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  • The question about the basics of LINQ to SQL working

    - by Alex
    I just started learning LINQ to SQL, and so far I'm impressed with the easy of use and good performance. I used to think that when doing LINQ queries like from Customer in DB.Customers where Customer.Age > 30 select Customer Get all customers from the database ("SELECT * FROM Customers"), move them to the Customers array and then make a search in that Array using .NET methods. This is very inefficient, what if there are hundreds of thousands of customers in the database? Making such big SELECT queries would kill the web application. Now after experiencing how actually fast LINQ to SQL is, I start to suspect that when doing that query I just wrote, LINQ somehow converts it to a SQL Query string SELECT * FROM Customers WHERE Age > 30 And only when necessary it will run the query. So my question is: am I right? And when is the query actually run? The reason why I'm asking is not only because I want to understand how it works in order to build good optimized applications, but because I came across the following problem. I have 2 tables, one of them is Books, the other has information on how many books were sold on certain days. My goal is to select books that had at least 50 sales/day in past 10 days. It's done with this simple query: from Book in DB.Books where (from Sale in DB.Sales where Sale.SalesAmount >= 50 and Sale.DateOfSale >= DateTime.Now.AddDays(-10) select Sale.BookID).Contains(Book.ID) select Book The point is, I have to use the checking part in several queries and I decided to create an array with IDs of all popular books: var popularBooksIDs = from Sale in DB.Sales where Sale.SalesAmount >= 50 and Sale.DateOfSale >= DateTime.Now.AddDays(-10) select Sale.BookID; BUT when I try to do the query now: from Book in DB.Books where popularBooksIDs.Contains(Book.ID) select Book It doesn't work! That's why I think that we can't use thins kinds of shortcuts in LINQ to SQL queries, like we can't use them in real SQL. We have to create straightforward queries, am I right?

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  • How slow are bit fields in C++

    - by Shane MacLaughlin
    I have a C++ application that includes a number of structures with manually controlled bit fields, something like #define FLAG1 0x0001 #define FLAG2 0x0002 #define FLAG3 0x0004 class MyClass { ' ' unsigned Flags; int IsFlag1Set() { return Flags & FLAG1; } void SetFlag1Set() { Flags |= FLAG1; } void ResetFlag1() { Flags &= 0xffffffff ^ FLAG1; } ' ' }; For obvious reasons I'd like to change this to use bit fields, something like class MyClass { ' ' struct Flags { unsigned Flag1:1; unsigned Flag2:1; unsigned Flag3:1; }; ' ' }; The one concern I have with making this switch is that I've come across a number of references on this site stating how slow bit fields are in C++. My assumption is that they are still faster than the manual code shown above, but is there any hard reference material covering the speed implications of using bit fields on various platforms, specifically 32bit and 64bit windows. The application deals with huge amounts of data in memory and must be both fast and memory efficient, which could well be why it was written this way in the first place.

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  • Java "Pool" of longs or Oracle sequence with reusable values

    - by Anthony Accioly
    Several months ago I implemented a solution to choose unique values from a range between 1 and 65535 (16 bits). This range is used to generate unique Route Targets suffixes, which for this customer massive network (it's a huge ISP) are a very disputed resource, so any free index needs to become immediately available to the end user. To tackle this requirement I used a BitSet. Allocate on the RT index with set and deallocate a suffix with clear. The method nextClearBit() can find the next available index. I handle synchronization / concurrency issues manually. This works pretty well for a small range... The entire index is small (around 10k), it is blazing fast and can be easy serialized into a Blob field. The problem is, some new devices can handle RTs of 32 bits (range 1 / 4294967296). Which can't be managed with a BitSet (it would, by itself, consume around 600Mb, plus be limited to int range). Even with this massive range available, the client still wants to free available Route Targets for the end user, mainly because the lowest ones (up to 65535) - which are compatible with old routers - are being heavily disputed. Before I tell the customer that this is impossible and he will have to conform with my reusable index for lower RTs (up to 65550) and use a database sequence for the other ones (which means that when the user frees a Route Target, it will not become available again). Would anyone shed some light? Maybe some kind soul already implemented a high performance number pool for Java (6 if it matters), or I am missing a killer feature of Oracle database (11R2 if it matters)... Wishful thinking. Thank you very much in advance.

