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• One Model to Rule Them All - VS2010 UML, ADO.NET Entity Data Model, and T4

  - by Eric J.

  I worked on a fairly large project a while back where we modeled the classes in Enterprise Architect and generated the (partial) POCO classes (complete with model-driven business rule validations), persistence (NHibernate mapping file) and DDL. Based on certain model attributes we could flag alternate generation strategies or indicate that a particular portion would be entirely hand-coded. There was a good deal of initial investment, but it paid large dividends over the lifetime of a 15 developer, 3 year project. I'm investigating doing something similar with the current Microsoft technology stack. The place I'm stuck is that class modeling is done with the VS 2010 UML tools, but logical data modeling is done with Entity Data Modeler. Is it a reasonable path to use VS 2010 UML as the "single source of truth" and code generate the edmx files based on the class model? That's the inverse of the common path to create the entity model and use a POCO generator to generate classes. However, a good class model can be used to generate much more than just the properties so I tend to view it as a better choice than the entity model.

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• Non-Relational Database Design

  - by Ian Varley

  I'm interested in hearing about design strategies you have used with non-relational "nosql" databases - that is, the (mostly new) class of data stores that don't use traditional relational design or SQL (such as Hypertable, CouchDB, SimpleDB, Google App Engine datastore, Voldemort, Cassandra, SQL Data Services, etc.). They're also often referred to as "key/value stores", and at base they act like giant distributed persistent hash tables. Specifically, I want to learn about the differences in conceptual data design with these new databases. What's easier, what's harder, what can't be done at all? Have you come up with alternate designs that work much better in the non-relational world? Have you hit your head against anything that seems impossible? Have you bridged the gap with any design patterns, e.g. to translate from one to the other? Do you even do explicit data models at all now (e.g. in UML) or have you chucked them entirely in favor of semi-structured / document-oriented data blobs? Do you miss any of the major extra services that RDBMSes provide, like relational integrity, arbitrarily complex transaction support, triggers, etc? I come from a SQL relational DB background, so normalization is in my blood. That said, I get the advantages of non-relational databases for simplicity and scaling, and my gut tells me that there has to be a richer overlap of design capabilities. What have you done? FYI, there have been StackOverflow discussions on similar topics here: the next generation of databases changing schemas to work with Google App Engine choosing a document-oriented database

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• Extract <name> attribute from KML

  - by Ozaki

  I am using OpenLayers for a mapping service. In which I have several KML layers that are using KML feeds from server to populate data on the map. It currently plots: images / points / vector lines & shapes. But on these points it will not add a label with the value of the for the placemark in the KML. What I have currently tried is: ////////////////////KML Feed for * Layer// var surveylinelayer = new OpenLayers.Layer.Vector("First KML Layer", { projection: new OpenLayers.Projection("EPSG:4326"), strategies: [new OpenLayers.Strategy.Fixed()], protocol: new OpenLayers.Protocol.HTTP({ url: firstKMLURL, format: new OpenLayers.Format.KML({ extractStyles: true, extractAttributes: true }) }), styleMap: new OpenLayers.StyleMap({ "default": KMLStyle }) }); then the Style as follows: var KMLStyle = new OpenLayers.Style({ //label: "${name}", // This method will display nothing fillOpacity: 1, pointRadius: 10, fontColor: "#7E3C1C", fontSize: "13px", fontFamily: "Courier New, monospace", fontWeight: "strong", labelXOffset: "0", labelYOffset: "-15" }, { //dynamic label context: { label: function(feature) { return "Feature Name: " + feature.attributes.name; // also displays nothing } } }); Example of the KML: <Placemark> <name>POI1</name> <Style> <LabelStyle> <color>ffffffff</color> </LabelStyle> </Style> <Point> <coordinates>0.000,0.000</coordinates> </Point> </Placemark> When debugging I just hit "feature is undefined" and am unsure why it would be undefined in this instance?

