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  • What is the most elegant way to validate the presence of ONLY one out of two attributes using Rails?

    - by marcgg
    class Followup < ActiveRecord::Base belongs_to :post belongs_to :comment end This model needs to only have either a post or a comment, but only one of the two. Here's the rspec for what I'm trying to do: it "should be impossible to have both a comment and a post" do followup = Followup.make followup.comment = Comment.make followup.should be_valid followup.post = Post.make followup.should_not be_valid end I can see a bunch of ways of doing this, but what would be the most elegant way of doing this?

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  • How do you go from an abstract project description to actual code?

    - by Jason
    Maybe its because I've been coding around two semesters now, but the major stumbling block that I'm having at this point is converting the professor's project description and requirements to actual code. Since I'm currently in Algorithms 101, I basically do a bottom-up process, starting with a blank whiteboard and draw out the object and method interactions, then translate that into classes and code. But now the prof has tossed interfaces and abstract classes into the mix. Intellectually, I can recognize how they work, but am stubbing my toes figuring out how to use these new tools with the current project (simulating a web server). In my professors own words, mapping the abstract description to Java code is the real trick. So what steps are best used to go from English (or whatever your language is) to computer code? How do you decide where and when to create an interface, or use an abstract class?

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  • Is it better to use List or Collection?

    - by Vivin Paliath
    I have an object that stores some data in a list. The implementation could change later, and I don't want to expose the internal implementation to the end user. However, the user must have the ability to modify and access this collection of data. Currently I have something like this: public List<SomeDataType> getData() { return this.data; } public void setData(List<SomeDataType> data) { this.data = data; } Does this mean that I have allowed the internal implementation details to leak out? Should I be doing this instead? public Collection<SomeDataType> getData() { return this.data; } public void setData(Collection<SomeDataType> data) { this.data = new ArrayList<SomeDataType>(data); }

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  • Why Shouldn't I Programmatically Submit Username/Password to Facebook/Twitter/Amazon/etc?

    - by viatropos
    I wish there was a central, fully customizable, open source, universal login system that allowed you to login and manage all of your online accounts (maybe there is?)... I just found RPXNow today after starting to build a Sinatra app to login to Google, Facebook, Twitter, Amazon, OpenID, and EventBrite, and it looks like it might save some time. But I keep wondering, not being an authentication guru, why couldn't I just have a sleek login page saying "Enter username and password, and check your login service", and then in the background either scrape the login page from say EventBrite and programmatically submit the form with Mechanize, or use an API if there was one? It would be so much cleaner and such a better user experience if they didn't have to go through popups and redirects and they could use any previously existing accounts. My question is: What are the reasons why I shouldn't do something like that? I don't know much about the serious details of cookies/sessions/security, so if you could be descriptive or point me to some helpful links that would be awesome. Thanks!

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  • What is the best practice of using return keyword?

    - by Artic
    What is the best practice of using return keyword? If i need to return something from method which pattern is better to use? public boolean method(){ if (case1){ return true; } if (case 2){ return false; } return false; } or public boolean method(){ boolean result = false; if (case1){ result = true; } if (case 2){ result = false; } return result; }

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  • actionscript-3: refactor interface inheritance to get rid of ambiguous reference error

    - by maxmc
    hi! imagine there are two interfaces arranged via composite pattern, one of them has a dispose method among other methods: interface IComponent extends ILeaf { ... function dispose() : void; } interface ILeaf { ... } some implementations have some more things in common (say an id) so there are two more interfaces: interface ICommonLeaf extends ILeaf { function get id() : String; } interface ICommonComponent extends ICommonLeaf, IComponent { } so far so good. but there is another interface which also has a dispose method: interface ISomething { ... function dispose() : void; } and ISomething is inherited by ICommonLeaf: interface ICommonLeaf extends ILeaf, ISomething { function get id() : String; } As soon as the dispose method is invoked on an instance which implements the ICommonComponent interface, the compiler fails with an ambiguous reference error because ISomething has a method called dispose and ILeaf also has a dispose method, both living in different interfaces (IComponent, ISomething) within the inheritace tree of ICommonComponent. I wonder how to deal with the situation if the IComponent, the ILeaf and the ISomething can't change. the composite structure must also work for for the ICommonLeaf & ICommonComponent implementations and the ICommonLeaf & ICommonComponent must conform to the ISomething type. this might be an actionscript-3 specific issue. i haven't tested how other languages (for instance java) handle stuff like this.

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  • Is my method for avoiding dynamic_cast<> faster than dynamic_cast<> itself ?

