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• Google App Engine Database Index

  - by fjsj

  I need to store a undirected graph in a Google App Engine database. For optimization purposes, I am thinking to use database indexes. Using Google App Engine, is there any way to define the columns of a database table to create its index? I will need some optimization, since my app uses this stored undirected graph on a content-based filtering for item recommendation. Also, the recommender algorithm updates the weights of some graph's edges. If it is not possible to use database indexes, please suggest another method to reduce query time for the graph table. I believe my algorithm does more data retrieval operations from graph table than write operations. PS: I am using Python.

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• Caching instances in a jee web app

  - by SibzTer

  Hi, Consider the scenario of a typical webapp with JSFs on the front and ejb3, with Hibernate as JPA provider, talking to backend database such as mysql, etc. The main user actions are login and mostly CRUD operations (minus any D(elete) operations). And the App Server is GlassFish of course. Given this scenario, how and where all would one go about providing caching to improve performance? From what I have googled, I have seen that hibernate provides some sort of caching through different cache providers. Is there any sort of caching that can be provided for the jsf pages? How about session beans or entity beans on the ejb side of things? Also, I just read about memcached and was wondering if this was something to consider?

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• How do i handle a heavy page?

  - by Ulhas Tuscano

  I have been asked to design & develop a page in asp.net which contains 7 tabs.Each table contains 2 Editable gridview & clicking on gridview cell should open a popup & that popup will open a new popup ( I would say nested popup). even when i switch from one tab to another. It should hold the griddata & whenever user will finish all the operations he/she will click on save button which will save all the data contained in the tabs. The page is really too too too heavy. It will definitely take a long time to load as it contains gridview operations , popup related jobs, tab data & tab switching. I am finding the best way i can achieve this with an acceptable speed of operation. Any suggestions or help would be greatly appreciated.

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• Simple Emacs keybindings

  - by User1

  I have two operations that I do all the time in Emacs: Create a new buffer and paste the clipboard. [C-S-n] Close the current buffer. [C-S-w] Switch to the last viewed buffer [C-TAB] I feel like a keyboard acrobat when doing the first two operations. I think it would be worth trying some custom keybindings and macros. A few questions about this customization: How would I make a macro for #1? Are these good keybindings (i know this is a bit subjective, but they might be used by something popular that I don't use) Has anyone found a Ctrl-Tab macro that will act like Alt-Tab in Linux/Windows? Specifically, I want it have a stack of buffers according to the last viewed timestamp (most recent on top). I want to continue cycling through the stack until I let go of the ctrl key. When the ctrl key is released, I want the current buffer to get an updated position on the stack.

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• What's the proper way to use sqlite on the iPhone?

  - by Elliot Chen

  Hi, Experts: Can you please give some suggestions on sqlite using on the iPhone? Within my application, I use a sqlite DB to store all local data. Two methods can be used to retrieve those data during running time. 1, Load all the data into memory at initialization stage. (More memory used, less DB open/close operation needed) 2, Read corresponding records when necessary, free the occupied memory after using. (Good habit for memory using, but much DB open/close operations needs). I prefer to use method 2, but not sure whether too many DB opening/closing operations could affect app's efficiency. Or do you think I can 'upgrade' method 2 by opening DB when app launches and closing DB when app quits? Thanks for your suggestions very much!

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• List of checkboxes

  - by Andrea Girardi

  Hi all, Happy New Year to all. I'm a newbie in VB.NET and ASP.NET. This is my problem: I retrieve a list of records from DB and, for every row, I need to show 4 checkboxes. I can use a checkboxlist for every rows, but it's not so clear how I can process the results after the submit. I've some object and some operations available for that object. From database I extract a list of object with all operations. For every operation I want to show a check box to enable or disable the operation. The result is something like that: OBJ1 - url - [] [x] [] OBJ2 - url - [] [x] [x] On url I've an href to another page created using the Id retrieved from DB. To create that I used this code: <td class="column-filename"> <strong> <asp:Label runat="server" Text='<%#DataBinder.Eval(Container.DataItem, "GroupName")%>'></asp:Label> </strong> </td> <td align="left"> <span style="vertical-align:middle"> <asp:CheckBoxList runat="server" ID="operations" RepeatDirection="Horizontal" RepeatLayout="Table"> <asp:ListItem Text="View"></asp:ListItem> <asp:ListItem Text="Upload"></asp:ListItem> <asp:ListItem Text="Move"></asp:ListItem> <asp:ListItem Text="Delete"></asp:ListItem> <asp:ListItem Text="Rename"></asp:ListItem> <asp:ListItem Text="Replace"></asp:ListItem> </asp:CheckBoxList> </span> </td> </asp> </asp> my problem is: how can I parse all checkboxes? could you help me or send me a link or any other resources to solve my issue? many thanks! Andrea

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• Preview result of update/insert query without comitting changes to database in MySQL?

