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• How do I maintain coherency between model and view-model in MVVM pattern?

  - by Mike Garrett

  Problem Statement I'm writing a very basic WPF application to alter the contents of a configuration file. The data format is an XML file with a schema. I want to use it as a learning project for MVVM, so I have duly divided the code into Model: C# classes auto-generated from xsd.exe View-Model: View-friendly representation of the Model. View: Xaml and empty code behind I understand how the View-Model can make View-binding a breeze. However, doesn't that leave the View-Model <- Model semantics very awkward? Xsd.exe generates C# classes with arrays for multiple XML elements. However, at the V-VM level you need Observable Collections. Questions: Does this really mean I have to keep two completely different collection types representing the same data in coherence? What are the best practices for maintaining coherence between the Model and the View-Model?

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• django left join with null

  - by SledgehammerPL

  The model: class Product(models.Model): name = models.CharField(max_length = 128) def __unicode__(self): return self.name class Receipt(models.Model): name = models.CharField(max_length=128) components = models.ManyToManyField(Product, through='ReceiptComponent') class Admin: pass def __unicode__(self): return self.name class ReceiptComponent(models.Model): product = models.ForeignKey(Product) receipt = models.ForeignKey(Receipt) quantity = models.FloatField(max_length=9) unit = models.ForeignKey(Unit) def __unicode__(self): return unicode(self.quantity!=0 and self.quantity or '') + ' ' + unicode(self.unit) + ' ' + self.product.genitive The idea: there are a components on stock. I'd like to find out which recipes I can made with components which I have. It's not easy - but possible - I made a SQL view, which gets the solution. But I'm learning python and Django so I'd like to make it Django-style ;D The concept of solution: get the set of recipes which has at last one component: list_of_available_components = ReceiptComponent.objects.filter(product__in=list_of_available_products).distinct() list_of_related_receipts = Receipt.objects.filter(receiptcomponent__in = list_of_available_components).distinct() get recipes (from list_of_related_receipts) which has not at last one component list_of_incomplete_recipes = (SELECT * FROM drinkbook_receiptcomponent LEFT JOIN drinkstore_stock_products USING(product_id) WHERE drinkstore_stock_products.stock_id IS NULL AND receipt_id IN (SELECT receipt_id FROM drinkbook_receiptcomponent JOIN drinkstore_stock_products USING(product_id))) get recipes (from list_of_related_receipts) which are not in "list_of_incomplete_recipes"

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• [Flex 4] Removing sort arrows from AdvancedDataGridColumn Header.

  - by zeroDivisible

  Hello, I am doing this simple project using Flex 4 SDK and I got stuck with this simple problem: I have turned sortable property for AdvancedDataGridColumn to false, but the column header is still rendered as: As You can see, my label for this header is "06", but the column header is divided and it keeps the place for sort arrow. How can I change this? I would like my column header to contain only my label. I know that most probably I need to do some magic with AdvancedDataGridHeaderRenderer but I just started learning Flex and would like to receive some help. Thank You for help. Best regards, Mike.

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• How can I implement my own version of a MVC framework in ASP.NET?

  - by ace

  Hi - I would like to know how I can go about implementing my own version of a MVC framework in ASP.NET? I know there already is Microsoft provided ASP.NET MVC framework, but I want to learn MVC and thought the best way would be to implement my own flavor of a MVC framework on top of ASP.NET. Any thoughts / guidance ? Also, can anyone point me to a page where I can learn more about how microsoft implemented ASP.NET MVC ? I'm more interested in learning about the under the hood plumbing that goes on to implement the framework on top of asp.net, do they use HttpHandlers / HttpModules ? Thanks.

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• Jquery: how make div slide in and out

  - by Jeddizero

  Hi, I am currently learning jQuery. I'd like to know how to make an image slide in when you click on its edge, then click again and it slides away. Similar to this: http://www.karenmillen.com/ If you see the right hand side and click, there is the effect that i'm looking for. I assume this will involve making a div and giving it a background image then using some jquery to make the div slide into view. Of course the div could have other content such as html. Any ideas? Would the .slideDown() method work?

