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  • To Interface or Not?: Creating a polymorphic model relationship in Ruby on Rails dynamically..

    - by Globalkeith
    Please bear with me for a moment as I try to explain exactly what I would like to achieve. In my Ruby on Rails application I have a model called Page. It represents a web page. I would like to enable the user to arbitrarily attach components to the page. Some examples of "components" would be Picture, PictureCollection, Video, VideoCollection, Background, Audio, Form, Comments. Currently I have a direct relationship between Page and Picture like this: class Page < ActiveRecord::Base has_many :pictures, :as => :imageable, :dependent => :destroy end class Picture < ActiveRecord::Base belongs_to :imageable, :polymorphic => true end This relationship enables the user to associate an arbitrary number of Pictures to the page. Now if I want to provide multiple collections i would need an additional model: class PictureCollection < ActiveRecord::Base belongs_to :collectionable, :polymorphic => true has_many :pictures, :as => :imageable, :dependent => :destroy end And alter Page to reference the new model: class Page < ActiveRecord::Base has_many :picture_collections, :as => :collectionable, :dependent => :destroy end Now it would be possible for the user to add any number of image collections to the page. However this is still very static in term of the :picture_collections reference in the Page model. If I add another "component", for example :video_collections, I would need to declare another reference in page for that component type. So my question is this: Do I need to add a new reference for each component type, or is there some other way? In Actionscript/Java I would declare an interface Component and make all components implement that interface, then I could just have a single attribute :components which contains all of the dynamically associated model objects. This is Rails, and I'm sure there is a great way to achieve this, but its a tricky one to Google. Perhaps you good people have some wise suggestions. Thanks in advance for taking the time to read and answer this.

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  • gae error:AttributeError: 'NoneType' object has no attribute 'user_is_member'

    - by zjm1126
    class Thread(db.Model): members = db.StringListProperty() def user_is_member(self, user): return str(user) in self.members and thread = Thread.get(db.Key.from_path('Thread', int(id))) is_member = thread.user_is_member(user) but the error is : Traceback (most recent call last): File "D:\Program Files\Google\google_appengine\google\appengine\ext\webapp\__init__.py", line 511, in __call__ handler.get(*groups) File "D:\Program Files\Google\google_appengine\google\appengine\ext\webapp\util.py", line 62, in check_login handler_method(self, *args) File "D:\zjm_code\forum_blog_gae\main.py", line 222, in get is_member = thread.user_is_member(user) AttributeError: 'NoneType' object has no attribute 'user_is_member' why ? thanks

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  • Python: Hack to call a method on an object that isn't of its class

    - by cool-RR
    Assume you define a class, which has a method which does some complicated processing: class A(object): def my_method(self): # Some complicated processing is done here return self And now you want to use that method on some object from another class entirely. Like, you want to do A.my_method(7). This is what you'd get: TypeError: unbound method my_method() must be called with A instance as first argument (got int instance instead). Now, is there any possibility to hack things so you could call that method on 7? I'd want to avoid moving the function or rewriting it. (Note that the method's logic does depend on self.) One note: I know that some people will want to say, "You're doing it wrong! You're abusing Python! You shouldn't do it!" So yes, I know, this is a terrible terrible thing I want to do. I'm asking if someone knows how to do it, not how to preach to me that I shouldn't do it.

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  • Multiple has_many's of the same model

    - by Koning Baard
    I have these models: Person has_many :messages_form_person, :foreign_key => :from_user_id, :class_name => :messages has_many :messages_to_person, :foreign_key => :to_user_id, :class_name => :messages Message belongs_to :to_person, :foreign_key => :to_user_id, :class_name => :person belongs_to :from_person, :foreign_key => :to_user_id, :class_name => :person And this view: person#show <% @person.messages_to_person.each do |message| %> <%=h message.title %> <% end %> But I get this error: TypeError in People#show Showing app/views/people/show.html.erb where line #26 raised: can't convert Symbol into String Extracted source (around line #26): 23: <%=h @person.biography %> 24: </p> 25: 26: <% @person.messages_to_person.each do |message| %> 27: 28: <% end %> 29: I basicly want that people can send eachother messages. Can anyone help me? Thanks.

