ... } and I also have a component for drawing dynamic image: <o:dynamicImage width="200" height="300" data="#{bean.readyChartImage}/> This component generates html just as I need but it's parameter is array of bytes or RenderedImage i.e. it needs method in bean like this: public RenderedImage getReadyChartImage () { ... } So, one approach is to use propertyChangedListener on submit to set data (Collection<Integer>) for drawing chart and then use <o:dynamicImage /> component. But I'd like to create my own component which receives data and draws chart. I'm using facelets but it's not so important indeed. Any ideas how to create the desired component? P.S. One solution I was thinking about is not to use <o:dynamicImage/> and use some servlet to stream image. But I don't know how to implement that correctly and how to tie jsf component with servlet and how to save already built chart images (generating new same image for each request can cause performance problems imho) and so on..

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• red black tree balancing?

  - by Anirudh Kaki

  i am working to generate tango tree, where i need to check whether every sub tree in tango is balanced or not. if its not balanced i need to make it balance? I trying so hard to make entire RB-tree balance but i not getting any proper logic so can any one help me out?? here i am adding code to check how to find my tree is balanced are not but when its not balanced how can i make it balance. static boolean verifyProperty5(rbnode n) { int left = 0, right = 0; if (n != null) { bh++; left = blackHeight(n.left, 0); right = blackHeight(n.right, 0); } if (left == right) { System.out.println("black height is :: " + bh); return true; } else { System.out.println("in balance"); return false; } } public static int blackHeight(rbnode root, int len) { bh = 0; blackHeight(root, path1, len); return bh; } private static void blackHeight(rbnode root, int path1[], int len) { if (root == null) return; if (root.color == "black"){ root.black_count = root.parent.black_count+1; } else{ root.black_count = root.parent.black_count; } if ((root.left == null) && (root.right == null)) { bh = root.black_count; } blackHeight(root.left, path1, len); blackHeight(root.right, path1, len); }

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• Why are my Fluent NHibernate SubClass Mappings generating redundant columns?

  - by Brook

  I'm using Fluent NHibernate 1.x build 694, built against NH 3.0 I have the following entities public abstract class Card { public virtual int Id { get; set; } public virtual string Name { get; set; } public virtual string Description { get; set; } public virtual Product Product { get; set; } public virtual Sprint Sprint { get; set; } } public class Story:Card { public virtual double Points { get; set; } public virtual int Priority { get; set; } public virtual IList<Task> Tasks { get; set; } } And the following mappings public class CardMap:ClassMap<Card> { public CardMap() { Id(c => c.Id) .Index("Card_Id"); Map(c => c.Name) .Length(50) .Not.Nullable(); Map(c => c.Description) .Length(1024) .Not.Nullable(); References(c=>c.Product) .Not.Nullable(); References(c=>c.Sprint) .Nullable(); } } public class StoryMap : SubclassMap<Story> { public StoryMap() { Map(s => s.Points); Map(s => s.Priority); HasMany(s => s.Tasks); } } When I generate my Schema, the tables are created as follows Card --------- Id Name Description Product_id Sprint_id Story ------------ Card_id Points Priority Product_id Sprint_id What I would have expected would have been to see the columns Product_id and Sprint_id ONLY in the Card table, not the Story table. What am I doing wrong or misunderstanding?

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• binding nested json object value to a form field

  - by Jack

  I am building a dynamic form to edit data in a json object. First, if something like this exists let me know. I would rather not build it but I have searched many times for a tool and have found only tree like structures that require entering quotes. I would be happy to treat all values as strings. This edit functionality is for end users so it needs to be easy an not intimidating. So far I have code that generates nested tables to represent a json object. For each value I display a form field. I would like to bind the form field to the associated nested json value. If I could store a reference to the json value I would build an array of references to each value in a json object tree. I have not found a way to do that with javascript. My last resort approach will be to traverse the table after edits are made. I would rather have dynamic updates but a single submit would be better than nothing. Any ideas? // the json in files nests only a few levels. Here is the format of a simple case, { "researcherid_id":{ "id_key":"researcherid_id", "description":"Use to retrieve bibliometric data", "url_template" :[ { "name": "Author Detail", "url": "http://www.researcherid.com/rid/${key}" } ] } } $.get('file.json',make_json_form); function make_json_form(response) { dataset = $.secureEvalJSON(response); // iterate through the object and generate form field for string values. } // Then after the form is edited I want to display the raw updated json (then I want to save it but that is for another thread) // now I iterate through the form and construct the json object // I would rather have the dataset object var updated on focus out after each edit. function show_json(form_id){ var r = {}; var el = document.getElementById(form_id); table_to_json(r,el,null); $('body').html(formattedJSON(r)); }

