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  • How to store data in mysql, to get the fastest performance?

    - by Oden
    Hey, I'm thinking about it, witch of the following two query types would give me the fastest performance for a user messaging module inside my site: The first one i thought about is a multi table setup, witch has a connection table, and a main table. The connection table holds the connection between accounts, and the messaging table. In this case a query would look like following, to get some data of the author, and the messages he has sent: SELECT m.*, a.username FROM messages AS m LEFT JOIN connection_table ON (message_id = m.id) LEFT JOIN accounts AS a ON (account_id = a.id) WHERE m.id = '32341' Inserting into it is a little bit more "complicated". My other idea, and in my thought the better solution of this problem is that i store the data i would use in a connection table in the same table where is store the data of the mail. Sounds like i would get lots of duplicated entries, but no, because i have a field witch has text type and holds user ids like this: *24*32*249* If I want to query them, i use the mysql LIKE method. Deleting is an other problem, but for this i have one more field where i store who has deleted the post. Sad about that i don't know how to join this. So what would you recommend? Are there other ways?

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  • Machine leaning algorithm for data classification.

    - by twk
    Hi all, I'm looking for some guidance about which techniques/algorithms I should research to solve the following problem. I've currently got an algorithm that clusters similar-sounding mp3s using acoustic fingerprinting. In each cluster, I have all the different metadata (song/artist/album) for each file. For that cluster, I'd like to pick the "best" song/artist/album metadata that matches an existing row in my database, or if there is no best match, decide to insert a new row. For a cluster, there is generally some correct metadata, but individual files have many types of problems: Artist/songs are completely misnamed, or just slightly mispelled the artist/song/album is missing, but the rest of the information is there the song is actually a live recording, but only some of the files in the cluster are labeled as such. there may be very little metadata, in some cases just the file name, which might be artist - song.mp3, or artist - album - song.mp3, or another variation A simple voting algorithm works fairly well, but I'd like to have something I can train on a large set of data that might pick up more nuances than what I've got right now. Any links to papers or similar projects would be greatly appreciated. Thanks!

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  • Application Design: Single vs. Multiple Hits to the DB

    - by shyneman
    I'm building a service that performs a set of configured activities based on the type of request that it receives. Each activity involves going to the database and retrieving/updating some kind of information. The logic for each activity can be generalized and re-used across different request types. The activities may need to participate in a transaction for the duration of the servicing the request. One option, I'm considering is having each activity maintain its own access to DAL/database. This fully encapsulates the activity into a stand-alone re-usable piece, but hitting the database multiple times for one request doesn't seem like a viable option. I don't really know how to easily implement the concept of a transaction across the multiple activities here either. The second option is to encapsulate ALL the activities into one big activity and hit the database once. But this does not allow re-use and configuration of these activities for different requests. Does anyone have any suggestions and input about what should be the best way to approach my problem? Thanks for any help.

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  • Facebook Stream.Get -- How to access data in array?

    - by user316841
    On stream.get, I try to echo $feeds["posts"][$i]["attachment"]["href"]; It return the URL, but, in the same array scope where "type" is located (which returns string: video, etc), trying $feeds["posts"][$i]["attachment"]["type"] returns nothing at all! Here's an array through PHP's var_dump: http://pastie.org/930475 So, from testing I suppose this is protected by Facebook? Does that makes sense at all? Here it's full: http://pastie.org/930490, but not all attachment/media/types has values. It's also strange, because I can't access through [attachment][media][href] or [attachment][media][type], and if I try [attachment][media][0][type] or href, it gives me a string offset error. ["attachment"]=> array(8) { ["media"]=> array(1) { [0]=> array(5) { ["href"]=> string(55) "http://www.facebook.com/video/video.php?v=1392999461587" ["alt"]=> string(13) "IN THE STUDIO" ["type"]=> string(5) "video" My question is, is this protected by Facebook? Or we can actually access this array position?