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  • QListWidget drag and drop items disappearing from list

    - by ppalasek
    Hello, I'm having trouble implementing a QListWidget with custom items that can be reordered by dragging and dropping. The problem is when I make a fast double click (a very short drag&drop) on an item, the item sometimes disappears from the QListWidget. This is the constructor for my Widget: ListPopisiDragDrop::ListPopisiDragDrop(QWidget *parent) : QListWidget(parent) { setSelectionMode(QAbstractItemView::SingleSelection); setDragEnabled(true); viewport()->setAcceptDrops(true); setDefaultDropAction(Qt::MoveAction); setDropIndicatorShown(true); setDragDropMode(QAbstractItemView::InternalMove); } also the drop event: void ListPopisiDragDrop::dropEvent(QDropEvent *event){ int startRow=currentIndex().row(); QListWidget::dropEvent(event); int endRow=currentIndex().row(); //more code... } Custom items are made by implementing paint() and sizeHint() functions from QAbstractItemDelegate. When the problem with disappearing items happens, the dropEvent isn't even called. I really don't know what is happening and if I'm doing something wrong. Any help is appreciated. Thanks! Edit: I'm running the application on a Symbian S60 5th edition phone. Edit2: If I add this line to the constructor: setDragDropOverwriteMode(true); the item in the list still disappears, but an empty row stays in it's place.

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  • How to use MySQL geospatial extensions with spherical geometries

    - by Joshua
    Hi Everyone, I would like to store thousands of latitude/longitude points in a MySQL db. I was successful at setting up the tables and adding the data using the geospatial extensions where the column 'coord' is a Point(lat, lng). Problem: I want to quickly find the 'N' closest entries to latitude 'X' degrees and longitude 'Y' degrees. Since the Distance() function has not yet been implemented, I used GLength() function to calculate the distance between (X,Y) and each of the entries, sorting by ascending distance, and limiting to 'N' results. The problem is that this is not calculating shortest distance with spherical geometry. Which means if Y = 179.9 degrees, the list of closest entries will only include longitudes of starting at 179.9 and decreasing even though closer entries exist with longitudes increasing from -179.9. How does one typically handle the discontinuity in longitude when working with spherical geometries in databases? There has to be an easy solution to this, but I must just be searching for the wrong thing because I have not found anything helpful. Should I just forget the GLength() function and create my own function for calculating angular separation? If I do this, will it still be fast and take advantage of the geospatial extensions? Thanks! josh UPDATE: This is exactly what I am describing above. However, it is only for SQL Server. Apparently SQL Server has a Geometry and Geography datatypes. The geography does exactly what I need. Is there something similar in MySQL?

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  • How to iterate JPA collections in Google App engine

    - by palto
    Hi I use Google App Engine with datanucleus and JPA. I'm having a real hard time grasping how I'm supposed to read stuff from data store and pass it to JSP. If I load a list of POJOs with entitymanager and pass it to JSP, it crashes to org.datanucleus.exceptions.NucleusUserException: Object Manager has been closed. I understand why this is happening. Obviously because I fetch the list, close the entity manager and pass it to JSP, at which point it will fail because the list is lazy. How do I make the list NOT lazy without resorting to hacks like calling size() or something like that? Here is what I'm trying to do: @Override protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { req.setAttribute("parties", getParties()); RequestDispatcher dispatcher = getServletContext().getRequestDispatcher("/WEB-INF/parties.jsp"); dispatcher.forward(req, resp); } private List<Party> getParties(){ EntityManager em = entityManagerProvider.get(); try{ Query query = em.createQuery("SELECT p FROM Party p"); return query.getResultList(); }finally{ em.close(); } }

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  • Largest triangle from a set of points

    - by Faken
    I have a set of random points from which i want to find the largest triangle by area who's verticies are each on one of those points. So far I have figured out that the largest triangle's verticies will only lie on the outside points of the cloud of points (or the convex hull) so i have programmed a function to do just that (using Graham scan in nlogn time). However that's where I'm stuck. The only way I can figure out how to find the largest triangle from these points is to use brute force at n^3 time which is still acceptable in an average case as the convex hull algorithm usually kicks out the vast majority of points. However in a worst case scenario where points are on a circle, this method would fail miserably. Dose anyone know an algorithm to do this more efficiently? Note: I know that CGAL has this algorithm there but they do not go into any details on how its done. I don't want to use libraries, i want to learn this and program it myself (and also allow me to tweak it to exactly the way i want it to operate, just like the graham scan in which other implementations pick up collinear points that i don't want).

