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• adding one time options to items

  - by rap-uvic

  Hello, I'm building an Event Registration site. For any given event, we'll have a handful of items to choose from. I have a table for these items. For each event we might have special options for users. For example, for one of the events new users get to buy an item which is not available to other users. This may not apply to all the events. For other events we might have some other restriction on items. I will obviously be checking this programmatically on application side. I would like to though, set up a column containing flag in the items table. But I don't find it feasible because this condition may only apply to one particular event. I don't want all the future items to have this column. What is a good approach to take in such a situation? Should I create a special "restrictions" table and just do a join? How would I handle this on the application side?

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• Are Multiple Iterators possible in php?

  - by artvolk

  Good day! I know that C# allows multiple iterators using yield, like described here: http://stackoverflow.com/questions/1754041/is-multiple-iterators-is-possible-in-c In PHP there is and Iterator interface. Is it possible to implement more than one iteration scenario for a class? More details (EDIT): For example I have class TreeNode implementing single tree node. The whole tree can be expressed using only one this class. I want to provide iterators for iterating all direct and indirect children of current node, for example using BreadthFirst or DepthFirst order. I can implement this Iterators as separate classes but doing so I need that tree node should expose it's children collection as public. C# pseudocode: public class TreeNode<T> { ... public IEnumerable<T> DepthFirstEnumerator { get { // Some tree traversal using 'yield return' } } public IEnumerable<T> BreadthFirstEnumerator { get { // Some tree traversal using 'yield return' } } }

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• O(log n) algorithm for computing rank of union of two sorted lists?

  - by Eternal Learner

  Given two sorted lists, each containing n real numbers, is there a O(log?n) time algorithm to compute the element of rank i (where i coresponds to index in increasing order) in the union of the two lists, assuming the elements of the two lists are distinct? I can think of using a Merge procedure to merge the 2 lists and then find the A[i] element in constant time. But the Merge would take O(n) time. How do we solve it in O(log n) time?

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• Aren't Information Expert / Tell Don't Ask at odds with Single Responsibility Principle?

  - by moffdub

  It is probably just me, which is why I'm asking the question. Information Expert, Tell Don't Ask, and SRP are often mentioned together as best practices. But I think they are at odds. Here is what I'm talking about: Code that favors SRP but violates Tell Don't Ask, Info Expert: Customer bob = ...; // TransferObjectFactory has to use Customer's accessors to do its work, // violates Tell Don't Ask CustomerDTO dto = TransferObjectFactory.createFrom(bob); Code that favors Tell Don't Ask / Info Expert but violates SRP: Customer bob = ...; // Now Customer is doing more than just representing the domain concept of Customer, // violates SRP CustomerDTO dto = bob.toDTO(); If they are indeed at odds, that's a vindication of my OCD. Otherwise, please fill me in on how these practices can co-exist peacefully. Thank you. Edit: someone wants a definition of the terms - Information Expert: objects that have the data needed for the operation should host the operation Tell Don't Ask: don't ask objects for data in order to do work; tell the objects to do the work Single Responsibility Principle: each object should have a narrowly defined responsibility

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• Algorithm to represent Decision tables

  - by driveBy

  What would be the best algorithm to use if you wanted to store Decision tables in code, i've looked at the Adjacency matrix and Binary tree would anyone consider this to be the right direction? What other choices to I have?

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• How to make this OO?