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• Listing time every second as a Bash script

  - by Caleb

  Hello all, first time here as I've finally started to learn programming. Anyway, I'm just trying to print the time in nanoseconds every second here, and I have this: #!/usr/bin/env bash while true; do date=(date +%N) ; echo $date ; sleep 1 ; done Now, that simply yields a string of date's, which isn't what I want. My learning has been rather messy, so I hope you'll excuse me for this if it's really simple. Also, I did manage to fine this, that worked on the prompt: while true ; do date +%N ; sleep 1 ; done But that obviously doesn't work as a script.

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• Shall i learn Assembly Language or C, to Understand how "real programming" works?

  - by Daniel Upton

  Hello, World.. I'm a web developer mostly working in Ruby and C#.. I wanna learn a low level language so i dont look like an ass infront of my (computer science expert) boss. Ive heard a lot of purist buzz about how assembly language is the only way to learn how computers actually work, but on the other hand C would probably be more useful as a language rather than just for theory. So my question is.. Would Learning C teach me enough computer science theory / low level programming to not look like a common dandy (complete tool)? Thanks! Daniel

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• simple python file writing question

  - by aharon

  I'm learning Python, and have run into a bit of a problem. On my OSX install of Python 3.1, this happens in the console: >>> filename = "test" >>> reader = open(filename, 'r') >>> writer = open(filename, 'w') >>> reader.read() '' >>> writer.write("hello world\n") 12 >>> reader.read() '' And calling more test in BASH confirms that there is nothing in test. What's going on? Thanks.

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• Good portfolio projects

  - by David

  Hi, I am a recent graduate and am looking to start a career in web development. Its kind of a catch 22 at the moment as I have a fair bit of programming experience from university but not really in web development and to get a job in web development a portfolio is typically required. So, I am looking to start a building a few application in order to have something to show potential employers. Im more into the backend stuff although am just as comfortable with front end development. Does anyone have any thoughts on some potential projects that would be both relatively quick (as i need to get a job soon!) to build but show off enough programming knowlege / skills to be impressive to employers. At the moment i am also learning to use the zend framework and I would hope to find work using such a framework (mvc). My initial thoughts would be things like a webmail app or maybe a custom CMS. Any ideas would be greatley appreciated.

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• Php PEAR, Database Abstraction & Factory Methods

  - by pws5068

  I'm interested in learning more about design practices in PHP for Database Abstraction & Factory methods. For background, my site is a special-interest social networking community currently in beta mode. Currently, I've started moving my old code for object retrieval to factory methods. However, I do feel like I'm limiting myself by keeping a lot of SQL table names and structure separated in each function/method. Questions: 1.) Is there a reason to use PEAR (or similar) if I dont anticipate switching databases? 2.) Can PEAR interface with the MySqli prepared statements I currently use? 3.) Will it help me separate table names from each method? (If no, what other design patterns might I want to research?) 4.) Will it slow down my site once I have a significantly large member base?

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• Is using decimal ranges in a switch impossible in C#?

  - by phobia

  I'm justing starting out learning C# and I've become stuck at something very basic. For my first "app" I thought I'd go for something simple, so I decided for a BMI calculator. The BMI is calculated into a decimal type which I'm now trying to use in a switch statement, but aparently decimal can't be used in a switch? What would be the C# solution for this: decimal bmi = calculate_bmi(h, w); switch (bmi) { case < 18.5: bmi_description = "underweight."; break; case > 25: bmi_description = "overweight"; case > 30: bmi_description = "very overweight"; case > 40: bmi_description = "extreme overweight"; break; }

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• nested form & habtm

  - by brewster

  so i am trying to save to a join table in a habtm relationship, but i am having problems. from my view, i pass in a group id with: = link_to "Create New User", new_user_url(:group => 1) User model (user.rb) class User < ActiveRecord::Base has_and_belongs_to_many :user_groups accepts_nested_attributes_for :user_groups end UserGroups model (user_groups.rb) class UserGroup < ActiveRecord::Base has_and_belongs_to_many :users end users_controller.rb def new @user = User.new(:user_group_ids => params[:group]) end in the new user view, i have access to the User.user_groups object, however when i submit the form, not only does it not save into my join table (user_groups_users), but the object is no longer there. all the other objects & attributes of my User object are persistent except for the user group. i just started learning rails, so maybe i am missing something conceptually here, but i have been really struggling with this.

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• Why are the contents of my UITableViewCell disappearing?

