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• Should I use a class in this: Reading a XML file using lxml.

  - by PulpFiction

  Hi everyone. This question is in continuation to my previous question, in which I asked about passing around an ElementTree. I need to read the XML files only and to solve this, I decided to create a global ElementTree and then parse it wherever required. My question is: Is this an acceptable practice? I heard global variables are bad. If I don't make it global, I was suggested to make a class. But do I really need to create a class? What benefits would I have from that approach. Note that I would be handling only one ElementTree instance per run, the operations are read-only. If I don't use a class, how and where do I declare that ElementTree so that it available globally? (Note that I would be importing this module) Please answer this question in the respect that I am a beginner to development, and at this stage I can't figure out whether to use a class or just go with the functional style programming approach.

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• how to enforce multiple unique fields in database table

  - by oo

  i have a table called Cars and the primary key of the table is 'id'. I also have a field called 'name'. I would like to make sure no one enters the same name twice even though it wont break my db integrity. what is the best way of doing this?

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• How to structure data... Sequential or Hierarchical?

  - by Ryan

  I'm going through the exercise of building a CMS that will organize a lot of the common documents that my employer generates each time we get a new sales order. Each new sales order gets a 5 digit number (12222,12223,122224, etc...) but internally we have applied a hierarchy to these numbers: + 121XX |--01 |--02 + 122XX |--22 |--23 |--24 In my table for sales orders, is it better to use the 5 digital number as an ID and populate up or would it be better to use the hierarchical structure that we use when referring to jobs in regular conversation? The only benefit to not populating sequentially seems to be formatting the data later on in my view, but that doesn't sound like a good enough reason to go through the extra work. Thanks

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• What exactly is GRASP's Controller about?

  - by devoured elysium

  What is the idea behind Grasp's Controller pattern? My current interpretation is that sometimes you want to achieve something that needs to use a couple of classes but none of those classes could or has access to the information needed to do it, so you create a new class that does the job, having references to all the needed classes(this is, could be the information expert). Is this a correct view of what Grasp's Controller is about? Generally when googling or SO'ing controller, I just get results about MVC's (and whatnot) which are topics that I don't understand about, so I'd like answers that don't assume I know ASP.NET's MVC or something :( Thanks

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• In web project can we write core services layer without knowledge of UI ?

  - by Silent Warrior

  I am working on web project. We are using flex as UI layer. My question is often we are writing core service layer separately from web/UI layer so we can reuse same services for different UI layer/technology. So practically is it possible to reuse same core layer services without any changes/addition in API with different kind of UI technologies/layers. For e.g. same core service layer with UI technology which supports synchronized request response (e.g. jsp etc.) and non synchronize or event driven UI technology (e.g Ajax, Flex, GWT etc.) or with multiple devices like (computers, mobiles, pdas etc.). Personally I feel its very tough to write core service layer without any knowledge of UI. Looking for thoughts from other people.

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• Creating our own APIs

  - by Markii

  We need a bunch of APIs for our service and are looking at the job as being quite tedious for starting from scratch because we need strict user restrictions such as max queries and usage statistics. Are there any pre-made services or scripts for this already?

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• Makefile: expand dependencies

  - by Danyel

  First off, the title is very generic because there are just tons of ways of how to possibly solve this. However, I'm looking for a clean and neat way. Situation: I have two equal object files foo.o and foo-pi.o, the latter of which is position-independent (compiled with -fPIC). Both depend on foo.h and bar.h. Problem: How do I, without code duplication, declare dependency of all foo*.o to bar.h? Solutions so far: $(shell bash -c 'echo -ne foo{-pi,}.o'}: bar.h $(addsuffix .o, $(addprefix fo, o-pi o)): bar.h The first solution is not portable on systems that don't support bash, the second is a dirty solution since I could not figure out how to use empty strings in addprefix.

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• Need a field / flag / status number for mutliple use ?

  - by Jules

  I want to create a field in my database which will be easy to query. I think if I give a bit of background this will make more sense. My table has listings shown on my website. I run a program which looks at the listings a decides whether to hide them from being shown on the site. I also hide listings manually for various reasons. I want to store these reasons in a field, so more than one reason could be made for hiding. So I need some form of logic to determine which reasons have been used. Can anyone offer me any guidance on what will be future-proof aka new reasons and what will be quick and easy to query upon ?

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• How to find the maximized contiguous SUM in an array (which contains +ve and -ve numbers)?