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• python-social-auth AuthCanceled exception

  - by vero4ka

  I'm using python-social-auth in my Django application for authentication via Facebook. But when a user tries to login and when it's been refirected to Facebook app page clicks on "Cancel" button, appears the following exception: ERROR 2014-01-03 15:32:15,308 base :: Internal Server Error: /complete/facebook/ Traceback (most recent call last): File "/home/vera/virtualenv/myapp/local/lib/python2.7/site-packages/django/core/handlers/base.py", line 114, in get_response response = wrapped_callback(request, *callback_args, **callback_kwargs) File "/home/vera/virtualenv/myapp/local/lib/python2.7/site-packages/django/views/decorators/csrf.py", line 57, in wrapped_view return view_func(*args, **kwargs) File "/home/vera/virtualenv/myapp/local/lib/python2.7/site-packages/social/apps/django_app/utils.py", line 45, in wrapper return func(request, backend, *args, **kwargs) File "/home/vera/virtualenv/myapp/local/lib/python2.7/site-packages/social/apps/django_app/views.py", line 21, in complete redirect_name=REDIRECT_FIELD_NAME, *args, **kwargs) File "/home/vera/virtualenv/myapp/local/lib/python2.7/site-packages/social/actions.py", line 54, in do_complete *args, **kwargs) File "/home/vera/virtualenv/myapp/local/lib/python2.7/site-packages/social/strategies/base.py", line 62, in complete return self.backend.auth_complete(*args, **kwargs) File "/home/vera/virtualenv/myapp/local/lib/python2.7/site-packages/social/backends/facebook.py", line 63, in auth_complete self.process_error(self.data) File "/home/vera/virtualenv/myapp/local/lib/python2.7/site-packages/social/backends/facebook.py", line 56, in process_error super(FacebookOAuth2, self).process_error(data) File "/home/vera/virtualenv/myapp/local/lib/python2.7/site-packages/social/backends/oauth.py", line 312, in process_error raise AuthCanceled(self, data.get('error_description', '')) AuthCanceled: Authentication process canceled Is the any way to catch it Django?

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• Debugging strategy to find the cause of bad_alloc

  - by SalamiArmi

  I have a fairly serious bug in my program - occasional calls to new() throw a bad_alloc. From the documentation I can find on bad_alloc, it seems to be thrown for these reasons: When the computer runs out of memory (which definitely isn't happening, I have 4GB of RAM, program throws bad_alloc when using less than 5MB (checked in taskmanager) with nothing serious running in the background). If the memory becomes too fragmented to allocate new blocks (which, again, is unlikely - the largest sized block I ever allocate would be about 1KB, and that doesn't get done more than 100 times before the crash occurs). Based on these descriptions, I don't really have anywhere in which a bad_alloc could be thrown. However, the application I am running runs more than one thread, which could possibly be contributing to the problem. By testing all of the objects on a single thread, everything seems to be working smoothly. The only other thing that I can think of that is going on here could be some kind of race-condition caused by calling new() in more than one place at the same time, but I've tried adding mutexes to prevent that behaviour to no effect. Because the program is several hundred lines and I have no idea where the problem actually lies, I'm not sure of what, if any, code snippets to post. Instead, I was wondering if there were any tools that will help me test for this kind of thing, or if there are any general strategies that can help me with this problem. I'm using Microsoft Visual Studio 2008, with Poco for threading.

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• What is best strategy to handle exceptions & errors in Rails?

  - by Nick Gorbikoff

  Hello. I was wondering if people would share their best practices / strategies on handling exceptions & errors. Now I'm not asking when to throw an exception ( it has been throroughly answered here: SO: When to throw and Exception) . And I'm not using this for my application flow - but there are legitimate exceptions that happen all the time. For example the most popular one would be ActiveRecordNotFound. What would be the best way to handle it? The DRY way? Right now I'm doing a lot of checking within my controller so if Post.find(5) returns Nil - I check for that and throw a flash message. However while this is very granular - it's a bit cumbersome in a sense that I need to check for exceptions like that in every controller, while most of them are essentially the same and have to do with record not found or related records not found - such as either Post.find(5) not found or if you are trying to display comments related to post that doesn't exist, that would throw an exception (something like Post.find(5).comments[0].created_at) I know you can do something like this in ApplicationController and overwrite it later in a particular controller/method to get more granular support, however would that be a proper way to do it? class ApplicationController < ActionController::Base rescue_from ActiveRecord::RecordInvalid do |exception| render :action => (exception.record.new_record? ? :new : :edit) end end

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• Non-blocking TCP buffer issues.