    - by ereOn
    Hi, I was answering a question a few minutes ago and it raised to me another one: In one of my projects, I do some network message parsing. The messages are in the form of: [1 byte message type][2 bytes payload length][x bytes payload] The format and content of the payload are determined by the message type. I have a class hierarchy, based on a common class Message. To instanciate my messages, i have a static parsing method which gives back a Message* depending on the message type byte. Something like: Message* parse(const char* frame) { // This is sample code, in real life I obviously check that the buffer // is not NULL, and the size, and so on. switch(frame[0]) { case 0x01: return new FooMessage(); case 0x02: return new BarMessage(); } // Throw an exception here because the mesage type is unknown. } I sometimes need to access the methods of the subclasses. Since my network message handling must be fast, I decived to avoid dynamic_cast<> and I added a method to the base Message class that gives back the message type. Depending on this return value, I use a static_cast<> to the right child type instead. I did this mainly because I was told once that dynamic_cast<> was slow. However, I don't know exactly what it really does and how slow it is, thus, my method might be as just as slow (or slower) but far more complicated. What do you guys think of this design ? Is it common ? Is it really faster than using dynamic_cast<> ? Any detailed explanation of what happen under the hood when one use dynamic_cast<> is welcome !

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  • Transform.Translation problem on rotation

    - by eco_bach
    I am using the following to scale and reposition a UIView layer when the device rotates to landscape. [containerView.layer setValue:[NSNumber numberWithFloat: 0] forKeyPath: @"transform.translation.x"]; [containerView.layer setValue:[NSNumber numberWithFloat: 0] forKeyPath: @"transform.translation.y"]; [containerView.layer setValue:[NSNumber numberWithFloat: 1] forKeyPath: @"transform.scale.x"]; //[NSNumber numberWithInt:1] [containerView.layer setValue:[NSNumber numberWithFloat: 1] forKeyPath: @"transform.scale.y"]; and then the folowing when rotating back to portrait [containerView.layer setValue:[NSNumber numberWithFloat: -75] forKeyPath: @"transform.translation.x"]; [containerView.layer setValue:[NSNumber numberWithFloat: 0] forKeyPath: @"transform.translation.y"]; [containerView.layer setValue:[NSNumber numberWithFloat: .7] forKeyPath: @"transform.scale.x"]; //[NSNumber numberWithInt:1] [containerView.layer setValue:[NSNumber numberWithFloat: .7] forKeyPath: @"transform.scale.y"]; The problem is that after rotaing back to portrait, the layer is 'travelling' ie the x,y offset are gradually changing(increasing x, decreasing y). Scale seems fine (ie doesn't increment, decrement on repeated rotations) Can anyone suggest a proper solution?

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  • Use of infix operator hack in production code (Python)

    - by Casebash
    What is your opinion of using the infix operator hack in production code? Issues: The effect this will have on speed. The potential for a clashes with an object with these operators already defined. This seems particularly dangerous with generic code that is intended to handle objects of any type. It is a shame that this isn't built in - it really does improve readability

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  • Generic data input form in asp.net mvc application

    - by Diego
    Hello, I have an application that have EF 16 classes that share this information: They all are classes only with a key field and a description. I think it should be a waste if I make a controller with just 1 method just to present a form to fill these classes info, then I was thinking in to make a generic form(with key, description) and dynamically fill the right class through a sort of selection the selected info in any way, any good suggestion or pattern to do that? Where the generic methods should be located.

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  • Bad method names and what it says about code structure.

    - by maxfridbe
    (Apologies in advance if this is a re-post but I didn't find similar posts) What bad method name patterns have you seen in code and what did it tell you about the code. For instance, I keep seeing: public void preform___X___IfNecessary(...); I believe that this is bad because the operation X has an inversion of conditions. Note that this is a public method because classes methods might legitimately require private helpers like this

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  • Design patterns to avoid

    - by Brian Rasmussen
    A lot of people seem to agree, that the Singleton pattern has a number of drawbacks and some even suggest to avoid the pattern all together. There's an excellent discussion here. Please direct any comments about the Singleton pattern to that question. Are there other design patterns, that should be avoided or used with great care?

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  • NHibernate session management in ASP.NET MVC

    - by Kevin Pang
    I am currently playing around with the HybridSessionBuilder class found on Jeffrey Palermo's blog post: http://jeffreypalermo.com/blog/use-this-nhibernate-wrapper-to-keep-your-repository-classes-simple/ Using this class, my repository looks like this: public class UserRepository : IUserRepository { private readonly ISessionBuilder _sessionBuilder; public UserRepository(ISessionBuilder sessionBuilder) { _sessionBuilder = sessionBuilder; } public User GetByID(string userID) { using (ISession session = _sessionBuilder.GetSession()) { return session.Get<User>(userID); } } } Is this the best way to go about managing the NHibernate session / factory? I've heard things about Unit of Work and creating a session per web request and flushing it at the end. From what I can tell, my current implementation isn't doing any of this. It is basically relying on the Repository to grab the session from the session factory and use it to run the queries. Are there any pitfalls to doing database access this way?

