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• Falling Sand simulation

  - by Erik Forbes

  I'm trying to re-create a 'falling sand' simulation, similar to those various web toys that are out there doing the same thing - and I'm failing pretty hard. I'm not really sure where to begin. I'm trying to use cellular automata to model the behavior of the sand particles, but I'm having trouble figuring out how to make the direction in which I update the 'world' not matter... For example, one of the particle types I'd like to have is Plant. When Plant comes in contact with Water, Plant turns that Water particle into another Plant particle. The problem here though is that if I'm updating the game world from top to bottom and left to right, then a Plant particle placed in the middle of a sea of Water particles will immediately cause all of the Water particles to the right and below that new Plant particle to turn into Plants. This is not the behavior I am expecting. =( I'm having difficulty explaining exactly my difficulty, so I'll try to add more information as best I can as I go along. Suffice it to say that this is very much outside my box, as it were, and I don't even know what to search for.

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• When to choose which machine learning classifier?

  - by LM

  Suppose I'm working on some classification problem. (Fraud detection and comment spam are two problems I'm working on right now, but I'm curious about any classification task in general.) How do I know which classifier I should use? (Decision tree, SVM, Bayesian, logistic regression, etc.) In which cases is one of them the "natural" first choice, and what are the principles for choosing that one? Examples of the type of answers I'm looking for (from Manning et al.'s "Introduction to Information Retrieval book": http://nlp.stanford.edu/IR-book/html/htmledition/choosing-what-kind-of-classifier-to-use-1.html): a. If your data is labeled, but you only have a limited amount, you should use a classifier with high bias (for example, Naive Bayes). [I'm guessing this is because a higher-bias classifier will have lower variance, which is good because of the small amount of data.] b. If you have a ton of data, then the classifier doesn't really matter so much, so you should probably just choose a classifier with good scalability. What are other guidelines? Even answers like "if you'll have to explain your model to some upper management person, then maybe you should use a decision tree, since the decision rules are fairly transparent" are good. I care less about implementation/library issues, though. Also, for a somewhat separate question, besides standard Bayesian classifiers, are there 'standard state-of-the-art' methods for comment spam detection (as opposed to email spam)? [Not sure if stackoverflow is the best place to ask this question, since it's more machine learning than actual programming -- if not, any suggestions for where else?]

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• How do I use this indirect relationship?

  - by tyjkenn

  I'm working on incorporating a reputation system into my site, similar to SO. Here is how it is structured: User hasMany Project User hasMany Answer Project hasMany Rating Answer hasMany Rating Rating belongsTo Project where Rating.parent_type = Project Rating belongsTo Answer where Rating.parent_type = Answer Rating's value field will be a number between 1 and 5. The user should gain +10 for every 5-star review, +5 for every 4-star review, and +1 for every 3-star review. The way I currently have it set up is this: a recalcRep($id) action in the UsersController (along with other actions in other controllers, when necessary) calls the calcRep($id) method inside the User model, which is supposed to calculate the reputation of a user with an id of $id. public function calcRep($id) { $rep = 0; $data = $this->Rating->find('all'); //does not work, because it is not directly associated foreach($data as $rating) { if(($rating['Rating']['parent_type'] == 'Project' && $rating['Project']['user_id']==$id) or ($rating['Rating']['parent_type'] == 'Answer' && $rating['Answer']['user_id']==$id)) { if($rating['Rating']['value']==5) { $rep += 10; } else if($rating['Rating']['value']==4) { $rep += 5; } else if($rating['Rating']['value']==3) { $rep += 2; } } } $data['User']['reputation'] = $rep; $this->save($data); } I may be approaching this in completely the wrong way, but I can't figure out how to find all the ratings that belong to any of the children of a specific user.