  - by Poni

  Hi! I think I'm in a problem. I have two TCP apps connected to each other which use winsock I/O completion ports to send/receive data (non-blocking sockets). Everything works just fine until there's a data transfer burst. The sender starts sending incorrect/malformed data. I allocate the buffers I'm sending on the stack, and if I understand correctly, that's a wrong to do, because these buffers should remain as I sent them until I get the "write complete" notification from IOCP. Take this for example: void some_function() { char cBuff[1024]; // filling cBuff with some data WSASend(...); // sending cBuff, non-blocking mode // filling cBuff with other data WSASend(...); // again, sending cBuff // ..... and so forth! } If I understand correctly, each of these WSASend() calls should have its own unique buffer, and that buffer can be reused only when the send completes. Correct? Now, what strategies can I implement in order to maintain a big sack of such buffers, how should I handle them, how can I avoid performance penalty, etc'? And, if I am to use buffers that means I should copy the data to be sent from the source buffer to the temporary one, thus, I'd set SO_SNDBUF on each socket to zero, so the system will not re-copy what I already copied. Are you with me? Please let me know if I wasn't clear.

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• In Ruby, how to implement global behaviour?

  - by Gordon McAllister

  Hi all, I want to implement the concept of a Workspace. This is a global concept - all other code will interact with one instance of this Workspace. The Workspace will be responsible for maintaining the current system state (i.e. interacting with the system model, persisting the system state etc) So what's the best design strategy for my Workspace, bearing in mind this will have to be testable (using RSpec now, but happy to look at alternatives). Having read thru some open source projects out there and I've seen 3 strategies. None of which I can identify as "the best practice". They are: Include the singleton class. But how testable is this? Will the global state of Workspace change between tests? Implemented all behaviour as class methods. Again how do you test this? Implemented all behaviour as module methods. Not sure about this one at all! Which is best? Or is there another way? Thanks, Gordon

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• Best pratice: How do I implement a list that can be rendered both server-side and client-side?

  - by André Pena

  Technologies involved: ASP.NET Web-forms Javascript (jQuery for instance) Case To make it clearer let's give the Stackoverflow authors list as an example. This list can be manipulated at client-side. I can search, page and so forth. So obviously we would need to call jQuery.ajax to retrieve the HTML of each page given a search. Alright. Now this leaves me with the first question: What is the best way to render the response for the jQuery.ajax at server-side? I can't use templates I suppose, so the most obvious solution I think is to create the HTML tags as server-controls and render them as the result of an ASHX request? Is this is best approach? Nice. That solved we have yet another problem: When the user first enters the Authors List the first list page should already come from the server completely rendered alright? Of course we could render the first page as well as an ajax call but I don't think it's better. This time I CAN use templates to render the list but this template couldn't be reused in case 1. What do I do? Now the final question: Now we have 2 rendering strategies: 1) Client and 2) Server. How do I reuse code for the 2 renderings? What are the best pratices for solving these problems?

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• Best pratice: How do I implement a list similar to Stackoverflow's Users List?

