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  • Java's Scanner class: using left- and right buttons with Bash

    - by Bart K.
    I'm not too familiar with Linux/Bash, so I can't really find the right terms to search for. Take the snippet: public class Main { public static void main(String[] args) { java.util.Scanner keyboard = new java.util.Scanner(System.in); while(true) { System.out.print("$ "); String in = keyboard.nextLine(); if(in.equals("q")) break; System.out.println(" "+in); } } } If I run it on my Linux box using Bash, I can't use any of the arrow buttons (I'm only interested in the left- and right button, btw). For example, if I type "test" and then try to go back by pressing the left button, ^[[D appears instead of my cursor going back one place: $ test^[[D I've tried the newer Console class as well, but the end result is the same. On Windows' cmd.exe shell, I don't have this problem. So, the question is: is there a way to change my Java code so that I can use the arrow keys without Bash transforming them in sequences like ^[[D but actually move the cursor instead? I'm hoping that I can solve this on a "programming level". If this is not possible, then I guess I'd better try my luck on Superuser to see if there's something I need to change on my Bash console. Thanks in advance.

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  • GWT, MVP, and UIBinding - How to get the best of all worlds

    - by Stephane Grenier
    With MVP, you normally bind the View (UI) with the Presenter in the Presenter. However with the latest version of GWT, especially with UIBinding, you can do the following in the View: @UiHandler("loginButton") void onAboutClicked(ClickEvent event) { // my login code } Which basically exchanges a lot of anonymous inner class code for some quick annotation code. Very nice!! The problem is that this code is in the view and not the presenter... So I thought maybe: @UiHandler("loginButton") void onAboutClicked(ClickEvent event) { myPresenter.onAboutClicked(...); } But there are several problems with this approach. The most important, you blur the lines between View and Presenter. Who does which binding, in some cases it's the View, in others it's the presenter (binding to events not in your current view but that need to be attached - for example a system wide update event). You still get the benefit of being able to unit test your presenter, but at what cost. The responsibilities are messy now. For example the binding is sometimes in the View and others times in the Presenter level. I can see the code falling into all kinds of chaos with time. I also thought of extending the Presenter to the View, so that you could do this in the View. The problem here is that you lose the Presenter's ability to run standard unit tests! That's a major issue. That and the lines again become blurred. So my question, does anyone have a good method of taking advantage of the annotation from UIBinding within the MVP pattern without blurring the lines and losing the advantages of the MVP pattern?

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  • python scritp problem once build and package it

    - by Apache
    hi expert, i've written python script to scan wifi and send data to the server, i set interval value, so it keep on scanning and send the data, it read from config.txt file where i set the interval value to scan, i also add yes/no in my config file, so is 'no' it will scan only once and if 'yes' it will scan according to the interval level, my code as below import time,..... from threading import Event, Thread class RepeatTimer(Thread): def __init__(self, interval, function, iterations=0, args=[], kwargs={}): Thread.__init__(self) self.interval = interval self.function = function self.iterations = iterations self.args = args self.kwargs = kwargs self.finished = Event() def run(self): count = 0 while not self.finished.is_set() and (self.iterations <= 0 or count < self.iterations): self.finished.wait(self.interval) if not self.finished.is_set(): self.function(*self.args, **self.kwargs) count += 1 def cancel(self): self.finished.set() def scanWifi(self): #scanning process and sending data done here obj = JW() if status == "yes": t = RepeatTimer(int(intervalTime),obj.scanWifi) t.start() else: obj.scanWifi() once i package my code, its only run when i set my config file set to 'no' where it scan only once, but when i set my config file to 'yes', there is no progress at all, so i found that there is problem with my class RepeatTimer(Timer) once build, but don't know how to solve can anyone help me thanks

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  • Keeping track of leading zeros with BitSet in Java

    - by Ryan
    So, according to this question there are two ways to look at the size of a BitSet. size(), which is legacy and not really useful. I agree with this. The size is 64 after doing: BitSet b = new BitSet(8); length(), which returns the index of the highest set bit. In the above example, length() will return 0. This is somewhat useful, but doesn't accurately reflect the number of bits the BitSet is supposed to be representing in the event you have leading zeros. The information I'm dealing with rarely(if ever) falls evenly into 8-bit bytes, and the leading 0s are just as important to me as the 1s. I have some data fields that are 333 bits long, some that are 20, etc. Is there a better way to deal with bit-level details in Java that will keep track of leading zeros? Otherwise, I'm going to have to 'roll my own', so to speak. To which I have a few ideas already, but I'd prefer not to reinvent the wheel if possible.

