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  • Drawing information from relational databases in Rails

    - by Trip
    I am trying to pull the name of the Artist from the Albums database. These are my two models class Album < ActiveRecord::Base belongs_to :artist validates_presence_of :title validates_length_of :title, :minimum => 5 end class Artist < ActiveRecord::Base has_many :albums end And here is the Albums Controller def index @ albums = Album.all respond_to do |format| format.html # index.html.erb format.xml { render :xml => @albums } end end And the View from the index: <% @albums.each do |album| %> <tr> <td><%=h album.id %></td> <td><%=h album.title %></td> <td><%=h album.artist.name %></td> </tr <% end %> My end result html is coming out like this for the artist field! # and if i set it to artist.name I get this: undefined method `name' for nil:NilClass

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  • Specifying Language for a grammar

    - by darkie15
    Hi All, Is there any specific methodology followed to specify a language for given grammar ?? i.e. Is it necessary to run all the production rules given in a grammar to determine the language it represents? I don't have an example as such since the one I am working on is a homework question. Regards, darkie15

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  • Broadcastreceiver to obtain ServiceState information

    - by Andrew
    Hi, Does anyone know of a way to obtain the phone service state (IN_SERVICE, OUT_OF_SERVICE, EMERGENCY_ONLY, POWER_OFF) in android. I was hoping there would be a broadcastreciever to identify the changes, but I can't find anything. I know there's a listener but I'm not sure how I would use that from my app as it runs as a service using a WakefulIntentService (by thecommonsguy). With something like battery level (ie BATTERY_LOW, BATTERY_OKAY) it's quite easy, but I just can't work out a similar things for phone service changes.

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  • Learning material on SAT (Boolean Satisfiability Problem)

    - by Jules
    What are good documents to read on SAT (Boolean satisfiability problem) solvers. I have not been able to find good material via Google. The documents I found were either birds eye view, too advanced or corrupted PDF files... Which papers/documents do you recommend to learn about the algorithms in modern practical SAT solvers?

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  • How do you avoid an invalid search space in a genetic algorithm?

    - by Dave
    I am developing a GA for a school project and I've noticed that upon evaluating my functions for fitness, an individual is equivalent to its inverse. For example, the set (1, 1, -1, 1) is equivalent to (-1, -1, 1, -1). To shrink my search space and reach a solution more efficiently, how can I avoid my crossovers from searching in this second half of the search space?

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  • Task vs. process, is there really any difference?

    - by DASKAjA
    Hi there, I'm studying for my final exams in my CS major on the subject distributed systems and operating systems. I'm in the need for a good definition for the terms task, process and threads. So far I'm confident that a process is the representation of running (or suspended, but initiated) program with its own memory, program counter, registers, stack, etc (process control block). Processes can run threads which share memory, so that communication via shared memory is possible in contrast to processes which have to communicate via IPC. But what's the difference between tasks and process. I often read that they're interchangable and that the term task isn't used anymore. Is that really true?

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  • Get more error information from unhandled error

    - by Andrew Simpson
    I am using C# in a desktop application. I am calling a DLL written in C that I do not have the source code for. Whenever I call this DLL I get an untrapped error which I trap in an UnhandledException event/delegate. The error is : object reference not set to an instance of an object But the stack trace is empty. When I Googled this the info back was that the error was being hanlded eleswhere and then rethrown. But this can only be in the DLL I do not have the source code for. So, is there anyway I can get more info about this error? This is my code... in program.cs... AppDomain.CurrentDomain.UnhandledException += new UnhandledExceptionEventHandler(CurrentDomain_UnhandledException); static void CurrentDomain_UnhandledException(object sender, UnhandledExceptionEventArgs e) { try { Exception _ex = (Exception)e.ExceptionObject; //the stact trace property is empty here.. } finally { Application.Exit(); } } My DLL... [DllImport("AutoSearchDevice.dll", EntryPoint = "Start", ExactSpelling = false, CallingConvention = CallingConvention.StdCall)] public static extern int Start(int ASD_HANDLE); An I call it like so: public static void AutoSearchStart() { try { Start(m_pASD); } catch (Exception ex) { } }

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  • how to merge file lines having the same first word in python?

    - by user1377135
    I have written a program to merge lines in a file containing the same first word in python. However I am unable to get the desired output. Can anyone please suggest me the mistake in my program? input "file.txt" line1: a b c line2: a b1 c1 line3: d e f line4: i j k line5: i s t line6: i m n ` output a b c a b1 c1 d e f i j k i s t i m n my code a = [line.split() for line in open('file.txt')] L=[] for i in range(0,len(a)): j=i while True: if a[j][0] == a[j+1][0]: L.append(a[j]) L.append(a[j+1]) j=j+2 else: print a[i] print L break

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  • P-NP-Problem: What are the most promising methods?