  - by barfoon

  Hey everyone, I am learning about using the checkmark cell accessory and am wondering why the contents of my cell is disappearing when toggling it. Here is my code: + (void) toggleCheckmarkedCell:(UITableViewCell *)cell { if (cell.accessoryType == UITableViewCellAccessoryNone) cell.accessoryType = UITableViewCellAccessoryCheckmark; else cell.accessoryType = UITableViewCellAccessoryNone; } And here is didSelectRowAtIndexPath: UITableViewCell *cell = [tableView cellForRowAtIndexPath:indexPath]; [cell setSelectionStyle:UITableViewCellSelectionStyleNone]; [RootViewController toggleCheckmarkedCell:cell]; The checkmark is toggling on/off and is visible but the main contents of the cell disappears. Can anyone explain why this is happening? Thank you,

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• Reuse ASP.NET Control Multiple Times on Page

  - by macinjosh

  I feel somewhat foolish asking such a simple question, but I can't seem to find an answer. I'm new to ASP.NET (C#), but I'm learning by building a simple set of web pages that display a report. I have a variable that represents a company name. I need to output this variable in multiple places on the web page. The only way I have found to output a variable this is with: company_name.Text = "Acme Windows"; then <asp:literal id="company_name" runat="server" /> My problem is that I want to use company_name in multiple places on the page. Do I really have to create a separate variable holding the the same value for each time it is placed on the page? If I just copy the above XML code to all the places I want to show the variable it obviously creates a compile error since that ID is already defined. I feel like I'm missing something very obvious.

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• why do we all learn and study java or .net or why java or .net are popular?

  - by tadeze

  My question to be clear is why do we all need to learn java or .net(C#) , still java or .net are more popular than delphi or c++ and even there are lot of resource,articles or books compared to c++ or delphi about java and .net. However, I heard majority, if I am right about 80% of software are developed using c++ or delphi in the software industry. so, why do we bother about other languages specifically about the cosmopolitan languages such as java or .net in education as well as for job interview. Although, still I know the elegance of java and .net, their safe code execution,fully objected oriented behavior ...etc, but still according to the statics they are not preferred on software develpement as a primary language mainly because of their execution time compared to c++ or delphi. So my question are why do they choose them for jobs or educational purpose and everything else? why do we lose our time learning these language if we are forced to use the other languages in the industry?

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• Are there any purely functional Schemes or Lisps?

  - by nickname

  Over the past few months, I've put a lot of effort into learning (or attempting to learn) several functional programming languages. I really like math, so they have been very natural for me to use. Simply to be more specific, I have tried Common Lisp, Scheme, Haskell, OCaml, and (a little bit of) Erlang. I did not like the syntax of OCaml and do not have enough Erlang knowledge to make a judgment on it yet. Because of its consistent and beautiful (non-)syntax, I really like Scheme. However, I really do appreciate the stateless nature of purely functional programming languages such as Haskell. Haskell looks very interesting, but the amount of inconsistent and non-extendable syntax really bothered me. In the interest of preventing a Lisp vs Haskell flame war, just pretend that I can't use Haskell for some other reason. Therefore, my question is: Are there any purely functional Schemes (or Lisps in general)?

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• How does a programmer think?

  - by Gordon Potter

  This may be a hopelessly vague question. But I am interested to hear whatever logical thought processes people go through when learning a new concept or trying to get their brain around code they might not have ever seen before. Basically, what general steps does one take to to break down problems and what does it take to "get it"? If you were to diagram a flowchart of how your mental process works when you look at code or try to solve a problem what might it look like? What common references, tips, and mental assumptions do you find useful in problem solving? How is this different between different domains? For example in what ways is a web programmer's thought process similar or different from a traditional desktop app developer's process?

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• Initialize window code Mac OS X

  - by Jarle

  I'm currently reading "the red book" for learning OpenGL properly, and in one of the first examples, the author writes a line that says "InitializeAWindowPlease();" as a place holder for the code that will make a window to draw the OpenGL content in. Since I'm using Xcode for my programing, I know that I "get" a window to work with automatically (and that I have to make my own OpenGL view in interfacebuilder). How can I make this with pure code? I'm trying to learn programming, and I'm not to happy about taking "shortcuts" all the time. How can I make a window to draw my openGL stuff in? With Objective-C and C code I would love to see it. My goal is that I can make it without opening interface builder at all:)

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• What are the best uses for each programming language?