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• Help regarding Android NDK

  - by Siva Kumar

  I am a beginner in using Android NDK. I am using Eclipse and I installed cygwin to build the c file to generate the .so file But while building the c file in cygwin I am always getting the error make: ***No rule to make target 'file.c' ... .Stop I tried building different C codes but for every file it says the same error .. Here is the source code: public class ndktest extends Activity { static { System.loadLibrary("ndkt"); } private native void helloLog(String logThis); @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); helloLog("this is to test log file"); } } file.c void Java_com_ndktest_helloLog(JNIEnv * env, jobject this, jstring logThis) { jboolean isCopy; const char * szLogThis = (*env)->GetStringUTFChars(env, logThis, &isCopy); (*env)->ReleaseStringUTFChars(env, logThis, szLogThis); } And here is my Android.mk LOCAL_PATH := $(call my-dir) include $(CLEAR_VARS) LOCAL_LDLIBS := -llog LOCAL_MODULE := ndkt LOCAL_SRC_FILES := file.c include $(BUILD_SHARED_LIBRARY) I searched for the solution for the cause of error ... but nothing works for me. Can anyone tell me where I am making the mistake ? Thanks, Siva Kumar

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• How do I model teams and gameplay in this scorekeeping application?

  - by Eric Hill

  I'm writing a scorekeeping application for card game that has a few possibly-interesting constraints. The application accepts user registrations for players, then lets them check-in to a particular game (modeled as Event). After the final player registers, the app should generate teams, singles or doubles, depending on the preference of the person running the game and some validations (can't do doubles if there's an odd number checked in). There are @event.teams.count rounds in the game. To sum up: An event consists of `@event.teams.count` rounds; Teams can have 1 or more players Events have n or n/2 teams (depending on whether it's singles or doubles) Users will be members of different teams at different events Currently I have a rat's nest of associations: class User < ActiveRecord::Base has_many :teams, :through => :players has_many :events, :through => :teams class Event < ActiveRecord::Base has_many :rounds has_many :teams has_many :players, :through => :teams class Player < ActiveRecord::Base belongs_to :user belongs_to :team end class Team < ActiveRecord::Base has_many :players belongs_to :event end class Round < ActiveRecord::Base belongs_to :event belongs_to :user end The sticky part is team generation. I have basically a "start game" button that should freeze the registrations and pair up teams either singly or doubly, and render to Round#new so that the first (and subsequent) matches can be scored. Currently I'm implementing this as a check on Round#new that calls Event#generate_teams and displays the view: # Event#generate_teams def generate_teams # User has_many :events, :through => :registrations # self.doubles is a boolean denoting 2 players per team registrations.in_groups_of(self.doubles ? 2 : 1, nil).each do |side| self.teams << Player.create(self,side) end end Which doesn't work. Should there maybe be a Game model that ties everything together rather than (my current method) defining the game as an abstraction via the relationships between Events, Users, and Rounds (and Teams and Players and etc.)? My head is swimming.

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• Which CMS do I need? Needs to be easy to post a certain kind of post

  - by Vian Esterhuizen

  Hi, I'm creating a site for a video store and it needs to be CMS. I'm doing this for free so I need to use a free CMS like Wordpress, Drupal or Joomla. Do I need a new CMS, a plugin or some PHP of my own? What I need: User accounts Categories Custom post Here's the site as it stands with WP: http://sundancevideo.ca. Right now an experimental site to try to work this out. What I've done now, is created a "Draft" that includes a template table with images and text and so on. The user would then have to copy everything, past into a new post and replace necessary. This really isn't working well. As you may notice by the condition of the posts. What I would prefer is if it was integrated into the WP UI. Like a field for "Description" and field for "Image" where they can upload the images as necessary. This would then generate post, with a table including all the information and images, for as many movies that were added in the UI. Please ask if I'm not being clear. Please help, any suggestions are welcome. Thank you, Vian

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• SQL Server database change workflow best practices