  - by Camsoft

  I am writing a script to import CSV files into existing tables within my database. I decided to do the insert/update operations myself using PHP and INSERT/UPDATE statements, and not use MySQL's LOAD INFILE command, I have good reasons for this. What I would like to do is emulate the insert/update operations and display the results to the user, and then give them the option of confirming that this is OK, and then committing the changes to the database. I'm using InnoDB database engine with support for transactions. Not sure if this helps but was thinking down the line of insert/update, query data, display to user, then either commit or rollback transaction? Any advise would be appreciated.

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• given a database, how do you generate CRUD forms for j2ee?

  - by zeroin23

  given a database schemas, is it possible to automatically generate forms for crud operations on the tables?

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• How to expose an entity via alternate keys with spring data rest

  - by dan carter

  Spring-data-rest does a great job exposing entities via their primary key for GET, PUT and DELETE etc. operations. /myentityies/123 It also exposes search operations. /myentities/search/byMyOtherKey?myOtherKey=123 In my case the entities have a number of alternate keys. The systems calling us, will know the objects by these IDs, rather than our internal primary key. Is it possible to expose the objects via another URL and have the GET, PUT and DELETE handled by the built-in spring-data-rest controllers? /myentities/myotherkey/456 We'd like to avoid forcing the calling systems to have to make two requests for each update. I've tried playing with @RestResource path value, but there doesn't seem to be a way to add additional paths.

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• Prims vs Polys: what are the pros and cons of each?

  - by Richard Inglis

  I've noticed that most 3d gaming/rendering environments represent solids as a mesh of (usually triangular) 3d polygons. However some examples, such as Second Life, or PovRay use solids built from a set of 3d primitives (cube, sphere, cone, torus etc) on which various operations can be performed to create more complex shapes. So my question is: why choose one method over the other for representing 3d data? I can see there might be benefits for complex ray-tracing operations to be able to describe a surface as a single mathematical function (like PovRay does), but SL surely isn't attempting anything so ambitious with their rendering engine. Equally, I can imagine it might be more bandwidth-efficient to serve descriptions of generalised solids instead of arbitrary meshes, but is it really worth the downside that SL suffers from (ie modelling stuff is really hard, and usually the results are ugly) - was this just a bad decision made early in SL's development that they're now stuck with? Or is it an artefact of what's easiest to implement in OpenGL?

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• Blit Queue Optimization Algorithm

  - by martona

  I'm looking to implement a module that manages a blit queue. There's a single surface, and portions of this surface (bounded by rectangles) are copied to elsewhere within the surface: add_blt(rect src, point dst); There can be any number of operations posted, in order, to the queue. Eventually the user of the queue will stop posting blits, and ask for an optimal set of operations to actually perform on the surface. The task of the module is to ensure that no pixel is copied unnecessarily. This gets tricky because of overlaps of course. A blit could re-blit a previously copied pixel. Ideally blit operations would be subdivided in the optimization phase in such a way that every block goes to its final place with a single operation. It's tricky but not impossible to put this together. I'm just trying to not reinvent the wheel. I looked around on the 'net, and the only thing I found was the SDL_BlitPool Library which assumes that the source surface differs from the destination. It also does a lot of grunt work, seemingly unnecessarily: regions and similar building blocks are a given. I'm looking for something higher-level. Of course, I'm not going to look a gift horse in the mouth, and I also don't mind doing actual work... If someone can come forward with a basic idea that makes this problem seem less complex than it does right now, that'd be awesome too. EDIT: Thinking about aaronasterling's answer... could this work? Implement customized region handler code that can maintain metadata for every rectangle it contains. When the region handler splits up a rectangle, it will automatically associate the metadata of this rectangle with the resulting sub-rectangles. When the optimization run starts, create an empty region handled by the above customized code, call this the master region Iterate through the blt queue, and for every entry: Let srcrect be the source rectangle for the blt beng examined Get the intersection of srcrect and master region into temp region Remove temp region from master region, so master region no longer covers temp region Promote srcrect to a region (srcrgn) and subtract temp region from it Offset temp region and srcrgn with the vector of the current blt: their union will cover the destination area of the current blt Add to master region all rects in temp region, retaining the original source metadata (step one of adding the current blt to the master region) Add to master region all rects in srcrgn, adding the source information for the current blt (step two of adding the current blt to the master region) Optimize master region by checking if adjacent sub-rectangles that are merge candidates have the same metadata. Two sub-rectangles are merge candidates if (r1.x1 == r2.x1 && r1.x2 == r2.x2) | (r1.y1 == r2.y1 && r1.y2 == r2.y2). If yes, combine them. Enumerate master region's sub-rectangles. Every rectangle returned is an optimized blt operation destination. The associated metadata is the blt operation`s source.

