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  • Modeling a cellphone bill: should I use single-table inheritance or polymorphic associations?

    - by Horace Loeb
    In my domain: Users have many Bills Bills have many BillItems (and therefore Users have many BillItems through Bills) Every BillItem is one of: Call SMS (text message) MMS (multimedia message) Data Here are the properties of each individual BillItem (some are common): My question is whether I should model this arrangement with single-table inheritance (i.e., one "bill_items" table with a "type" column) or polymorphism (separate tables for each BillItem type), and why.

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  • Recommendations for a C++ polymorphic, seekable, binary I/O interface

    - by Trevor Robinson
    I've been using std::istream and ostream as a polymorphic interface for random-access binary I/O in C++, but it seems suboptimal in numerous ways: 64-bit seeks are non-portable and error-prone due to streampos/streamoff limitations; currently using boost/iostreams/positioning.hpp as a workaround, but it requires vigilance Missing operations such as truncating or extending a file (ala POSIX ftruncate) Inconsistency between concrete implementations; e.g. stringstream has independent get/put positions whereas filestream does not Inconsistency between platform implementations; e.g. behavior of seeking pass the end of a file or usage of failbit/badbit on errors Don't need all the formatting facilities of stream or possibly even the buffering of streambuf streambuf error reporting (i.e. exceptions vs. returning an error indicator) is supposedly implementation-dependent in practice I like the simplified interface provided by the Boost.Iostreams Device concept, but it's provided as function templates rather than a polymorphic class. (There is a device class, but it's not polymorphic and is just an implementation helper class not necessarily used by the supplied device implementations.) I'm primarily using large disk files, but I really want polymorphism so I can easily substitute alternate implementations (e.g. use stringstream instead of fstream for unit tests) without all the complexity and compile-time coupling of deep template instantiation. Does anyone have any recommendations of a standard approach to this? It seems like a common situation, so I don't want to invent my own interfaces unnecessarily. As an example, something like java.nio.FileChannel seems ideal. My best solution so far is to put a thin polymorphic layer on top of Boost.Iostreams devices. For example: class my_istream { public: virtual std::streampos seek(stream_offset off, std::ios_base::seekdir way) = 0; virtual std::streamsize read(char* s, std::streamsize n) = 0; virtual void close() = 0; }; template <class T> class boost_istream : public my_istream { public: boost_istream(const T& device) : m_device(device) { } virtual std::streampos seek(stream_offset off, std::ios_base::seekdir way) { return boost::iostreams::seek(m_device, off, way); } virtual std::streamsize read(char* s, std::streamsize n) { return boost::iostreams::read(m_device, s, n); } virtual void close() { boost::iostreams::close(m_device); } private: T m_device; };

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  • Polymorphic Queue

    - by metdos
    Hello Everyone, I'm trying to implement a Polymorphic Queue. Here is my trial: QQueue <Request *> requests; while(...) { QString line = QString::fromUtf8(client->readLine()).trimmed(); if(...)){ Request *request=new Request(); request->tcpMessage=line.toUtf8(); request->decodeFromTcpMessage(); //this initialize variables in request using tcpMessage if(request->requestType==REQUEST_LOGIN){ LoginRequest loginRequest; request=&loginRequest; request->tcpMessage=line.toUtf8(); request->decodeFromTcpMessage(); requests.enqueue(request); } //Here pointers in "requests" do not point to objects I created above, and I noticed that their destructors are also called. LoginRequest *loginRequest2=dynamic_cast<LoginRequest *>(requests.dequeue()); loginRequest2->decodeFromTcpMessage(); } } Unfortunately, I could not manage to make work Polymorphic Queue with this code because of the reason I mentioned in second comment.I guess, I need to use smart-pointers, but how? I'm open to any improvement of my code or a new implementation of polymorphic queue. Thanks.

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  • Cannot delete podcast from iPod Touch

    - by rybl
    I am having a problem with my iPod/iTunes where an episode of a single podcast cannot be deleted. The episode in question does not show up in iTunes or as being on the iPod when I drill down and look at the podcasts on the iPod in iTunes. It also does not play if I try to play it on the iPod; it just waits a second and skips to the next podcast. I have iTunes 9.2.0.61, my iPod has OS version 4 (although I was having this problem before I upgraded), and Windows 7 64bit. I would really prefer a solution that does not require me to completely wipe the iPod because I have a bunch of WiFi keys stored that I don't want to have to dig up again.