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  • Automatically install and launch a code-signed application from Safari

    - by Thomas Jung
    Is it possible and if so what are the steps necessary to package (or build) a Mac OS X application and code-sign it so that it can be downloaded with Safari and automatically launch? ... possibly after the user responds to some sort of dialog explaining that it is a signed application and the publisher has been verified. An example of the user experience I am trying to create is "installing Google Chrome for the first time on Windows", which is a 3-click, less-than-a-minute process. For the concerned among you: I am not trying to create a drive-by download. I am fine with some sort of intermittent user step approving the download. I just want to make the installation as quick and painless as possible and not require the user drag the app from a mounted DMG into the application folder. This may not 100% jibe with established Mac OS X user interaction guidelines, but it would work better for the not-power users. I only need the high-level steps or pointers to resources ... my google-fu was weak on this one.

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  • WPF compile error "IDictionary must have a Key attribute"

    - by the empirical programmer
    I've created control styles I want to use among multiple xaml pages in my WPF app. To do this I created a Resources.xaml and added the styles there. Then in my pages I add this code <Grid.Resources> <ResourceDictionary> <ResourceDictionary.MergedDictionaries> <ResourceDictionary Source="pack://application:,,,/SampleEventTask;component/Resources.xaml" /> </ResourceDictionary.MergedDictionaries> </ResourceDictionary> </Grid.Resources> On two pages this works fine, but on the 3rd page I get a compile error that says: All objects added to an IDictionary must have a Key attribute or some other type of key associated with them. If I add a key to this, as such ResourceDictionary x:Key="x", then the compile error goes but on running the app it errors finding the style. I can make the compile error go away and have the app run by just moving original (no key specified) "ResourceDictionary" xaml from the top level Grid into a contained Grid on that page. But I don't understand what is going on here. Any suggestions as to what the problem is, I'm just missing something or doing something incorrectly. Is there a better way to share styles? thanks

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  • Unit Testing in the real world

    - by Malfist
    I manage a rather large application (50k+ lines of code) by myself, and it manages some rather critical business actions. To describe the program simple, I would say it's a fancy UI with the ability to display and change data from the database, and it's managing around 1,000 rental units, and about 3k tenants and all the finances. When I make changes, because it's so large of a code base, I sometimes break something somewhere else. I typically test it by going though the stuff I changed at the functional level (i.e. I run the program and work through the UI), but I can't test for every situation. That is why I want to get started with unit testing. However, this isn't a true, three tier program with a database tier, a business tier, and a UI tier. A lot of the business logic is performed in the UI classes, and many things are done on events. To complicate things, everything is database driven, and I've not seen (so far) good suggestions on how to unit test database interactions. How would be a good way to get started with unit testing for this application. Keep in mind. I've never done unit testing or TDD before. Should I rewrite it to remove the business logic from the UI classes (a lot of work)? Or is there a better way?

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  • Reading UTF-8 XML and writing it to a file with Python