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  • Can't send flash message from Model method

    - by Andy
    Hello, I'm trying to prevent a record that has a relationship to another record from being deleted. I can stop the deletion but not send a flash message as I had hoped! class Purchaseitem < ActiveRecord::Base before_destroy :check_if_ingredient ... def check_if_ingredient i = Ingredient.find(:all, :conditions => "purchaseitem_id = #{self.id}") if i.length > 0 self.errors.add(:name) flash.now[:notice] = "#{self.name} is in use as an ingredient and cannot be deleted" return false end end This will prevent a the delete wihthout the flash line, and when I add it I get: undefined local variable or method `flash' for # Any help would be much appreciated!

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  • Measuring the time to create and destroy a simple object

    - by portoalet
    From Effective Java 2nd Edition Item 7: Avoid Finalizers "Oh, and one more thing: there is a severe performance penalty for using finalizers. On my machine, the time to create and destroy a simple object is about 5.6 ns. Adding a finalizer increases the time to 2,400 ns. In other words, it is about 430 times slower to create and destroy objects with finalizers." How can one measure the time to create and destroy an object? Do you just do: long start = System.nanoTime(); SimpleObject simpleObj = new SimpleObject(); simpleObj.finalize(); long end = System.nanoTime(); long time = end - start;

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  • Model self referential collections in Rails

    - by Najitaka
    I have written an application for an online clothing store in Rails 2.3.5. I want to show related Products when a customer views the Product Detail page. For example, if the customer views the detail page for a suit, I'd like to display the accessory products that match the dress such as a vest, shoes, and belt. I have named the related products an Ensemble. However, the vest, shoes, and belts are also Products which is what has me struggling. I have it working as follows but I know it's not the Rails way. I have a Products table for all of the products. Not important here but I also have a ProductDetails table. I have an Ensembles table that has the following columns: product_id - the main or origination product, the one displayed on the detail page outfit_id - the related or accessory product In setting up the data, on the Products list, for each Product I have an Ensemble link. This link takes you to the index action in the Ensembles controller. Using the id from the "main" Product, I find all of the associated Ensemble rows by product_id or I create a new ensemble and assign the id from the main product as the product_id. I'd like to just be able to do @product.related_products to get an Ensemble collection. Also on the index page I list the columns of the main product so the user can be sure their main product was the one they selected from the list. I also have a select list of the other products, with an Add to Ensemble action. Finally on the same index page, I have a table that displays the products that are already in the ensemble and in that list each row has a destroy link to remove a particular product from the ensemble. It would be nice if given a single Ensemble row @ensemble I could do @ensemble.product to get the Product related to the outfit_id of the ensemble row. I've got it working without associations but I have to run queries in the controller to build my own @product, @ensemble, and @ensembles collections. Also the only way I found to destroy an ensemble row is by Ensemble.connection.delete(sql to delete), simple @ensemble.destroy doesn't work. Anyone know how I would set up the associations or have a link to a site explaining a similar setup. None of the examples I found use the same table. They have A related to B through C. I want A related to other A through B.

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  • Using a model to represent the overall state of a view

    - by James P.
    Is there a standard practise for representing the state of a user interface that is not linked to a single Component? For example, a Swing interface could have a series of tabs with a constraint that a single tab should only be displayed once per a given entity type (this could be represented as a HashSet). Or a message could give the result of the last operation carried out. Or a JPanel could be linked to a single entity instance for editing purposes.

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  • Pass form object value to static method

    - by jrubengb
    Hi, I need to take a form object value and pass it into a static method: public void SetCalendarStartSafe(DateTime startDateSafe) { startDateSafe = calendarStart.Value; } private static DataTable GetData() { frmMain frm = new frmMain(); DateTime startDate = new frmMain(); frm.SetCalendarStartSafe(startDate); } However I keep getting today's current date whenever I try this approach, even if the specified calendar date on the form is different. How can I can the user-specified calendar date from the original frmMain object? Thanks in advance for any guidance.