  - by VirtuosiMedia

  I come from a web developer background, so I'm fairly familiar with PHP and JavaScript, but I'd eventually like to branch out into other languages. At this point, I don't have a particular direction or platform that I'm leaning toward as far as learning a new language or what I would use it for, but I would like to learn a little bit more about programming languages in general and what each one is used for. I've often heard (and I agree) that you should use the right tool for the job, so what jobs are each programming language best suited for? Edit: If you've worked with some of the newer or more obscure languages, please share for those as well.

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• Beginner having a problem with classes

  - by David

  I'm working through O'Reilly's "Learning Python" and having a problem with classes. I think I understand the concept, but in practice have stumbled upon this problem. Fron page 88-89: >>> class Worker: def __innit__(self, name, pay): self.name=name self.pay=pay def lastName(self): return self.name.split()[-1] def giveRaise(self, percent): self.pay*=(1.0+percent) Then the book says "Calling the class like a function generates instances of a new type ...etc" and gives this example. bob = Worker('Bob Smith', 50000) This gives me this error: TypeError: this constructor takes no arguments. And then I start muttering profanities. So what am I doing wrong here? Thanks for the help.

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• microsoft certification in c# 3.5 and its tutorials

  - by user238284

  i am 2010 passed out. i am interested in completing a certification in c#. certifications available are MCTS Exam 70 536 (for framework 3.5 / 2) and MCTS Exam 70 515(for framework 4.0). wer wil i get its proper study material and tutorials. is there any recommendation from u about, from which exam a beginner in c# should start with.. please help me ....... **thanking u** http://www.microsoft.com/learning/en/us/certification/cert-vstudio.aspx#tab2 http://en.csharp-online.net/CSharp_Certification%2C_Development%2C_and_Training

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• jquery atrr("href") is not consistent ..in sharepoint

  - by alienavatar

  Hi all I have a jquery function(This is not written by me anyway still I am learning). In that we are replacing urls using f.attr("href") in several places. I am not understanding that from where this href value will be binded. And why the value(f.attr("href")) is changing place to place. I mean to say it is having some value @ one location and if I give the same it is giving me different value at other location. I read in article that The .attr() method gets the attribute value for only the first element in the matched set..What is the matched set means

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• How to overcome an apparent REST vs. DRY dilemma in rails?

  - by Chris

  A rails app I'm working on features examples of quadratic equations. Obviously, these are all of a common structure: ax^2 + bx + c = 0. I don't want to store every single example of these. I'd rather generate them from a template. Storing hundreds of possible versions of this structure seems highly wasteful and un-DRY. On the other hand, if I generate them, I can't access them again reliably as I could if they were simply multiple database objects. I'm sure there must be a way to overcome this, but I'm still learning rails and I'm obviously not grasping something here. Thanks.

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• When is it good to start using project management applications?

  - by Mr.Gando

  Hello, I was wondering, when is the right time or the correct project size to start using project management applications ( like Redmine or Trac ). I have a serious project, for now it's only me developing, but I use redmine to set my project versions, issues, and estimations. I think it's a good idea, because you never know when somebody else is going to join the team, and also allows me to organize myself effectively. I ask this question because I was Teaching Assistant at my university for one year in a row for a course, and I got questions about this very very often. While I'm a believer of the KISS principle, I think that learning to use this tools early is a win-win most of the time. I really believe that we can avoid this question to become argumentative, and that there's somewhat of a consensus about this issue, which I consider quite important in todays software development world. So, when is the right time ? what is the correct project/team size ?

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• Find all clauses related to an atom

  - by Luc Touraille

  This is probably a very silly question (I just started learning Prolog a few hours ago), but is it possible to find all the clauses related to an atom? For example, assuming the following knowledge base: cat(tom). animal(X) :- cat(X). , is there a way to obtain every possible information about tom (or at least all the facts that are explicitly stated in the base)? I understand that a query like this is not possible: ?- Pred(tom). so I thought I could write a rule that would deduce the correct information: meta(Object, Predicate) :- Goal =.. [Predicate, Object], call(Goal). so that I could write queries such as ?- meta(tom, Predicate). but this does not work because arguments to call are not sufficiently instantiated. So basically my question is: is this at all possible, or is Prolog not design to provide this kind of information? And if it is not possible, why?

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