  - by André Pena

  Technologies involved: ASP.NET Web-forms Javascript (jQuery for instance) Case To make it clearer let's give the Stackoverflow Users list as an example. This list can be manipulated at client-side. I can search, page and so forth. So obviously we would need to call jQuery.ajax to retrieve the HTML of each page given a search. Alright. Now this leaves me with the first question: What is the best way to render the response for the jQuery.ajax at server-side? I can't use templates I suppose, so the most obvious solution I think is to create the HTML tags as server-controls and render them as the result of an ASHX request? Is this is best approach? Nice. That solved we have yet another problem: When the user first enters the Authors List the first list page should already come from the server completely rendered alright? Of course we could render the first page as well as an ajax call but I don't think it's better. This time I CAN use templates to render the list but this template couldn't be reused in case 1. What do I do? Now the final question: Now we have 2 rendering strategies: 1) Client and 2) Server. How do I reuse code for the 2 renderings? What are the best pratices for solving these problems?

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• Testing fault tolerant code

  - by Robert

  I’m currently working on a server application were we have agreed to try and maintain a certain level of service. The level of service we want to guaranty is: if a request is accepted by the server and the server sends on an acknowledgement to the client we want to guaranty that the request will happen, even if the server crashes. As requests can be long running and the acknowledgement time needs be short we implement this by persisting the request, then sending an acknowledgement to the client, then carrying out the various actions to fulfill the request. As actions are carried out they too are persisted, so the server knows the state of a request on start up, and there’s also various reconciliation mechanisms with external systems to check the accuracy of our logs. This all seems to work fairly well, but we have difficult saying this with any conviction as we find it very difficult to test our fault tolerant code. So far we’ve come up with two strategies but neither is entirely satisfactory: Have an external process watch the server code and then try and kill it off at what the external process thinks is an appropriate point in the test Add code the application that will cause it to crash a certain know critical points My problem with the first strategy is the external process cannot know the exact state of the application, so we cannot be sure we’re hitting the most problematic points in the code. My problem with the second strategy, although it gives more control over were the fault takes, is I do not like have code to inject faults within my application, even with optional compilation etc. I fear it would be too easy to over look a fault injection point and have it slip into a production environment.

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• Omniauth/Devise/Facebook: Auth route is not recognized

  - by M. Cypher

  I've been working on this problem for 7 hours now, and I still have no idea. Maybe one of you can help me. I'm simply trying to integrate the OAuth feature of Devise 1.2rc, which uses Omniauth, into my Rails application. I've been using this tutorial by Devise: https://github.com/plataformatec/devise/wiki/OmniAuth%3A-Overview I have done everything they tell you to... Yes, I have added the following line to my devise.rb: config.omniauth :facebook, "APP ID", "APP SECRET" I have added :omniauthable to my user model, as well as the class function as described in the tutorial I have implemented the omniauth_callbacks controller, as well as the callback function, and I have specified the omniauth_callbacks controller in my routes.rb When I run "rake middleware" it does list the Omniauth middleware: use OmniAuth::Strategies::Facebook I have installed Devise directly from the Git repo, master branch, so it's up-to-date I have installed Omniauth 1.2.0.beta5, which is the latest version. In my Gemfile it says: gem 'oa-oauth', '0.2.0.beta5', :require = 'omniauth/oauth' I have restarted the server, obviously However, when I try to request this URL: http://localhost:3000/auth/facebook it simply says ActionController::RoutingError (No route matches "/auth/facebook"): /user/auth/facebook doesn't work either. Since I unfortunately don't have the time to take apart the entire Omniauth and Devise gems and understand every line of code in them, maybe one of you could tell me what the problem might be.

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• Image drawing library for Haskell?

