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  • Derived class linker - is this wrong?

    - by bobobobo
    We have this situation: A B ^ ^ | / C so class A { } class B { } class C : public A, public B { } Now, B wants to access a property in C. How do you do this? The solution I came up with is to place a pointer in B to an instance of C, which is only active (not null) if this B is in fact a C.

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  • Repository pattern with lazying loading using POCO

    - by Simon G
    Hi, I'm in the process of starting a new project and creating the business objects and data access etc. I'm just using plain old clr objects rather than any orms. I've created two class libraries: 1) Business Objects - holds all my business objects, all this objects are light weight with only properties and business rules. 2) Repository - this is for all my data access. The majority of my objects will have child list in and my question is what is the best way to lazy load these values as I don't want to bring back unnecessary information if I dont need to. I've thought about when using the "get" on the child property to check if its "null" and if it is call my repository to get the child information. This has two problems from what I can see: 1) The object "knows" how to get itself I would rather no data access logic be held in the object. 2) This required both classes to reference each other which in visual studio throws a circular dependency error. Does anyone have any suggestions on how to overcome this issue or any recommendations on my projects layout and where it can be improved? Thanks

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  • Private constructor and public parameter constructor -C#

    - by Amutha
    I heard that private constructor prevent object creation from outside world. When i have a code public class Product { public string Name { get;set;} public double Price {get;set;} Product() { } public Product(string _name,double _price) { } } here still i can declare public constructor(parameter),won't it spoil the purpose of private constructor? When do we need both private and public constructor(parameter) in code? I need detailed explanation please.

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  • Which pattern should be used for editing properties with modal view controller on iPhone?

    - by Matthew Daugherty
    I am looking for a good pattern for performing basic property editing via a modal view on the iPhone. Assume I am putting together an application that works like the Contacts application. The "detail" view controller displays all of the contact's properties in a UITableView. When the UITableView goes into edit mode a disclosure icon is displayed in the cells. Clicking a cell causes a modal "editor" view controller to display a view that allows the user to modify the selected property. This view will often contain only a single text box or picker. The user clicks Cancel/Save and the "editor" view is dismissed and the "detail" view is updated. In this scenario, which view is responsible for updating the model? The "editor" view could update the property directly using Key-Value Coding. This appears in the CoreDataBooks example. This makes sense to me on some level because it treats the property as the model for the editor view controller. However, this is not the pattern suggested by the View Controller Programming Guide. It suggests that the "editor" view controller should define a protocol that the "detail" controller adopts. When the user indicates they are done with the edit, the "detail" view controller is called back with the entered value and it dismisses the "editor" view. Using this approach the "detail" controller updates the model. This approach seems problematic if you are using the same "editor" view for multiple properties since there is only a single call-back method. Would love to get some feedback on what approach works best.

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  • Are soft deletes a good idea?

    - by Khou
    Are soft deletes a good idea or a bad idea? Instead of actually deleting a record in your database, you would just flag it as "IsDeleted" = true, and upon recovery of the record you could just flag it as "False". Is this a good idea?

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  • Entity Attribute Value Database vs. strict Relational Model Ecommerce question

    - by Dr. Zim
    It is safe to say that the EAV/CR database model is bad. That said, Question: What database model, technique, or pattern should be used to deal with "classes" of attributes describing e-commerce products which can be changed at run time? In a good E-commerce database, you will store classes of options (like TV resolution then have a resolution for each TV, but the next product may not be a TV and not have "TV resolution"). How do you store them, search efficiently, and allow your users to setup product types with variable fields describing their products? If the search engine finds that customers typically search for TVs based on console depth, you could add console depth to your fields, then add a single depth for each tv product type at run time. There is a nice common feature among good e-commerce apps where they show a set of products, then have "drill down" side menus where you can see "TV Resolution" as a header, and the top five most common TV Resolutions for the found set. You click one and it only shows TVs of that resolution, allowing you to further drill down by selecting other categories on the side menu. These options would be the dynamic product attributes added at run time. Further discussion: So long story short, are there any links out on the Internet or model descriptions that could "academically" fix the following setup? I thank Noel Kennedy for suggesting a category table, but the need may be greater than that. I describe it a different way below, trying to highlight the significance. I may need a viewpoint correction to solve the problem, or I may need to go deeper in to the EAV/CR. Love the positive response to the EAV/CR model. My fellow developers all say what Jeffrey Kemp touched on below: "new entities must be modeled and designed by a professional" (taken out of context, read his response below). The problem is: entities add and remove attributes weekly (search keywords dictate future attributes) new entities arrive weekly (products are assembled from parts) old entities go away weekly (archived, less popular, seasonal) The customer wants to add attributes to the products for two reasons: department / keyword search / comparison chart between like products consumer product configuration before checkout The attributes must have significance, not just a keyword search. If they want to compare all cakes that have a "whipped cream frosting", they can click cakes, click birthday theme, click whipped cream frosting, then check all cakes that are interesting knowing they all have whipped cream frosting. This is not specific to cakes, just an example.