  - by kubi

  The Background My group has 4 SQL Server Databases: Production UAT Test Dev I work in the Dev environment. When the time comes to promote the objects I've been working on (tables, views, functions, stored procs) I make a request of my manager, who promotes to Test. After testing, she submits a request to an Admin who promotes to UAT. After successful user testing, the same Admin promotes to Production. The Problem The entire process is awkward for a few reasons. Each person must manually track their changes. If I update, add, remove any objects I need to track them so that my promotion request contains everything I've done. In theory, if I miss something testing or UAT should catch it, but this isn't certain and it's a waste of the tester's time, anyway. Lots of changes I make are iterative and done in a GUI, which means there's no record of what changes I made, only the end result (at least as far as I know). We're in the fairly early stages of building out a data mart, so the majority of the changes made, at least count-wise, are minor things: changing the data type for a column, altering the names of tables as we crystallize what they'll be used for, tweaking functions and stored procs, etc. The Question People have been doing this kind of work for decades, so I imagine there have got to be a much better way to manage the process. What I would love is if I could run a diff between two databases to see how the structure was different, use that diff to generate a change script, use that change script as my promotion request. Is this possible? If not, are there any other ways to organize this process? For the record, we're a 100% Microsoft shop, just now updating everything to SQL Server 2008, so any tools available in that package would be fair game.

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• How do I access the CodeDomProvider from a class inheriting from Microsoft.VisualStudio.TextTemplating.VSHost.BaseCodeGeneratorWithSite?

  - by Charlie

  Does anyone know how to get a CodeDomProvider in the new Microsoft.VisualStudio.TextTemplating.VSHost.BaseCodeGeneratorWithSite from the Visual Studio 2010 SDK? I used to get access to it just by in mere inheritance of the class Microsoft.CustomTool.BaseCodeGeneratorWithSite, but now with this new class it is not there. I see a GlobalServiceProvider and a SiteServiceProvider but I can't find any example on how to use them. Microsoft.VisualStudio.TextTemplating.VSHost.BaseCodeGeneratorWithSite: http://msdn.microsoft.com/en-us/library/bb932625.aspx I was to do this: public class Generator : Microsoft.VisualStudio.TextTemplating.VSHost.BaseCodeGeneratorWithSite { public override string GetDefaultExtension() { // GetDefaultExtension IS ALSO NOT ACCESSIBLE... return this.InputFilePath.Substring(this.InputFilePath.LastIndexOf(".")) + ".designer" + base.GetDefaultExtension(); } // This method is being called every time the attached xml is saved. protected override byte[] GenerateCode(string inputFileName, string inputFileContent) { try { // Try to generate the wrapper file. return GenerateSourceCode(inputFileName); } catch (Exception ex) { // In case of a faliure - print the exception // as a comment in the source code. return GenerateExceptionCode(ex); } } public byte[] GenerateSourceCode(string inputFileName) { Dictionary<string, CodeCompileUnit> oCodeUnits; // THIS IS WHERE CodeProvider IS NOT ACCESSIBLE CodeDomProvider oCodeDomProvider = this.CodeProvider; string[] aCode = new MyCustomAPI.GenerateCode(inputFileName, ref oCodeDomProvider); return Encoding.ASCII.GetBytes(String.Join(@" ", aCode)); } private byte[] GenerateExceptionCode(Exception ex) { CodeCompileUnit oCode = new CodeCompileUnit(); CodeNamespace oNamespace = new CodeNamespace("System"); oNamespace.Comments.Add(new CodeCommentStatement(MyCustomAPI.Print(ex))); oCode.Namespaces.Add(oNamespace); string sCode = null; using (StringWriter oSW = new StringWriter()) { using (IndentedTextWriter oITW = new IndentedTextWriter(oSW)) { this.CodeProvider.GenerateCodeFromCompileUnit(oCode, oITW, null); sCode = oSW.ToString(); } } return Encoding.ASCII.GetBytes(sCode ); } } Thanks for your help!

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• Maven build fails on an Ant FTP task failure

  - by fraido

  I'm using the FTP Ant task with maven-antrun-plugin <plugin> <groupId>org.apache.maven.plugins</groupId> <artifactId>maven-antrun-plugin</artifactId> <executions> <execution> <id>ftp</id> <phase>generate-resources</phase> <configuration> <tasks> <ftp action="get" server="${ftp.server.ip}" userid="${ftp.server.userid}" password="${ftp.server.password}" remotedir="${ftp.server.remotedir}" depends="yes" verbose="yes" skipFailedTransfers="true" ignoreNoncriticalErrors="true"> <fileset dir="target/test-classes/testdata"> <include name="**/*.html" /> </fileset> </ftp> </tasks> </configuration> <goals> <goal>run</goal> </goals> </execution> </executions> ... the problem is that my build fails when the folder ${ftp.server.remotedir} doesn't exist. I tried to specify skipFailedTransfers="true" ignoreNoncriticalErrors="true but these don't fix the problem and the build keeps failing. An Ant BuildException has occured: could not change remote directory: 550 /myBadDir: The system cannot find the file specified. Do you know how to instruct my maven build to don't care about this Ant task error