    - by phimuemue
    Hello everybody, I know that P=NP has not been solved up to now, but can anybody tell me something about the following: What are currently the most promising mathematical / computer scientific methods that could be helpful to tackle this problem? Or are there even none such methods known to be potentially helpful up to now? Is there any (free) compendium on this topic where I can find all / most of the research done in this area?

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  • x509 certificate Information

    - by sid
    Certificate: Data: Version: 3 (0x2) Serial Number: 95 (0x5f) Signature Algorithm: sha1WithRSAEncryption Issuer: C=, O=, CN= Validity Not Before: Apr 22 16:42:11 2008 GMT Not After : Apr 22 16:42:11 2009 GMT Subject: C=, O=, CN=, L=, ST= Subject Public Key Info: Public Key Algorithm: rsaEncryption RSA Public Key: (1024 bit) Modulus (1024 bit): ... ... ... Exponent: 65537 (0x10001) X509v3 extensions: X509v3 Key Usage: critical Digital Signature, Key Encipherment X509v3 Extended Key Usage: critical Code Signing X509v3 Authority Key Identifier: keyid: ... Signature Algorithm: sha1WithRSAEncryption a9:55:56:9b:9e:60:7a:57:fd:7:6b:1e:c0:79:1c:50:62:8f: ... ... -----BEGIN CERTIFICATE----- ... ... ... -----END CERTIFICATE----- In This Certificate, Which is the public key? is Modulus? what does the Signature Algorithm, a9:55:56:... represent (is it message digest)? And what is between -----BEGIN CERTIFICATE----- & -----END CERTIFICATE-----, is That the whole certificate? As I am novice, little bit confusing between the message digest and public key? Thanks in Advance-opensid

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  • What is the best way to implement this composite GetHashCode()

    - by Frank Krueger
    I have a simple class: public class TileName { int Zoom, X, Y; public override bool Equals (object obj) { var o = obj as TileName; return (o != null) && (o.Zoom == Zoom) && (o.X == X) && (o.Y == Y); } public override int GetHashCode () { return (Zoom + X + Y).GetHashCode(); } } I was curious if I would get a better distribution of hash codes if I instead did something like: public override int GetHashCode () { return Zoom.GetHashCode() + X.GetHashCode() + Y.GetHashCode(); } This class is going to be used as a Dictionary key, so I do want to make sure there is a decent distribution.

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  • update table with information from IDirectory

    - by sue
    I have a table with 4 columns, LoginID, LastName, FirstName, Email. The data for LoginID was populated from an other table. I have to write a small routine to update this table, by sending in the LoginID and with help of IDirectory routines, get the Lastname, firstname and email. This is what i'm attempting to do, but getting confused with the right syntax. using (TSADRequestEntities context = UnityHelper.Resolve()) { var fpvalues = context.FOCALPOINTs.ToList(); foreach (var item in fpvalues) { IEnumerable<UserInfo> query = UnityHelper.Resolve<IUserDirectory>().Search(item.LoginID); //Here, FocalPoint is the table that has the loginID and the other fields //I need to update. the query shld now hv info on lastname etc..how do I //retrieve that value and update the table? } }

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  • Creating a Web Service to automatically get information

    - by Sean P
    I want to create some sort of method of creating a web service that will run automatically and run DB queries and some API calls which will then store data that I can use/call without taking the processing or time penalty of doing it every time a user access my web service. Is this possible? If so, point me in the right direction on how to implement something like this Using vb.net and ASP.net Thanks in advance!!

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  • VB.NET Get Assembly Version information

    - by Berlioz
    How do I get my .NET Winforms app 2.0 to automatically update it's publish revision integer subsequent to issuing the publish command from within VS08. Trying to use the following C# as a guide object[] attrs = System.Reflection.Assembly.GetEntryAssembly().GetCustomAttributes(true); foreach (object o in attrs) if (o.GetType() == typeof(System.Reflection.AssemblyFileVersionAttribute)) label1.Text = ((System.Reflection.AssemblyFileVersionAttribute) o).Version;

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  • Are .NET's regular expressions Turing complete?

    - by Robert
    Regular expressions are often pointed to as the classical example of a language that is not Turning complete. For example "regular expressions" is given in as the answer to this SO question looking for languages that are not Turing complete. In my, perhaps somewhat basic, understanding of the notion of Turning completeness, this means that regular expressions cannot be used check for patterns that are "balanced". Balanced meaning have an equal number of opening characters as closing characters. This is because to do this would require you to have some kind of state, to allow you to match the opening and closing characters. However the .NET implementation of regular expressions introduces the notion of a balanced group. This construct is designed to let you backtrack and see if a previous group was matched. This means that a .NET regular expressions: ^(?<p>a)*(?<-p>b)*(?(p)(?!))$ Could match a pattern that: ab aabb aaabbb aaaabbbb ... etc. ... Does this means .NET's regular expressions are Turing complete? Or are there other things that are missing that would be required for the language to be Turing complete?