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• MVC: Submit one form from a page with multiple forms

  - by Rob

  I'm working in an ASP.NET 3.5 MVC application where i've got a view with multiple forms in it. Form 1 contains information about products and will form a shoppingcart with a remove button. Form 2 is as below and is to be used to get the information from the shoppingcart and create an order of it. <% using (Html.BeginForm()) { %> <%=Html.Hidden(Order.ProductId", "E63EF586-F625-4C8D-B82E-E63A6FA4A63C")%> <%=Html.Hidden(Order.Amount", 1)%> <input type="submit" value="Pay" /> <%} % The first form contains a similar beginform with a foreach loop to get the information about the products from the model. When i use the submit button on the second form everything seems to be submitted and the action in the controller for the first form is trying to handle the request. That is where the error occurce because the information in the viewmodel isn't corresponding to what is being expected. The controller which is trying to handle the request: [AcceptVerbs(HttpVerbs.Post)] public ActionResult ShowShoppingcartForm([Bind(Prefix = "Order")] MyViewmodel viewModel) { //.. } The controller which is expected to handle the request: [AcceptVerbs(HttpVerbs.Post)] public ActionResult SaveOrder([Bind(Prefix = "Order")] MyViewmodel viewModel) { throw new NotImplementedException(); }

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• How to tell which dataform button ended edit when using EventToCommand

  - by Rodd

  I'm new to SilverLight and Mvvm-Light. I have a DataForm on my view that displays/edits a SelectedPerson property (a Person object) of my view model. I want to execute a command on my viewmodel when the user clicks the Save button but don't want to take action if the user clicks cancel. I added the following to my ViewModel: public RelayCommand PersonEditEnded {get; set;} ... public void Initialize() { PersonEditEnded = new RelayCommand(DoSomething); ... } public void DoSomething() { } I added the following to my View: <toolkit:DataForm x:Name="PersonForm" ... CurrentItem="{Binding SelectedPerson, Mode=TwoWay}"> <i:Interaction.Triggers> <i:EventTrigger EventName="EditEnded"> <gs:EventToCommand Command="{Binding PersonEditEnded, Mode=OneWay}"/> </i:EventTrigger> </i:Interaction.Triggers> </toolkit:DataForm> This works and the DoSomething method is being called when the user presses Submit. However, DoSomething is also called when user presses Cancel. Is there a way to know which button was pressed or to supress the call when Cancel is pressed? Thanks for whatever help you can offer!

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• Is there a way to set two C#.Net projects to trust one another?

  - by Eric

  I have two C#.NET projects in a single solution ModelProject and PluginProject. PlugInProject is a plug-in for another application, and consequently references its API. PlugInProject is used to extract data from the application it plugs into. ModelProject contains the data model of classes that are extracted by PlugInProject. The extracted data can be used independent of the application or the plug-in, which is why I am keeping PlugInProject separate from ModelProject. I want ModelProject to remain independent of PlugInProject, and the Applications API. Or in other words I want someone to be able to access the extracted data without needing access to PlugInProject, the application, or the application's API. The problem I'm running into though is PlugInProject needs to be able to create and modify classes in ModelProject. However, I'd prefer to not make these actions public to anyone using ModelProject. The extracted data should effectively be read-only, unless later modified by PlugInProject. How can I keep these projects separate but give PlugInProject exclusive access to ModelProject? Is this possible?

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• Saving owned/child objects in Hibernate

  - by maxdj

  I'm having a hard time wrapping my head around the way hibernate objects work. Here's a little chunk of what my model looks like: JobOpening: @ManyToMany(fetch=FetchType.EAGER,cascade=CascadeType.ALL) @JoinTable( name="jobOpening_questionSet", joinColumns=@JoinColumn(name="jobOpenings_id"), inverseJoinColumns=@JoinColumn(name="questionSets_id") ) @IndexColumn(name="question_sets_idx",base=0,nullable=false) public List<QuestionSet> getQuestionSets() { return questionSets; } QuestionSet: @ManyToMany(mappedBy="questionSets",fetch=FetchType.EAGER) public Set<JobOpening> getJobOpenings() { return jobOpenings; } @OneToMany(cascade=CascadeType.ALL,fetch=FetchType.EAGER) @IndexColumn(name="questions_idx",base=0) @JoinColumn(name="questionset_id",nullable=false) public List<FormQuestion> getQuestions() { return questions; } FormQuestion: @ManyToOne @JoinColumn(name="questionset_id", insertable=false, updatable=false, nullable=false) @OnDelete(action=OnDeleteAction.CASCADE) public QuestionSet getQuestionSet() { return questionSet; } Now how would I go about, say, modifying a question in the question set, or changing which jobs a questionset is associated with? For example, to edit a question in a questionset, I imagine I should be able to just get the question via its id, change some values, and merge() it back in, but this doesn't work. I'm using Hibernate from Spring (appfuse), usually as detached objects.