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  • Problem in filtering records using Dataview (C#3.0)

    - by Newbie
    I have a data table . The data table is basically getting populated from excel sheet. And there are many excel sheets. Henceforth, I have written a utility method for accomplishing the same. Now in some of the excel sheets, there are date columns and in some it is not(only text/string). My function is populating the values properly into the datatable from the excell sheet. But there are many blank rows in the excel sheets some are filled with NULL , some with " ". So I need to filter those records (which are NULL or " " ) first before further processing. What I am after is to use a dataview and apply the filter over there. DataView dv = dataTable.DefaultView; dv.RowFilter = ColumnName + " <> ''"; Well by using metedata (GetOleDbSchemaTable(OleDbSchemaGuid.Columns, restrection)) I was able to get the column names from the excel sheet , so getting the column names is not an issue. But the problem is as I said in some Excel sheet there are date fileds some are not. So the Filter condition of the Dataview needs to be proper. If I apply the above logic, and if it encounters a Datafield, it is throwing error Cannot perform '<' operation on System.DateTime and System.String. Could you people please help me out? I need to filter columns(not known at compile time + their data types) which can have NULL and " " I am using C#3.0 Thanks

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  • Why does first call to java.io.File.createTempFile(String,String,File) take 5 seconds on Citrix?

    - by Ben Roling
    While debugging slow startup of an Eclipse RCP app on a Citrix server, I came to find out that java.io.createTempFile(String,String,File) is taking 5 seconds. It does this only on the first execution and only for certain user accounts. Specifically, I am noticing it Citrix anonymous user accounts. I have not tried many other types of accounts, but this behavior is not exhibited with an administrator account. Also, it does not matter if the user has access to write to the given directory or not. If the user does not have access, the call will take 5 seconds to fail. If they do have access, the call with take 5 seconds to succeed. This is on a Windows 2003 Server. I've tried Sun's 1.6.0_16 and 1.6.0_19 JREs and see the same behavior. I googled a bit expecting this to be some sort of known issue, but didn't find anything. It seems like someone else would have had to have run into this before. The Eclipse Platform uses File.createTempFile() to test various directories to see if they are writeable during initialization and this issue adds 5 seconds to the startup time of our application. I imagine somebody has run into this before and might have some insight. Here is sample code I executed to see that it is indeed this call that is consuming the time. I also tried it with a second call to createTempFile and notice that subsequent calls return nearly instantaneously. public static void main(final String[] args) throws IOException { final File directory = new File(args[0]); final long startTime = System.currentTimeMillis(); File file = null; try { file = File.createTempFile("prefix", "suffix", directory); System.out.println(file.getAbsolutePath()); } finally { System.out.println(System.currentTimeMillis() - startTime); if (file != null) { file.delete(); } } } Sample output of this program is the following: C:\java.exe -jar filetest.jar C:/Temp C:\Temp\prefix8098550723198856667suffix 5093

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  • Enumerating pixel formats for adaptors and modes with OpenGL

    - by Robinson
    I'm trying to code an OpenGL path for my 3D engine. The D3D path enumerates all device adaptors, all modes (by mode I mean bit depth, dimensions, available windowed, and refresh rate) for each adaptor and then all pixel formats available for the given mode and adaptor, along side certain useful caps (shader version, filter types, etc.). So, I have broadly got the following protected functions in the class: // Enumerate all back/front buffer combinations. virtual void EnumerateBackFrontBufferCombinations(CComPtr<IDirect3D9>& d3d9); // Enumerate all depth/stencil formats. virtual void EnumerateDepthStencilFormats(CComPtr<IDirect3D9>& d3d9); // Enumerate all multi-sample formats. virtual void EnumerateMultiSampleTypes(CComPtr<IDirect3D9>& d3d9); // Enumerate all device formats, i.e. dynamic, static, render target, etc. virtual void EnumerateMapFormats(CComPtr<IDirect3D9>& d3d9); // Enumerate all capabilities. virtual void EnumerateCapabilities(CComPtr<IDirect3D9>& d3d9); The adaptors are enumerated with EnumDisplayDevices, the modes (resolutions and refresh rates) are enumerated with EnumDisplaySettings, so this can be done for either GL or D3D. The other functions I'm not so sure about with OpenGL. What are the equivalents to the IDirect3D9's CheckDeviceType, CheckDeviceFormat, CheckDeviceMultiSampleType, CheckDepthStencilMatch? I know I can use DescribePixelFormat, given a DC, but you kind-of need to have created the window before you can use a DC with it, but you can't create the window correctly until you know what formats you're going to use. Any tips you can give me? Thanks.