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  • Implementing a scrabble trainer (cheater)

    - by bstullkid
    Hello, I've recently been playing alot of online scrabble so I decided to make a program that quickly searches through a dictionary of 200,000+ words with an input of up to any 26 letters. My first attempt was fail as it took a while when you input 8 or more letters (just a basic look through dictionary and cancel out a letter if its found kind of thing), so I made a tree like structure containing only an array of 26 of the same structure and a flag to indicate the end of a word, doing that It can output all possible words in under a second even with an input of 26 characters. But it seems that when I input 12 or more letters with some of the same characters repeated i get duplicates; can anyone see why I would be getting duplicates with this code? (ill post my program at the bottom) Also, the next step once the duplicates are weeded out is to actually be able to input the letters on the game board and then have it calculate the best word you can make on a given board. I am having trouble trying to figure out a good algorithm that can analyze a scrabble board and an input of letters and output a result; the possible words that could be made I have no problem with but actually checking a board efficiently (ie can this word fit here, or here etc... without creating a non dictionary word in the process on some other string of letters) Anyone have a idea for an approach at that? (given a scrabble board, and an input of 7 letters, find all possible valid words or word sets that you can make) lol crap i forgot to email myself the code from my other computer thats in another state... ill post it on monday when I get back there! btw the dictionary im using is sowpods (http://www.calvin.edu/~rpruim/scrabble/ospd3.txt)

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  • How to detect whether an EventWaitHandle is waiting?

    - by AngryHacker
    I have a fairly well multi-threaded winforms app that employs the EventWaitHandle in a number of places to synchronize access. So I have code similar to this: List<int> _revTypes; EventWaitHandle _ewh = new EventWaitHandle(false, EventResetMode.ManualReset); void StartBackgroundTask() { _ewh.Reset(); Thread t = new Thread(new ThreadStart(LoadStuff)); t.Start(); } void LoadStuff() { _revTypes = WebServiceCall.GetRevTypes() // ...bunch of other calls fetching data from all over the place // using the same pattern _ewh.Set(); } List<int> RevTypes { get { _ewh.WaitOne(); return _revTypes; } } Then I just call .RevTypes somewehre from the UI and it will return data to me when LoadStuff has finished executing. All this works perfectly correctly, however RevTypes is just one property - there are actually several dozens of these. And one or several of these properties are holding up the UI from loading in a fast manner. Short of placing benchmark code into each property, is there a way to see which property is holding the UI from loading? Is there a way to see whether the EventWaitHandle is forced to actually wait?

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  • How To Update EF 4 Entity In ASP.NET MVC 3?

    - by Jason Evans
    Hi there. I have 2 projects - a class library containing an EDM Entity Framework model and a seperate ASP.NET MVC project. I'm having problems with how your suppose to edit and save changes to an entity using MVC. In my controller I have: public class UserController : Controller { public ActionResult Edit(int id) { var rep = new UserRepository(); var user = rep.GetById(id); return View(user); } [HttpPost] public ActionResult Edit(User user) { var rep = new UserRepository(); rep.Update(user); return View(user); } } My UserRepository has an Update method like this: public void Update(User user) { using (var context = new PDS_FMPEntities()) { context.Users.Attach(testUser); context.ObjectStateManager.ChangeObjectState(testUser, EntityState.Modified); context.SaveChanges(); } } Now, when I click 'Save' on the edit user page, the parameter user only contains two values populated: Id, and FirstName. I take it that is due to the fact that I'm only displaying those two properties in the view. My question is this, if I'm updating the user's firstname, and then want to save it, what am I suppose to do about the other User properties which were not shown on the view, since they now contain 0 or NULL values in the user object? I've been reading a lot about using stub entities, but I'm getting nowhere fast, in that none of the examples I've seen actually work. i.e. I keep getting EntityKey related exceptions. Can someone point me to a good tutorial/example of how to update EF 4 entities using a repository class, called by an MVC front-end? Cheers. Jas.