  - by siva

  ContigSum(i,j) as the sum of the contiguous elements a[i] through a[j], i<=j and a[] contains +ve & -ve numbers Could you please tell me a time efficient solution to find maximized contiguous SUM in the array?

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• Why Is Java Missing Access Specifiers?

  - by Tom Tresansky

  Does anyone understand why Java is missing: An access specifier which allows access by the class and all subclasses, but NOT by other classes in the same package? (Protected-minus) An access specifier which allows access by the class, all classes in the same package, AND all classes in any sub-package? (Default-plus) An access specifier which adds classes in sub-packages to the entities currently allowed access by protected? (Protected-plus) I wish I had more choices than protected and default. In particular, I'm interested in the Protected-plus option. Say I want to use a Builder/Factory patterned class to produce an object with many links to other objects. The constructors on the objects are all default, because I want to force you to use the factory class to produce instances, in order to make sure the linking is done correctly. I want to group the factories in a sub-package to keep them all together and distinct from the objects they are instantiating---this just seems like a cleaner package structure to me. No can do, currently. I have to put the builders in the same package as the objects they are constructing, in order to gain the access to defaults. But separating project.area.objects from project.area.objects.builders would be so nice. So why is Java lacking these options? And, is there anyway to fake it?

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• Correct approach to validate attributes of an instance of class

  - by systempuntoout

  Having a simple Python class like this: class Spam(object): __init__(self, description, value): self.description = description self.value = value Which is the correct approach to check these constraints: "description cannot be empty" "value must be greater than zero" Should i: 1.validate data before creating spam object ? 2.check data on __init__ method ? 3.create an is_valid method on Spam class and call it with spam.isValid() ? 4.create an is_valid static method on Spam class and call it with Spam.isValid(description, value) ? 5.check data on setters declaration ? 6.... Could you recommend a well designed\Pythonic\not verbose (on class with many attributes)\elegant approach?

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• Related boolean columns -- seperate columns or bitpacked into an integer column?

  - by Earlz

  Hello I have a database for a certain record where it needs to store a 1 or a 0 for each day of the week. So which one would be better? Bitshifting each bit into an integer and just having an integer in the database named days or should we make all of them separate boolean values so to have sunday, monday, tuesday... columns?

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• Why use sinlgeton instead of static class?

  - by Jouke van der Maas

  When would a singleton actually be easier or better than a static class? It seems to me creating a singleton is just extra effort that's not actually needed, but I'm sure there is a good reason. Otherwise, they wouldn't be used, obviously.

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• Suggested improvements?

  - by J Harley

  Hello, I have been coding a site in pure HTML/CSS - using no server-side language. I was wondering if anyone had any feedback - is there anything that you would change etc...? Many Thanks, J View Site

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• Need recommendation for a table structure

  - by yapiskan

  I have an entity which has 4 different types of property that could have only one value for each case which are boolean, decimal, string or text. I don't want to define the table with 4 boolean, decimal, nvarchar and ntext columns. What would you recommend to cover this case?

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• What do I need to know before working on an IM application?

  - by John

  I'm looking into building an IM-type application using Java stack (for the server at least). I'd be interested to see any information/advice on how applications like Skype/AIM/MSN work, as well as know any technologies/APIs that might be relevant. Without giving away the idea itself, it's perhaps more akin to Google Wave than Skype, but information useful for either is very welcome. Specific points I have already thought of include: Server Vs P2P... for reasons of logging my system will require all communication to go through a central server. Is this how other IM tools work... especially when audio/video comes into the equation? Cross-communication with other systems. Are there APIs for this or do all IM providers work hard to keep their protocol secret? The nature of what I'm designing means integration could probably only be limited, but it definitely seems worthwhile from a business perspective

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• Setting the type of a field in a superclass from a subclass (Java)

  - by Ibolit

  Hi. I am writing a project on Google App Engine, within it I have a number of abstract classes that I hope I will be able to use in my future projects, and a number of concrete classes inheriting from them. Among other abstract classes I have an abstract servlet that does user management, and I hava an abstract user. The AbstractUser has all the necessary fields and methods for storing it in the datastore and telling whether the user is registered with my service or not. It does not implement any project specific functionality. The abstract servlet that manages users, refers only to the methods declared in the AbstractUser class, which allows it to generate links for logging in, logging out and registering (for unregistered users). In order to implement the project-specific user functionality I need to subclass the Abstract user. The servlets I use in my project are all indirect descendants from that abstract user management servlet, and the user is a protected field in it, so the descendant servlets can use it as their own field. However, whenever i want to access any project specific method of the concrete user, i need to cast it to that type. i.e. (abstract user managing servlet) ... AbstractUser user = getUser(); ... abstract protected AbstractUser getUser(); (project-specific abstract servlet) @Override protected AbstractUser getUser() { return MyUserFactory.getUser(); } any other project specific servlet: int a = ((ConcreteUser) user).getA(); Well, what i'd like to do is to somehow make the type of “user” in the superclass depend on something in the project-specific abstract class. Is it at all possible? And i don't want to move all the user-management stuff into a project-specific layer, for i would like to have it for my future projects already written :) Thank you for your help.