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  • How to create a generic C free function .

    - by nomemory
    I have some C structures related to a 'list' data structure. They look like this. struct nmlist_element_s { void *data; struct nmlist_element_s *next; }; typedef struct nmlist_element_s nmlist_element; struct nmlist_s { void (*destructor)(void *data); int (*cmp)(const void *e1, const void *e2); unsigned int size; nmlist_element *head; nmlist_element *tail; }; typedef struct nmlist_s nmlist; This way I can have different data types being hold in "nmlist_element-data" . The "constructor" (in terms of OOP) has the following signature: nmlist *nmlist_alloc(void (*destructor)(void *data)); Where "destructor" is specific function that de-allocated "data" (being hold by the nmlist_element). If I want to have a list containing integers as data, my "destructor" would like this: void int_destructor(void *data) { free((int*)data); } Still i find it rather "unfriendly" for me to write a destructor functions for every simple primitive data type. So is there a trick to write something like this ? (for primitives): void "x"_destructor(void *data, "x") { free(("x" *)data); } PS: I am not a macro fan myself, and in my short experience regarding C, i don't use them, unless necessary.

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  • Static files in (Java) App Engine not accessible.

    - by fiXedd
    The example documentation says that you simply need to place your files in war/ (or a subdirectory) and they should be accessible from the host (as long as they aren't JSPs or in WEB-INF). For example, if you place foo.css in war/ then you should be able to access it at http://localhost:8080/foo.css. However, this isn't working for me at all. NONE of my static files are accessible. The docs on appengine-web.xml say that you can also specifically denote certain types as static. I've tried this as well and it makes no difference. Am I missing something obvious? UPDATE: Turns out one of the mappings in my web.xml was a little too aggressive. The following was the culprit: <servlet> <servlet-name>Main</servlet-name> <servlet-class>MainServlet</servlet-class> </servlet> <servlet-mapping> <servlet-name>Main</servlet-name> <url-pattern>/</url-pattern> </servlet-mapping> It seems that it was grabbing everything that wasn't grabbed be one of the other rules, which I don't understand because there was no * on the end of the url-pattern. It also seems to be directly contradictory to the documentation that says: Note: Static files, files that are served verbatim to users such as images, CSS or JavaScript, are handled separately from paths mentioned in the deployment descriptor. A request for a URL path that matches a path to a file in the WAR that's considered a static file will serve the file, regardless of servlet and filter mappings in the deployment descriptor. You can exclude files from those treated as static files using the appengine-web.xml file. So, how can I have a rule that matches the base of my domain (eg. http://www.example.com/) and still allows the static files to filter through?

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  • How can I use a single-table inheritance and single controller to make this more DRY?