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  • Should I define a single "DataContext" and pass references to it around or define muliple "DataConte

    - by Nate Bross
    I have a Silverlight application that consists of a MainWindow and several classes which update and draw images on the MainWindow. I'm now expanding this to keep track of everything in a database. Without going into specifics, lets say I have a structure like this: MainWindow Drawing-Surface Class1 -- Supports Drawing DataContext + DataServiceCollection<T> w/events Class2 -- Manages "transactions" (add/delete objects from drawing) Class3 Each "Class" is passed a reference to the Drawing Surface so they can interact with it independently. I'm starting to use WCF Data Services in Class1 and its working well; however, the other classes are also going to need access to the WCF Data Services. (Should I define my "DataContext" in MainWindow and pass a reference to each child class?) Class1 will need READ access to the "transactions" data, and Class2 will need READ access to some of the drawing data. So my question is, where does it make the most sense to define my DataContext? Does it make sense to: Define a "global" WCF Data Service "Context" object and pass references to that in all of my subsequent classes? Define an instance of the "Context" for each Class1, Class2, etc Have each method that requires access to data define its own instance of the "Context" and use closures handle the async load/complete events? Would a structure like this make more sense? Is there any danger in keeping an active "DataContext" open for an extended period of time? Typical usecase of this application could range from 1 minute to 40+ minutes. MainWindow Drawing-Surface DataContext Class1 -- Supports Drawing DataServiceCollection<DrawingType> w/events Class2 -- Manages "transactions" (add/delete objects from drawing) DataServiceCollection<TransactionType> w/events Class3 DataServiceCollection<T> w/events

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  • Using static variable in function vs passing variable from caller

    - by Patrick
    I have a function which spawns various types of threads, one of the thread types needs to be spawned every x seconds. I currently have it like this: bool isTime( Time t ) { return t >= now(); } void spawner() { while( 1 ) { Time t = now(); if( isTime( t ) )//is time is called in more than one place in the real function { launchthread() t = now() + offset; } } } but I'm thinking of changing it to: bool isTime() { static Time t = now(); if( t >= now() ) { t = now() + offset; return true; } return false; } void spawner() { if( isTime() ) launchthread(); } I think the second way is neater but I generally avoid statics in much the same way I avoid global data; anyone have any thoughts on the different styles?

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  • Best practice for storage and retrieval of error messages.

    - by ferrari fan
    What is a best practice for storing user messages in a configuration file and then retrieving them for certain events throughout an application? I was thinking of having 1 single configuration file with entries such as REQUIRED_FIELD = {0} is a required field INVALID_FORMAT = The format for {0} is {1} etc. and then calling them from a class that would be something like this public class UIMessages { public static final String REQUIRED_FIELD = "REQUIRED_FIELD"; public static final String INVALID_FORMAT = "INVALID_FORMAT"; static { // load configuration file into a "Properties" object } public static String getMessage(String messageKey) { // return properties.getProperty(messageKey); } } Is this the right way to approach this problem or is there some de-facto standard already in place?

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  • Checking for empty arrays: count vs empty

    - by Dan McG
    This question on 'How to tell if a PHP array is empty' had me thinking of this question Is there a reason that count should be used instead of empty when determining if an array is empty or not? My personal thought would be if the 2 are equivalent for the case of empty arrays you should use empty because it gives a boolean answer to a boolean question. From the question linked above, it seems that count($var) == 0 is the popular method. To me, while technically correct, makes no sense. E.g. Q: $var, are you empty? A: 7. Hmmm... Is there a reason I should use count == 0 instead or just a matter of personal taste? As pointed out by others in comments for a now deleted answer, count will have performance impacts for large arrays because it will have to count all elements, whereas empty can stop as soon as it knows it isn't empty. So, if they give the same results in this case, but count is potentially inefficient, why would we ever use count($var) == 0?

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  • Specification: Use cases for CRUD

    - by Mario Ortegón
    I am writing a Product requirements specification. In this document I must describe the ways that the user can interact with the system in a very high level. Several of these operations are "Create-Read-Update-Delete" on some objects. The question is, when writing use cases for these operations, what is the right way to do so? Can I write only one Use Case called "Manage Object x" and then have these operations as included Use Cases? Or do I have to create one use case per operation, per object? The problem I see with the last approach is that I would be writing quite a few pages that I feel do not really contribute to the understanding of the problem. What is the best practice?

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