  - by absz

  I'm working on a Haskell program for playing spatial games: I have a graph of a bunch of "individuals" playing the Prisoner's Dilemma, but only with their immediate neighbors, and copying the strategies of the people who do best. I've reached a point where I need to draw an image of the world, and this is where I've hit problems. Two of the possible geometries are easy: if people have four or eight neighbors each, then I represent each one as a filled square (with color corresponding to strategy) and tile the plane with these. However, I also have a situation where people have six neighbors (hexagons) or three neighbors (triangles). My question, then, is: what's a good Haskell library for creating images and drawing shapes on them? I'd prefer that it create PNGs, but I'm not incredibly picky. I was originally using Graphics.GD, but it only exports bindings to functions for drawing points, lines, arcs, ellipses, and non-rotated rectangles, which is not sufficient for my purposes (unless I want to draw hexagons pixel by pixel*). I looked into using foreign import, but it's proving a bit of a hassle (partly because the polygon-drawing function requires an array of gdPoint structs), and given that my requirements may grow, it would be nice to use an in-Haskell solution and not have to muck about with the FFI (though if push comes to shove, I'm willing to do that). Any suggestions? * That is also an option, actually; any tips on how to do that would also be appreciated, though I think a library would be easier.

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• Is a GWT app running on Google App Engine protected from CSRF

  - by gerdemb

  I'm developing a GWT app running on the Google App Engine and wondering if I need to worry about Cross-site request forgery or is that automatically taken care of for me? For every RPC request that requires authentication, I have the following code: public class BookServiceImpl extends RemoteServiceServlet implements BookService { public void deleteInventory(Key<Inventory> inventoryKey) throws NotLoggedInException, InvalidStateException, NotFoundException { DAO dao = new DAO(); // This will throw NotLoggedInException if user is not logged in User user = dao.getCurrentUser(); // Do deletion here } } public final class DAO extends DAOBase { public User getCurrentUser() throws NotLoggedInException { currentUser = UserServiceFactory.getUserService().getCurrentUser(); if(currentUser == null) { throw new NotLoggedInException(); } return currentUser; } I couldn't find any documentation on how the UserService checks authentication. Is it enough to rely on the code above or do I need to to more? I'm a beginner at this, but from what I understand to avoid CSRF attacks some of the strategies are: adding an authentication token in the request payload instead of just checking a cookie checking the HTTP Referer header I can see that I have cookies set from Google with what look like SID values, but I can't tell from the serialized Java objects in the payloads if tokens are being passed or not. I also don't know if the Referer header is being used or not. So, am I worrying about a non-issue? If not, what is the best strategy here? This is a common enough problem, that there must be standard solutions out there...

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• How do you refactor a large messy codebase?

  - by Ricket

  I have a big mess of code. Admittedly, I wrote it myself - a year ago. It's not well commented but it's not very complicated either, so I can understand it -- just not well enough to know where to start as far as refactoring it. I violated every rule that I have read about over the past year. There are classes with multiple responsibilities, there are indirect accesses (I forget the technical term - something like foo.bar.doSomething()), and like I said it is not well commented. On top of that, it's the beginnings of a game, so the graphics is coupled with the data, or the places where I tried to decouple graphics and data, I made the data public in order for the graphics to be able to access the data it needs... It's a huge mess! Where do I start? How would you start on something like this? My current approach is to take variables and switch them to private and then refactor the pieces that break, but that doesn't seem to be enough. Please suggest other strategies for wading through this mess and turning it into something clean so that I can continue where I left off!

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• Django Database design -- Is this a good stragety for overriding defaults

  - by rh0dium

  Hi SO's I have a question on good database design practices and I would like to leverage you guys for pointers. The project started out simple. Hey we have a bunch of questions we want answered for every project (no problem) Which turned into... Hey we have so many questions can we group them into sections (yup we can do that) Which lead into.. Can we weight these questions and I don't really want some of these questions for my project (Yes but we are getting difficult) And then I'm thinking they will want to have each section have it's own weight.. Requirements So there's the requirements - For n number of project Allow a admin member the ability select the questions for a project Allow the admin member to re-weigh or use the default weights for the questions Allow the admin member to re-weight the sections Allow team members to answer the questions. So here is what I came up with. Please feel free to comment and provide better examples models.py from django.db import models from django.contrib.sites.models import Site from django.conf import settings class Section(models.Model): """ This describes the various sections for a checklist: """ name = models.CharField(max_length=64) description = models.TextField() class Question(models.Model): """ This simply provides a simple way to list out the questions. """ question = models.CharField(max_length=255) answer_type = models.CharField(max_length=16) description = models.TextField() section = models.ForeignKey(Section) class ProjectQuestion(models.Model): """ These are the questions relevant to the project """ question = models.ForeignKey(Question) answer = models.CharField(max_length=255) required = models.BooleanField(default=True) weight = models.FloatField(default = XXX) class Project(models.Model): """ Here is where we want to gather our questions """ questions = models.ManyToManyField(ProjectQuestion) Immediate questions: - When I start a project - any ideas on how to "pre-populate" the questions (and ultimately the weights) for the project? - Is there a generally accepted method for doing this process that I am missing? Basically the idea that you refer to the questions overide your own default weight, and store the answer? - It appears that a good chuck of the work will be done in the views and that a lot of checking will need to occur there? Is that OK? Again - feel free to give me better strategies!! Thanks