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• CQRS and email notification

  - by t0PPy

  Reading up on CQRS there is a lot of talk of email notification - i'm wondering where to get the data from. Imagine a senario where one user invites other users to an event. To inform a user that he has been invitet to an event, he is send an email. The concrete mecanics might go like this: A "CreateEvent" command with an associated collection of user to invite, is received by the server. A new meeting aggregate is created and a method "InviteUser" is called for each user that is to be invited. Each time a user is invited to an event, a domain event "UserWasInvitedToEvent" is raised. An email notification sender picks up the domain event and sends out the notification email. Now my question is this: Where do i go for information to include in the email? Say i want to include a description of the event as well as the users name. Since this is CQRS i can't get it thru my domain model; All the properties of the domain objects are private! Should i then query the write side? Or maybe move email notification to a different service entirely? Any thoughts will be much appriciated!

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• Understanding many to many relationships and Entity Framework

  - by Anders Svensson

  I'm trying to understand the Entity Framework, and I have a table "Users" and a table "Pages". These are related in a many-to-many relationship with a junction table "UserPages". First of all I'd like to know if I'm designing this relationship correctly using many-to-many: One user can visit multiple pages, and each page can be visited by multiple users..., so am I right in using many2many? Secondly, and more importantly, as I have understood m2m relationships, the User and Page tables should not repeat information. I.e. there should be only one record for each user and each page. But then in the entity framework, how am I able to add new visits to the same page for the same user? That is, I was thinking I could simply use the Count() method on the IEnumerable returned by a LINQ query to get the number of times a user has visited a certain page. But I see no way of doing that. In Linq to Sql I could access the junction table and add records there to reflect added visits to a certain page by a certain user, as many times as necessary. But in the EF I can't access the junction table. I can only go from User to a Pages collection and vice versa. I'm sure I'm misunderstanding relationships or something, but I just can't figure out how to model this. I could always have a Count column in the Page table, but as far as I have understood you're not supposed to design database tables like that, those values should be collected by queries... Please help me understand what I'm doing wrong...

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• Blackberry app stuck trying to access a server.

  - by Tejaswi Yerukalapudi

  Hi, I've built a ASP.NET webservice and I'm trying to access it from a Blackberry. I've been testing it out with multiple devices and the simulator and it works fine, but there's just the one Blackberry 9000 (It's not the model, I've tried it out with another Blackberry 9000), and it's stuck waiting for a response from the server. Relevant section of the code that accesses this - System.out.println("IN ntwk access thread, start point"); HttpConnection connection = (HttpConnection)Connector.open(serviceURL + WSNAME); connection.setRequestMethod(HttpConnection.POST); connection.setRequestProperty("Content-type", "application/x-www-form-urlencoded"); connection.setRequestProperty("Content-length", Integer.toString(postData1.length)); OutputStream requestOutput = connection.openOutputStream(); requestOutput.write(postData1); requestOutput.close(); final int responseCode = connection.getResponseCode(); if(responseCode!= HttpConnection.HTTP_OK) { //Process the error condition } // Request succeeded process the data. It seems to be getting stuck after connection.getResponseCode(). Is there some way I can verify what's going wrong with this particular device? Thanks, Teja

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• Action Mailer: How do I render dynamic data in an email body that is stored in the database?