    - by Harri
    I'm trying to parse UTF-8 XML file and save some parts of it to another file. Problem is, that this is my first Python script ever and I'm totally confused about the character encoding problems I'm finding. My script fails immediately when it tries to write non-ascii character to a file, but it can print it to command prompt (at least in some level) Here's the XML (from the parts that matter at least, it's a *.resx file which contains UI strings) <?xml version="1.0" encoding="utf-8"?> <root> <resheader name="foo"> <value>bar</value> </resheader> <data name="lorem" xml:space="preserve"> <value>ipsum öä</value> </data> </root> And here's my python script from xml.dom.minidom import parse names = [] values = [] def getStrings(path): dom = parse(path) data = dom.getElementsByTagName("data") for i in range(len(data)): name = data[i].getAttribute("name") names.append(name) value = data[i].getElementsByTagName("value") values.append(value[0].firstChild.nodeValue.encode("utf-8")) def writeToFile(): with open("uiStrings-fi.py", "w") as f: for i in range(len(names)): line = names[i] + '="'+ values[i] + '"' #varName='varValue' f.write(line) f.write("\n") getStrings("ResourceFile.fi-FI.resx") writeToFile() And here's the traceback: Traceback (most recent call last): File "GenerateLanguageFiles.py", line 24, in writeToFile() File "GenerateLanguageFiles.py", line 19, in writeToFile line = names[i] + '="'+ values[i] + '"' #varName='varValue' UnicodeDecodeError: 'ascii' codec can't decode byte 0xc3 in position 2: ordinal not in ran ge(128) How should I fix my script so it would read and write UTF-8 characters properly? The files I'm trying to generate would be used in test automation with Robots Framework.

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  • Strange behaviour using Drag and Drop in word 2003 automation in headers

    - by Oliver Hanappi
    Hi! I am developing a template based addin for Word 2003 which allows the user to drag and drop elements from a listbox into the word document. Unfortunately I'm getting a really strange behaviour when trying to drop elements in the document's header. Open the template and type something in the header Close the header and insert some content on the page Add a page break. Switch to page layout mode where and set zoom level to "Two Pages" Open the header Slowly Drag and Drop an list item from the list box to the header. See multiple Page Setups dialogs occur which cause Word to crash. Here is my code: // in ThisDocument.cs public MyUserControl _control; public void Init() { _control = new MyUserControl(); ActionsPane.Controls.Add(_control); ActionsPane.Visible = true; } // in MyUserControl.cs public void listBox1_MouseDown(object sender, MouseEventArgs e) { DoDragDrop("something", DragDropEffects.Copy); } Have I done somethinkg wrong with implementing Drag and Drop? Is there a workaround for this strange behaviour? Thanks in advance, Oliver Hanappi

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  • What would be the safest way to store objects of classes derived from a common interface in a common

    - by Svenstaro
    I'd like to manage a bunch of objects of classes derived from a shared interface class in a common container. To illustrate the problem, let's say I'm building a game which will contain different actors. Let's call the interface IActor and derive Enemy and Civilian from it. Now, the idea is to have my game main loop be able to do this: // somewhere during init std::vector<IActor> ActorList; Enemy EvilGuy; Civilian CoolGuy; ActorList.push_back(EvilGuy); ActorList.push_back(CoolGuy); and // main loop while(!done) { BOOST_FOREACH(IActor CurrentActor, ActorList) { CurrentActor.Update(); CurrentActor.Draw(); } } ... or something along those lines. This example obviously won't work but that is pretty much the reason I'm asking here. I'd like to know: What would be the best, safest, highest-level way to manage those objects in a common heterogeneous container? I know about a variety of approaches (Boost::Any, void*, handler class with boost::shared_ptr, Boost.Pointer Container, dynamic_cast) but I can't decide which would be the way to go here. Also I'd like to emphasize that I want to stay away as far as possible from manual memory management or nested pointers. Help much appreciated :).

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  • Readability and IF-block brackets: best practice

    - by MasterPeter
    I am preparing a short tutorial for level 1 uni students learning JavaScript basics. The task is to validate a phone number. The number must not contain non-digits and must be 14 digits long or less. The following code excerpt is what I came up with and I would like to make it as readable as possible. if ( //set of rules for invalid phone number phoneNumber.length == 0 //empty || phoneNumber.length > 14 //too long || /\D/.test(phoneNumber) //contains non-digits ) { setMessageText(invalid); } else { setMessageText(valid); } A simple question I can not quite answer myself and would like to hear your opinions on: How to position the surrounding (outermost) brackets? It's hard to see the difference between a normal and a curly bracket. Do you usually put the last ) on the same line as the last condition? Do you keep the first opening ( on a line by itself? Do you wrap each individual sub-condition in brackets too? Do you align horizontally the first ( with the last ), or do you place the last ) in the same column as the if? Do you keep ) { on a separate line or you place the last ) on the same line with the last sub-condition and then place the opening { on a new line? Or do you just put the ) { on the same line as the last sub-condition? Community wiki. EDIT Please only post opinions regarding the usage and placement of brackets. The code needs not be re-factored. This is for people who have only been introduced to JavaScript a couple of weeks ago. I am not asking for opinions how to write the code so it's shorter or performs better. I would only like to know how do you place brackets around IF-conditions.