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• What's the proper way to use sqlite at xCode?

  - by Elliot Chen

  Hi, Experts: Can you please give some suggestions on sqlite using at xcode? Within my application, I use a sqlite DB to store all local data. Two methods can be used to retrieve those data during running time. 1, Load all the data into memory at initialization stage. (More memory used, less DB open/close operation needed) 2, Read corresponding records when necessary, free the occupied memory after using. (Good habit for memory using, but much DB open/close operations needs). I prefer to use method 2, but not sure whether too many DB opening/closing operations could affect app's efficiency. Or do you think I can 'upgrade' method 2 by opening DB when app launches and closing DB when app quits? Thanks for your suggestions very much!

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• what are the best practices to prevent sql injections

  - by s2xi

  Hi, I have done some research and still confused, This is my outcome of that research. Can someone please comment and advise to how I can make these better or if there is a rock solid implementation already out there I can use? Method 1: array_map('trim', $_GET); array_map('stripslashes', $_GET); array_map('mysql_real_escape_string', $_GET); Method 2: function filter($data) { $data = trim(htmlentities(strip_tags($data))); if (get_magic_quotes_gpc()) $data = stripslashes($data); $data = mysql_real_escape_string($data); return $data; } foreach($_GET as $key => $value) { $data[$key] = filter($value); }

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• Big-O for Eight Year Olds?

  - by Jason Baker

  I'm asking more about what this means to my code. I understand the concepts mathematically, I just have a hard time wrapping my head around what they mean conceptually. For example, if one were to perform an O(1) operation on a data structure, I understand that the amount of operations it has to perform won't grow because there are more items. And an O(n) operation would mean that you would perform a set of operations on each element. Could somebody fill in the blanks here? Like what exactly would an O(n^2) operation do? And what the heck does it mean if an operation is O(n log(n))? And does somebody have to smoke crack to write an O(x!)?

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• design patterns for hierarchical structures

  - by JLBarros

  Anyone knows some design patterns for hierarchical structures? For example, to manage inventory categories, accounting chart of accounts, divisions of human resources, etc.. Thank you very much in advance EDIT: Thanks for your interest. I am looking for a better way of dealing with hierarchical items to which they should apply operations depending on the level of hierarchy. I have been studying the patterns by Martin Fowler, for example Accounting, but I wonder if there are other more generic. The problem is that operations apply to the items must be possible to change even at run time and may depend on other external variables. I thought of a kind of strategy pattern but would like to combine it with the fact that it is a hierarchical scheme. I would appreciate any reference to hierarchical patterns and you'll take care of them in depth.

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• Article about code density as a measure of programming language power

  - by prosseek

  I remember reading an article saying something like "The number of bugs introduced doesn't vary much with different programming languages, but it depends pretty much on SLOC (source lines of code). So, using the programming language that can implement the same functions with smaller SLOC is preferable in terms of stability." The author wanted to stress the advantages of using Functional Programming, as normally one can program with a smaller number of LOC. I remember the author cited a research paper about the irrelevance of choice of programming language and the number of bugs. Is there anyone who knows the research paper or the article?

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• Questions about "casting operation" in OOP

  - by rhapsodyn

  When programming, we usually use some type-casting operations. When the casting happens on the objects "on the same level", it feels ok. But when it happens on the ojects "on the different levels"(mainly between father and son), it feels weird. Considering this: Class Son extends Father WhenSon s = (Son)father;, it's absolutely unreasonable. Because a "Son" is not a "Father" anymore, "Son" may grow up with some new properties "Father" doesn't have, the casting operation makes these properties unknown. On the other hand, Father f = (Father)son seems reasonable, but according to LSP "An instance of a derived should be able to replace any instance of its superclass" A "Son" can do anything his "Father" can, so the casting operation seems useless. So can i say that these casting operations are agaisnt OO design principle but necessary?

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• given a database, how do you generate CRUD forms for Java EE?

  - by zeroin23

  given a database schemas, is it possible to automatically generate forms for crud operations on the tables?

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• Good overview tool / board for visualizing Subversion branch acitivity?