  - by Brandon Toone

  I have Action Mailer setup to render an email using the body attribute of my Email model (in the database). I want to be able to use erb in the body but I can't figure out how to get it to render in the sent email message. I'm able to get the body as a string with this code # models/user_mailer.rb def custom_email(user, email_id) email = Email.find(email_id) recipients user.email from "Mail It Example <[email protected]>" subject "Hello From Mail It" sent_on Time.now # pulls the email body and passes a string to the template views/user_mailer/customer_email.text.html.erb body :msg => email.body end I came across this article http://rails-nutshell.labs.oreilly.com/ch05.html which says I can use render but I'm only able to get render :text to work and not render :inline # models/user_mailer.rb def custom_email(user, email_id) email = Email.find(email_id) recipients user.email from "Mail It Example <[email protected]>" subject "Hello From Mail It" sent_on Time.now # body :msg => email.body body :msg => (render :text => "Thanks for your order") # renders text and passes as a variable to the template # body :msg => (render :inline => "We shipped <%= Time.now %>") # throws a NoMethodError end

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• Getting the name of a child class in the parent class (static context)

  - by Benoit Myard

  Hi everybody, I'm building an ORM library with reuse and simplicity in mind; everything goes fine except that I got stuck by a stupid inheritance limitation. Please consider the code below: class BaseModel { /* * Return an instance of a Model from the database. */ static public function get (/* varargs */) { // 1. Notice we want an instance of User $class = get_class(parent); // value: bool(false) $class = get_class(self); // value: bool(false) $class = get_class(); // value: string(9) "BaseModel" $class = __CLASS__; // value: string(9) "BaseModel" // 2. Query the database with id $row = get_row_from_db_as_array(func_get_args()); // 3. Return the filled instance $obj = new $class(); $obj->data = $row; return $obj; } } class User extends BaseModel { protected $table = 'users'; protected $fields = array('id', 'name'); protected $primary_keys = array('id'); } class Section extends BaseModel { // [...] } $my_user = User::get(3); $my_user->name = 'Jean'; $other_user = User::get(24); $other_user->name = 'Paul'; $my_user->save(); $other_user->save(); $my_section = Section::get('apropos'); $my_section->delete(); Obviously, this is not the behavior I was expecting (although the actual behavior also makes sense).. So my question is if you guys know of a mean to get, in the parent class, the name of child class.

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• Write a program which works out which is the lowest priced computer in an ArrayList of computer obje

  - by Eoin

  Hello everybody! I am trying to study some java and cannot get my head around this question! Any help would be really appreciated and would help me in further studies! Thank you so much in advance! Eoin from Dublin, Ireland. ArrayList of Objects Write a program which works out which is the lowest priced computer in an ArrayList of computer objects. You should have two classes, one called ComputerTest, and the other called Computer. In the ComputerTest class you should: Have a main method which declares an ArrayList of type Computer called computerList, each element of which represents a computer. Initialise the first three entries of the ArrayList Call a static method which prints out the lowest price computer, called lowestPrice The parameter of this method is (i) an ArrayList of type Computer i.e. ArrayList data Sample output: The lowest priced computer is the Cheapo400 at 399 euro. The Computer class should have: Private instance variables: manufacturer, model, price and quality. Quality is a rating from 1 to 10. public get and set methods to retrieve and set/change the value of the four instance variables a default constructor a constructor that takes four parameters

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• backbone.js removing template from DOM upon success

  - by timpone

  I'm writing a simple message board app to learn backbone. It's going ok (a lot of the use of this isn't making sense) but am a little stuck in terms of how I would remove a form / html from the dom. I have included most of the code but you can see about 4 lines up from the bottom, the part that isn't working. How would I remove this from the DOM? thx in advance var MbForm=Backbone.View.extend({ events: { 'click button.add-new-post': 'savePost' }, el: $('#detail'), template:_.template($('#post-add-edit-tmpl').html()), render: function(){ var compiled_template = this.template(); this.$el.html(compiled_template); return this; }, savePost: function(e){ //var self=this; //console.log("I want you to say Hello!"); data={ header: $('#post_header').val(), detail: $('#post_detail').val(), forum_id: $('#forum_id').val(), post_id: $('#post_id').val(), parent_id: $('#parent_id').val() }; this.model.save(data, { success: function(){ alert('this saved'); //$(this.el).html('this is what i want'); this.$el.remove();// <- this is the part that isn't working /* none of these worked - error Uncaught TypeError: Cannot call method 'unbind' of undefined this.$el.unbind(); this.$el.empty(); this.el.unbind(); this.el.empty(); */ //this.unbind(); //self.append('this is appended'); } });

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• how can I save/keep-in-sync an in-memory graph of objects with the database?

