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  • Why are alloc and init called separately in Objective-C?

    - by André Hoffmann
    Note: I'm relatively new to Objective-C and am coming from Java and PHP. Could someone explain to me why I always have to first allocate and then initialize an instance? Couldn't this be done in the init methods like this: + (MyClass*)init { MyClass *instance = [MyClass alloc]; [instance setFoo:@"bla"]; return instance; } + (MyClass*)initWithString:(NSString*)text { MyClass *instance = [MyClass init]; [instance setFoo:text]; return instance; } ... Is this just a relict from the old C days or is there something that I'm not seeing? I know this isn't a problem as I could as well always call alloc and init, but since it's a bit tedious I'd like to at least know why I'm doing it. I'm liking the expressiveness of the language so far, but this is something that I want to fully understand in order to think the Objective-C way. Thank you!

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  • Best way to store sales tax information

    - by Seph
    When designing a stock management database system (sales / purchases) what would be the best way to store the various taxes and other such amounts? A few of the fields that could be saved are: Unit price excluding tax Unit price including tax Tax per item Total excluding tax (rounded to 2 decimals) Total including tax (rounded to 2 decimals) Total tax (rounded to 2 decimals) Currently the most reasonable solution so far is storing down (roughly) item, quantity, total excluding tax (rounded) and the total tax (rounded). Can anyone suggest some better way of storing this details for a generic system? Also, given the system needs to be robust, what should be done if there were multiple tax values (eg: state and city) which might need to be separated, in this case a separate table would be in order, but would it be considered excessive to just have a rowID and some taxID mapping to a totalTax column?

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  • How my Website looks like under Different Screen Resolutions?

    - by strakastroukas
    Back in the past, i found a third party webpage that was able to capture and save images of my website in different resolutions and browsers. Of course i have no more that bookmark... So is there any webpage or application where i can see how my webpage looks like in different resolution? And here are the resolutions i would like to check for... 1. 1024x768 24.56% 2. 1280x800 22.06% 3. 1280x1024 13.42% 4. 1366x768 7.10% 5. 1440x900 6.68%

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  • How should I model the database for this problem? And which ORM can handle it?

    - by Kristof Claes
    I need to build some sort of a custom CMS for a client of ours. These are some of the functional requirements: Must be able to manage the list of Pages in the site Each Page can contain a number of ColumnGroups A ColumnGroup is nothing more than a list of Columns in a certain ColumnGroupLayout. For example: "one column taking up the entire width of the page", "two columns each taking up half of the width", ... Each Column can contain a number ContentBlocks Examples of a ContentBlock are: TextBlock, NewsBlock, PictureBlock, ... ContentBlocks can be given a certain sorting within a Column A ContentBlock can be put in different Columns so that content can be reused without having to be duplicated. My first quick draft of how this could look like in C# code (we're using ASP.NET 4.0 to develop the CMS) can be found at the bottom of my question. One of the technical requirements is that it must be as easy as possible to add new types of ContentBlocks to the CMS. So I would like model everything as flexible as possible. Unfortunately, I'm already stuck at trying to figure out how the database should look like. One of the problems I'm having has to do with sorting different types of ContentBlocks in a Column. I guess each type of ContentBlock (like TextBlock, NewsBlock, PictureBlock, ...) should have it's own table in the database because each has it's own different fields. A TextBlock might only have a field called Text whereas a NewsBlock might have fields for the Text, the Summary, the PublicationDate, ... Since one Column can have ContentBlocks located in different tables, I guess I'll have to create a many-to-many association for each type of ContentBlock. For example: ColumnTextBlocks, ColumnNewsBlocks and ColumnPictureBlocks. The problem I have with this setup is the sorting of the different ContentBlocks in a column. This could be something like this: TextBlock NewsBlock TextBlock TextBlock PictureBlock Where do I store the sorting number? If I store them in the associaton tables, I'll have to update a lot of tables when changing the sorting order of ContentBlocks in a Column. Is this a good approach to the problem? Basically, my question is: What is the best way to model this keeping in mind that it should be easy to add new types of ContentBlocks? My next question is: What ORM can deal with that kind of modeling? To be honest, we are ORM-virgins at work. I have been reading a bit about Linq-to-SQL and NHibernate, but we have no experience with them. Because of the IList in the Column class (see code below) I think we can rule out Linq-to-SQL, right? Can NHibernate handle the mapping of data from many different tables to one IList? Also keep in mind that this is just a very small portion of the domain. Other parts are Users belonging to a certain UserGroup having certain Permissions on Pages, ColumnGroups, Columns and ContentBlocks. The code (just a quick first draft): public class Page { public int PageID { get; set; } public string Title { get; set; } public string Description { get; set; } public string Keywords { get; set; } public IList<ColumnGroup> ColumnGroups { get; set; } } public class ColumnGroup { public enum ColumnGroupLayout { OneColumn, HalfHalf, NarrowWide, WideNarrow } public int ColumnGroupID { get; set; } public ColumnGroupLayout Layout { get; set; } public IList<Column> Columns { get; set; } } public class Column { public int ColumnID { get; set; } public IList<IContentBlock> ContentBlocks { get; set; } } public interface IContentBlock { string GetSummary(); } public class TextBlock : IContentBlock { public string GetSummary() { return "I am a piece of text."; } } public class NewsBlock : IContentBlock { public string GetSummary() { return "I am a news item."; } }