  - by Sam

  Our team is sometimes finding it a bit confusing and time-consuming to figure out which subversion operations have been perrformed on our different branches in Subversion. Example, when has the Development branch last been merged into the Trunk? When was this particular Tag created, based on what branch etc etc. All of this information can of course be extracted from the Subversion Log, but thats always a manual, time-consuming and error-prone process. Simplest solution seems to be a simple whiteboard with a visualization of all the different branches/tags/trunk in Subversion and people drawing on it, whenever something significant happens. But we're not averse to finding some kind of a digital solution as well, stored centrally. Obviously both systems depend on people actually maintaining the model, but you'll always more or less have that. What do you use as best practice for keeping a clear view on all Subversion operations in the current Sprint (or beyond)?

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• DispatcherOperations.Wait()

  - by Mark

  What happens if you call dispatcherOperation.Wait() on an operation that has already completed? Also, the docs say that it returns a DispatcherOperationStatus, but wouldn't that always be Completed since it (supposedly) doesn't return until it's done? I was trying to use it like this: private void Update() { while (ops.Count > 0) ops.Dequeue().Wait(); } public void Add(T item) { lock (sync) { if (dispatcher.CheckAccess()) { list.Add(item); OnCollectionChanged(new NotifyCollectionChangedEventArgs(NotifyCollectionChangedAction.Add, item)); } else { ops.Enqueue(dispatcher.BeginInvoke(new Action<T>(Add), item)); } } } I'm using this in WPF, so all the Add operations have to occur on the UI thread, but I figured I could basically just queue them up without having to wait for it to switch threads, and then just call Update() before any read operations to ensure that the list is up to date, but my program started hanging.

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• Can I compose a WCF callback contract out of multiple interfaces?

  - by mafutrct

  Followup question to http://stackoverflow.com/questions/2502930/how-can-i-compose-a-wcf-contract-out-of-multiple-interfaces. I tried to merge multiple callback interfaces in a single interface. This yields an InvalidOperationException claiming that the final interface contains no operations. Technically, this is true, however, the inherited interfaces do contain operations. How can I fix this? Or is this a limitation of WCF? Edit: interface A { [OperationContract]void X(); } interface B { [OperationContract]void Y(); } interface C: A, B {} // this is the public callback contract

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• How can CopyOnWriteArrayList be thread-safe?

  - by Shooshpanchick

  I've taken a look into OpenJDK's sources of CopyOnWriteArrayList and it seems that all write operations are protected by the same lock and read operations are not protected at all. As I understand, under JMM all accesses to a variable (both read and write) should be protected by lock or reordering effects may occur. For example, set(int, E) method contains these lines (under lock): /* 1 */ int len = elements.length; /* 2 */ Object[] newElements = Arrays.copyOf(elements, len); /* 3 */ newElements[index] = element; /* 4 */ setArray(newElements); The get(int) method, on the other hand, only does return get(getArray(), index);. In my understanding of JMM, this means that get may observe the array in an inconsistent state if statements 1-4 are reordered like 1-2(new)-4-2(copyOf)-3. Do I understand JMM incorrectly or is there any other explanations on why CopyOnWriteArrayList is thread-safe?

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• How do I do import hooks in IronPython/Silverlight?

  - by ahlatimer

  I'm extending TryPython to (along with various other things) allow users to save a file and subsequently import that file. TryPython overloads the built in file operations, so I need to know what parts of import need to hooked into in order for import to use the overloaded file operations. Really, a basic overview of IronPython's import when used in Silverlight would be extremely helpful. I don't need a complete working solution (although I won't stop you from writing one! :). I'm a Python newbie, and I really have no idea where to even begin. Thanks!

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• Processing large recordsets in Rails

  - by japancheese

  Hello, I'm trying to perform a daily operation on a larger than normal dataset (2m+ records). However, Rails seems to take a very long time performing operations on such a dataset. Operations like Dataset.all.each do |data| ... end take a very long time to complete (I assume this is because it can't fit all the items into memory at once, right?). Does anyone have any strategies on how I could handle this situation? I know SQL would probably speed up the process, but I'm looking to use the Rails environment as I can do many more complicated things to the data than I can with just SQL statements.

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• API verbs for an interruptible operation

  - by 280Z28

  I have a long running task as part of my application. The task can be started, paused, resumed, and cancelled. I'm trying to find the best interface for these operations. Two seem clear: Pause and Cancel. This leaves the start and resume operations. I could include both Start and Resume. This has the downside of either requiring the API consumer to check the state before starting/resuming the operation to call the right method, or making the methods aliases of each other. I'm thinking I should include either Start or Resume, but I don't know which one is the most appropriate. Does anyone have any examples in the .NET Framework of such behavior? I prefer to follow established patterns whenever they are available.

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