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  • Is this a correct Interlocked synchronization design?

    - by Dan Bryant
    I have a system that takes Samples. I have multiple client threads in the application that are interested in these Samples, but the actual process of taking a Sample can only occur in one context. It's fast enough that it's okay for it to block the calling process until Sampling is done, but slow enough that I don't want multiple threads piling up requests. I came up with this design (stripped down to minimal details): public class Sample { private static Sample _lastSample; private static int _isSampling; public static Sample TakeSample(AutomationManager automation) { //Only start sampling if not already sampling in some other context if (Interlocked.CompareExchange(ref _isSampling, 0, 1) == 0) { try { Sample sample = new Sample(); sample.PerformSampling(automation); _lastSample = sample; } finally { //We're done sampling _isSampling = 0; } } return _lastSample; } private void PerformSampling(AutomationManager automation) { //Lots of stuff going on that shouldn't be run in more than one context at the same time } } Is this safe for use in the scenario I described?

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  • Java appliction design question

    - by ring bearer
    Hi I have a hobby project, which is basically to maintain 'todo' tasks in the way I like. One task can be described as: public class TodoItem { private String subject; private Date dueBy; private Date startBy; private Priority priority; private String category; private Status status; private String notes; } as you can imagine I would have 1000 todo items at a given time. What is the best strategy to store a todo item? (currently on an XML file) such that all the items are loaded quickly up on app start up(the application shows kind of a dashboard of all the items at start up) What is the best way to design its back-end so that it can be ported to android/or a J2ME based phone Currently this is done using java swing. What should be the concerns so that it works efficiently on a device where memory is limited? Thanks!

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  • How do I design a cryptographic hash function?

    - by Eyal
    After reading the following about why one-way hash functions are one-way, I would like to know how to design a hash function. http://stackoverflow.com/questions/1038307/help-me-better-understand-cryptographic-hash-functions/1047106#1047106 Before everyone gets on my case: Yes, I know that it's a bad idea to not use a proven and tested hash function. I would still like to know how it's done. I'm familiar with Feistel-network ciphers but those are necessarily reversible, horrible for a cryptographic hash. Is there some sort of construction that is well-used in cryptographic hashing? Something that makes it very one-way?

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  • Future proof Primary Key design in postgresql

    - by John P
    I've always used either auto_generated or Sequences in the past for my primary keys. With the current system I'm working on there is the possibility of having to eventually partition the data which has never been a requirement in the past. Knowing that I may need to partition the data in the future, is there any advantage of using UUIDs for PKs instead of the database's built-in sequences? If so, is there a design pattern that can safely generate relatively short keys (say 6 characters instead of the usual long one e6709870-5cbc-11df-a08a-0800200c9a66)? 36^6 keys per-table is more than sufficient for any table I could imagine. I will be using the keys in URLs so conciseness is important.

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  • Advice Needed To Normalise Database

    - by c11ada
    hey all, im trying to create a database for a feedback application in ASP.net i have the following database design. Username (PK) QuestionNo (PK) QuestionText FeedbackNo (PK) Username UserFeedbackNo (PK) FeedbackNo (FK) QuestionNo (FK) Answer Comment a user has a unique username a user can have multiple feedbacks i was wondering if the database design i have here is normalised and suitable for the application

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  • Is a base class with shared fields and functions good design

    - by eych
    I've got a BaseDataClass with shared fields and functions Protected Shared dbase as SqlDatabase Protected Shared dbCommand as DBCommand ... //also have a sync object used by the derived classes for Synclock'ing Protected Shared ReadOnly syncObj As Object = New Object() Protected Shared Sub Init() //initializes fields, sets connections Protected Shared Sub CleanAll() //closes connections, disposes, etc. I have several classes that derive from this base class. The derived classes have all Shared functions that can be called directly from the BLL with no instantiation. The functions in these derived classes call the base Init(), call their specific stored procs, call the base CleanAll() and then return the results. So if I have 5 derived classes with 10 functions each, totaling 50 possible function calls, since they are all Shared, the CLR only calls one at a time, right? All calls are queued to wait until each Shared function completes. Is there a better design with having Shared functions in your DAL and still have base class functions? Or since I have a base class, is it better to move towards instance methods within the DAL?

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  • A series of simple Aggregate Root questions (Domain Driven Design)

    - by Robert
    I have a few (hopefully) simple questions about aggregate roots in domain driven design: Is it okay to have an aggregate root as a property of another aggregate root? Is it okay to have a given entity inside two or more aggregate roots? My final question is a bit more involved. I have a website that has a few entities that really belong to a "website" aggregate root. They are 'News', 'Products', and 'Users'. There isn't a 'Website' table in the database, but a 'Website' seems like a good aggregate root for these three entities. How is this usually achieved? Thanks!