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  • Displaying an NSString on a Custom View

    - by ilovetacos
    I have an interface that has an NSTextField, NSButton, and an NSView. When I type something in the textfield and press the button, I want the text to be drawn in the NSView. So far I have everything connected and working, except for the view. How can I connect the text and the view so that every time I press the button, the text is drawn to the view?

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  • Modifying my website to allow anonymous comments

    - by David
    I write the code for my own website as an educational/fun exercise. Right now part of the website is a blog (like every other site out there :-/) which supports the usual basic blog features, including commenting on posts. But I only have comments enabled for logged-in users; I want to alter the code to allow anonymous comments - that is, I want to allow people to post comments without first creating a user account on my site, although there will still be some sort of authentication involved to prevent spam. Question: what information should I save for anonymous comments? I'm thinking at least display name and email address (for displaying a Gravatar), and probably website URL because I eventually want to accept OpenID as well, but would anything else make sense? Other question: how should I modify the database to store this information? The schema I have for the comment table is currently comment_id smallint(5) // The unique comment ID post_id smallint(5) // The ID of the post the comment was made on user_id smallint(5) // The ID of the user account who made the comment comment_subject varchar(128) comment_date timestamp comment_text text Should I add additional fields for name, email address, etc. to the comment table? (seems like a bad idea) Create a new "anonymous users" table? (and if so, how to keep anonymous user ids from conflicting with regular user ids) Or create fake user accounts for anonymous users in my existing users table? Part of what's making this tricky is that if someone tries to post an anonymous comment using an email address (or OpenID) that's already associated with an account on my site, I'd like to catch that and prompt them to log in.

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  • Can the Singleton be replaced by Factory?

    - by lostiniceland
    Hello Everyone There are already quite some posts about the Singleton-Pattern around, but I would like to start another one on this topic since I would like to know if the Factory-Pattern would be the right approach to remove this "anti-pattern". In the past I used the singleton quite a lot, also did my fellow collegues since it is so easy to use. For example, the Eclipse IDE or better its workbench-model makes heavy usage of singletons as well. It was due to some posts about E4 (the next big Eclipse version) that made me start to rethink the singleton. The bottom line was that due to this singletons the dependecies in Eclipse 3.x are tightly coupled. Lets assume I want to get rid of all singletons completely and instead use factories. My thoughts were as follows: hide complexity less coupling I have control over how many instances are created (just store the reference I a private field of the factory) mock the factory for testing (with Dependency Injection) when it is behind an interface In some cases the factories can make more than one singleton obsolete (depending on business logic/component composition) Does this make sense? If not, please give good reasons for why you think so. An alternative solution is also appreciated. Thanks Marc

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  • How To Implement The Query Side Of CQS in DDD?