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  • Setting up SVN (subvsersion) to manage our companies files, how to exclude large files from being ve

    - by Roeland
    Me and two other guys recently started our own web development company. We each work from our homes and have decided we want to keep one central location for all of our files. These files include word documents, spreadsheets, client files, designs.. etc. Anything pertaining to our company. I have a pretty solid internet connection and a windows 2008 server box sitting at home so I set up a subversion repository. Our file repository will look something like this. Clients Company A Design (photoshop files, wireframes, concepts) Documents ( logins, quotes, proposals etc) Site Backups Company B Design Documents Site Backups Prospects Company C Company D Our Company Our Website Documents (contract, operating procudres) My question is in regards to design files. The photoshop files that my designer works with range in sizes from 10mb to 100mb. I don't think we need to keep these files version-ed as this would eat up space incredibly fast. How do I go about controlling which files get version-ed, and which files are just stored. What I am thinking is that all documents need to be version-ed, and any files other then that should not be. Any help would be appreciated, thanks! Edit I am also curious whether this is the way to go. I just like this system since it keeps version of all my documents and at the same time. Also essentially I will have 3 backups in 3 different locations (3 local copies) so no need for backing it up. I am unsure of how svn would perform as purely a huge file repository.

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  • I can't login to my Django app when debug is set to False

    - by Eric
    I have a very strange problem, and I don't know how to fix or debug it. Short Story: I get locked out of my Django app when Debug is set to False. Long story: Case 1 (the first time it happened): 1. I enter my login info, but It just redirects to the login page. 2. I restart the server, try to login, and it works fine, I get in. 3. a few hours later I come back, log out, try to log back in and I can't. It just redirects to the login page. Case 2 (I figure out how to provoke the login failure): 1. I restart the server and am able to login to the site. 2. I log in and log out several times, everything is fine. 3. I go to a non-existing page and get a server error. 4. I log out and try to log back in, and I can't, just get redirected back to the login page. Case 3 (I can't provoke the login failure with Debug set to True): 1. I restart the server and am able to login to the site. 2. I log in and log out several times, everything is fine. 3. I go to a non-existing page and get a traceback. 4. I log out and log back in, everything works. 5. I wait and play around with it and can't get the login to fail while in Debug mode. Please help!

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  • How Optimize sql query make it faster

    - by user502083
    Hello every one : I have a very simple small database, 2 of tables are: Node (Node_ID, Node_name, Node_Date) : Node_ID is primary key Citation (Origin_Id, Target_Id) : PRIMARY KEY (Origin_Id, Target_Id) each is FK in Node Now I write a query that first find all citations that their Origin_Id has a specific date and then I want to know what are the target dates of these records. I'm using sqlite in python the Node table has 3000 record and Citation has 9000 records, and my query is like this in a function: def cited_years_list(self, date): c=self.cur try: c.execute("""select n.Node_Date,count(*) from Node n INNER JOIN (select c.Origin_Id AS Origin_Id, c.Target_Id AS Target_Id, n.Node_Date AS Date from CITATION c INNER JOIN NODE n ON c.Origin_Id=n.Node_Id where CAST(n.Node_Date as INT)={0}) VW ON VW.Target_Id=n.Node_Id GROUP BY n.Node_Date;""".format(date)) cited_years=c.fetchall() self.conn.commit() print('Cited Years are : \n ',str(cited_years)) except Exception as e: print('Cited Years retrival failed ',e) return cited_years Then I call this function for some specific years, But it's crazy slowwwwwwwww :( (around 1 min for a specific year) Although my query works fine, it is slow. would you please give me a suggestion to make it faster? I'd appreciate any idea about optimizing this query :) I also should mention that I have indices on Origin_Id and Target_Id, so the inner join should be pretty fast, but it's not!!!

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  • How can i mock or test my deferred execution functionality?

    - by cottsak
    I have what could be seen as a bizarre hybrid of IQueryable<T> and IList<T> collections of domain objects passed up my application stack. I'm trying to maintain as much of the 'late querying' or 'lazy loading' as possible. I do this in two ways: By using a LinqToSql data layer and passing IQueryable<T>s through by repositories and to my app layer. Then after my app layer passing IList<T>s but where certain elements in the object/aggregate graph are 'chained' with delegates so as to defer their loading. Sometimes even the delegate contents rely on IQueryable<T> sources and the DataContext are injected. This works for me so far. What is blindingly difficult is proving that this design actually works. Ie. If i defeat the 'lazy' part somewhere and my execution happens early then the whole thing is a waste of time. I'd like to be able to TDD this somehow. I don't know a lot about delegates or thread safety as it applies to delegates acting on the same source. I'd like to be able to mock the DataContext and somehow trace both methods of deferring (IQueryable<T>'s SQL and the delegates) the loading so that i can have tests that prove that both functions are working at different levels/layers of the app/stack. As it's crucial that the deferring works for the design to be of any value, i'd like to see tests fail when i break the design at a given level (separate from the live implementation). Is this possible?