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  • Change all instances of object to iframe for IE using Jquery

    - by geckomist
    I was wondering if it would be possible to use jquery to change all object tags on a site automatically to iframe for IE 8 and below. I would like this so that it can be xhtml 1.1 valid and not have to be double coded all the time and you would not have to focus on non-standard browsers. The data attribute would have to be changed to src, I would like frameborder="0" to be inserted, and all styles set to the object tag also set to the iframe tag. I don't want this to turn into a debate on iframes vs objects, I just thing this would be a huge time saver and would encourage proper strict xhtml coding. Thanks for any input!

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  • I serialized a C++ object, how to allocate memory for it without knowing what type it is?

    - by Neo_b
    Hello, I have serialized a C++ object and I wish to allocate space for it, although I can't use the "new" operator, because I do not know the object's class. I tried using malloc(sizeof(object)), although trying to typecast the pointer to the type the serialized object is of, the program shut down. Where is the information about the object class stored? class object { public: virtual void somefunc(); int someint; }; class objectchild:public object { } object *o=(object*)malloc(sizeof(objectchild)); cout << int(dynamic_cast<objectchild*>(o)) << endl; This causes a program shutdown. Thank you in advance.

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  • How to clone a model's attributes easily?

    - by Zabba
    I have these models: class Address < ActiveRecord::Base belongs_to :event attr_accessible :street, :city validates :street, :city, :presence => true end class Event < ActiveRecord::Base has_one :address accepts_nested_attributes_for :address end If I do the below assignment in the Events create action and save the event I get an error: #Use the current user's address for the event @event.address_attributes = current_user.address.attributes #Error occurs at the above mentioned line ActiveRecord::RecordNotFound (Couldn't find Address with ID=1 for Event with ID=) I think what's happening is that all the address's attributes (including the primary key) is getting assigned in the @event.address_attributes = line. But all I really want is the "real data" (street, city), not the primary keys or created_at etc to get copied over. I suppose I could write a small method to do this sort of selective copy but I can't help but feel there must be some built-in method for this? What's the best/right way to do this?

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  • Object reference not set to an instance of an object

    - by Ste
    I have this function that create runtime textbox: int i = 0; private TextBox[] addressBox = new TextBox[100]; private void appendNewTab() { addressBox[i] = new TextBox(); addressBox[i].KeyPress += new KeyPressEventHandler(this.addressBox_KeyPress); i++; } void addressBox_KeyPress(object sender, KeyPressEventArgs e) { if (e.KeyChar == (char)13) { MessageBox.Show(addressBox[i].Text); } } but i have Object reference not set to an instance of an object here MessageBox.Show(addressBox[i].Text); any suggestion?

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  • Can i use a model object directly in a find

    - by user340100
    Hi, Can i pass a_teacher directly into the find? or do i have to compare each of its attributes as i have done here? thanks a_teacher = Techer.new(:name => "Bob", :age => 30) self.classes.all(:conditions => ["teacher.name = ? AND teacher.age = ?", a_teacher.name,a_teacher.age], :joins => :teacher)

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  • Make object by it's name

    - by Ockonal
    Hello, is it possible to return exemplar of object using passed type name (string) in c++? I have some base abstract class Base and a few derivates. Example code: class Base { /* ... */ }; class Der1 : public Base { /* ... */ }; class Der2 : public Base { /* ... */ }; And I need function like: Base *objectByType(const std::string &name); Number of derivates classes are changeable and I don't want to make something like switching of name and returning by hands new object type. Is it possible in c++ to do that automatically anyway? p.s. usage should looks like: dynamic_cast<Der1>(objectByType("Der1")); I need pure c++ code (crossplatform). Using boost is permissible.

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  • .NET project: unified wrapper for object databases.

    - by Steve
    I am considering doing a project which would provide unified API and tools (import/export, etc.) for object databases (e.g. Caché, Objectivity) for .NET. It would provide: schema generation from CLR classes, generation of C# classes from given OODBMs schema, API for deleting, creating and updating objects, Linq provider, API for calling object's methods on DB server, some of OODBMs provide some kind of SQL support, so API for this, providers for Caché and Objectivity in first phase. Does any project which implements any of above exist? Can this be achieved with NHibernate dialects? or are OODBMs so different than RDBMs that it worth doing separate framework for them?