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  • Using MongoDB with Ruby On Rails and the Mongomapper plugin

    - by Micke
    Hello, i am currently trying to learn Ruby On Rails as i am a long-time PHP developer so i am building my own community like page. I have came pritty far and have made the user models and suchs using MySQL. But then i heard of MongoDB and looked in to it a little bit more and i find it kinda nice. So i have set it up and i am using mongomapper for the connection between rails and MongoDB. And i am now using it for the News page on the site. I also have a profile page for every User which includes their own guestbook so other users can come to their profile and write a little message to them. My thought now is to change the User models from using MySQL to start using MongoDB. I can start by showing how the models for each User is set up. The user model: class User < ActiveRecord::Base has_one :guestbook, :class_name => "User::Guestbook" The Guestbook model model: class User::Guestbook < ActiveRecord::Base belongs_to :user has_many :posts, :class_name => "User::Guestbook::Posts", :foreign_key => "user_id" And then the Guestbook posts model: class User::Guestbook::Posts < ActiveRecord::Base belongs_to :guestbook, :class_name => "User::Guestbook" I have divided it like this for my own convenience but now when i am going to try to migrate to MongoDB i dont know how to make the tables. I would like to have one table for each user and in that table a "column" for all the guestbook entries since MongoDB can have a EmbeddedDocument. I would like to do this so i just have one Table for each user and not like now when i have three tables just to be able to have a guestbook. So my thought is to have it like this: The user model: class User include MongoMapper::Document one :guestbook, :class_name => "User::Guestbook" The Guestbook model model: class User::Guestbook include MongoMapper::EmbeddedDocument belongs_to :user many :posts, :class_name => "User::Guestbook::Posts", :foreign_key => "user_id" And then the Guestbook posts model: class User::Guestbook::Posts include MongoMapper::EmbeddedDocument belongs_to :guestbook, :class_name => "User::Guestbook" But then i can think of one problem.. That when i just want to fetch the user information like a nickname and a birthdate then it will have to fetch all the users guestbook posts. And if each user has like a thousand posts in the guestbook it will get really much to fetch for the system. Or am i wrong? Do you think i should do it any other way? Thanks in advance and sorry if i am hard to understand but i am not so educated in the english language :)

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  • Fastest gap sequence for shell sort ?

    - by Tony
    According to Marcin Ciura's Optimal (best known) sequence of increments for shell sort algorithm. The best sequence for shellsort is 1, 4, 10, 23, 57, 132, 301, 701... But how can I generate such a sequence ? In Marcin Ciura's paper he said : Both Knuth’s and Hibbard’s sequences are relatively bad, because they are defined by simple linear recurrences but most algorithm books I searched , they all tend to use Knuth’s sequence : k = 3k + 1 ; because it's easy to generate , what's your way of generating shellsort sequence ?

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  • Windows Vista Update Now Wont Boot Up

    - by thatryan
    My friend just updated her Windows Vista to service pack 1, or tried to. Now it wont boot up. Just black screen, some errors etc. I tried googling it and lots of people had this problem it seems. Anyone find a fix for it? I read somewhere I believe that Microsoft said to delete some files, Nvidia maybe? But I can not find that again, I forgot the exact error code I searched for before. Does anyone know what I am talking about? LOL Thanks guys.