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  • Android: Constructing a triangle based on Geographical information

    - by Aidan
    Hi Guys, I'm constructing a geolocation based application and I'm trying to figure out a way to make my application realise when a user is facing the direction of the given location (a particular long / lat co-ord). I've got the math figured, I just have the triangle to construct. Here's a further clarification of what I want to do.. I just want to know is there a way to get java to construct 2 other co-ordinates based on my orientation in relation to true north and my current co-ordinate? I'd like to construct a tri-angle, 45 degrees out each way of my current location (one of the points) and 1 kilometer in that direction. The problem is I don't know how to make Android/Java recognise that I want to find that point in the direction I'm currently facing.. Anyone got any ideas?

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  • Approximate timings for various operations on a "typical desktop PC" anno 2010

    - by knorv
    In the article "Teach Yourself Programming in Ten Years" Peter Norvig (Director of Research, Google) gives the following approximate timings for various operations on a typical 1GHz PC back in 2001: execute single instruction = 1 nanosec = (1/1,000,000,000) sec fetch word from L1 cache memory = 2 nanosec fetch word from main memory = 10 nanosec fetch word from consecutive disk location = 200 nanosec fetch word from new disk location (seek) = 8,000,000 nanosec = 8 millisec What would the corresponding timings be for your definition of a typical PC desktop anno 2010?

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  • Ship maritime AIS information API

    - by James Cadd
    Is there an API or Web Service that can be used to read AIS data? Most links I read starting at Wikipedia (http://en.wikipedia.org/wiki/Automatic_Identification_System) say that AIS data is freely available but I'm having a hard time finding a provider of the data. A C# example or language agnostic web service would be helpful.

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  • Log information inside a JUnit Suite

    - by Alex Marinescu
    I'm currently trying to write inside a log file the total number of failed tests from a JUnite Suite. My testsuite is defined as follows: @RunWith(Suite.class) @SuiteClasses({Class1.class, Class2.class etc.}) public class SimpleTestSuite {} I tried to define a rule which would increase the total number of errors when a test fails, but apparently my rule is never called. @Rule public MethodRule logWatchRule = new TestWatchman() { public void failed(Throwable e, FrameworkMethod method) { errors += 1; } public void succeeded(FrameworkMethod method) { } }; Any ideas on what I should to do to achieve this behaviour?

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  • Rails - session information being cleared?

    - by Jty.tan
    Hi! I'm having a weird issue that I can't track down... For context, I have resources of Users, Registries, and Giftlines. Each User has many Registries. Each Registry has many Giftlines. It's a belongs to association for them in a reverse manner. What is basically happening, is that when I am creating a giftline, the giftline itself is created properly, and linked to its associated Registry properly, but then in the process of being redirected back to the Registry show page, the session[:user_id] variable is cleared and I'm logged out. As far as I can tell, where it goes wrong is here in the registries_controller: def show @registry = Registry.find(params[:id]) @user = User.find(@registry.user_id) if (params[:user_id] && (@user.login != params[:user_id]) ) flash[:notice] = "User #{params[:user_id]} does not have such a registry." redirect_to user_registries_path(session[:user_id]) end end Now, to be clear, I can do a show of the registry normally, and nothing weird happens. It's only when I've added a giftline does the session[:user_id] variable get cleared. I used the debugger and this is what seems to be happening. (rdb:19) list [20, 29] in /Users/kriston/Dropbox/ruby_apps/bee_registered/app/controllers/registries_controller.rb 20 render :action => 'new' 21 end 22 end 23 24 def show => 25 @registry = Registry.find(params[:id]) 26 @user = User.find(@registry.user_id) 27 if (params[:user_id] && (@user.login != params[:user_id]) ) 28 flash[:notice] = "User #{params[:user_id]} does not have such a registry." 29 redirect_to user_registries_path(session[:user_id]) (rdb:19) session[:user_id] "tester" (rdb:19) So from there we can see that the code has gotten back to the show command after the item had been added, and that the session[:user_id] variable is still set. (rdb:19) list [22, 31] in /Users/kriston/Dropbox/ruby_apps/bee_registered/app/controllers/registries_controller.rb 22 end 23 24 def show 25 @registry = Registry.find(params[:id]) 26 @user = User.find(@registry.user_id) => 27 if (params[:user_id] && (@user.login != params[:user_id]) ) 28 flash[:notice] = "User #{params[:user_id]} does not have such a registry." 29 redirect_to user_registries_path(session[:user_id]) 30 end 31 end (rdb:19) session[:user_id] "tester" (rdb:19) Stepping on, we get to this point. And the session[:user_id] is still set. At this point, the URL is of the format localhost:3000/registries/:id, so params[:user_id] fails, and the if condition doesn't occur. (Unless I am completely wrong .<) So then the next bit occurs, which is (rdb:19) list [1327, 1336] in /Library/Ruby/Gems/1.8/gems/actionpack-2.3.5/lib/action_controller/base.rb 1327 end 1328 1329 def perform_action 1330 if action_methods.include?(action_name) 1331 send(action_name) => 1332 default_render unless performed? 1333 elsif respond_to? :method_missing 1334 method_missing action_name 1335 default_render unless performed? 1336 else (rdb:19) session[:user_id] "tester" And then when I hit next... (rdb:19) next 2: session[:user_id] = /Library/Ruby/Gems/1.8/gems/actionpack-2.3.5/lib/action_controller/filters.rb:618 return index if nesting != 0 || aborted (rdb:19) list [613, 622] in /Library/Ruby/Gems/1.8/gems/actionpack-2.3.5/lib/action_controller/filters.rb 613 private 614 def call_filters(chain, index, nesting) 615 index = run_before_filters(chain, index, nesting) 616 aborted = @before_filter_chain_aborted 617 perform_action_without_filters unless performed? || aborted => 618 return index if nesting != 0 || aborted 619 run_after_filters(chain, index) 620 end 621 622 def run_before_filters(chain, index, nesting) (rdb:19) session {:user_id=>nil, :session_id=>"49992cdf2ddc708b441807f998af7ddc", :return_to=>"/registries", "flash"=>{}, :_csrf_token=>"xMDI0oDaOgbzhQhDG7EqOlGlxwIhHlB6c71fWgOIKcs="} The session[:user_id] is cleared, and when the page renders, I'm logged out. .< Sooo.... Any idea why this is occurring? It just occurred to me that I'm not sure if I'm meant to be pasting large chunks of debug output in here... Somebody point out to me if I'm not meant to be doing this. . And yes, this only occurs when I have added a giftitem, and it is sending me back to the registry page. When I'm viewing it, the same code occurs, but the session[:user_id] variable isn't cleared. It's driving me mildly insane. Thanks!