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  • Checking if an SSH tunnel is up and running

    - by Jarmund
    I have a perl script which, when destilled a bit, looks like this: my $randport = int(10000 + rand(1000)); # Random port as other scripts like this run at the same time my $localip = '192.168.100.' . ($port - 4000); # Don't ask... backwards compatibility system("ssh -NL $randport:$localip:23 root\@$ip -o ConnectTimeout=60 -i somekey &"); # create the tunnel in the background sleep 10; # Give the tunnel some time to come up # Create the telnet object my $telnet = new Net::Telnet( Timeout => 10, Host => 'localhost', Port => $randport, Telnetmode => 0, Errmode => \&fail, ); # SNIPPED... a bunch of parsing data from $telnet The thing is that the target $ip is on a link with very unpredictable bandwidth, so the tunnel might come up right away, it might take a while, it might not come up at all. So a sleep is necessary to give the tunnel some time to get up and running. So the question is: How can i test if the tunnel is up and running? 10 seconds is a really undesirable delay if the tunnel comes up straight away. Ideally, i would like to check if it's up and continue with creating the telnet object once it is, to a maximum of, say, 30 seconds.

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  • Advise guidance on how to form this jQuery script for show/hide fade element

    - by Rick
    Hey guys.. I basically have several links on the left side of the screen and on the right is a preview window. Below the preview window is another box for the affiliate link code. So what I am trying to do is create an affiliate page where you choose the banner size on the left by clicking on the link and on the right you see it dynamically change to the banner size and the code changes accordingly as well. So far I have the following code and it works but it seems very very cumbersome and bloated. Can you see if I can trim this down? jQuery(".banner-style li").click(function() { jQuery(".banner-style li").removeClass("selected"); jQuery(this).addClass("selected"); var $banner = jQuery(this).attr("class"); $banner = $banner.replace(" selected",""); jQuery(".preview img").fadeOut('fast',function() { jQuery(".preview img").attr("src", "http://localhost/site/banners/"+$banner+".jpg") .fadeIn('slow'); }); jQuery(".code p").removeClass('hide').hide(); jQuery(".code p."+$banner).show(); }); Also to note the funny thing is in FF, when you click for the first to on any link, the original image on the right fades out and in real quick and then it loads the "clicked" image. This does not happen in other browsers...

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  • What library can I use to do simple, lightweight message passing?

    - by Mike
    I will be starting a project which requires communication between distributed nodes(the project is in C++). I need a lightweight message passing library to pass very simple messages(basically just strings of text) between nodes. The library must have the following characteristics: No external setup required. I need to be able to get everything up-and-running in my code - I don't want to require the user to install any packages or edit any configuration files(other than a list of IP addresses and ports to connect to). The underlying protocol which the library uses must be TCP(or if it is UDP, the library must guarantee the eventual receipt of the message). The library must be able to send and receive arbitrarily large strings(think up to 3GB+). The library needn't support any security mechanisms, fault tolerance, or encryption - I just need it to be fast, simple, and easy to use. I've considered MPI, but concluded it would require too much setup on the user's machine for my project. What library would you recommend for such a project? I would roll my own, but due to time constraints, I don't think that will be feasible.

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  • Is it possible to install into Program Files with limited privileges?

    - by Marek
    I have an application that will be deployed as MSI package (authored in WiX). I am deciding whether to specify elevated or limited privileges as required for the installer. The application does not include anything requiring elevated privileges besides the default install location, which is under Program Files. Now the problem: If I specify elevated privileges, then the user is prompted by UAC for administrator password during the installation. This is not required and prevents non-admin users from installing. If I specify limited privileges, then the user is presented with a dialog to select install location with Program Files being default. In case they do not change the install location (95 % of end users probably won't), then the installer will fail with a message that they should contact the Administrator or run the application as administrator. If they launch the installer as Administrator then they can install into Program Files without problem - but most of the users won't probably know how to launch an installer as administrator. I can potentially set the default install location to e.g. C:\Company name\Program\, but this seems nonstandard to me and majority of users will not probably like this (they are probably used to installing into Program Files). How do you solve this problem with installing applications under limited user accounts?