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  • Recommend .NET data access layer/middle tier

    - by Simon G
    Hi, I'm currently creating an MVC application that will likely to expand to include a silverlight, wpf and possible windows phone all using the same data. So I've created a class library to keep all my objects in and I've created the MVC app. My question is what would be the best way to access the data? Taking into account possible expansion in the future. Should I use web services/WCF? RIA Services? Remoting? Or something else. What have people used in the past and what do you recommend? Thanks

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  • Help:Graph contest problem: maybe a modified Dijkstra or another alternative algorithm

    - by newba
    Hi you all, I'm trying to do this contest exercise about graphs: XPTO is an intrepid adventurer (a little too temerarious for his own good) who boasts about exploring every corner of the universe, no matter how inhospitable. In fact, he doesn't visit the planets where people can easily live in, he prefers those where only a madman would go with a very good reason (several millions of credits for instance). His latest exploit is trying to survive in Proxima III. The problem is that Proxima III suffers from storms of highly corrosive acids that destroy everything, including spacesuits that were especially designed to withstand corrosion. Our intrepid explorer was caught in a rectangular area in the middle of one of these storms. Fortunately, he has an instrument that is capable of measuring the exact concentration of acid on each sector and how much damage it does to his spacesuit. Now, he only needs to find out if he can escape the storm. Problem The problem consists of finding an escape route that will allow XPTOto escape the noxious storm. You are given the initial energy of the spacesuit, the size of the rectangular area and the damage that the spacesuit will suffer while standing in each sector. Your task is to find the exit sector, the number of steps necessary to reach it and the amount of energy his suit will have when he leaves the rectangular area. The escape route chosen should be the safest one (i.e., the one where his spacesuit will be the least damaged). Notice that Rodericus will perish if the energy of his suit reaches zero. In case there are more than one possible solutions, choose the one that uses the least number of steps. If there are at least two sectors with the same number of steps (X1, Y1) and (X2, Y2) then choose the first if X1 < X2 or if X1 = X2 and Y1 < Y2. Constraints 0 < E = 30000 the suit's starting energy 0 = W = 500 the rectangle's width 0 = H = 500 rectangle's height 0 < X < W the starting X position 0 < Y < H the starting Y position 0 = D = 10000 the damage sustained in each sector Input The first number given is the number of test cases. Each case will consist of a line with the integers E, X and Y. The following line will have the integers W and H. The following lines will hold the matrix containing the damage D the spacesuit will suffer whilst in the corresponding sector. Notice that, as is often the case for computer geeks, (1,1) corresponds to the upper left corner. Output If there is a solution, the output will be the remaining energy, the exit sector's X and Y coordinates and the number of steps of the route that will lead Rodericus to safety. In case there is no solution, the phrase Goodbye cruel world! will be written. Sample Input 3 40 3 3 7 8 12 11 12 11 3 12 12 12 11 11 12 2 1 13 11 11 12 2 13 2 14 10 11 13 3 2 1 12 10 11 13 13 11 12 13 12 12 11 13 11 13 12 13 12 12 11 11 11 11 13 13 10 10 13 11 12 8 3 4 7 6 4 3 3 2 2 3 2 2 5 2 2 2 3 3 2 1 2 2 3 2 2 4 3 3 2 2 4 1 3 1 4 3 2 3 1 2 2 3 3 0 3 4 10 3 4 7 6 3 3 1 2 2 1 0 2 2 2 4 2 2 5 2 2 1 3 0 2 2 2 2 1 3 3 4 2 3 4 4 3 1 1 3 1 2 2 4 2 2 1 Sample Output 12 5 1 8 Goodbye cruel world! 5 1 4 2 Basically, I think we have to do a modified Dijkstra, in which the distance between nodes is the suit's energy (and we have to subtract it instead of suming up like is normal with distances) and the steps are the ....steps made along the path. The pos with the bester binomial (Energy,num_Steps) is our "way out". Important : XPTO obviously can't move in diagonals, so we have to cut out this cases. I have many ideas, but I have such a problem implementing them... Could someone please help me thinking about this with some code or, at least, ideas? Am I totally wrong?