  - by Greg

  Question - What is a good best practice approach for how can I save/keep-in-sync an jn-memory graph of objects with the database? Background: That is say I have the classes Node and Relationship, and the application is building up a graph of related objects using these classes. There might be 1000 nodes with various relationships between them. The application needs to query the structure hence an in-memory approach is good for performance no doubt (e.g. traverse the graph from Node X to find the root parents) The graph does need to be persisted however into a database with tables NODES and RELATIONSHIPS. Therefore what is a good best practice approach for how can I save/keep-in-sync an jn-memory graph of objects with the database? Ideal requirements would include: build up changes in-memory and then 'save' afterwards (mandatory) when saving, apply updates to database in correct order to avoid hitting any database constraints (mandatory) keep persistence mechanism separate from model, for ease in changing persistence layer if needed, e.g. don't just wrap an ADO.net DataRow in the Node and Relationship classes (desirable) mechanism for doing optimistic locking (desirable) Or is the overhead of all this for a smallish application just not worth it and I should just hit the database each time for everything? (assuming the response times were acceptable) [would still like to avoid if not too much extra overhead to remain somewhat scalable re performance]

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• Auto complete from database using CodeIgniter (Active Record)

  - by Ralph David Abernathy

  I have a form on my website in which one is able to submit a cat. The form contains inputs such as "Name" and "Gender", but I am just trying to get the auto completion to work with the "Name" field. Here is what my jquery looks like : $(document).ready(function() { $( "#tags" ).autocomplete({ source: '/Anish/auto_cat' }); }); Here is what my model looks like: public function auto_cat($search_term) { $this->db->like('name', $search_term); $response = $this->db->get('anish_cats')->result_array(); // var_dump($response);die; return $response; } } Here is my controller: public function auto_cat(){ $search_term = $this->input->get('term'); $cats = $this->Anish_m->auto_cat($search_term); } And here is my view: <head> <link rel="stylesheet" href="http://code.jquery.com/ui/1.10.3/themes/smoothness/jquery-ui.css" /> <script src="http://code.jquery.com/jquery-1.9.1.js"></script> <script src="http://code.jquery.com/ui/1.10.3/jquery-ui.js"></script> <link rel="stylesheet" href="/resources/demos/style.css" /> </head> <h1>Anish's Page</h1> <form action="/Anish/create" method="POST"> <div class="ui-widget"> <label for="tags">Name</label><input id="tags" type="text" name="name"> </div> <div> <label>Age</label><input type="text" name="age"> </div> <div> <label>Gender</label><input type="text" name="gender"> </div> <div> <label>Species</label><input type="text" name="species"> </div> <div> <label>Eye Color</label><input type="text" name="eye_color"> </div> <div> <label>Color</label><input type="text" name="color"> </div> <div> <label>Description</label><input type="text" name="description"> </div> <div> <label>marital status</label><input type="text" name="marital_status"> </div> <br> <button type="submit" class="btn btn-block btn-primary span1">Add cat</button> </form> <br/><br/><br/><br/> <table class="table table-striped table-bordered table-hover"> <thead> <tr> <th>Name</th> <th>Gender</th> <th>Age</th> <th>Species</th> <th>Eye Color</th> <th>Color</th> <th>Description</th> <th>Marital Status</th> <th>Edit</th> <th>Delete</th> </tr> </thead> <tbody> <?php foreach ($cats as $cat):?> <tr> <td> <?php echo ($cat['name']);?><br/> </td> <td> <?php echo ($cat['gender']);?><br/> </td> <td> <?php echo ($cat['age']);?><br/> </td> <td> <?php echo ($cat['species']);?><br/> </td> <td> <?php echo ($cat['eye_color']);?><br/> </td> <td> <?php echo ($cat['color']);?><br/> </td> <td> <?php echo ($cat['description']);?><br/> </td> <td> <?php echo ($cat['marital_status']);?><br/> </td> <td> <form action="/Anish/edit" method="post"> <input type="hidden" value="<?php echo ($cat['id']);?>" name="Anish_id_edit"> <button class="btn btn-block btn-info">Edit</button> </form> </td> <td> <form action="/Anish/delete" method="post"> <input type="hidden" value="<?php echo ($cat['id']);?>" name="Anish_id"> <button class="btn btn-block btn-danger">Delete</button> </form> </td> </tr> <?php endforeach;?> </tbody> </table> I am stuck. In my console, I am able to see this output when I type the letter 'a' if I uncomment the var_dump in my model: array(4) { [0]=> array(9) { ["id"]=> string(2) "13" ["name"]=> string(5) "Anish" ["gender"]=> string(4) "Male" ["age"]=> string(2) "20" ["species"]=> string(3) "Cat" ["eye_color"]=> string(5) "Brown" ["color"]=> string(5) "Black" ["description"]=> string(7) "Awesome" ["marital_status"]=> string(1) "0" } [1]=> array(9) { ["id"]=> string(2) "16" ["name"]=> string(5) "Anish" ["gender"]=> string(2) "fe" ["age"]=> string(2) "23" ["species"]=> string(2) "fe" ["eye_color"]=> string(2) "fe" ["color"]=> string(2) "fe" ["description"]=> string(2) "fe" ["marital_status"]=> string(1) "1" } [2]=> array(9) { ["id"]=> string(2) "17" ["name"]=> string(1) "a" ["gender"]=> string(1) "a" ["age"]=> string(1) "4" ["species"]=> string(1) "a" ["eye_color"]=> string(1) "a" ["color"]=> string(1) "a" ["description"]=> string(1) "a" ["marital_status"]=> string(1) "0" } [3]=> array(9) { ["id"]=> string(2) "18" ["name"]=> string(4) "Matt" ["gender"]=> string(6) "Female" ["age"]=> string(2) "80" ["species"]=> string(6) "ferret" ["eye_color"]=> string(4) "blue" ["color"]=> string(4) "pink" ["description"]=> string(5) "Chill" ["marital_status"]=> string(1) "0" } }