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• The Immerman-Szelepcsenyi Theorem

  - by Daniel Lorch

  In the Immerman-Szelepcsenyi Theorem, two algorithms are specified that use non-determinisim. There is a rather lengthy algorithm using "inductive counting", which determines the number of reachable configurations for a given non-deterministic turing machine. The algorithm looks like this: Let m_{i+1}=0 For all configurations C Let b=0, r=0 For all configurations D Guess a path from I to D in at most i steps If found Let r=r+1 If D=C or D goes to C in 1 step Let b=1 If r<m_i halt and reject Let m_{i+1}=m_{i+1}+b I is the starting configuration. m_i is the number of configurations reachable from the starting configuration in i steps. This algorithm only calculates the "next step", i.e. m_i+1 from m_i. This seems pretty reasonable, but since we have nondeterminisim, why don't we just write: Let m_i = 0 For all configurations C Guess a path from I to C in at most i steps If found m_i = m_i + 1 What is wrong with this algorithm? I am using nondeterminism to guess a path from I to C, and I verify reachability I am iterating through the list of ALL configurations, so I am sure to not miss any configuration I respect space bounds I can generate a certificate (the list of reachable configs) I believe I have a misunderstanding of the "power" of non-determinisim, but I can't figure out where to look next. I am stuck on this for quite a while and I would really appreciate any help.

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• Associate "Code/Properties/Stuff" with Fields in C# without reflection. I am too indoctrinated by J

  - by AlexH

  I am building a library to automatically create forms for Objects in the project that I am working on. The codebase is in C#, and essentially we have a HUGE number of different objects to store information about different things. If I send these objects to the client side as JSON, it is easy enough to programatically inspect them to generate a form for all of the properties. The problem is that I want to be able to create a simple way of enforcing permissions and doing validation on the client side. It needs to be done on a field by field level. In javascript I would do this by creating a parallel object structure, which had some sort of { permissions : "someLevel", validator : someFunction } object at the nodes. With empty nodes implying free permissions and universal validation. This would let me simply iterate over the new object and the permissions object, run the check, and deal with the result. Because I am overfamilar with the hammer that is javascript, this is really the only way that I can see to deal with this problem. My first implementation thus uses reflection to let me treat objects as dictionaries, that can be programatically iterated over, and then I just have dictionaries of dictionaries of PermissionRule objects which can be compared with. Very javascripty. Very awkward. Is there some better way that I can do this? Essentially a way to associate a data set with each property, and then iterate over those properties. Or else am I Doing It Wrong?

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• SQL placeholder in WHERE IN issue, inserted strings fail.

  - by Alastair Pitts

  As part of my jobs, I need to writes SQL queries to connect to our PI database. To generate a query, I need to pass an array of tags (essentially primary keys), but these have to be inserted as strings. As this will be a modular query and used for multiple tags, a placeholder is being used. The query relies upon the use of the WHERE IN statement, which is where the placeholder is, like below: SELECT SUM(value * 5/1000) as "Hourly Flow [kL]" from piarchive..pitotal WHERE tag IN (?) AND time between ? and ? and timestep = '1d' and calcbasis = 'Eventweighted' and value <> '' The issue is the format in which the tags are to be passed in as. If I add them directly into the query (for testing), they go in the format (these are example numbers): '000000012','00000032','005050236','4560236' and the query looks like: SELECT SUM(value * 5/1000) as "Hourly Flow [kL]" from piarchive..pitotal WHERE tag IN ('000000012','00000032','005050236','4560236') AND time between ? and ? and timestep = '1d' and calcbasis = 'Eventweighted' and value <> '' which works. If I try and add the same tags into the placeholder, the query fails. If I only add 1 tag, with no quotes (using the placeholder), the query works. Why is this happening? Is there anyway around it?

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• tail call generated by clang 1.1 and 1.0 (llvm 2.7 and 2.6)

  - by ony

  After compilation next snippet of code with clang -O2 (or with online demo): #include <stdio.h> #include <stdlib.h> int flop(int x); int flip(int x) { if (x == 0) return 1; return (x+1)*flop(x-1); } int flop(int x) { if (x == 0) return 1; return (x+0)*flip(x-1); } int main(int argc, char **argv) { printf("%d\n", flip(atoi(argv[1]))); } I'm getting next snippet of llvm assembly in flip: bb1.i: ; preds = %bb1 %4 = add nsw i32 %x, -2 ; <i32> [#uses=1] %5 = tail call i32 @flip(i32 %4) nounwind ; <i32> [#uses=1] %6 = mul nsw i32 %5, %2 ; <i32> [#uses=1] br label %flop.exit I thought that tail call means dropping current stack (i.e. return will be to the upper frame, so next instruction should be ret %5), but according to this code it will do mul for it. And in native assembly there is simple call without tail optimisation (even with appropriate flag for llc) Can sombody explain why clang generates such code? As well I can't understand why llvm have tail call if it can simply check that next ret will use result of prev call and later do appropriate optimisation or generate native equivalent of tail-call instruction?