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  • problem bex error

    - by Vaibhav Gandhi
    Problem signature: Problem Event Name: BEX Application Name: iexplore.exe Application Version: 8.0.6001.18882 Application Timestamp: 4b3ed243 Fault Module Name: msjava.dll Fault Module Version: 5.0.2752.0 Fault Module Timestamp: 35747274 Exception Offset: 000c5a6c Exception Code: c0000005 Exception Data: 00000008 OS Version: 6.0.6001.2.1.0.768.3 Locale ID: 1033 Additional Information 1: fd00 Additional Information 2: ea6f5fe8924aaa756324d57f87834160 Additional Information 3: fd00 Additional Information 4: ea6f5fe8924aaa756324d57f87834160

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  • learning inkscape for webapp/website

    - by creativz
    Hello, I'm quite impressed with Incskape, it's very powerfull. That's why I wanted to start learning it. But how should I start (to learn it efficiently)? Should I read a book (anybody can recommend me a good one?) or just (inefficiently) do some tutorials on the internet. I really want to learn it to make professional graphics for a webapp or website. So how should I tackle it? Thanks!

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  • Dealing with the lack of closures in Objective-C

    - by Sean Clark Hess
    Maybe it's just the fact that I've been using http://nodejs.org/ lately, but the lack of closures in Objective-C (iphone) has been really hard to work around. For example, I'm creating service classes. Each service class can have several methods, each of which makes a different URL request. I can use the delegate pattern, but that means that I have to create a new service each time I want to call a method on it (because it has to store the delegate and selector for that request, and new method calls would overwrite them). Even more difficult for me is the fact that I can't easily keep local variables around in the scope for a callback. I have to store anything I want to send back to the delegate on the service class itself, which makes it harder to have more than one method on each class. How do you pros do it? Should I just quit whining and do it another way?

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  • Invoice Discount: Negative line items vs Internal properties

    - by FreshCode
    Should discount on invoice items and entire invoices be negative line items or separate properties of an invoice? In a similar question, Should I incorporate list of fees/discounts into an order class or have them be itemlines, the asker focuses more on orders than invoices (which is a slightly different business entity). Discount is proposed to be separate from order items since it is not equivalent to a fee or product and may have different reporting requirements. Hence, discount should not simply be a negative line item. Previously I have successfully used negative line items to clearly indicate and calculate discount, but this feels inflexible and inaccurate from a business perspective. Now I am opting to add discount to each line item, along with an invoice-wide discount. Is this the right way to do it? Should each item have its own discount amount and percentage? Domain Model Code Sample This is what my domain model, which maps to an SQL repository, looks like: public class Invoice { public int ID { get; set; } public Guid JobID { get; set; } public string InvoiceNumber { get; set; } public Guid UserId { get; set; } // user who created it public DateTime Date { get; set; } public decimal DiscountPercent { get; set; } // all lines discount %? public decimal DiscountAmount { get; set; } // all lines discount $? public LazyList<InvoiceLine> InvoiceLines { get; set; } public LazyList<Payment> Payments { get; set; } // for payments received public boolean IsVoided { get; set; } // Invoices are immutable. // To change: void -> new invoice. public decimal Total { get { return (1.0M - DiscountPercent) * InvoiceLines.Sum(i => i.LineTotal) - DiscountAmount; } } } public class InvoiceLine { public int ID { get; set; } public int InvoiceID { get; set; } public string Title { get; set; } public decimal Quantity { get; set; } public decimal LineItemPrice { get; set; } public decimal DiscountPercent { get; set; } // line discount %? public decimal DiscountAmount { get; set; } // line discount amount? public decimal LineTotal { get { return (1.0M - DiscountPercent) * (this.Quantity * (this.LineItemPrice)) - DiscountAmount; } } }

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  • Tree data structure in iphone with coredata

    - by ebabchick
    Hi, I am looking to store a tree structure in CoreData for iphone. Can someone give me some tips on the best way to go about this? Basically I want to have a bunch of folders that people can dive into in a table view, and I want to have leaves of the tree be photos. The thing is, I want to be able to let the user edit these folders on-the-fly and add folders and content (photos) at their discretion. I'm relatively new to CoreData. Any help would be appreciated. Thanks.

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  • Using C# and Repository Factory and the error: The requested database is not defined in configurati

    - by odiseh
    hi I am using Repository factory for visual studio 2008 for a personal project. It generated a class called ProductRepository which inherits from Repository. The ProductRepository has a constructor which gets a database name as string and passes it to its base (I mean Repository ). So when I try to debug my project step by step, I pass my database name to ProductRepository but it raises the following error: The requested database is not defined in configuration. What's wrong?

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  • Database change management tools?