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• Seed has_many relation using mass assignment

  - by rnd

  Here are my two models: class Article < ActiveRecord::Base attr_accessible :content has_many :comments end class Comment < ActiveRecord::Base attr_accessible :content belongs_to :article end And I'm trying to seed the database in seed.rb using this code: Article.create( [{ content: "Hi! This is my first article!", comments: [{content: "It sucks"}, {content: "Best article ever!"}] }], without_protection: true) However rake db:seed gives me the following error message: rake aborted! Comment(#28467560) expected, got Hash(#13868840) Tasks: TOP => db:seed (See full trace by running task with --trace) It is possible to seed the database like this? If yes a follow-up question: I've searched some and it seems that to do this kind of (nested?) mass assignment I need to add 'accepts_nested_attributes_for' for the attributes I want to assign. (Possibly something like 'accepts_nested_attributes_for :article' for the Comment model) Is there a way to allow this similar to the 'without_protection: true'? Because I only want to accept this kind of mass assignment when seeding the database.

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• Overriding to_xml for collection of ActiveRecord objects

  - by Chirantan

  Okay, I know you can override the to_xml method for a single instance of ActiveRecord object and it works just fine for me. But how would I go about overriding the to_xml method for collection of objects? Suppose for Task model instance, I implemented to_xml which looks like this. def to_xml super(:methods => [:tag_list], :include => {:project => {:include => {:folder => {}}}, :folder => {}}) end Works just fine when a single task is to be serialized to xml. But when my code runs for collection of tasks, like in the following piece of code render :xml => @tasks.to_xml I get wrong number of arguments (1 for 0) /home/chirantan/.gem/ruby/1.8/gems/activesupport-2.3.5/lib/active_support/core_ext/array/conversions.rb:189:in `to_xml' /home/chirantan/.gem/ruby/1.8/gems/activesupport-2.3.5/lib/active_support/core_ext/array/conversions.rb:189:in `to_xml' /home/chirantan/.gem/ruby/1.8/gems/activesupport-2.3.5/lib/active_support/core_ext/array/conversions.rb:189:in `each' /home/chirantan/.gem/ruby/1.8/gems/activesupport-2.3.5/lib/active_support/core_ext/array/conversions.rb:189:in `to_xml' /var/lib/gems/1.8/gems/builder-2.1.2/lib/builder/xmlbase.rb:134:in `call' /var/lib/gems/1.8/gems/builder-2.1.2/lib/builder/xmlbase.rb:134:in `_nested_structures' /var/lib/gems/1.8/gems/builder-2.1.2/lib/builder/xmlbase.rb:58:in `method_missing' /var/lib/gems/1.8/gems/builder-2.1.2/lib/builder/xmlbase.rb:31:in `tag!' /~/blah/app/controllers/tasks_controller.rb:412:in `completed' How do I make this work?