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  • List of Big-O for PHP functions?

    - by Kendall Hopkins
    After using PHP for a while now, I've noticed that not all PHP built in functions as fast as expected. Consider the below two possible implementations of a function that finds if a number is prime using a cached array of primes. //very slow for large $prime_array $prime_array = array( 2, 3, 5, 7, 11, 13, .... 104729, ... ); $result_array = array(); foreach( $array_of_number => $number ) { $result_array[$number] = in_array( $number, $large_prime_array ); } //still decent performance for large $prime_array $prime_array => array( 2 => NULL, 3 => NULL, 5 => NULL, 7 => NULL, 11 => NULL, 13 => NULL, .... 104729 => NULL, ... ); foreach( $array_of_number => $number ) { $result_array[$number] = array_key_exists( $number, $large_prime_array ); } This is because in_array is implemented with a linear search O(n) which will linearly slow down as $prime_array grows. Where the array_key_exists function is implemented with a hash lookup O(1) which will not slow down unless the hash table gets extremely populated (in which case it's only O(logn)). So far I've had to discover the big-O's via trial and error, and occasionally looking at the source code. Now for the question... I was wondering if there was a list of the theoretical (or practical) big O times for all* the PHP built in functions. *or at least the interesting ones For example find it very hard to predict what the big O of functions listed because the possible implementation depends on unknown core data structures of PHP: array_merge, array_merge_recursive, array_reverse, array_intersect, array_combine, str_replace (with array inputs), etc.

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  • Entity Framework + MySQL - Why is the performance so terrible?

    - by Cyril Gupta
    When I decided to use an OR/M (Entity Framework for MySQL this time) for my new project I was hoping it would save me time, but I seem to have failed it (for the second time now). Take this simple SQL Query SELECT * FROM POST ORDER BY addedOn DESC LIMIT 0, 50 It executes and gives me results in less than a second as it should (the table has about 60,000 rows). Here's the equivalent LINQ To Entities query that I wrote for this var q = (from p in db.post orderby p.addedOn descending select p).Take(50); var q1 = q.ToList(); //This is where the query is fetched and timed out But this query never even executes it times out ALWAYS (without orderby it takes 5 seconds to run)! My timeout is set to 12 seconds so you can imagine it is taking much more than that. Why is this happening? Is there a way I can see what is the actual SQL Query that Entity Framework is sending to the db? Should I give up on EF+MySQL and move to standard SQL before I lose all eternity trying to make it work? I've recalibrated my indexes, tried eager loading (which actually makes it fail even without the orderby clause) Please help, I am about to give up OR/M for MySQL as a lost cause.

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  • Why is my quick sort so slow?

    - by user513075
    Hello, I am practicing writing sorting algorithms as part of some interview preparation, and I am wondering if anybody can help me spot why this quick sort is not very fast? It appears to have the correct runtime complexity, but it is slower than my merge sort by a constant factor of about 2. I would also appreciate any comments that would improve my code that don't necessarily answer the question. Thanks a lot for your help! Please don't hesitate to let me know if I have made any etiquette mistakes. This is my first question here. private class QuickSort implements Sort { @Override public int[] sortItems(int[] ts) { List<Integer> toSort = new ArrayList<Integer>(); for (int i : ts) { toSort.add(i); } toSort = partition(toSort); int[] ret = new int[ts.length]; for (int i = 0; i < toSort.size(); i++) { ret[i] = toSort.get(i); } return ret; } private List<Integer> partition(List<Integer> toSort) { if (toSort.size() <= 1) return toSort; int pivotIndex = myRandom.nextInt(toSort.size()); Integer pivot = toSort.get(pivotIndex); toSort.remove(pivotIndex); List<Integer> left = new ArrayList<Integer>(); List<Integer> right = new ArrayList<Integer>(); for (int i : toSort) { if (i > pivot) right.add(i); else left.add(i); } left = partition(left); right = partition(right); left.add(pivot); left.addAll(right); return left; } }

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  • ListView causing OutOfMemory Error