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  • javascript normalize whitespace and other plain-text formatting routines

    - by dreftymac
    Background: The language is JavaScript. The goal is to find a library or pre-existing code to do low-level plain-text formatting. I can write it myself, but why re-invent the wheel. The issue is: it is tough to determine if a "wheel" is out there, since any search for JavaScript libraries pulls up an ocean of HTML-centric stuff. I am not interested in HTML necessarily, just text. Example: I need a JavaScript function that changes this: BEFORE: nisi ut aliquip | ex ea commodo consequat duis |aute irure dolor in esse cillum dolore | eu fugiat nulla pariatur |excepteur sint occa in culpa qui | officia deserunt mollit anim id |est laborum ... into this ... AFTER: nisi ut aliquip | ex ea commodo consequat duis | aute irure dolor in esse cillum dolore | eu fugiat nulla pariatur | excepteur sint occa in culpa qui | officia deserunt mollit anim id | est laborum Question: Does it exist, a JavaScript library that is non-html-web-development-centric that has functions for normalizing spaces in delimited plain text, justifying and spacing plain text? Rationale: Investigating JavaScript for use in a programmer's text editor.

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  • DIY intellisense on XPath - design approach? (WinForms app)

    - by Cheeso
    I read the DIY Intellisense article on code project, which was referenced from the Mimic Intellisense? question here on SO. I wanna do something similar, DIY intellisense, but for XPath not C#. The design approach used there makes sense to me: maintain a tree of terms, and when the "completion character" is pressed, in the case of C#, a dot, pop up the list of possible completions in a textfield. Then allow the user to select a term from the textfield either through typing, arrow keys, or double-click. How would you apply this to XPath autocompletion? should there be an autocomplete key? In XPath there is no obvious separator key like "dot" in C#. should the popup be triggered explicitly in some other way, let's say ctrl-. ? or should the parser try to autocomplete continuously? If I do the autocomplete continuously, how to scale it properly? There are 93 xpath functions, not counting overloads. I certainly don't want to popup a list of 93 choices. How do I decide when I've narrowed it enough to offer a useful lsit of possible completions? How to populate the tree of possible completions? For C#, it's easy: walk the type space via reflection. At a first level, the "syntax tree" for C# seems like a single tree, and the list of completions at any point depends on the graph of nodes you've traversed to that point. Typing System.Console. traverses to a certain node in that tree, and the list of completions is the set of child nodes available at that node in the tree. On the other hand, the xpath syntax seems like it is a "flatter" tree - function names, axis names, literals. Does this make sense? what have I not considered?

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  • Asp net aspx page and webcontrol issue

    - by Josemalive
    Hello, I have a class that inherits from Page, called APage. public abstract class APage: Page { protected Repeater ExampleRepeater; .... protected override void OnLoad(EventArgs e) { if (null != ExampleRepeater) { ExampleRepeater.DataSource = GetData(); ExampleRepeater.DataBind(); } base.OnLoad(e); } } For other hand i have an aspx page called Default that inherits from this APage: public partial class Default : APage { } on the design part of this Default page, i have a repeater: <asp:Repeater ID="ExampleRepeater" runat="server"> <ItemTemplate> <%# DataBinder.Eval(Container.DataItem, "Name") %><br/> </ItemTemplate> </asp:Repeater> This repeater is datasourced at the base APage load event, but at this level this web control is null. Do you have any idea why the control is null in the base page? Thanks in advance. Best Regards. Jose.

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  • Best approach for a multi-tab ASP.NET AJAX control?