  - by John

  Hello, Sorry for the poor title,I'm new to OOP so I don't know what is the term for what I need to do. I have, say, 10 different Objects that inherit one Object.They have different amount and type of class members,but all of them have one property in common - Visible. type TObj1=class(TObject) private a:integer; ...(More members) Visible:Boolean; end; TObj2=class(TObject) private b:String; ...(More members) Visible:Boolean; end; ...(Other 8 objects) For each of them I have a variable. var Obj1:TObj1; Obj2:TObj2; Obj3:TObj3; ....(Other 7 objects) Rule 1: Only one object can be initialized at a time(others have to be freed) to be visible. For this rule I have a global variable var CurrentVisibleObj:TObject; //Because they all inherit TObject Finally there is a procedure that changes visibility. procedure ChangeObjVisibility(newObj:TObject); begin CurrentVisibleObj.Free; //Free the old object CurrentVisibleObj:=newObj; //assign the new object CurrentVisibleObj:= ??? //Create new object CurrentVisibleObj.Visible:=true; //Set visibility to new object end; There is my problem,I don't know how to initialize it,because the derived class is unknown. How do I do this? I simplified the explanation,in the project there are TFrames each having different controls and I have to set visible/not visible the same way(By leaving only one frame initialized). Sorry again for the title,I'm very new to OOP.

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• Working with foreigh keys - cannot insert

  - by Industrial

  Hi everyone! Doing my first tryouts with foreign keys in a mySQL database and are trying to do a insert, that fails for this reason: Integrity constraint violation: 1452 Cannot add or update a child row: a foreign key constraint fails Does this mean that foreign keys restrict INSERTS as well as DELETES and/or UPDATES on each table that is enforced with foreign keys relations? Thanks!

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• I cannot grok MVC, what it is, and what it is not?

  - by Hao

  I cannot grok what MVC is, what mindset or programming model should I acquire so MVC stuff can instantly "lightbulb" on my head? If not instantly, what simple programs/projects should I try to do first so I can apply the neat things MVC brings to programming. OOP is intuitive and easier, object is all around us, and the benefits of code reuse using OOP-paradigm instantly click to anyone. You can probably talk to anybody about OOP in a few minutes and lecture some examples and they would get it. While OOP somehow raise the intuitiveness aspect of programming, MVC seems to do the opposite. I'm getting negative thoughts that some future employers(or even clients) would look down upon me for not using MVC technology. Though I probably get the skinnable aspect of MVC, but when I try to apply it to my own project, I don't know where to start. And also some programmers even have diverging views on how to accomplish MVC properly. Take this for instance from Jeff's post about MVC: The view is simply how you lay the data out, how it is displayed. If you want a subset of some data, for example, my opinion is that is a responsibility of the model. So maybe some programmers use MVC, but they somehow inadvertently use the View or the Controller to extract a subset of data. Why we can't have a definitive definition of what and how to accomplish MVC properly? And also, when I search for MVC .NET programs, most of it applies to web programs, not desktop apps, this intrigue me further. My guess is, this is most advantageous to web apps, there's not much problem about intermixed view(html) and controller(program code) in desktop apps.

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• should I ever put a major version number into a C#/Java namespace?

  - by Andrew Patterson

  I am designing a set of 'service' layer objects (data objects and interface definitions) for a WCF web service (that will be consumed by third party clients i.e. not in-house, so outside my direct control). I know that I am not going to get the interface definition exactly right - and am wanting to prepare for the time when I know that I will have to introduce a breaking set of new data objects. However, the reality of the world I am in is that I will also need to run my first version simultaneously for quite a while. The first version of my service will have URL of http://host/app/v1service.svc and when the times comes by new version will live at http://host/app/v2service.svc However, when it comes to the data objects and interfaces, I am toying with putting the 'major' version of the interface number into the actual namespace of the classes. namespace Company.Product.V1 { [DataContract(Namespace = "company-product-v1")] public class Widget { [DataMember] string widgetName; } public interface IFunction { Widget GetWidgetData(int code); } } When the time comes for a fundamental change to the service, I will introduce some classes like namespace Company.Product.V2 { [DataContract(Namespace = "company-product-v2")] public class Widget { [DataMember] int widgetCode; [DataMember] int widgetExpiry; } public interface IFunction { Widget GetWidgetData(int code); } } The advantages as I see it are that I will be able to have a single set of code serving both interface versions, sharing functionality where possible. This is because I will be able to reference both interface versions as a distinct set of C# objects. Similarly, clients may use both interface versions simultaneously, perhaps using V1.Widget in some legacy code whilst new bits move on to V2.Widget. Can anyone tell why this is a stupid idea? I have a nagging feeling that this is a bit smelly.. notes: I am obviously not proposing every single new version of the service would be in a new namespace. Presumably I will do as many non-breaking interface changes as possible, but I know that I will hit a point where all the data modelling will probably need a significant rewrite. I understand assembly versioning etc but I think this question is tangential to that type of versioning. But I could be wrong.