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  • MVC 4 Controller Compilation Error trying to return a Model

    - by Joe
    This is a newbie configuration problem I suspect. See return statement comment in code snippet. [HttpGet] public ActionResult TestService() { ViewBag.Message = "DataLayer Service"; Service dataLayerService = new Service {CookieContainer = new CookieContainer()}; dataLayerService.SetSessionAppName("SAND"); WebServiceModel webServiceModel = new WebServiceModel(); webServiceModel.Result = dataLayerService.GetSessionAppName(); return this.View(webServiceModel); // <== Cannot resolve View "TestService" }

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  • Automatically triggering standard spaceship controls to stop its motion

    - by Garan
    I have been working on a 2D top-down space strategy/shooting game. Right now it is only in the prototyping stage (I have gotten basic movement) but now I am trying to write a function that will stop the ship based on it's velocity. This is being written in Lua, using the Love2D engine. My code is as follows (note- object.dx is the x-velocity, object.dy is the y-velocity, object.acc is the acceleration, and object.r is the rotation in radians): function stopMoving(object, dt) local targetr = math.atan2(object.dy, object.dx) if targetr == object.r + math.pi then local currentspeed = math.sqrt(object.dx*object.dx+object.dy*object.dy) if currentspeed ~= 0 then object.dx = object.dx + object.acc*dt*math.cos(object.r) object.dy = object.dy + object.acc*dt*math.sin(object.r) end else if (targetr - object.r) >= math.pi then object.r = object.r - object.turnspeed*dt else object.r = object.r + object.turnspeed*dt end end end It is implemented in the update function as: if love.keyboard.isDown("backspace") then stopMoving(player, dt) end The problem is that when I am holding down backspace, it spins the player clockwise (though I am trying to have it go the direction that would be the most efficient at getting to the angle it would have to be) and then it never starts to accelerate the player in the direction opposite to it's velocity. What should I change in this code to get that to work? EDIT : I'm not trying to just stop the player in place, I'm trying to get it to use it's normal commands to neutralize it's existing velocity. I also changed math.atan to math.atan2, apparently it's better. I noticed no difference when running it, though.

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  • OO Design - polymorphism - how to design for handing streams of different file types

    - by Kache4
    I've little experience with advanced OO practices, and I want to design this properly as an exercise. I'm thinking of implementing the following, and I'm asking if I'm going about this the right way. I have a class PImage that holds the raw data and some information I need for an image file. Its header is currently something like this: #include <boost/filesytem.hpp> #include <vector> namespace fs = boost::filesystem; class PImage { public: PImage(const fs::path& path, const unsigned char* buffer, int bufferLen); const vector<char> data() const { return data_; } const char* rawData() const { return &data_[0]; } /*** other assorted accessors ***/ private: fs::path path_; int width_; int height_; int filesize_; vector<char> data_; } I want to fill the width_ and height_ by looking through the file's header. The trivial/inelegant solution would be to have a lot of messy control flow that identifies the type of image file (.gif, .jpg, .png, etc) and then parse the header accordingly. Instead of using vector<char> data_, I was thinking of having PImage use a class, RawImageStream data_ that inherits from vector<char>. Each type of file I plan to support would then inherit from RawImageStream, e.g. RawGifStream, RawPngStream. Each RawXYZStream would encapsulate the respective header-parsing functions, and PImage would only have to do something like height_ = data_.getHeight();. Am I thinking this through correctly? How would I create the proper RawImageStream subclass for data_ to be in the PImage ctor? Is this where I could use an object factory? Anything I'm forgetting?

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  • Can someone describe the nested set model from a C#/LINQ perspective?