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  • Value object or not for 3d points ?

    - by Stefano Borini
    I need to develop a geometry library in python, describing points, lines and planes in 3d space, and various geometry operations. Related to my previous question. The main issue in the design is if these entities should have identity or not. I was wondering if there's a similar library out there (developed in another language) to take inspiration from, what is the chosen design, and in particular the reason for one choice vs. the other.

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  • What are possible designs for the DCI architecture?

    - by Gabriel Šcerbák
    What are possibles designs for implementation of the DCI (data, contexts, interactions) architecture in different OOP languages? I thought of Policy based design (Andrei Alexandrescu) for C++, DI and AOP for Java. However, I also thought about using State design pattern for representing roles and some sort of Template method for the interactions... What are the other possibilities?

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  • any practices ,samples for ERD?

    - by just_name
    Q: I wanna any web sites , any books just for training on ERD and normalization ,, i wanna a lot of samples ,practices,and case studies with recommended answers, to strength myself in database design.and avoid the poor data base design i made . note:i don't need books to explain the concepts , what i need is practices ,examples,case studies with recommended answers. Thanks in advance.

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  • Set both Text and Value property of ComboBox in design time

    - by The King
    I need to add the following items to a combo box. Value DisplayText Mpost Posted Call Calling RScan Re-Scan These items are fairly static, and is not retrieved from any database... Hence thought of assigning these in design time itself. I'm Unable to use Items property as it asks only one value per item... Could you please help. Ps : In case you are suggesting BindingSource, could you please give me an example. I was not able to find one.

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  • Design an api using rails and change the forgot password functionality

    - by ragupathi
    I have been using rails for developing web applications and now i need to do design an api for iphone application and since i used respond to json it also produces json but i use devise for authentication in my web application and when i send email and password along with the api it gives out {"user":{"authentication_token":"Lsusyd27ewgasga63","email":"[email protected]"}} and there is forgot password functionality in the iphone app but in the web application when clicking on forgot password button it sends an email to the users email, whereby the user has to go to his mail and click on the link sent and it will take to the change password path and after changing it the user will be login but in this iphone app i want to send the password to the user mail and the user can use that password and login. How can i do this? Also do i have to create new controllers for api or the web application controller is enough if it respond as json? please help me.

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  • NoSQL vs. MySQL when scalability is irrelevant

    - by Bryan Ward
    Recently I have read a lot about different NoSQL databases and how they are being effectively deployed by some major websites out there. I'm starting a project in which I think the schema-free nature of a database such as MongoDB would be tremendously useful. Everything I have read though seems to indicate that the main advantage of a NoSQL database is scalability. Is choosing a NoSQL database for the schema-free design just as legitimate a design decision as that of scalability?

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  • Form.cs not being updated by changes to Form.cs[Design]

    - by Kevin
    I am new to Visual Studio and I am just messing around with the controls to see how things work. I made one form that had a single button that, when pushed, simply printed "Hello World" to the screen. To try something more complicated I deleted that button and added various other tools to the Form. However the code in the Form.cs file was not updated to reflect these changes to the design and I can find no way to update it manually. Any advice is appreciated. Regards.

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  • Find the right parameters for an event without using Design Mode in Visual Studio 2010

    - by Jason
    Is there a way to know what parameters are needed by an event in Visual Studio 2010? Let's say I have a DropDownList control and I want to bind a method to the "OnSelectedIndexChanged", I would do something like this In the ASPX File: <asp:DropDownList ID="lstMyList" runat="server" OnSelectedIndexChanged="lstMyList_SelectedIndexChanged"></asp:DropDownList> In the codebehind: protected void lstMyList_SelectedIndexChanged(object sender, EventArgs e) { ... } Is there a way to know what parameters the method needs? (In this case, an object for the sender and an EventArgs parameter for the event.) I know you can easily create the method by double-clicking the right event in Design Mode, but it does a mess with your code so I prefer not to use it. Thanks!

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  • How to design this simple database?

    - by Vafello
    I have 2 tables - one storing user information (id, username, password) and the second one storing information about events (id, name, description, date, username(represents the user who created the event)). I would like to implement 'favourite events' functionality. This would allow the user to store his favourite events and later display them in a list. I am not sure how to implement this in terms of design. I need a simple solution. Something like storing the IDs of favourite events in a field in the user table. I am using mysql and php. Can anyone point me to the right direction?