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• Static and default constuctor

  - by Ram

  A non static class can have static as well as default constructor at the same time. What is the difference between these two constructors? When shall I go for only static or static with default constructor?

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• What pattern is this? php

  - by user151841

  I have several classes that are basically interfaces to database rows. Since the class assumes that a row already exists ( __construct expects a field value ), there is a public static function that allows creation of the row and returns an instance of the class. Here's an example ( without the actual database inserts ): class selfStarter { public $type; public function __construct( $type ) { $this->type = $type; } public static function create( $type ) { if ( ! empty($type) ) { $starter = & new selfStarter($type); return $starter; } } } $obj1 = selfStarter::create( "apple" ); $obj2 = & new selfStarter( "banana" ); What is this pattern called?

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• Constructors + Dependency Injection

  - by Sunny

  If I am writing up a class with more than 1 constructor parameter like: class A{ public A(Dependency1 d1, Dependency2 d2, ...){} } I usually create a "argument holder"-type of class like: class AArgs{ public Dependency1 d1 { get; private set; } public Dependency2 d2 { get; private set; } ... } and then: class A{ public A(AArgs args){} } Typically, using a DI-container I can configure the constructor for dependencies & resolve them & so there is minimum impact when the constructors need to change. Is this considered an anti-pattern and/or any arguments against doing this?

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• Database tables with dynamic information

  - by Tim Fennis

  I've googled this and found that it's almost impossible to create a database with dynamic collumns. I'll explain my problem first. I am making a webshop for a customer. It has multiple computer products for sale. CPU's HDD's RAM ect. All these products have different properties, a CPU has an FSB, RAM has a CAS latency. But this is very inconvenient because my orders table needs foreign keys to different tables which is impossible. An other option is to store all the product specific information in a varchar or blob field and let PHP figure it out. The problem with this solution is that the website needs a PC builder. A step-by-step guide to building your PC. So for instance if a customer decides he wants a new "i7 920" or whatever i want to be able to sellect all motherboards for socket 1366, which is impossible because all the data is stored in one field. I know it's possible to select all motherboards form the DB and let PHP figure out which ones are for socket 1366 but i was wondering, is there a better solution?

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• What is the definition of a Service object ?

  - by Maskime

  I've been working a lot with PHP. But recently i was sent on a work wich use Java. In PHP i used to do a lot of Singleton object but this pattern has not the same signification in Java that it has in PHP. So i wanted to go for an utility class (a class with static method) but my chief doesn't like this kind of classes and ask me to go for services object. So my guess was that a service object is just a class with a constructor that implement some public methods... Am i right ?

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• This is right way for database?

  - by ciss

  Hello, i have some issue with database. Okay, i have two models - Page and Item. Page for displaying some content. Item - this is item discription. So, i work on small ecommerce shop. Okay, all of this models can have some comments. So, this is my Comments model at this moment: Comments - string : id text : body integer : page_id integer : item_id So when some one add comment to page - page_id will be filled with current Page id. And if some one add comment to item - item_id will be filled. Okay, i know what the best way is to create STI or Polymorphic assoc, but does i really need this way for my situation? Sorry for my bad english, i'm from Russia.=)

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• What is it called when an object member returns the object, enabling you to string method calls?

  - by thepearson

  Perhaps I'm just not using the right Google-age. But I am trying to remember what the term is for when you return the object from one of it members to enable you to do something similar: class obj { obj function method() { return this } } obj->method()->method()->method()->method() I used to know this but it has totally escaped me.

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• Running a sharded DB from a single machine

  - by ming yeow

  This sounds kinda dumb, but I have a sharded DB that I no longer think I need to run on 2 machines, and would like to run on one single machine instead. Any ideas on how that can potentially be done? There are lots of resources on how i can achieve the converse, but very little on how this can be done

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