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• How to return all records and whether a related record exists?

  - by David Glenn

  Using Entity Framework 4 CTP5 I have a basic model and a basic DbContext that works public class Customer { public int CustomerId { get; set; } public int Name { get; set; } //... public ICollection<Address> Addresses { get; set; } public bool HasAddress { get { return Addresses.Count > 0; } } } public class Address { public int AddressId { get; set; } public string StreetLine1 { get; set; } //.... public Customer Customer { get; set; } } How can I query my DbContext to return all customers and whether they have an address? A customer can have multiple addresses and I don't want to return all the addresses for each customer when I am only interested in whether they have an address or not. I use context.Customers.Include(c => c.Addresses) but that returns all addresses for each customer

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• Hierarchical/Nested Database Structure for Comments

  - by Stephen Melrose

  Hi, I'm trying to figure out the best approach for a database schema for comments. The problem I'm having is that the comments system will need to allow nested/hierarchical comments, and I'm not sure how to design this out properly. My requirements are, Comments can be made on comments, so I need to store the tree hierarchy I need to be able to query the comments in the tree hierarchy order, but efficiently, preferably in a fast single query, but I don't know if this is possible I'd need to make some wierd queries, e.g. pull out the latest 5 root comments, and a maximum of 3 children for each one of those I read an article on the MySQL website on this very subject, http://dev.mysql.com/tech-resources/articles/hierarchical-data.html The "Nested Set Model" in theory sounds like it will do what I need, except I'm worried about querying the thing, and also inserting. If this is the right approach, How would I do my 3rd requirement above? If I have 2000 comments, and I add a new sub-comment on the first comment, that will be a LOT of updating to do. This doesn't seem right to me? Or is there a better approach for the type of data I'm wanting to store and query? Thank you

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• Access 2007 and Special/Unicode Characters in SQL

  - by blockcipher

  I have a small Access 2007 database that I need to be able to import data from an existing spreadsheet and put it into our new relational model. For the most part this seems to work pretty well. Part of the process is attempting to see if a record already exists in a target table using SQL. For example, if I extract book information out of the current row in the spreadsheet, it may contain a title and abstract. I use SQL to get the ID of a matching record, if it exists. This works fine except when I have data that's in a non-English language. In this case, it seems that there is some punctuation that is causing me problems. At least I think it's punctuation as I do have some fields that do not have punctuation and are non-English that do not give me any problems. Is there a built-in function that can escape these characters? Currently I have a small function that will escape the single quote character, but that isn't enough. Or, is there a list of Unicode characters that can interfere with how SQL wants data quoted? Thanks in advance.

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• why MVC instead of good old asp.net? Still not grasping why I should go this route??

  - by RJ

  I know this question has been asked before and I read all the answers but they still don't give me the answers I am looking for. I need something concrete. I volunteered to give a presentation on MVC to other developers in our group which forces me to learn it. The big question everyone has is: "What can MVC bring to the table that we can't do in asp.net or MVC can do faster. I have just gone through Nerd Dinner and actually created a complete website that sort of mimics Nerd Dinner. But as great a job that Scott Guthrie did on it, there are big gaps that aren't answered such as, how do I throw a textbox on the listing page with a button and do a simple search. In asp.net, I would throw a textbox, button and grid on the page and bind it to a sproc and away I go. What is the equivalent in MVC. I guess I need a really good tutorial on how to use MVC without using Linq-to-Sql. I know I am sort of babbling on about this but it is a very serious question that still seems to go unanswered. On a side note, the View page of MVC brings back nightmares of classic asp with all the in-line code that we got away from way back when with code behind pages. Yes, MVC has Controller and Model classes which are great but I still don't like the classic asp tags in the html. Help me out here, I really like the concept of MVC and want it to be successful but I need more!