    - by Laz
    I have implemented the command side of DDD using the domain model and repositories, but how do I implement the query side? Do I create an entirely new domain model for the UI, and where is this kept in the project structure...in the domain layer, the UI layer, etc? Also, what do I use as my querying mechanism, do I create new repositories specifically for the UI domain objects, something other than repositories, or something else?

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  • Should a developer be a designer?

    - by nepb
    I have been developing websites for quite some time and I am not so good in designing websites? My Boss is refering me to take some lessons on it. But I really want to stick to development rather than designing?

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  • Best Practice for Utilities Class?

    - by Sonny Boy
    Hey all, We currently have a utilities class that handles a lot of string formatting, date displays, and similar functionality and it's a shared/static class. Is this the "correct" way of doing things or should we be instanciating the utility class as and when we need it? Our main goal here is to reduce memory footprint but performance of the application is also a consideration. Thanks, Matt PS. We're using .NET 2.0

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  • Saving complex aggregates using Repository Pattern

    - by Kevin Lawrence
    We have a complex aggregate (sensitive names obfuscated for confidentiality reasons). The root, R, is composed of collections of Ms, As, Cs, Ss. Ms have collections of other low-level details. etc etc R really is an aggregate (no fair suggesting we split it!) We use lazy loading to retrieve the details. No problem there. But we are struggling a little with how to save such a complex aggregate. From the caller's point of view: r = repository.find(id); r.Ps.add(factory.createP()); r.Cs[5].updateX(123); r.Ms.removeAt(5); repository.save(r); Our competing solutions are: Dirty flags Each entity in the aggregate in the aggregate has a dirty flag. The save() method in the repository walks the tree looking for dirty objects and saves them. Deletes and adds are a little trickier - especially with lazy-loading - but doable. Event listener accumulates changes. Repository subscribes a listener to changes and accumulates events. When save is called, the repository grabs all the change events and writes them to the DB. Give up on repository pattern. Implement overloaded save methods to save the parts of the aggregate separately. The original example would become: r = repository.find(id); r.Ps.add(factory.createP()); r.Cs[5].updateX(123); r.Ms.removeAt(5); repository.save(r.Ps); repository.save(r.Cs); repository.save(r.Ms); (or worse) Advice please! What should we do?

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  • Avoiding Duplicate Data in DB (for use with Rails)

    - by ants
    I have five tables that I am trying to get to work nicely together but may need some help. I have three main tables: accounts members and roles. With two join tables account_members and account_member_roles. The accounts and members table are joined by account_members (fk account_id and member_id) table. The other 2 tables are the problem (roles and account_member_roles). A member of an account can have more than one role and I have the account_member_roles (fk account_member_id and role_id) table joining the account_members join table and the roles table. That seems logical but can you have a relationship with a join table? What I'd like to be able to do is when creaeting an account, for instance, I would like @account.save to include the roles and update the account_member_roles table neatly ..... but through the account_members join table. I've tried ..... accept_nested_attributes_for :members, :account_member_roles in the account.rb but I get ..... ActiveRecord::HasManyThroughCantAssociateThroughHasManyReflection (Cannot modify association 'Account#account_member_roles' because the source reflection class 'AccountMemberRole' is associated to 'AccountMember' via :has_many.) upon trying to save a record. Any advice on how I should approach this? CIA -ants

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  • ER Data Model - confused by diagram.

    - by Khou
    Hi im a little confused by this diagram http://www.b-eye-network.com/images/content/i030ht0104.gif (Last diagram in the article) 1 - In the "ACCOUNTING ENTRY" table it shows "DebitEntry" and "CreditEntry" i) is this two column or ii) is this two rows of data? or iii) is it two separate tables on its own, Acounting_entry_credit and Accounting_entry_debit? Same question with the "ACCOUNT" table, it shows asset account, livabilities account, equaity account? are they 3 columns or are they 3 rows? Source: http://www.tdan.com/view-articles/5227/

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  • What is the best approach to binding commands in a ViewModel to elements in the View?