    - by Angela
    I have three models, Calls, Emails, and Letters and those are basically templates of what gets sent to individuals, modeled as Contacts. When a Call is made, a row in model in ContactCalls gets created. If an Email is sent, an entry in ContactEmails is made. Each has its own controller: contact_calls_controller.rb and contact_emails_controller.rb. I would like to create a single table inheritance called ContactEvents which has types Calls, Emails, and Letters. But I'm not clear how I pass the type information or how to consolidate the controllers. Here's the two controllers I have, as you can see, there's alot of duplication, but some differences that needs to be preserved. In the case of letter and postcards (another Model), it's even more so. class ContactEmailsController < ApplicationController def new @contact_email = ContactEmail.new @contact_email.contact_id = params[:contact] @contact_email.email_id = params[:email] @contact = Contact.find(params[:contact]) @company = Company.find(@contact.company_id) contacts = @company.contacts.collect(&:full_name) contacts.each do |contact| @colleagues = contacts.reject{ |c| [email protected]_name } end @email = Email.find(@contact_email.email_id) @contact_email.subject = @email.subject @contact_email.body = @email.message @email.message.gsub!("{FirstName}", @contact.first_name) @email.message.gsub!("{Company}", @contact.company_name) @email.message.gsub!("{Colleagues}", @colleagues.to_sentence) @email.message.gsub!("{NextWeek}", (Date.today + 7.days).strftime("%A, %B %d")) @contact_email.status = "sent" end def create @contact_email = ContactEmail.new(params[:contact_email]) @contact = Contact.find_by_id(@contact_email.contact_id) @email = Email.find_by_id(@contact_email.email_id) if @contact_email.save flash[:notice] = "Successfully created contact email." # send email using class in outbound_mailer.rb OutboundMailer.deliver_campaign_email(@contact,@contact_email) redirect_to todo_url else render :action => 'new' end end AND: class ContactCallsController < ApplicationController def new @contact_call = ContactCall.new @contact_call.contact_id = params[:contact] @contact_call.call_id = params[:call] @contact_call.status = params[:status] @contact = Contact.find(params[:contact]) @company = Company.find(@contact.company_id) @contact = Contact.find(@contact_call.contact_id) @call = Call.find(@contact_call.call_id) @contact_call.title = @call.title contacts = @company.contacts.collect(&:full_name) contacts.each do |contact| @colleagues = contacts.reject{ |c| [email protected]_name } end @contact_call.script = @call.script @call.script.gsub!("{FirstName}", @contact.first_name) @call.script.gsub!("{Company}", @contact.company_name ) @call.script.gsub!("{Colleagues}", @colleagues.to_sentence) end def create @contact_call = ContactCall.new(params[:contact_call]) if @contact_call.save flash[:notice] = "Successfully created contact call." redirect_to contact_path(@contact_call.contact_id) else render :action => 'new' end end

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  • How to test if a doctrine records has any relations that are used

    - by murze
    Hi, I'm using a doctrine table that has several optional relations (of types Doctrine_Relation_Association and Doctrine_Relation_ForeignKey) with other tables. How can I test if a record from that table has connections with records from the related table. Here is an example to make my question more clear. Assume that you have a User and a user has a many to many relation with Usergroups and a User can have one Userrole How can I test if a give user is part of any Usergroups or has a role. The solution starts I believe with $relations = Doctrine_Core::getTable('User')->getRelations(); $user = Doctrine_Core::getTable('User')->findOne(1); foreach($relations as $relation) { //here should go a test if the user has a related record for this relation if ($relation instanceof Doctrine_Relation_Association) { //here the related table probably has more then one foreign key (ex. user_id and group_id) } if ($relation instanceof Doctrine_Relation_ForeignKey) { //here the related table probably has the primary key of this table (id) as a foreign key (user_id) } } //true or false echo $result I'm looking for a general solution that will work no matter how many relations there are between user and other tables. Thanks!

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  • Silverlight vs Flex

    - by 1kevgriff
    My company develops several types of applications. A lot of our business comes from doing multimedia-type apps, typically done in Flash. However, now that side of the house is starting to migrate towards doing Flex development. Most of our other development is done using .NET. I'm trying to make a push towards doing Silverlight development instead, since it would take better advantage of the .NET developers on staff. I prefer the Silverlight platform over the Flex platform for the simple fact that Silverlight is all .NET code. We have more .NET developers on staff than Flash/Flex developers, and most of our Flash/Flex developers are graphic artists (not real programmers). Only reason they push towards Flex right now is because it seems like the logical step from Flash. I've done development using both, and I honestly believe Silverlight is easier to work with. But I'm trying to convince people who are only Flash developers. So here's my question: If I'm going to go into a meeting to praise Silverlight, why would a company want to go with Silverlight instead of Flex? Other than the obvious "not everyone has Silverlight", what are the pros and cons for each?

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  • REST API - why use PUT DELETE POST GET?