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• Checking for nil in view in Ruby on Rails

  - by seaneshbaugh

  I've been working with Rails for a while now and one thing I find myself constantly doing is checking to see if some attribute or object is nil in my view code before I display it. I'm starting to wonder if this is always the best idea. My rationale so far has been that since my application(s) rely on user input unexpected things can occur. If I've learned one thing from programming in general it's that users inputting things the programmer didn't think of is one of the biggest sources of run-time errors. By checking for nil values I'm hoping to sidestep that and have my views gracefully handle the problem. The thing is though I typically for various reasons have similar nil or invalid value checks in either my model or controller code. I wouldn't call it code duplication in the strictest sense, but it just doesn't seem very DRY. If I've already checked for nil objects in my controller is it okay if my view just assumes the object truly isn't nil? For attributes that can be nil that are displayed it makes sense to me to check every time, but for the objects themselves I'm not sure what is the best practice. Here's a simplified, but typical example of what I'm talking about: controller code def show @item = Item.find_by_id(params[:id]) @folders = Folder.find(:all, :order => 'display_order') if @item == nil or @item.folder == nil redirect_to(root_url) and return end end view code <% if @item != nil %> display the item's attributes here <% if @item.folder != nil %> <%= link_to @item.folder.name, folder_path(@item.folder) %> <% end %> <% else %> Oops! Looks like something went horribly wrong! <% end %> Is this a good idea or is it just silly?

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• Adding a button or link to an inline in Django admin

  - by Lexo

  Hello, I have created the following django models: class Entry(SiteObject): parent = models.ForeignKey(Blog, related_name="entries") content = models.TextField(help_text = "The Content of the blog post") class EntryImage(models.Model): entry = models.ForeignKey(Entry, related_name="entryimages") imagewidth = models.PositiveIntegerField(editable=False,) imageheight = models.PositiveIntegerField(editable=False,) image_file = ImageWithThumbnailsField( #from sorl-thumbnail. Basically a wrapper for an ImageField that generates a thumbnail. upload_to="images/blogs", height_field="imageheight", width_field="imagewidth", help_text = "Select an image to upload.", thumbnail={'size': (360,720)}, generate_on_save=True, ) The EntryImage class shows up as an inline in the admin page for Entry. What I'd like to do is place a link or a button beside each of these inlines that does the following: Save the EntryImage Append <Image x> to the content of the Entry, where x is the number of the EntryImage. This will be replaced by the image's thumbnail using a template filter. Save the Entry Return to editing the Entry I have looked into this, but I just can't wrap my head around where I'm supposed to add this button or link. Has anyone else tried something similar? I've got JQuery available, since I'm using WYMEditor for the content field of the Entry class. Would this help? Thanks in advance, Lexo

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• Declaring a string array in class header file - compiler thinks string is variable name?

  - by Dave

  Hey everybody, I need a bit of a hand with declaring a string array in my class header file in C++. atm it looks like this: //Maze.h #include <string> class Maze { GLfloat mazeSize, mazeX, mazeY, mazeZ; string* mazeLayout; public: Maze ( ); void render(); }; and the constructor looks like this: //Maze.cpp #include <GL/gl.h> #include "Maze.h" #include <iostream> #include <fstream> Maze::Maze( ) { cin >> mazeSize; mazeLayout = new string[mazeSize]; mazeX = 2/mazeSize; mazeY = 0.25; mazeZ = 2/mazeSize; } I'm getting a compiler error that says: In file included from model-view.cpp:11: Maze.h:14: error: ISO C++ forbids declaration of ‘string’ with no type Maze.h:14: error: expected ‘;’ before ‘*’ token and the only sense that makes to me is that for some reason it thinks I want string as a variable name not as a type declaration. If anybody could help me out that would be fantastic, been looking this up for a while and its giving me the shits lol. Cheers guys

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