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• Testing system where App-level and Request-level IoC containers exist

  - by Bobby

  My team is in the process of developing a system where we're using Unity as our IoC container; and to provide NHibernate ISessions (Units of work) over each HTTP Request, we're using Unity's ChildContainer feature to create a child container for each request, and sticking the ISession in there. We arrived at this approach after trying others (including defining per-request lifetimes in the container, but there are issues there) and are now trying to decide on a unit testing strategy. Right now, the application-level container itself is living in the HttpApplication, and the Request container lives in the HttpContext.Current. Obviously, neither exist during testing. The pain increases when we decided to use Service Location from our Domain layer, to "lazily" resolve dependencies from the container. So now we have more components wanting to talk to the container. We are also using MSTest, which presents some concurrency dilemmas during testing as well. So we're wondering, what do the bright folks out there in the SO community do to tackle this predicament? How does one setup an application that, during "real" runtime, relies on HTTP objects to hold the containers, but during test has the flexibility to build-up and tear-down the containers consistently, and have the ServiceLocation bits get to those precise containers. I hope the question is clear, thanks!

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• Shortest Path algorithm of a different kind

  - by Ram Bhat

  Hey guys, Lets say you have a grid like this (made randomly) Now lets say you have a car starting randomly from one of the while boxes, what would be the shortest path to go through each one of the white boxes? you can visit each white box as many times as you want and cant Jump over the black boxes. The black boxes are like walls. In simple words you can move from white box to white box only.. You can move in any direction, even diagonally.

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• document.getElementById not working in IE

  - by Alloi

  Hi, I am using the below js code in order to change the class when a link is clicked. document.getElementById("gifts").setAttribute("class", "gkvSprite selected"); This is not working in IE but it does in FF and Chrome Then I changed the code to : document.getElementById("gifts").setAttribute("className", "gkvSprite selected"); Then it worked in IE stopped working in FF and Chrome. Could someone please help me out here? Thanks in Advance Alloi

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• iPhone Fonts: set small-caps

  - by Thomas Joos

  hi all, i'm branding an iphone app and the designer wants to display list items using Georgia. This is not a big deal, but he wants them do appear as small-caps.. is this possible to do in iPhone os3?

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• Should this even be a has_many :through association?

  - by GoodGets

  A Post belongs_to a User, and a User has_many Posts. A Post also belongs_to a Topic, and a Topic has_many Posts. class User < ActiveRecord::Base has_many :posts end class Topic < ActiveRecord::Base has_many :posts end class Post < ActiveRecord::Base belongs_to :user belongs_to :topic end Well, that's pretty simple and very easy to set up, but when I display a Topic, I not only want all of the Posts for that Topic, but also the user_name and the user_photo of the User that made that Post. However, those attributes are stored in the User model and not tied to the Topic. So how would I go about setting that up? Maybe it can already be called since the Post model has two foreign keys, one for the User and one for the Topic? Or, maybe this is some sort of "one-way" has_many through assiociation. Like the Post would be the join model, and a Topic would has_many :users, :through = :posts. But the reverse of this is not true. Like a User does NOT has_many :topics. So would this even need to be has_many :though association? I guess I'm just a little confused on what the controller would look like to call both the Post and the User of that Post for a give Topic. Edit: Seriously, thank you to all that weighed in. I chose tal's answer because I used his code for my controller; however, I could have just as easily chosen either j.'s or tim's instead. Thank you both as well. This was so damn simple to implement, and I think today marks the day that I'm beginning to fall in love with rails.