    - by Andre
    So -i was looking through some articles on creating REST API's. And some of them suggest using all types of HTTP requests: like PUT DELETE POST GET. So - we would create for example index.php and write API this way: $method = $_SERVER['REQUEST_METHOD']; $request = split("/", substr(@$_SERVER['PATH_INFO'], 1)); switch ($method) { case 'PUT': ....some put action.... break; case 'POST': ....some post action.... break; case 'GET': ....some get action.... break; case 'DELETE': ....some delete action.... break; } Ok - granted - I don't know much baout web services (yet). But - wouldn't it be easier to just accept JSON object through normal $_POST and then respond in JSON as well. We can easily serialize/deserialize via php's json_encode and json_decode and do whatever we want with that data without having to deal with different HTTP request methods... Am I missing something? UPDATE 1: Ok - after digging through various API's and learning a lot about XML-RPC, JSON-RPC, SOAP, REST I came to a conclusion that this type of API is sound. Actually stack exchange is pretty much using this approach on their sites and I do think that these people know what they are doing Stack Exchange API.

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  • PHP - upload.class image and $_FILES

    - by Ockonal
    Hello, I'm using class.upload.php to upload pictures onto the server. Here is my form: <form action="<?="http://".$_SERVER['SERVER_NAME'].$_SERVER['REQUEST_URI'];?>" method="post" enctype="multipart/form-data"> <table style="width: 100%; padding-top: 20px;"> <tr> <td>Image file:</td> <td><input type="file" name="image_file" /></td> </tr> <tr> <td>&nbsp;</td> <td align="right"><input type="submit" name="add_new" value="Add image" /><td></td> </tr> </table> </form> In php code I do: if( array_key_exists('add_new', $_POST) ) { echo 'add new is in array'; echo '<pre>'; print_r($_POST); print_r($_FILES); echo '</pre>'; $handle = new Upload($_FILES['image_file']); ... } Here is an output of print_r: Array ( [image_file] => somefile.png [add_new] => Add image ) Array ( ) As you can see second array is empty ($_FILES), so image doesn't upload. Why? operating system : Linux PHP version : 5.2.12 GD version : 2.0.34 supported image types : png jpg gif bmp open_basedir : /home/httpd/vhosts/kz-gbi.ru/httpdocs:/tmp

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  • Visual Studio breaks, and steps, but sometimes steps out

    - by James Wilkins
    Something very odd is going on. It's been going on for some time, but I've just ignored it up to now. I have both a Silverlight and WCF service in my solution, which shares .CS file between them (one project has a link to the file, which exists in the other project). While debugging the Silverlight app, pressing the F10 key steps through code as normal, and when I get to a method call which exists in the shared file (between the projects), and Press F11, it simply skips the method instead of stepping into it (and yes, the "Just My Code" option is not checked). If I put a breakpoint in the method I'm trying to get into, it works fine (as in the debugger will break on the line), but as soon as I step (F10) it exits the method (and with F11 [step into] also). Ok, on first thought, you might think it's to do with the link, but no, it isn't. I tried removing the link and using a copy instead, but the same thing happens. And no, it's not the debug symbols, I looked into that already. The method I'm trying to step through is static, and is in a non-static partial class, in a file shared by both projects. My guess: The same types and static methods exist in the WCF and Silverlight ... would the debugger get confused?

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  • Full-text search in C++

    - by Jen
    I have a database of many (though relatively short) HTML documents. I want users to be able to search this database by entering one or more search words in a C++ desktop application. Hence, I’m looking for a fast full-text search solution. Ideally, it should: Skip common words, such as the, of, and, etc. Support stemming, i.e. search for run also finds documents containing runner, running and ran. Be able to update its index in the background as new documents are added to the database. Be able to provide search word suggestions (like Google Suggest) To illustrate, assume the database has just two documents: Document 1: This is a test of text search. Document 2: Testing is fun. The following words should be in the index: fun, search, test, testing, text. If the user types t in the search box, I want the application to be able to suggest test, testing and text (Ideally, the application should be able to query the search engine for the 10 most common search words starting with t). A search for testing should return both documents. Can you suggest a C or C++ based solution? (I’ve briefly reviewed CLucene and Xapian, but I’m not sure if either will address my needs, especially querying the search word indexes for the suggest feature).