    - by NovaJoe
    Looking for some implementation advice: I have a page that has a 3-tab ajaxToolkit:TabContainer. The purpose of the page is to expose a calculator that has two basic inputs: geo-location and date. The three tabs are labeled "City and State", "Postal Code", and "GPS Coordinates". The layout of each tab container is the same for each tab, with the exception of the location section; the location section changes because each type of location has different inputs. For example, to specify city/state, there will be three fields: city, country, and state (country and state will use cascading drop-down lists). But Postal code requires only one field (which will validate via regular expression for allowed countries). See the example design mockup: So, what I WOULD LIKE to do (in order to minimize duplicate code), is to have a common control that contains the layout and structure of the calculator without specifying anything about the location section. Then, I'd like to be able to pull in each of the unique location controls based on what tab is selected. The tab structure exists at the page level, not in a control. Any advice? I was looking at templated controls (see MSDN article here), but I'm not convinced that it's the right solution. If I HAVE to create three separate controls with similar layouts and common elements, then that's what I have to do. But REALLY, I'd prefer a more elegant, inheritance-based solution. Any advice would be greatly appreciated. Thanks.

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  • Specific complex array sorting

    - by TheDeadMedic
    Okay, a before; Array ( 'home' => array('order' => 1), 'about' => array(), 'folio' => array('order' => 2), 'folio/web' => array('order' => 2), 'folio/print' => array('order' => 1) 'contact' => array('order' => 2) ) And a desired after; Array ( 'home' => array('order' => 1), 'contact' => array('order' => 2), 'folio' => array('order' => 2), 'folio/print' => array('order' => 1), 'folio/web' => array('order' => 2), 'about' => array() ) I know, horrific (don't ask!) See how the slash in the key indicates children, and how the order is nested accordingly? And items without orders are simply shifted to the bottom. But also how multiple 'same level' items with the same order are merely sorted by key?

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  • What is best practice (and implications) for packaging projects into JAR's?

    - by user245510
    What is considered best practice deciding how to define the set of JAR's for a project (for example a Swing GUI)? There are many possible groupings: JAR per layer (presentation, business, data) JAR per (significant?) GUI panel. For significant system, this results in a large number of JAR's, but the JAR's are (should be) more re-usable - fine-grained granularity JAR per "project" (in the sense of an IDE project); "common.jar", "resources.jar", "gui.jar", etc I am an experienced developer; I know the mechanics of creating JAR's, I'm just looking for wisdom on best-practice. Personally, I like the idea of a JAR per component (e.g. a panel), as I am mad-keen on encapsulation, and the holy-grail of re-use accross projects. I am concerned, however, that on a practical, performance level, the JVM would struggle class loading over dozens, maybe hundreds of small JAR's. Each JAR would contain; the GUI panel code, necessary resources (i.e. not centralised) so each panel can stand alone. Does anyone have wisdom to share?

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  • HTTP 1.0 vs 1.1

    - by Jason Baker
    Could somebody give me a brief overview of the differences between HTTP 1.0 and HTTP 1.1? I've spent some time with both of the RFCs, but haven't been able to pull out a lot of difference between them. Wikipedia says this: HTTP/1.1 (1997-1999) Current version; persistent connections enabled by default and works well with proxies. Also supports request pipelining, allowing multiple requests to be sent at the same time, allowing the server to prepare for the workload and potentially transfer the requested resources more quickly to the client. But that doesn't mean a lot to me. I realize this is a somewhat complicated subject, so I'm not expecting a full answer, but can someone give me a brief overview of the differences at a bit lower level? By this I mean that I'm looking for the info I would need to know to implement either an HTTP server or application. I realize that this can be a somewhat complicated subject (based on what I know about HTTP as of right now), so I'm not necessarily looking for a full answer. I'm really more looking for a nudge in the right direction so that I can figure it out on my own.

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  • Creating a window manager type overlay for Mac OS X

    - by zorg1379
    I want to make my own window manager for OS X, or at least give it the appearance of a new one. I have many designs written down in a book, and would like to implement them. These include altering, or even completely removing, menu bars, creating entirely new guis for switching applications, etc. I know that OS X does not have a window manager, and that basically the functions that an X11 window manager would perform are done by Carbon, Cocoa, the Dock application, and the window server. I've read that it would take an incredible amount of reverse engineering to write my own api, etc. at the hardware level. I am still not that good at programming though, and don't have that kind of time. That's why I was thinking of maybe running an application on top of OS X that will function like a separate window manager - and do everything that the normal OS GUI / window manager would do. Is this possible? For example: making a custom button that would appear upon a certain key combination, that could be clicked to access a document viewer, change the time, minimize a window, etc. Is there some way to access functionality to basic tasks / actions like this without using the default OS X button controls, and implementing them with my own GUI? I am talking about more than a simple theme change, I want to completely change the user experience. This means that this application would be run in a full screen mode that blocks out default OS X menu bars. I've heard something about using graphics architectures to plug in your own window manager? Would this be an option too? If so, how would I go about doing that? Thank you,