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• How can I properly handle 404s in ASP.NET MVC?

  - by Brian

  I am just getting started on ASP.NET MVC so bear with me. I've searched around this site and various others and have seen a few implementations of this. EDIT: I forgot to mention I am using RC2 Using URL Routing: routes.MapRoute( "Error", "{*url}", new { controller = "Errors", action = "NotFound" } //404s ); The above seems to take care of requests like this (assuming default route tables setup by initial MVC project): "/blah/blah/blah/blah" Overriding HandleUnknownAction() in the controller itself: //404s - handle here (bad action requested protected override void HandleUnknownAction(string actionName) { ViewData["actionName"] = actionName; View("NotFound").ExecuteResult(this.ControllerContext); } However the previous strategies do not handle a request to a Bad/Unknown controller. For example, I do not have a "/IDoNotExist", if I request this I get the generic 404 page from the web server and not my 404 if I use routing + override. So finally, my question is: Is there any way to catch this type of request using a route or something else in the MVC framework itself? OR should I just default to using Web.Config customErrors as my 404 handler and forget all this? I assume if I go with customErrors I'll have to store the generic 404 page outside of /Views due to the Web.Config restrictions on direct access. Anyway any best practices or guidance is appreciated.

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• Saving Abstract and Sub classes to database

  - by bretddog

  Hi, I have an abstract class "StrategyBase", and a set of sub classes, StrategyA/B/C etc. The sub classes use some of the properties of the base class, and have some individual properties. My question is how to save this to a database. I'm currently using SqlCE, and Linq-To-Sql by creating entity classes automatically with SqlMetal.exe. I've seen there are three solutions shown in this question, but I'm not able to see how these solutions will work or not with SqlMetal/entity classes. Though it seems to me the "concrete table inheritance" would probably work without any manual modifying. What about the other two, would they be problematic? For "Single Table Inheritance" wouldn't all classes get all variables, even though they don't need them? And for the "Class table inheritance" solution I can't really see at all how that will map into the entity-classes for a useful purpose. I may note that I extend these partial entity classes for making the classes of my business objects. I may also consider moving to EntityFramework instead of SqlMetal/Linq2Sql, so would be nice also to know if that makes any difference to what schema is easy to implement. One likely important thing to note is that I will constantly be develop new strategies, which makes me have to modify the program code, and probably the database shcema; when adding a new strategy. Sorry the question is a bit "all over the place", but hopefully it's some clear advantages/disadvantages here that you may be able to advice. ? Cheers!

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• Using SQL dB column as a lock for concurrent operations in Entity Framework