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  • OO model for nsxmlparser when delegate is not self

    - by richard
    Hi, I am struggling with the correct design for the delegates of nsxmlparser. In order to build my table of Foos, I need to make two types of webservice calls; one for the whole table and one for each row. It's essentially a master-query then detail-query, except the master-query-result-xml doesn't return enough information so i then need to query the detail for each row. I'm not dealing with enormous amounts of data. Anyway - previously I've just used NSXMLParser *parser = [[NSXMLParser alloc]init]; [parser setDelegate:self]; [parser parse]; and implemented all the appropriate delegate methods in whatever class i'm in. In attempt at cleanliness, I've now created two separate delegate classes and done something like: NSXMLParser *xp = [[NSXMLParser alloc]init]; MyMasterXMLParserDelegate *masterParserDelegate = [[MyMasterXMLParser]alloc]init]; [xp setDelegate:masterParserDelegate]; [xp parse]; In addition to being cleaner (in my opinion, at least), it also means each of the -parser:didStartElement implementations don't spend most of the time trying to figure out which xml they're parsing. So now the real crux of the problem. Before i split out the delegates, i had in the main class that was also implementing the delegate methods, a class-level NSMutableArray that I would just put my objects-created-from-xml in when -parser:didEndElement found the 'end' of each record. Now the delegates are in separate classes, I can't figure out how to have the -parser:didEndElement in the 'detail' delegate class "return" the created object to the calling class. At least, not in a clean OO way. I'm sure i could do it with all sorts of nasty class methods. Does the question make sense? Thanks.

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  • Help me clean up this crazy lambda with the out keyword

    - by Sarah Vessels
    My code looks ugly, and I know there's got to be a better way of doing what I'm doing: private delegate string doStuff( PasswordEncrypter encrypter, RSAPublicKey publicKey, string privateKey, out string salt ); private bool tryEncryptPassword( doStuff encryptPassword, out string errorMessage ) { ...get some variables... string encryptedPassword = encryptPassword(encrypter, publicKey, privateKey, out salt); ... } This stuff so far doesn't bother me. It's how I'm calling tryEncryptPassword that looks so ugly, and has duplication because I call it from two methods: public bool method1(out string errorMessage) { string rawPassword = "foo"; return tryEncryptPassword( (PasswordEncrypter encrypter, RSAPublicKey publicKey, string privateKey, out string salt) => encrypter.EncryptPasswordAndDoStuff( // Overload 1 rawPassword, publicKey, privateKey, out salt ), out errorMessage ); } public bool method2(SecureString unencryptedPassword, out string errorMessage) { return tryEncryptPassword( (PasswordEncrypter encrypter, RSAPublicKey publicKey, string privateKey, out string salt) => encrypter.EncryptPasswordAndDoStuff( // Overload 2 unencryptedPassword, publicKey, privateKey, out salt ), out errorMessage ); } Two parts to the ugliness: I have to explicitly list all the parameter types in the lambda expression because of the single out parameter. The two overloads of EncryptPasswordAndDoStuff take all the same parameters except for the first parameter, which can either be a string or a SecureString. So method1 and method2 are pretty much identical, they just call different overloads of EncryptPasswordAndDoStuff. Any suggestions? Edit: if I apply Jeff's suggestions, I do the following call in method1: return tryEncryptPassword( (encrypter, publicKey, privateKey) => { var result = new EncryptionResult(); string salt; result.EncryptedValue = encrypter.EncryptPasswordAndDoStuff( rawPassword, publicKey, privateKey, out salt ); result.Salt = salt; return result; }, out errorMessage ); Much the same call is made in method2, just with a different first value to EncryptPasswordAndDoStuff. This is an improvement, but it still seems like a lot of duplicated code.

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  • Good data structure for efficient insert/querying on arbitrary properties

    - by Juliet
    I'm working on a project where Arrays are the default data structure for everything, and every query is a linear search in the form of: Need a customer with a particular name? customer.Find(x => x.Name == name) Need a customer with a particular unique id? customer.Find(x => x.Id == id) Need a customer of a particular type and age? customer.Find(x => x is PreferredCustomer && x.Age >= age) Need a customer of a particular name and age? customer.Find(x => x.Name == name && x.Age == age) In almost all instances, the criteria for lookups is well-defined. For example, we only search for customers by one or more of the properties Id, Type, Name, or Age. We rarely search by anything else. Is a good data structure to support arbitrary queries of these types with lookup better than O(n)? Any out-of-the-box implementations for .NET?