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  • ActiveRecord has_many and polymorphic

    - by leomayleomay
    I've came into a problem while working with AR and polymorphic, here's the description, class Base < ActiveRecord::Base; end class Subscription < Base set_table_name :subscriptions has_many :posts, :as => :subscriptable end class Post < ActiveRecord::Base belongs_to :subscriptable, :polymorphic => true end in the console, >> s = Subscription.create(:name => 'test') >> s.posts.create(:name => 'foo', :body => 'bar') and it created a Post like: #<Post id: 1, name: "foo", body: "bar", subscriptable_type: "Base", subscriptable_id: 1, created_at: "2010-05-10 12:30:10", updated_at: "2010-05-10 12:30:10"> the subscriptable_type is Base but Subscription, anybody can give me a hand on this?

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  • ActiveRecord, has_many, polymorphic and STI

    - by leomayleomay
    I've came into a problem while working with AR and polymorphic, here's the description, class Base < ActiveRecord::Base; end class Subscription < Base set_table_name :subscriptions has_many :posts, :as => :subscriptable end class Post < ActiveRecord::Base belongs_to :subscriptable, :polymorphic => true end in the console, >> s = Subscription.create(:name => 'test') >> s.posts.create(:name => 'foo', :body => 'bar') and it created a Post like: #<Post id: 1, name: "foo", body: "bar", subscriptable_type: "Base", subscriptable_id: 1, created_at: "2010-05-10 12:30:10", updated_at: "2010-05-10 12:30:10"> the subscriptable_type is Base but Subscription, anybody can give me a hand on this?

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  • Authlogic with nested attributes and polymorphic associations

    - by ferparra
    Hi all! I'm having trouble with the following code: User < AR acts_as_authentic belongs_to :owner, :polymorphic => true end Worker < AR has_one :user, :as => :owner accepts_nested_attributes_for :user end Employer < AR has_one :user, :as => :owner accepts_nested_attributes_for :user end I'd like to create registration forms based on user types, and to include authentication fields such as username and password. I currently do this: UserRegistrationController < AC #i.e. a new Employer def new @employer = Employer.new @employer.build_user end ... end I then include User fields with fields_for. All views render fine, but here's the catch: I cannot build a User, it tells me :password is a wrong method, so I guess the authentication logic was bypassed. What should I do? Am I doing it wrong altogether? Should I drop polymorphic associations in favor of Single Table Inheritance? Whatever I do, I have to make sure it plays nicely with Authlogic.

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  • Thinking sphinx: Problems with polymorphic associations

    - by auralbee
    Hello, I recently switched from ultrasphinx to thinking_sphinx for full-text search. I am trying to figure out how to index fields of polymorphic associations. I found some information but I still have some problems, although it seems to be easy. Here is my setup: class Info < ActiveRecord::Base belongs_to :mappable, :polymorphic => true define_index indexes mappable_type indexes mappable(:name), :as => :mappable_name end class A < ActiveRecord::Base has_many :infos, :as => :mappable end class B < ActiveRecord::Base has_many :infos, :as => :mappable end Amongst others, I want to do a search in the name column of A and B (both classes have this column), so I added the field to my index. When I do rake thinking_sphinx:index I get the following error: Generating Configuration to .../config/development.sphinx.conf rake aborted! undefined method `connection' for Object:Class .../.gem/ruby/1.8/gems/thinking-sphinx-1.3.16/lib/thinking_sphinx/ association.rb:149:in `casted_options' Any idea? Am I missing something? Thanks in advance. Tobi

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  • Modeling multiple polymorphic relationships using Hibernate

    - by f-potter
    Ruby on Rails has polymorphic relations which are really useful for implementing functionality such as commenting, tagging and rating to name a few. We can have a comment, tag or rating class which has a many to one polymorphic relationship with a commentable, taggable and rateable object. Also, a given domain object can choose to implement any combination of such relations. So, it can for example be commentable, taggable and rateable at the same time. I couldn't think up of a straightforward way to duplicate this functionality in Hibernate. Ideally, there would be a Comment class which will have a many to one relationship with a Commentable class and a Commentable class will conversely have a one to many relationship with Comments. It will be ideal if the concrete domain classes can inherit from a number of such classes, say Commentable and Taggable. Things seem a little complicated as a Java class can only extend one other class and some code might end up being duplicated across a number of classes. I wanted to know what are the best practices for modeling such relationships neatly and concisely using Hibernate?