  - by Sid

  We have a long running user operation that is handled by a pool of worker processes. Data input and output is from Azure SQL. The master Azure SQL table structure columns are approximated to [UserId, col1, col2, ... , col N, beingProcessed, lastTimeProcessed ] beingProcessed is boolean and lastTimeProcessed is DateTime. The logic in every worker role is: public void WorkerRoleMain() { while(true) { try { dbContext db = new dbContext(); // Read foreach (UserProfile user in db.UserProfile .Where(u => DateTime.UtcNow.Subtract(u.lastTimeProcessed) > TimeSpan.FromHours(24) & u.beingProcessed == false)) { user.beingProcessed = true; // Modify db.SaveChanges(); // Write // Do some long drawn processing here ... ... ... user.lastTimeProcessed = DateTime.UtcNow; user.beingProcessed = false; db.SaveChanges(); } } catch(Exception ex) { LogException(ex); Sleep(TimeSpan.FromMinutes(5)); } } // while () } With multiple workers processing as above (each with their own Entity Framework layer), in essence beingProcessed is being used a lock for MutEx purposes Question: How can I deal with concurrency issues on the beingProcessed "lock" itself based on the above load? I think read-modify-write operation on the beingProcessed needs to be atomic but I'm open to other strategies. Open to other code refinements too.

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• C++0x rvalue references and temporaries

  - by Doug

  (I asked a variation of this question on comp.std.c++ but didn't get an answer.) Why does the call to f(arg) in this code call the const ref overload of f? void f(const std::string &); //less efficient void f(std::string &&); //more efficient void g(const char * arg) { f(arg); } My intuition says that the f(string &&) overload should be chosen, because arg needs to be converted to a temporary no matter what, and the temporary matches the rvalue reference better than the lvalue reference. This is not what happens in GCC and MSVC. In at least G++ and MSVC, any lvalue does not bind to an rvalue reference argument, even if there is an intermediate temporary created. Indeed, if the const ref overload isn't present, the compilers diagnose an error. However, writing f(arg + 0) or f(std::string(arg)) does choose the rvalue reference overload as you would expect. From my reading of the C++0x standard, it seems like the implicit conversion of a const char * to a string should be considered when considering if f(string &&) is viable, just as when passing a const lvalue ref arguments. Section 13.3 (overload resolution) doesn't differentiate between rvalue refs and const references in too many places. Also, it seems that the rule that prevents lvalues from binding to rvalue references (13.3.3.1.4/3) shouldn't apply if there's an intermediate temporary - after all, it's perfectly safe to move from the temporary. Is this: Me misreading/misunderstand the standard, where the implemented behavior is the intended behavior, and there's some good reason why my example should behave the way it does? A mistake that the compiler vendors have somehow all made? Or a mistake based on common implementation strategies? Or a mistake in e.g. GCC (where this lvalue/rvalue reference binding rule was first implemented), that was copied by other vendors? A defect in the standard, or an unintended consequence, or something that should be clarified?

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• Advice Please: SQL Server Identity vs Unique Identifier keys when using Entity Framework

  - by c.batt

  I'm in the process of designing a fairly complex system. One of our primary concerns is supporting SQL Server peer-to-peer replication. The idea is to support several geographically separated nodes. A secondary concern has been using a modern ORM in the middle tier. Our first choice has always been Entity Framework, mainly because the developers like to work with it. (They love the LiNQ support.) So here's the problem: With peer-to-peer replication in mind, I settled on using uniqueidentifier with a default value of newsequentialid() for the primary key of every table. This seemed to provide a good balance between avoiding key collisions and reducing index fragmentation. However, it turns out that the current version of Entity Framework has a very strange limitation: if an entity's key column is a uniqueidentifier (GUID) then it cannot be configured to use the default value (newsequentialid()) provided by the database. The application layer must generate the GUID and populate the key value. So here's the debate: abandon Entity Framework and use another ORM: use NHibernate and give up LiNQ support use linq2sql and give up future support (not to mention get bound to SQL Server on DB) abandon GUIDs and go with another PK strategy devise a method to generate sequential GUIDs (COMBs?) at the application layer I'm leaning towards option 1 with linq2sql (my developers really like linq2[stuff]) and 3. That's mainly because I'm somewhat ignorant of alternate key strategies that support the replication scheme we're aiming for while also keeping things sane from a developer's perspective. Any insight or opinion would be greatly appreciated.