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  • Properly populating tables in an Object Relational database

    - by chaosTechnician
    I've got a homework assignment that requires that I use Oracle 10g Express to implement an Object Relational database to track phone billing data. I have a superclass of Communications with subclasses of Call, Text, and Data. I'm hitting a snag with properly populating these tables so that I can find the appropriate data in the various tables. My Types and Tables are declared as such: create type CommunicationType as object ( -- column names here ) not final; create type CallType under CommunicationType ( -- column names here ); create type TextType under CommunicationType ( -- column names here ); create type DataType under CommunicationType ( -- column names here ); create table Communications of CommunicationType ( -- Primary and Foreign key constraints here ); create table Calls of CallType; create table Texts of TextType; create table Datas of DataType; When I try to insert data into one of the subclasses, its entry doesn't appear in the superclass. Likewise if I insert into the superclass, it doesn't show up in the appropriate subclass. For example, insert into Calls values (CallType( -- Values -- )); doesn't show any data in Communications. Nor does insert into Communications values (CallType( -- Values -- )); show anything in Calls. What am I doing wrong?

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  • How do I make my ArrayList Thread-Safe? Another approach to problem in Java?

    - by thechiman
    I have an ArrayList that I want to use to hold RaceCar objects that extend the Thread class as soon as they are finished executing. A class, called Race, handles this ArrayList using a callback method that the RaceCar object calls when it is finished executing. The callback method, addFinisher(RaceCar finisher), adds the RaceCar object to the ArrayList. This is supposed to give the order in which the Threads finish executing. I know that ArrayList isn't synchronized and thus isn't thread-safe. I tried using the Collections.synchronizedCollection(c Collection) method by passing in a new ArrayList and assigning the returned Collection to an ArrayList. However, this gives me a compiler error: Race.java:41: incompatible types found : java.util.Collection required: java.util.ArrayList finishingOrder = Collections.synchronizedCollection(new ArrayList(numberOfRaceCars)); Here is the relevant code: public class Race implements RaceListener { private Thread[] racers; private ArrayList finishingOrder; //Make an ArrayList to hold RaceCar objects to determine winners finishingOrder = Collections.synchronizedCollection(new ArrayList(numberOfRaceCars)); //Fill array with RaceCar objects for(int i=0; i<numberOfRaceCars; i++) { racers[i] = new RaceCar(laps, inputs[i]); //Add this as a RaceListener to each RaceCar ((RaceCar) racers[i]).addRaceListener(this); } //Implement the one method in the RaceListener interface public void addFinisher(RaceCar finisher) { finishingOrder.add(finisher); } What I need to know is, am I using a correct approach and if not, what should I use to make my code thread-safe? Thanks for the help!

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  • Java Scanner newline parsing with regex (Bug?)

    - by SEK
    I'm developing a syntax analyzer by hand in Java, and I'd like to use regex's to parse the various token types. The problem is that I'd also like to be able to accurately report the current line number, if the input doesn't conform to the syntax. Long story short, I've run into a problem when I try to actually match a newline with the Scanner class. To be specific, when I try to match a newline with a pattern using the Scanner class, it fails. Almost always. But when I perform the same matching using a Matcher and the same source string, it retrieves the newline exactly as you'd expect it too. Is there a reason for this, that I can't seem to discover, or is this a bug, as I suspect? FYI: I was unable to find a bug in the Sun database that describes this issue, so if it is a bug, it hasn't been reported. Example Code: Pattern newLinePattern = Pattern.compile("(\\r\\n?|\\n)", Pattern.MULTILINE); String sourceString = "\r\n\n\r\r\n\n"; Scanner scan = new Scanner(sourceString); scan.useDelimiter(""); int count = 0; while (scan.hasNext(newLinePattern)) { scan.next(newLinePattern); count++; } System.out.println("found "+count+" newlines"); // finds 7 newlines Matcher match = newLinePattern.matcher(sourceString); count = 0; while (match.find()) { count++; } System.out.println("found "+count+" newlines"); // finds 5 newlines