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  • WCF Data Services - neither .Expand or .LoadProperty seems to do what I need

    - by TomK
    I am building a school management app where they track student tardiness and absences. I've got three entities to help me in this. A Students entity (first name, last name, ID, etc.); a SystemAbsenceTypes entity with SystemAbsenceTypeID values for Late, Absent-with-Reason, Absent-without-Reason; and a cross-reference table called StudentAbsences (matching the student IDs with the absence-type ID, plus a date, and a Notes field). What I want to do is query my entities for a given student, and then add up the number of each kind of Absence, for a given date range. I prepare my currentStudent object without a problem, then I do this... Me.Data.LoadProperty(currentStudent, "StudentAbsences") 'Loads the cross-ref data lblDaysLate.Text = (From ab In currentStudent.StudentAbsences Where ab.SystemAbsenceTypes.SystemAbsenceTypeID = Common.enuStudentAbsenceTypes.Late).Count.ToString ...and this second line fails, complaining it has no value for an object. I presume the problem is that while it DOES see that there are (let's say) four absences for the currentStudent (ie, currentStudent.StudentAbsences.Count = 4) -- it can't yet "peer into" each one of the absences to look at its type. How do I use .Expand or .LoadProperty to make this happen? I tried fiddling with .LoadProperty but it doesn't take a two-level syntax like so... Data.LoadProperty(currentStudent,"StudentAbsences.SystemAbsenceTypeID") or the like. Is there some other technique?

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  • Restrict access to connection pool in Weblogic?

    - by Andrew White
    In short, how can I restrict access to connection pool X based on application name or JAR name? A simple use case might help... A business web-app (call it WEB_APP_A) uses pool Y to do basic look-up SQL. Some users of this web-app have access to also update some sensitive data in the database. This code is provided by a JAR file (call it HR_JAR) that can be dropped in where needed. This JAR uses pool X for all of it's connections. We don't want developers of WEB_APP_A using pool X. We only want HR_JAR using pool X. This is to keep devs of WEB_APP_A from accidentally or intentionally abusing the access pool X provides. Some considerations: This is legacy code so HR_JAR is here to stay We are running on Weblogic 9.2 We can not keep passwords in any from in the source code We have researched weblogic user level authn/authz for JDBC resources but then this begs the question; how do we secure the user creds we use to become a user per app/jar? Ideas? Thoughts? I can elaborate more on what I have tried, but I wanted fresh ideas.

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  • Flexible design - customizable entity model, UI and workflow

    - by Ngm
    Hi All, I want to achieve the following aspects in the software I am building: 1. Customizable entity model 2. Customizable UI 3. Customizable workflow I have thought about an approach to achieve this, I want you to review this and make suggestions: Entity objects should be plain objects and will hold just data Separate Entity model and DB Schema by using an framework (like NHibernate?). This will allow easy modification of entity objects. Business logic to fetch/modify entities has to be granular enough so that they can be invoked as part of the workflow. Business objects should not hold any state, and hence will contain only static methods The workflow will decide depending upon the "state" of an entity/entities which methods on business object/objects to invoke. The workflow should obtain the results of the processing and then pass on the business objects to the appropriate UI screen. The UI screen has to contain instructions about how to display a given entity/entites. Possibly the UI has to be generated dynamically based on a set of UI instructions. (like XUL) What do you think about this approach? Suggest which existing frameworks (like NHiberante, Window Workflow) fit into this model, so that I will not spend time on coding these frameworks Also suggest is there any asp.net framework that can generate dynamic asp.net ajax pages based on a set of UI instructions (like Mozilla XUL)? I have recently been exploring Apache Ofbiz and was impressed by its ability to customize most areas of the application: UI, workflow, entities. Is there any similar (not necessarily an ERP system) application developed in C#/.Net which offers a similar level of customization? I am looking for examples of applications developed in C# that are highly customizable in terms of UI, Workflow and Entity Model