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• C: 8x8 -> 16 bit multiply precision guaranteed by integer promotions?

  - by craig-blome

  I'm trying to figure out if the C Standard (C90, though I'm working off Derek Jones' annotated C99 book) guarantees that I will not lose precision multiplying two unsigned 8-bit values and storing to a 16-bit result. An example statement is as follows: unsigned char foo; unsigned int foo_u16 = foo * 10; Our Keil 8051 compiler (v7.50 at present) will generate a MUL AB instruction which stores the MSB in the B register and the LSB in the accumulator. If I cast foo to a unsigned int first: unsigned int foo_u16 = (unsigned int)foo * 10; then the compiler correctly decides I want a unsigned int there and generates an expensive call to a 16x16 bit integer multiply routine. I would like to argue beyond reasonable doubt that this defensive measure is not necessary. As I read the integer promotions described in 6.3.1.1, the effect of the first line shall be as if foo and 10 were promoted to unsigned int, the multiplication performed, and the result stored as unsigned int in foo_u16. If the compiler knows an instruction that does 8x8-16 bit multiplications without loss of precision, so much the better; but the precision is guaranteed. Am I reading this correctly? Best regards, Craig Blome

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• PostgreSQL, Foreign Keys, Insert speed & Django

  - by Miles

  A few days ago, I ran into an unexpected performance problem with a pretty standard Django setup. For an upcoming feature, we have to regenerate a table hourly, containing about 100k rows of data, 9M on the disk, 10M indexes according to pgAdmin. The problem is that inserting them by whatever method literally takes ages, up to 3 minutes of 100% disk busy time. That's not something you want on a production site. It doesn't matter if the inserts were in a transaction, issued via plain insert, multi-row insert, COPY FROM or even INSERT INTO t1 SELECT * FROM t2. After noticing this isn't Django's fault, I followed a trial and error route, and hey, the problem disappeared after dropping all foreign keys! Instead of 3 minutes, the INSERT INTO SELECT FROM took less than a second to execute, which isn't too surprising for a table <= 20M on the disk. What is weird is that PostgreSQL manages to slow down inserts by 180x just by using 3 foreign keys. Oh, disk activity was pure writing, as everything is cached in RAM; only writes go to the disks. It looks like PostgreSQL is working very hard to touch every row in the referred tables, as 3MB/sec * 180s is way more data than the 20MB this new table takes on disk. No WAL for the 180s case, I was testing in psql directly, in Django, add ~50% overhead for WAL logging. Tried @commit_on_success, same slowness, I had even implemented multi row insert and COPY FROM with psycopg2. That's another weird thing, how can 10M worth of inserts generate 10x 16M log segments? Table layout: id serial primary, a bunch of int32, 3 foreign keys to small table, 198 rows, 16k on disk large table, 1.2M rows, 59 data + 89 index MB on disk large table, 2.2M rows, 198 + 210MB So, am I doomed to either drop the foreign keys manually or use the table in a very un-Django way by defining saving bla_id x3 and skip using models.ForeignKey? I'd love to hear about some magical antidote / pg setting to fix this.

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• Having an issue with Nullable MySQL columns in SubSonic 3.0 templates

  - by omegawkd

  Looking at this line in the Settings.ttinclude string CheckNullable(Column col){ string result=""; if(col.IsNullable && col.SysType !="byte[]" && col.SysType !="string") result="?"; return result; } It describes how it determines if the column is nullable based on requirements and returns either "" or "?" to the generated code. Now I'm not too familiar with the ? nullable type operator but from what I can see a cast is required. For instance, if I have a nullable integer MySQL column and I generate the code using the default template files it returns a line similar to this: int? _User_ID; When trying to compile the project I get the error: Cannot implicitly convert type 'int?' to 'int'. An explicit conversion exists (are you missing a cast?) I checked teh Settings files for the other database types and they all seems to have the same routine. So my question is, is this behaviour expected or is this a bug? I need to solve it one way or the other before I can procede. Thanks for your help.

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