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• Flex: Push the Button

  - by Rachel

  For what real time scenarios/use cases one should go to Flex Technology ? What real time problems you have solved using Flex Technology ? What real time problems have you faced because of using Flex Technology and what was your work around for that use case ?

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• How to properly name record creation(insertion) datetime field ?

  - by alpav

  If I create a table with datetime default getdate() field that is intended to keep date&time of record insertion, which name is better to use for that field ? I like to use Created and I've seen people use DateCreated or CreateDate. Other possible candidates that I can think of are: CreatedDate, CreateTime, TimeCreated, CreateDateTime, DateTimeCreated, RecordCreated, Inserted, InsertedDate, ... From my point of view anything with Date inside name looks bad because it can be confused with date part in case if I have 2 fields: CreateDate,CreateTime, so I wonder if there are any specific recommendations/standards in that area based on real reasons, not just style, mood or consistency. Of course, if there are 100 existing tables and this is table 101 then I would use same naming convention as used in those 100 tables for the sake of consistency, but this question is about first table in first database in first server in first application.

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• How implement the Open Session in View pattern in NHibernate?

  - by MCardinale

  I'm using ASP.NET MVC + NHibernate + Fluent NHibernate and having a problem with lazy loading. Through this question (http://stackoverflow.com/questions/2519964/how-to-fix-a-nhibernate-lazy-loading-error-no-session-or-session-was-closed), I've discovered that I have to implement the Open Session in View pattern , but I don't know how. In my repositories classes, I use methods like this public ImageGallery GetById(int id) { using(ISession session = NHibernateSessionFactory.OpenSession()) { return session.Get<ImageGallery>(id); } } public void Add(ImageGallery imageGallery) { using(ISession session = NHibernateSessionFactory.OpenSession()) { using(ITransaction transaction = session.BeginTransaction()) { session.Save(imageGallery); transaction.Commit(); } } } And this is my Session Factory helper class: public class NHibernateSessionFactory { private static ISessionFactory _sessionFactory; private static ISessionFactory SessionFactory { get { if(_sessionFactory == null) { _sessionFactory = Fluently.Configure() .Database(MySQLConfiguration.Standard.ConnectionString(MyConnString)) .Mappings(m => m.FluentMappings.AddFromAssemblyOf<ImageGalleryMap>()) .ExposeConfiguration(c => c.Properties.Add("hbm2ddl.keywords", "none")) .BuildSessionFactory(); } return _sessionFactory; } } public static ISession OpenSession() { return SessionFactory.OpenSession(); } } Someone could help me to implements Open Session in View pattern? Thank you.

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• Program to find canonical cover or minimum number of functional dependencies

  - by Sev

  I would like to know if there is a program or algorithm to find canonical cover or minimum number of functional dependencies? For example: If you have: R = (A,B,C) <-- these are tables: A,B,C And dependencies: A ? BC B ? C A ? B AB ? C The canonical cover (or minimum number of dependencies) is: A ? B B ? C Is there a program that can accomplish this? If not, any code/pseudocode to help me write one would be appreciated. Prefer in Python or Java.

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• Reasons to start a new project in COBOL

  - by luvieere

  Are there any feasible reasons to start a new project in COBOL? What benefits of this language one would find convincing enough to start a new project in it? I'm thinking more about viewing the language in terms of Behavior Driven Development, something related to the steps involved in using a framework such as Cucumber, only that behavior description and step definition would be integrated into one unit by using tha language's features.

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• Perl vs Python but with more style than normally

  - by user350571

  I'm learning perl and everytime I search for perl stuff in the internet I get some random page with people saying that perl should die because code written in it looks like a lesson in steganography. Then they say that python is clean and stuff like that. Now, I know that those comparisons are always stupid and made by fellows that feel that languages are a extension of their boring personality so, let me ask instead: can you give me the implementation of a widely known algorithm to deal with a data structure like red-black trees in both languages so I can compare?