    - by Chad
    I know the nested set model doesn't pertain to the C# language or LINQ directly... it's what I'm using to develop my web app. For hierarchical data (categories with sub-categories in my case), I'm currently using something similar to the Adjacency List model. At the moment, I've only got 2 levels of categories, but I'd like to take it further and allow for n levels of categories using the nested set model. I'm not quite clear on how to use it in a C# context. Here's the article I'm reading on the nested set model. Though this article cleared up my confusion some, I still have a big ?? in my head: - Is inserting, updating or deleting categories tedious? It looks like the left and right numbers would require re-numbering... what would the LINQ queries look like for the following scenarios? Delete a child node (re-number all node's left/right values) Delete a parent node (what do you do with the orphans?) Move a child node to a different parent node (renumber again) If my understanding is correct, at all times the child node's left/right values will always be between the parent node's left/right values, am I correct? Seems easy enough, if only the categories were static... most likely I need to spend more time to get my head around the concept. Any help is greatly appreciated!

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  • i m trying to return list<object> from webmethod but gives error

    - by girish
    System.InvalidOperationException: There was an error generating the XML document. --- System.InvalidOperationException: The type WebService.Property.Property_Users was not expected. Use the XmlInclude or SoapInclude attribute to specify types that are not known statically. at System.Xml.Serialization.XmlSerializationWriter.WriteTypedPrimitive(String name, String ns, Object o, Boolean xsiType) at Microsoft.Xml.Serialization.GeneratedAssembly.XmlSerializationWriter1.Write1_Object(String n, String ns, Object o, Boolean isNullable, Boolean needType) at Microsoft.Xml.Serialization.GeneratedAssembly.XmlSerializationWriter1.Write8_ArrayOfAnyType(Object o) at Microsoft.Xml.Serialization.GeneratedAssembly.ListOfObjectSerializer.Serialize(Object objectToSerialize, XmlSerializationWriter writer) at System.Xml.Serialization.XmlSerializer.Serialize(XmlWriter xmlWriter, Object o, XmlSerializerNamespaces namespaces, String encodingStyle, String id) --- End of inner exception stack trace --- at System.Xml.Serialization.XmlSerializer.Serialize(XmlWriter xmlWriter, Object o, XmlSerializerNamespaces namespaces, String encodingStyle, String id) at System.Xml.Serialization.XmlSerializer.Serialize(TextWriter textWriter, Object o, XmlSerializerNamespaces namespaces) at System.Xml.Serialization.XmlSerializer.Serialize(TextWriter textWriter, Object o) at System.Web.Services.Protocols.XmlReturnWriter.Write(HttpResponse response, Stream outputStream, Object returnValue) at System.Web.Services.Protocols.HttpServerProtocol.WriteReturns(Object[] returnValues, Stream outputStream) at System.Web.Services.Protocols.WebServiceHandler.WriteReturns(Object[] returnValues) at System.Web.Services.Protocols.WebServiceHandler.Invoke() public List<object> GetDataByModuleName(string ModuleName) { List<Property_Users> obj_UserList = new List<Property_Users>(); // performing some operation that add data to obj_UserList List < Object > myList = new List<object>(); return ConvertToObjectList<Property_Users>(obj_UserList); } public List<Object> ConvertToObjectList<N>(List<N> sourceList) { List<Object> result = new List<Object>(); foreach (N item in sourceList) { result.Add(item as Object); } return result; } [WebMethod] public List<object> GetDataByModuleName(string ModuleName) { List<object> obj_list = new List<object>(); obj_list = BAL_GeneralService.GetDataByModuleName(ModuleName); return obj_list; }

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  • Two objects with dependencies for each other. Is that bad?

    - by Kasper Grubbe
    Hi SO. I am learning a lot about design patterns these days. And I want to ask you about a design question that I can't find an answer to. Currently I am building a little Chat-server using sockets, with multiple Clients. Currently I have three classes. Person-class which holds information like nick, age and a Room-object. Room-class which holds information like room-name, topic and a list of Persons currently in that room. Hotel-class which have a list of Persons and a list of Rooms on the server. I have made a diagram to illustrate it (Sorry for the big size!): http://i.imgur.com/Kpq6V.png I have a list of players on the server in the Hotel-class because it would be nice to keep track of how many there are online right now (Without having to iterate through all of the rooms). The persons live in the Hotel-class because I would like to be able to search for a specific Person without searching the rooms. Is this bad design? Is there another way of achieve it? Thanks.

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