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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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• 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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• Securing WinForms Application suggestions

  - by Sarah Fordington

  I've been looking for a simple key/license system for our users. Its partly to stop piracy (avoid users from sharing the application around) and the other half to track the number of 'licensed users' we have. I have already read a few good suggestions on SO but I'm curious as to how people have implemented the 30 day evaluation criteria. Do you generate a key that stores the date somewhere and do a comparison each time or is it a little more complicated - deleting the file/removing the registry shouldn't deactivate. Are there any example implementations out there that can give me a head start? The irony is that our PM doesn't want to license a third-party system to do it for us. This is for a Windows Forms application.

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• Common one-to-many table for multiple entities

  - by Ben V

  Suppose I have two tables, Customer and Vendor. I want to have a common address table for customer and vendor addresses. Customers and Vendors can both have one to many addresses. Option 1 Add columns for the AddressID to the Customer and Vendor tables. This just doesn't seem like a clean solution to me. Customer Vendor Address -------- --------- --------- CustomerID VendorID AddressID AddressID1 AddressID1 Street AddressID2 AddressID2 City... Option 2 Move the foreign key to the Address table. For a Customer, Address.CustomerID will be populated. For a Vendor, Address.VendorID will be populated. I don't like this either - I shouldn't need to modify the address table every time I want to use it for another entity. Customer Vendor Address -------- --------- --------- CustomerID VendorID AddressID CustomerID VendorID Option 3 I've also seen this - only 1 foreign key column on the Address table with another column to identify which foreign key table the address belongs to. I don't like this one because it requires all the foreign key tables to have the same type of ID. It also seems messy once you start coding against it. Customer Vendor Address -------- --------- --------- CustomerID VendorID AddressID FKTable FKID So, am I just too picky, or is there something I haven't thought of?

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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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• Cocoa Key event problem

  - by Oscar

  I'm trying to build my first cocoa application. done some iPhone developing before. I have a hard time understanding how to layout my project. i making a Pong game and my current design is to allocate an NSWindowController from my appDelegate. I then use custom view to act as paddles and ball. My problem is that i can't get the window controller to capture key events. Am i thinking wrong here? My idea is to have a controller class with all the logic, should i subclass another class for that?

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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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• Pressing "Home" in Vim on an Indented Line

  - by Reid

  I have a bad habit of using the 'home' key to go back to the beginning of a line. As I recently started using vim (and loving it!) I noticed that when I press the home key on a lined that is indented, it returns me to the very beginning of the line. In Notepad++ (the editor I used to use) it would return me to the beginning of the code on that line, right after the indent. Is there some way to replicate this behavior in vim? Usually, when I'm pressing home it's in the Insert mode for me to (usually) stick a variable there. I have set smartindent in my vimrc, with set noautoindent as a "tips" page told me to make sure to disable autoindent (although it didn't seem to be enabled in the first place - perhaps that option is extraneous.) Thanks in advance.

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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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• 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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• 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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• 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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• 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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• 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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• Rails Nested Attributes, Relationship for Shared or Common Object

  - by SooDesuNe

  This has to be a common problem, so I'm surprised that Google didn't turn up more answers. I'm working on a rails app that has several different kinds of entities, those entities by need a relation to a different entity. For example: Address: a Model that stores the details of a street address (this is my shared entity) PersonContact: a Model that includes things like home phone, cell phone and email address. This model needs to have an address associated with it DogContact: Obviously, if you want to contact a dog, you have to go to where it lives. So, PersonContact and DogContact should have foreign keys to Address. Even, though they are really the "owning" object of Address. This would be fine, except that accepts_nested_attributes_for is counting on the foreign key being in Address to work correctly. What's the correct strategy to keep the foreign key in Address, but have PersonContact and DogContact be the owning objects?

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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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• 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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• 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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• 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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• 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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