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• Best Fit Scheduling Algorithim

  - by Teegijee

  I'm writing a scheduling program with a difficult programming problem. There are several events, each with multiple meeting times. I need to find an arrangement of meeting times such that each schedule contains any given event exactly once, using one of each event's multiple meeting times. Obviously I could use brute force, but that's rarely the best solution. I'm guessing this is a relatively basic computer science problem, which I'll learn about once I am able to start taking computer science classes. In the meantime, I'd prefer any links where I could read up on this, or even just a name I could Google.

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• Algorithm to determine which points should be visible on a map based on zoom

  - by lgratian

  Hi! I'm making a Google Maps-like application for a course at my Uni (not something complex, it should load the map of a city for example, not the whole world). The map can have many layers, including markers (restaurants, hospitals, etc.) The problem is that when you have many points and you zoom out the map it doesn't look right. At this zoom level only some points need to be visible (and at the maximum map size, all points). The question is: how can you determine which points should be visible for a specified zoom level? Because I have implemented a PR Quadtree to speed up rendering I thought that I could define some "high-priority" markers (that are always visible, defined in the map editor) and put them in a queue. At each step a marker is removed from the queue and all it's neighbors that are at least D units away (D depends on the zoom levels) are chosen and inserted in the queue, and so on. Is there any better way than the algorithm I thought of? Thanks in advance!

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• Idiom vs. pattern

  - by Roger Pate

  In the context of programming, how do idioms differ from patterns? I use the terms interchangeably and normally follow the most popular way I've heard something called, or the way it was called most recently in the current conversation, e.g. "the copy-swap idiom" and "singleton pattern". The best difference I can come up with is code which is meant to be copied almost literally is more often called pattern while code meant to be taken less literally is more often called idiom, but such isn't even always true. This doesn't seem to be more than a stylistic or buzzword difference. Does that match your perception of how the terms are used? Is there a semantic difference?

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• Building a many-to-many db schema using only an unpredictable number of foreign keys

  - by user1449855

  Good afternoon (at least around here), I have a many-to-many relationship schema that I'm having trouble building. The main problem is that I'm only working with primary and foreign keys (no varchars or enums to simplify things) and the number of many-to-many relationships is not predictable and can increase at any time. I looked around at various questions and couldn't find something that directly addressed this issue. I split the problem in half, so I now have two one-to-many schemas. One is solved but the other is giving me fits. Let's assume table FOO is a standard, boring table that has a simple primary key. It's the one in the one-to-many relationship. Table BAR can relate to multiple keys of FOO. The number of related keys is not known beforehand. An example: From a query FOO returns ids 3, 4, 5. BAR needs a unique key that relates to 3, 4, 5 (though there could be any number of ids returned) The usual join table does not work: Table FOO_BAR primary_key | foo_id | bar_id | Since FOO returns 3 unique keys and here bar_id has a one-to-one relationship with foo_id. Having two join tables does not seem to work either, as it still can't map foo_ids 3, 4, 5 to a single bar_id. Table FOO_TO_BAR primary_key | foo_id | bar_to_foo_id | Table BAR_TO_FOO primary_key | foo_to_bar_id | bar_id | What am I doing wrong? Am I making things more complicated than they are? How should I approach the problem? Thanks a lot for the help.

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• Why eGet() in EMF returns Object rather than EObject?

  - by Gabriel Šcerbák

  I am working on some code using the EMF framework in Java, but it is really hard to use, e.g. I cannot implement OCL-like query API on top of EMF which would be type-safe. One of the reasons is that eGet() for a EStructuralFeature return just an Object, not EObject. So anything I would write must use much of null checking, type checking and type casting which is unsafe, not performant and cannot be generalized in a reusable way. Why doesn't EMF generate dummy implementations with EObject wrappers for arbitrary Object value? Implementing the EObject and hence the EClass interfaces even with simple throw UnsupportedOperationException is really a pain (the APIs are too big). The same holds for the eContainer() method which makes navigatinng the model upwards painful.

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