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• javascript toolkit for offline webapps

  - by anjanb

  hi all, we're building an survey webapp which will let the user to add new records to the survey when offline and will upload when the browser reconnects with the server. We've identified that this will need offline storage and hence google gears seems to be an obvious choice (we understand that adobe Flash has Offline Storage but not sure if that is the best way). I am aware of Dojo offline javascript toolkit which uses google gears for the underlying functionality. However, dojo offline is not part of the dojo toolkit after version 1.3. (currently dojo is 1.4.2). Google gears toolkit is currently frozen except for critical vulnerability fixes (it has not been updated almost for the last 1 yr) because they think that HTML 5 is the way to go ahead. Hence, we're looking for a higher abstraction on top of Google Gears engine TODAY, AND which will (in the future) switch the underlying engine to HTML5 if the browser supports HTML5 standards. We'd love to use Dojo but they have discontinued Dojo offline -- we'd prefer something that will be maintained for some time. Which are possible good strategies, JS toolkits/libraries to use for building this webapp ? Pls. advise.

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• Approach for fixing NoClassDefFoundError?

  - by DJC

  I'm seeing this question is getting asked a lot in many different contexts. Perhaps we can set some strategies for locating and fixing it? I'm noobish myself so all I can contribute are horror stories and questions, sorry... It seems this is thrown when a class is visible at compile time but not at run time... how can this happen? In my case I am developing an app that uses the Google APIs, in Eclipse, for the Android platform. I've configured the Project Properties / Java Build Path / Libraries to include the gdata .jars and all is well. When I execute in the emulator I get a force close and the logcat shows a NoClassDefFoundError on a simple new ContactsService("myApp"); I've also tried a new CalendarService("myApp") with the same results. Is it possible or desirable to statically bind at compile time to avoid the problem? How could dynamic binding of an add-on library work in the mobile environment anyway? Either it has to be bound into my .apk or else I need to "install" it? ... hmmm. Advice much appreciated.

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• Non-blocking TCP connection issues.

  - by Poni

  Hi! I think I'm in a problem. I have two TCP apps connected to each other which use winsock I/O completion ports to send/receive data (non-blocking sockets). Everything works just fine until there's a data transfer burst. The sender starts sending incorrect/malformed data. I allocate the buffers I'm sending on the stack, and if I understand correctly, that's a wrong to do, because these buffers should remain as I sent them until I get the "write complete" notification from IOCP. Take this for example: void some_function() { char cBuff[1024]; // filling cBuff with some data WSASend(...); // sending cBuff, non-blocking mode // filling cBuff with other data WSASend(...); // again, sending cBuff // ..... and so forth! } If I understand correctly, each of these WSASend() calls should have its own unique buffer, and that buffer can be reused only when the send completes. Correct? Now, what strategies can I implement in order to maintain a big sack of such buffers, how should I handle them etc'? And, if I am to use buffers that means I should copy the data to be sent from the source buffer to the temporary one, thus, I'd set SO_SNDBUF on each socket to zero, so the system will not re-copy what I already copied. Are you with me? Please let me know if I wasn't clear.

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• What is an efficient strategy for multiple threads posting jobs and waiting for response from a single thread?

  - by jakewins

  In java, what is an efficient solution to the following problem: I have multiple threads (10-20 or so) generating jobs ("Job Creators"), and a single thread capable of performing them ("The worker"). Once a job creator has posted a job, it should wait for the job to finish, yielding no result other than "it's done", before it keeps going. For sending the jobs to the worker thread, I think a ring buffer or similar standard fan-in setup would perhaps be a good approach? But for a Job Creator to find out that her job has been done, I'm not so sure.. The job creators could sleep, and the worker interrupt them when done.. Or each job creator could have an atomic boolean that it checks, and that the worker sets. I dunno, neither of those feel very nice. I'd like to do it with as few (none, if possible) locks as absolutely possible. So to be clear: What I'm looking for is speed, not necessarily simplicity. Does anyone have any suggestions? Links to reading about concurrency strategies would also be very welcome!

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