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  • Design interoperable web services

    - by Zyd
    Hi everyone, I'm designing a set of web services to allow our clients to connect from their apps to one of our systems. Our clients have their apps developed in all varieties of frameworks (.NET, Java, PHP, Python and even the occasional all JS app), so obviously WS is the way to go. Investigating a little about truly interop WS I've found that the way to go is to design first the WSDL and XSD and derive the implementations from there. What i'm really looking for is guidance if this is really the way to go. I've read that WCF creates interoperable WS but i'm not a fan of MS creating something standard. Should i use WCF or there is a good set of tools for designing WSDL and XSD without the pain i'm expecting. Thanks in advance

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  • Django design question: extending User to make users that can't log in

    - by jobrahms
    The site I'm working on involves teachers creating student objects. The teacher can choose to make it possible for a student to log into the site (to check calendars, etc) OR the teacher can choose to use the student object only for record keeping and not allow the student to log in. In the student creation form, if the teacher supplies a username and a password, it should create an object of the first kind - one that can log in, i.e. a regular User object. If the teacher does not supply a username/password, it should create the second type. The other requirement is that the teacher should be able to go in later and change a non-logging-in student to the other kind. What's the best way to design for this scenario? Subclass User and make username and password not required? What else would this affect?

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  • JavaScript Library Design

    - by JSMan2034
    I have a general question about the design of JavaScript Libraries. I am trying to consolidate common methods into one js file so they can be reused by different scripts. I have taken a look at how the JSON library is structured and believe it was a good approach. JSON for Javascript. So they start off creating an instance of the class: if (!this.JSON) { this.JSON = {}; } Then they do this: (function () { if (typeof JSON.stringify !== 'function') { JSON.stringify = function (value, replacer, space) { This is works perfect if you just want to do JSON.[function_name], but what if I want to have a more structured library such that I want: JSON.[subgroup].[function]. How would I structure my JS library in such a way? Any links to resources are greatly appreciated, thanks.

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  • How to design WCF Contracts?

    - by Amitabh
    We are designing a WCF layer which can be invoked either by a Asp.Net or a WinForm application. Our Application contains too many Entities. If we design WCF Contract around these entities then we get too many Contracts e.g IPartyService, IUserService, IPaymentService etc. So, I may end up with 30-40 Contracts? Is it a good idea or should we go for one huge contracts with around 100 operations? What are the pros and cons of each approach or is there a better way.

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  • How can I display a full designer file in c#?

    - by George Tyler
    So I just got a C# program from someone that compiles and gives me a fully functional application. However, when I want to see the .cs{Design] file it gives me the following error: .ErrorStyle { font-family: tahoma; font-size: 11 pt; .... How can I convert this to an actual Design file? I am working on Visual Studio C#. Thank you very much.

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  • What is some good software for designing MySQL databases?

    - by franzferdinand
    As above. Usually at work someone else does the database design, and when I do personal projects they're small enough to not really require more than five or six tables, but I'm about to start a personal project that I think will probably require around eleven or twelve tables and I'd like something to help me design it neatly and keep track of it.

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  • Bad Design? Constructor of composition uses `this`

    - by tanascius
    Example: class MyClass { Composition m_Composition; void MyClass() { m_Composition = new Composition( this ); } } I am interested in using depenency-injection here. So I will have to refactor the constructor to something like: void MyClass( Composition composition ) { m_Composition = composition; } However I get a problem now, since the Composition-object relies on the object of type MyClass which is just created. Can a dependency container resolve this? Is it supposed to do so? Or is it just bad design from the beginning on?

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  • iPhone app store approval - coredata design change

    - by satyam
    I created an app, uploaded to app store and approved by app store as well. Its ready for download. The app is based on coredata. Now I changed the design of the app to add new functionality. Changes include addition of new attributes to current entities, deletion of few entities etc. Now, if I upload the app to app store, does it approve or not? Do I have to put and Note saying that "Please uninstall old version and install new version?" Will my app be approved first of all or not.

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  • MVC design pattern - who loads view initially

    - by enableDeepak
    This query is about MVC design pattern in general and not ASP.net MVC framework I understand in MVC (desktop application): 1. User clicks something in view 2. this is passed on to controller to manage 3. controller makes some changes in Model 4. Model calls method on view which has the logic to refresh UI Questions around these: Q1) Can controller also modify View or Model only updates View? Q2) When screen loads for the first time, there is no Model change. Then, who fetches data from model and populates view? View directly calls Model and populates itself OR controller gets data and passes to view method OR some dummy event is raised at Model which updates View?

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