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  • how to check the login information for remote website with jQuery

    - by alhoseany
    hi, i have a form with 2 fields username: password: and a submit button. the user will enter his username and password for a remote website(not my website or my domain. eg. Gmail.com). i want once he click the submit button.a jQuery script check these login info on gmail.com and return back the result.they are wrong or working logins. and notify the user if it is wrong logins but if it is good working login info the form will submit. i don't know much jQuery but i am good with php. my search find that in order to do that i need to make cross-domain scripting by using php proxy between my jQuery script and the remote domain. i found also the simple php proxy. which looks great.but i dont know how to make the jQuery thing that connects all this together.

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  • SQL Query - 20mil records - Best practice to return information

    - by eqiz
    I have a SQL database that has the following table: Table: PhoneRecords ID(identity Seed) FirstName LastName PhoneNumber ZipCode Very simple straight forward table. This table has over 20million records. I am looking for the best way to do queries that pull out records based off area codes from the table. For instance here is an example query that I have done. SELECT phonenumber, firstname FROM [PhoneRecords] WHERE (phone LIKE '2012042%') OR (phone LIKE '2012046%') OR (phone LIKE '2012047%') OR (phone LIKE '2012083%') OR (phone LIKE '2012088%') OR (phone LIKE '2012841%') As you can see this is an ugly query, but it would get the job done (if I wasn't running into timeout issues) Can anyone tell me the best way for speed/optimization to do the above query to display the results? Currently that query above takes around 2 hours to complete on a 9gb 1600mhz ram, i7 930 quadcore OC'd 4.01ghz. I obviously have the computer power required to do such a query, but still takes too long for queries.

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  • Learning networking fundamentals

    - by bplus
    Not having a CS degree has left large holes in my programming related knowledge. In particular I'd really like to learn some of the computer networking stuff I would have got in a good CS degree. The problem I really have is "not knowing what I don't know". So far I know I don't know anything about the following (as far as computer networks are concearned) -sockets -ports -internet protocol (the whole IP stack I keep hearing about). Can anyone add more to the list? Can anyone suggest a project (writing a toy web server?) Thanks in advance

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  • Generate xml containing animation information from ms ppt 2003/07 file

    - by Ravisha
    I am planning to write an application which has UI from MS ppt.Here is where all the animation will be configured. My application will just read xmls containing animation configuration and run it on a target device(Cannot mention details w.r.t device right now ,apologies for that) Not necessary that i want xmls it self but if there is a way to get animation details directly from the ppt file i will be more than happy. I will be going ahead with C#.Net 3.0 with windows XP as my OS.MY office will be either 2003 or 07.Can switch to any of these versions Please give suggestions as what will be the starting point for the same.Thanks in advance Please Let me know if any more details are needed

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