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  • Can't combine "LINQ Join" with other tables

    - by FullmetalBoy
    The main problem is that I recieve the following message: "base {System.SystemException} = {"Unable to create a constant value of type 'BokButik1.Models.Book-Author'. Only primitive types ('such as Int32, String, and Guid') are supported in this context."}" based on this LinQ code: IBookRepository myIBookRepository = new BookRepository(); var allBooks = myIBookRepository.HamtaAllaBocker(); IBok_ForfattareRepository myIBok_ForfattareRepository = new Bok_ForfattareRepository(); var Book-Authors = myIBok_ForfattareRepository.HamtaAllaBok_ForfattareNummer(); var q = from booknn in allBooks join Book-Authornn in Book-Authors on booknn.BookID equals Book-Authornn.BookID select new { booknn.title, Book-AuthorID }; How shall I solve this problem to get a class instance that contain with property title and Book-AuthorID? // Fullmetalboy I also have tried making some dummy by using "allbooks" relation with Code Samples from the address http://www.hookedonlinq.com/JoinOperator.ashx. Unfortunately, still same problem. I also have taken account to Int32 due to entity framework http://msdn.microsoft.com/en-us/library/bb896317.aspx. Unfortunatley, still same problem. Using database with 3 tables and one of them is a many to many relationship. This database is used in relation with entity framework Book-Author Book-Author (int) BookID (int) Forfattare (int) Book BookID (int) title (string) etc etc etc

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  • error: invalid type argument of '->' (have 'struct node')

    - by Roshan S.A
    Why cant i access the pointer "Cells" like an array ? i have allocated the appropriate memory why wont it act like an array here? it works like an array for a pointer of basic data types. #include<stdio.h> #include<stdlib.h> #include<ctype.h> #define MAX 10 struct node { int e; struct node *next; }; typedef struct node *List; typedef struct node *Position; struct Hashtable { int Tablesize; List Cells; }; typedef struct Hashtable *HashT; HashT Initialize(int SIZE,HashT H) { int i; H=(HashT)malloc(sizeof(struct Hashtable)); if(H!=NULL) { H->Tablesize=SIZE; printf("\n\t%d",H->Tablesize); H->Cells=(List)malloc(sizeof(struct node)* H->Tablesize); should it not act like an array from here on? if(H->Cells!=NULL) { for(i=0;i<H->Tablesize;i++) the following lines are the ones that throw the error { H->Cells[i]->next=NULL; H->Cells[i]->e=i; printf("\n %d",H->Cells[i]->e); } } } else printf("\nError!Out of Space"); } int main() { HashT H; H=Initialize(10,H); return 0; } The error I get is as in the title-error: invalid type argument of '->' (have 'struct node').

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  • Detection of negative integers using bit operations

    - by Nawaz
    One approach to check if a given integer is negative or not, could be this: (using bit operations) int num_bits = sizeof(int) * 8; //assuming 8 bits per byte! int sign_bit = given_int & (1 << (num_bits-1)); //sign_bit is either 1 or 0 if ( sign_bit ) { cout << "given integer is negative"<<endl; } else { cout << "given integer is positive"<<endl; } The problem with this solution is that number of bits per byte couldn't be 8, it could be 9,10, 11 even 16 or 40 bits per byte. Byte doesn't necessarily mean 8 bits! Anyway, this problem can be easily fixed by writing, //CHAR_BIT is defined in limits.h int num_bits = sizeof(int) * CHAR_BIT; //no assumption. It seems fine now. But is it really? Is this Standard conformant? What if the negative integer is not represented as 2's complement? What if it's representation in a binary numeration system that doesn't necessitate only negative integers to have 1 in it's most significant bit? Can we write such code that will be both portable and standard conformant? Related topics: Size of Primitive data types Why is a boolean 1 byte and not 1 bit of size?

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