    - by Micah
    Anyone who has tried to implement RoutedCommands in WPF using M-V-VM has undoubtedly run into issues. Commands (non-UI commands that is) should be implemented in the ViewModel. For instance if I needed to save a CustomerViewModel then I would implement that as a command directly on my CustomerViewModel. However if I wanted to pop up a window to show the users addresses I would implement a ShowCustomerAddress command directly in the view since this a UI specific function. How do I define the command bindings in the viewmodel, and use them in the view?

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  • Python: Recursively access dict via attributes as well as index access?

    - by Luke Stanley
    I'd like to be able to do something like this: from dotDict import dotdictify life = {'bigBang': {'stars': {'planets': [] } } } dotdictify(life) #this would be the regular way: life['bigBang']['stars']['planets'] = {'earth': {'singleCellLife': {} }} #But how can we make this work? life.bigBang.stars.planets.earth = {'singleCellLife': {} } #Also creating new child objects if none exist, using the following syntax life.bigBang.stars.planets.earth.multiCellLife = {'reptiles':{},'mammals':{}} My motivations are to improve the succinctness of the code, and if possible use similar syntax to Javascript for accessing JSON objects for efficient cross platform development.(I also use Py2JS and similar.)

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  • do's and don'ts for writing mysql queries

    - by nik
    One thing I always wonder while writing query is that am I writing most optimized query or not? I know certain things like: 1) using SELECT field1, filed2 instead of SELECT * 2) Giving proper indexes to the tables but I am sure there are more things that should be kept in mind for writing queries, since most of the database can only grow more and optimal query will help gr8 in execution time, Can u share some tips and tricks on writing queries?

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  • O(log n) algorithm to find the element having rank i in union of pre-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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  • What is the basic pattern for using (N)Hibernate?

    - by Vilx-
    I'm creating a simple Windows Forms application with NHibernate and I'm a bit confused about how I'm supposed to use it. To quote the manual: ISession (NHibernate.ISession) A single-threaded, short-lived object representing a conversation between the application and the persistent store. Wraps an ADO.NET connection. Factory for ITransaction. Holds a mandatory (first-level) cache of persistent objects, used when navigating the object graph or looking up objects by identifier. Now, suppose I have the following scenario: I have a simple classifier which is a MSSQL table with two columns - ID (auto_increment) and Name (nvarchar). To edit this classifier I create a form which contains a single gridview and two buttons - OK and Cancel. The user can nearly directly edit the table in the gridview, and when he hits OK the changes he made are persisted to the DB (or if he hits cancel, nothing happens). Now, I have several questions about how to organize this: What should the lifetime of my ISession be? Should I create a single ISession for my whole application; an ISession for each of my forms (the application is single-threaded MDI); or an ISession for every DB operation/transaction? Does NHibernate offer some kind of built-in dirty tracking or must I do this myself? The manual mentions something like it here and there but does not go into details. How is this done? Is there not a huge overhead? Is it somehow tied with the cache(s) that NHibernate has? What are these caches for? Are they not specific to a single ISession? That is, if I use a seperate ISession for every transaction, won't it break the dirty tracking? How does the built-in dirty tracking detect deleted objects?

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  • C# Memoization of functions with arbitrary number of arguments