    - by zodeus
    We are currently in the process of solidifying a database change management process. We run MySql 5 running on RedHat 5. I have selected LiquiBase as the tool because it's open source and allows us to expand its functionality later if needed. It also seems to be one of the few free projects that are still active. Has anyone here had any experience using LiquiBase or other Db versioning tools? Company Background: We are an SaaS company providing a 7/24 hosted application. There are dozens of instances running different versions of the same database and we need a way to manage the deploy process as it's starting to get out of control. The databases have hundreds of tables and we typically do releases once every 3 months.

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  • Is this the correct way of speaking to a "Content Manager" Class?

    - by DeanMc
    I am creating a silverlight site. I am currently breaking out my ideas into pieces of functionality. One of the idea's I have is the concept of a content manager. This is essentially a UI control with 4 regions. Top, Bottom, Right & Left. I also have a collection of objects that are considered "Menu Items". These are controls that function as a way to navigate around, similar to links. The idea I have is to implement an IMenuItem interface. Among the standard pieces of information (Text, PageReference, etc) I was also going to hold a reference to the content manager. My idea behind this thinking is that I can pass the PageReference to a property on the ContentManager and then call a method which knows how to update the content manager accordingly. Is this the best way of implementing this or is their some sort of pattern for it?

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  • Logic / Probability Question: Picking from a bag

    - by Rosarch
    I'm coding a board game where there is a bag of possible pieces. Each turn, players remove randomly selected pieces from the bag according to certain rules. For my implementation, it may be easier to divide up the bag initially into pools for one or more players. These pools would be randomly selected, but now different players would be picking from different bags. Is this any different? If one player's bag ran out, more would be randomly shuffled into it from the general stockpile.

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  • How to explain to users the advantages of dumb primary key?

    - by Hao
    Primary key attractiveness I have a boss(and also users) that wants primary key to be sophisticated/smart/attractive control number(sort of like Social Security number, or credit card number format) I just padded the primary key(in Views) with zeroes to appease their desire to make the control number sophisticated,smart and attractive. But they wanted it as: first 2 digits as client code, then 4 digits as year year, then last 4 digits as transaction number on that client on a given year, then reset the transaction number of client to 1 when next year flows. Each client's transaction starts with 1. e.g. WM20090001, WM20090002, BB2009001, WM20100001, BB20100001 But as I wanted to make things as simple as possible, I forgo embedding their suggested smartness in primary key, I just keep the primary key auto increments regardless of client and year. But to make it not dull-looking(they really are adamant to make the primary key as smart control number), I made the primary key appears to them smart, on view query, I put the client code and four digit year code on front of the eight-zero padded autoincrement key, i.e. WM200900000001. Sort of slug-like information on autoincremented primary key. Keeping primary key autoincrement regardless of any other information, we are able keep other potential side effects problem when they edit a record, for example, if they made a mistake of entering the transaction on WM, then they edit the client code to BB, if we use smart primary key, the primary keys of WM customer will have gaps in their control number. Or worse yet, instead of letting the control numbers have gaps/holes, the user will request that subsequent records of that gap should shift up to that gap and have their subsequent primary keys re-adjust(decremented). How do you deal with these user requests(reasonable or otherwise)? Do you yield to their request? Or just continue using dumb primary key and explain them the repercussions of having a very smart/sophisticated primary key and educate them the significant advantages of having a dumb primary key? P.S. quotable quote(http://articles.techrepublic.com.com/5100-10878_11-1044961.html): "If you hold your tongue the first time users ask what is for them a reasonable request, things will work a lot better in the end."

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  • Difference between Singleton implemention using pointer and using static object

    - by Anon
    EDIT: Sorry my question was not clear, why do books/articles prefer implementation#1 over implementation#2? What is the actual advantage of using pointer in implementation of Singleton class vs using a static object? Why do most books prefer this class Singleton { private: static Singleton *p_inst; Singleton(); public: static Singleton * instance() { if (!p_inst) { p_inst = new Singleton(); } return p_inst; } }; over this class Singleton { public: static Singleton& Instance() { static Singleton inst; return inst; } protected: Singleton(); // Prevent construction Singleton(const Singleton&); // Prevent construction by copying Singleton& operator=(const Singleton&); // Prevent assignment ~Singleton(); // Prevent unwanted destruction };

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