    - by Michael
    So I am not really given a reason to the right of this error message. I am not exactly sure why this is happening but my guess though is that it has to do with the fact that there are around ~50 good quality drawables. Upon scrolling really fast, the app crashes. I feel as if I am mitigating most common issues with ListView and crashing such as using View Holders as well as only initiating the inflater once. Process: com.example.michael.myandroidappactivity, PID: 20103 java.lang.OutOfMemoryError at android.graphics.BitmapFactory.nativeDecodeAsset(Native Method) Here is the code public class ImageAdapter extends BaseAdapter { private Context context; private ArrayList<Integer> imageIds; private static LayoutInflater inflater; public ImageAdapter(Context _context, ArrayList<Integer> _imageIds) { context = _context; imageIds = _imageIds; } @Override public int getCount() { return imageIds.size(); } @Override public Object getItem(int position) { return null; } @Override public long getItemId(int position) { return 0; } static class ViewHolder{ ImageView img; } @Override public View getView(int position, View convertView, ViewGroup parent) { ViewHolder holder = null; View rowView = null; if(rowView==null) { LayoutInflater inflater = (LayoutInflater) context .getSystemService(Context.LAYOUT_INFLATER_SERVICE); rowView = inflater.inflate(R.layout.listview_layout, parent, false); holder = new ViewHolder(); holder.img = (ImageView) rowView.findViewById(R.id.flag); rowView.setTag(holder); } else { holder = (ViewHolder) rowView.getTag(); } holder.img.setImageResource(imageIds.get(position)); return rowView; } }

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  • Big-O for GPS data

    - by HH
    A non-critical GPS module use lists because it needs to be modifiable, new routes added, new distances calculated, continuos comparisons. Well so I thought but my team member wrote something I am very hard to get into. His pseudo code int k =0; a[][] <- create mapModuleNearbyDotList -array //CPU O(n) for(j = 1 to n) // O(nlog(m)) for(i =1 to n) for(k = 1 to n) if(dot is nearby) adj[i][j]=min(adj[i][j], adj[i][k] + adj[k][j]); His ideas transformations of lists to tables His worst case time complexity is O(n^3), where n is number of elements in his so-called table. Exception to the last point with Finite structure: O(mlog(n)) where n is number of vertices and m is an arbitrary constants Questions about his ideas why to waste resources to transform constantly-modified lists to table? Fast? only point where I to some extent agree but cannot understand the same upper limits n for each for-loops -- perhaps he supposed it circular why does the code take O(mlog(n)) to proceed in time as finite structure? The term finite may be wrong, explicit?

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  • How do I switch out Views in a Cocoa application?

    - by David Garcia
    So I'm beginning to learn how to use Cocoa. I think I've pretty much got it but I'm hung up on creating and switching views. I'm rewriting a game I made a little bit ago for practice. All I want is one window (preferably not resizable) and I want to be able to switch out views for different screens in the game. First, I have the main menu (Start Game, High Scores, Exit). Then I need a window for each screen (Gameplay screen, Highscore screen). What I'm getting confused with is how to design this. I looked up NSViewController thinking it manages views but it doesn't. It only manages one view by loading it really. I don't understand why I'd need to use NSViewController then. Couldn't I just have a window class that contains multiple subclasses of NSView and load them like that? I'm not sure I understand the purpose of the ViewController. Does my Window Class really need to subclass NSWindowController? I was trying to follow the example of Apple's ViewController example and it has a window controller class that's a subclass of NSWindowController. I don't see what the purpose was of subclassing that. All NSWindowController seems to add is - initWithPath:(NSString *)newPath but I fail to see the use in that either when I can just edit the plist file to open the window on start up. Apple's example also has an NSView variable and an NSViewController variable. Don't you only need one variable to store the current view? Thanks in advance guys, I'm really confused as to how this works.

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  • Tired of Exploring

    - by Abhi
    Dear All I am tired of my work. I am exploring all day and at the end of the day i feel that i have not gain anything. Its been 1 year & 3 month working in Wince 6.0 r3 but i feel that i have gained nothing. I feel like that i have wasted these month without doing anything. At fast i worked in GUI application in which i was gaining confidence but then i was shifted from that domain to something for which lot of knowledge is required i.e writing or adjusting BSP. Now at present i have shifted to work on silverlight which is again a new domain for me. My day starts from 10am and ends at 7pm @ office by doing nothing. I am tired completely. Can anyone help me what shall i do in this situation? How shall i start to achieve the target? Where should i stick "deadline" or "learning the target first" as deadline is also important? I am completely depressed.

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