    - by Lirik
    I'm trying to create a memoization interface for functions with arbitrary number of arguments, but I'm failing miserably. The first thing I tried is to define an interface for a function which gets memoized automatically upon execution: class EMAFunction:IFunction { Dictionary<List<object>, List<object>> map; class EMAComparer : IEqualityComparer<List<object>> { private int _multiplier = 97; public bool Equals(List<object> a, List<object> b) { List<object> aVals = (List<object>)a[0]; int aPeriod = (int)a[1]; List<object> bVals = (List<object>)b[0]; int bPeriod = (int)b[1]; return (aVals.Count == bVals.Count) && (aPeriod == bPeriod); } public int GetHashCode(List<object> obj) { // Don't compute hash code on null object. if (obj == null) { return 0; } // Get length. int length = obj.Count; List<object> vals = (List<object>) obj[0]; int period = (int) obj[1]; return (_multiplier * vals.GetHashCode() * period.GetHashCode()) + length;; } } public EMAFunction() { NumParams = 2; Name = "EMA"; map = new Dictionary<List<object>, List<object>>(new EMAComparer()); } #region IFunction Members public int NumParams { get; set; } public string Name { get; set; } public object Execute(List<object> parameters) { if (parameters.Count != NumParams) throw new ArgumentException("The num params doesn't match!"); if (!map.ContainsKey(parameters)) { //map.Add(parameters, List<double> values = new List<double>(); List<object> asObj = (List<object>)parameters[0]; foreach (object val in asObj) { values.Add((double)val); } int period = (int)parameters[1]; asObj.Clear(); List<double> ema = TechFunctions.ExponentialMovingAverage(values, period); foreach (double val in ema) { asObj.Add(val); } map.Add(parameters, asObj); } return map[parameters]; } public void ClearMap() { map.Clear(); } #endregion } Here are my tests of the function: private void MemoizeTest() { DataSet dataSet = DataLoader.LoadData(DataLoader.DataSource.FROM_WEB, 1024); List<String> labels = dataSet.DataLabels; Stopwatch sw = new Stopwatch(); IFunction emaFunc = new EMAFunction(); List<object> parameters = new List<object>(); int numRuns = 1000; long sumTicks = 0; parameters.Add(dataSet.GetValues("open")); parameters.Add(12); // First call for(int i = 0; i < numRuns; ++i) { emaFunc.ClearMap();// remove any memoization mappings sw.Start(); emaFunc.Execute(parameters); sw.Stop(); sumTicks += sw.ElapsedTicks; } Console.WriteLine("Average ticks not-memoized " + (sumTicks/numRuns)); sumTicks = 0; // Repeat call for (int i = 0; i < numRuns; ++i) { sw.Start(); emaFunc.Execute(parameters); sw.Stop(); sumTicks += sw.ElapsedTicks; } Console.WriteLine("Average ticks memoized " + (sumTicks/numRuns)); } The performance is confusing me... I expected the memoized function to be faster, but it didn't work out that way: Average ticks not-memoized 106,182 Average ticks memoized 198,854 I tried doubling the data instances to 2048, but the results were about the same: Average ticks not-memoized 232,579 Average ticks memoized 446,280 I did notice that it was correctly finding the parameters in the map and it going directly to the map, but the performance was still slow... I'm either open for troubleshooting help with this example, or if you have a better solution to the problem then please let me know what it is.

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  • Pattern/Matcher in Java?

    - by user1007059
    I have a certain text in Java, and I want to use pattern and matcher to extract something from it. This is my program: public String getItemsByType(String text, String start, String end) { String patternHolder; StringBuffer itemLines = new StringBuffer(); patternHolder = start + ".*" + end; Pattern pattern = Pattern.compile(patternHolder); Matcher matcher = pattern.matcher(text); while (matcher.find()) { itemLines.append(text.substring(matcher.start(), matcher.end()) + "\n"); } return itemLines.toString(); } This code works fully WHEN the searched text is on the same line, for instance: String text = "My name is John and I am 18 years Old"; getItemsByType(text, "My", "John"); immediately grabs the text "My name is John" out of the text. However, when my text looks like this: String text = "My name\nis John\nand I'm\n18 years\nold"; getItemsByType(text, "My", "John"); It doesn't grab anything, since "My" and "John" are on different lines. How do I solve this?

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  • What resources will help me understand the fundamentals of Relational Database Systems.

    - by Rachel
    This are few of the fundamental database questions which has always given me trouble. I have tried using google and wiki but I somehow I miss out on understanding the functionality rather than terminology. If possible would really appreciate if someone can share more insights on this questions using some visual representative examples. What is a key? A candidate key? A primary key? An alternate key? A foreign key? What is an index and how does it help your database? What are the data types available and when to use which ones?

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