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  • how to atomically claim a row or resource using UPDATE in mysql

    - by Igor
    i have a table of resources (lets say cars) which i want to claim atomically. if there's a limit of one resource per one user, i can do the following trick: UPDATE cars SET user = 'bob' WHERE user IS NULL LIMIT 1 SELECT * FROM cars WHERE user IS bob that way, i claim the resource atomically and then i can see which row i just claimed. this doesn't work when 'bob' can claim multiple cars. i realize i can get a list of cars already claimed by bob, claim another one, and then SELECT again to see what's changed, but that feels hackish. What I'm wondering is, is there some way to see which rows i just updated with my last UPDATE? failing that, is there some other trick to atomically claiming a row? i really want to avoid using SERIALIZABLE isolation level. If I do something like this: 1 SELECT id FROM cars WHERE user IS NULL 2 <here, my PHP or whatever picks a car id> 3 UPDATE cars SET user = 'bob' WHERE id = <the one i picked> would REPEATABLE READ be sufficient here? in other words, could i be guaranteed that some other transactions won't claim the row my software has picked during step 2?

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  • Detecting death of spawned process using Window CRT

    - by Michael Tiller
    Executive summary: I need a way to determine whether a Windows process I've spawned via _spawnl and am communicating with using FDs from _pipe has died. Details: I'm using the low-level CRT function in Windows (_eof, _read) to communicate with a process that was spawned via a call to _spawnl (with the P_NOWAIT) flag. I'm using _pipe to create file descriptors to communicate with this spawned process and passing those descriptors (the FD #) to it on the command line. It is worth mentioning that I don't control the spawned process. It's a black box to me. It turns out that the process we are spawning occasionally crashes. I'm trying to make my code robust to this by detecting the crash. Unfortunately, I can't see a way to do this. It seems reasonable to me to expect that a call to _eof or _read on one of those descriptors would return an error status (-1) if the process had died. Unfortunately, that isn't the case. It appears that the descriptors have a life of their own independent of the spawned process. So even though the process on the other end is dead, I get no error status on the file descriptor I'm using to communicate with it. I've got the PID for the nested process (returned from the _spanwnl call) but I don't see anything I can do with that. My code works really well except for one thing. I can't detect whether the spawned process is simply busy computing me an answer or has died. If I can use the information from _pipe and _spawnl to determine if the spawned process is dead, I'll be golden. Suggestions very welcome. Thanks in advance. UPDATE: I found a fairly simple solution and added it as the selected answer.

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  • How will Arel affect rails' includes() 's capabilities.

    - by Tim Snowhite
    I've looked over the Arel sources, and some of the activerecord sources for Rails 3.0, but I can't seem to glean a good answer for myself as to whether Arel will be changing our ability to use includes(), when constructing queries, for the better. There are instances when one might want to modify the conditions on an activerecord :include query in 2.3.5 and before, for the association records which would be returned. But as far as I know, this is not programmatically tenable for all :include queries: (I know some AR-find-includes make t#{n}.c#{m} renames for all the attributes, and one could conceivably add conditions to these queries to limit the joined sets' results; but others do n_joins + 1 number of queries over the id sets iteratively, and I'm not sure how one might hack AR to edit these iterated queries.) Will Arel allow us to construct ActiveRecord queries which specify the resulting associated model objects when using includes()? Ex: User :has_many posts( has_many :comments) User.all(:include => :posts) #say I wanted the post objects to have their #comment counts loaded without adding a comment_count column to `posts`. #At the post level, one could do so by: posts_with_counts = Post.all(:select => 'posts.*, count(comments.id) as comment_count', :joins => 'left outer join comments on comments.post_id = posts.id', :group_by => 'posts.id') #i believe #But it seems impossible to do so while linking these post objects to each #user as well, without running User.all() and then zippering the objects into #some other collection (ugly) #OR running posts.group_by(&:user) (even uglier, with the n user queries)

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