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  • Auto filling polymorphic table on save or on delete in django

    - by Mo J. Mughrabi
    Hi, Am working on an project in which I made an app "core" it will contain some of the reused models across my projects, most of those are polymorphic models (Generic content types) and will be linked to different models. Example below am trying to create audit model and will be linked to several models which may require auditing. This is the polls/models.py from django.db import models from django.contrib.auth.models import User from core.models import * from django.contrib.contenttypes import generic class Poll(models.Model): ## TODO: Document question = models.CharField(max_length=300) question_slug=models.SlugField(editable=False) start_poll_at = models.DateTimeField(null=True) end_poll_at = models.DateTimeField(null=True) is_active = models.BooleanField(default=True) audit_obj=generic.GenericRelation(Audit) def __unicode__(self): return self.question class Choice(models.Model): ## TODO: Document choice = models.CharField(max_length=200) poll=models.ForeignKey(Poll) audit_obj=generic.GenericRelation(Audit) class Vote(models.Model): ## TODO: Document choice=models.ForeignKey(Choice) Ip_Address=models.IPAddressField(editable=False) vote_at=models.DateTimeField("Vote at", editable=False) here is the core/modes.py from django.db import models from django.contrib.auth.models import User from django.contrib.contenttypes.models import ContentType from django.contrib.contenttypes import generic class Audit(models.Model): ## TODO: Document # Polymorphic model using generic relation through DJANGO content type created_at = models.DateTimeField("Created at", auto_now_add=True) created_by = models.ForeignKey(User, db_column="created_by", related_name="%(app_label)s_%(class)s_y+") updated_at = models.DateTimeField("Updated at", auto_now=True) updated_by = models.ForeignKey(User, db_column="updated_by", null=True, blank=True, related_name="%(app_label)s_%(class)s_y+") content_type = models.ForeignKey(ContentType) object_id = models.PositiveIntegerField(unique=True) content_object = generic.GenericForeignKey('content_type', 'object_id') and here is polls/admin.py from django.core.context_processors import request from polls.models import Poll, Choice from core.models import * from django.contrib import admin class ChoiceInline(admin.StackedInline): model = Choice extra = 3 class PollAdmin(admin.ModelAdmin): inlines = [ChoiceInline] admin.site.register(Poll, PollAdmin) Am quite new to django, what am trying to do here, insert a record in audit when a record is inserted in polls and then update that same record when a record is updated in polls.

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  • Problem in mutiple :dependent=> :destroy when multiple polymorphic is true

    - by piemesons
    I have four models question, answer, comment and vote.Consider it same as stackoverflow. Question has_many comments Answers has_many comments Questions has_many votes answers has_many votes comments has_many votes Here are the models (only relevant things) class Comment < ActiveRecord::Base belongs_to :commentable, :polymorphic => true has_many :votes, :as => :votable, :dependent => :destroy end class Question < ActiveRecord::Base has_many :comments, :as => :commentable, :dependent => :destroy has_many :answers, :dependent => :destroy has_many :votes, :as => :votable, :dependent => :destroy end class Vote < ActiveRecord::Base belongs_to :votable, :polymorphic => true end class Answer < ActiveRecord::Base belongs_to :question, :counter_cache => true has_many :comments, :as => :commentable , :dependent => :destroy end Now the problem is whenever i am trying to delete any question/answer/comment its giving me an error NoMethodError in QuestionsController#destroy undefined method `each' for 0:Fixnum if i remove this line from any of the model (question/answer/comment) has_many :votes, :as => :votable, :dependent => :destroy then it works perfectly. It seems there is a problem while deleting the records active record is not able to find out the proper path because of multiple joins within the tables.

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  • Show Notes: Bob Hensle on IT Strategies from Oracle

    - by Bob Rhubart
    The latest ArchBeat Podcast (RSS) features a conversation with Oracle Enterprise Architecture director Bob Hensle (LinkedIn). Bob talks about IT Strategies from Oracle, an extensive library of reference architectures, best practices, and other documents now available (it’s a freebie!) to registered Oracle Technology Network members. Listen to Part 1 Bob offers some background on the IT Strategies from Oracle project and an overview of the included documents. Listen to Part 2 (Feb 16) A discussion of how SOA and other issues are reflected in the IT Strategies documents. Share your feedback on any of the documents in the IT Strategies from Oracle Library: [email protected] For a nice complement to the IT Strategies from Oracle Library, check out Oracle Experiences in Enterprise Architecture, an ongoing series of short essays from members of the Oracle Enterprise Architecture team based on their field experience. In the Pipeline ArchBeat programs in the works include an interview with Dr. Frank Munz, the author of Middleware and Cloud Computing, excerpts from another architect virtual meet-up, and a conversation with Oracle ACE Director Debra Lilley about her insight into Fusion Applications. . Stayed tuned: RSS Technorati Tags: oracle,oracle technology network,software architecture,enterprise architecture,reference architecture del.icio.us Tags: oracle,oracle technology network,software architecture,enterprise architecture,reference architecture

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  • Not finding field in polymorphic association with Doctrine2

    - by dimirc
    I have a polymorphic association (Class Table Inheritance) and I need use DQL to query entities of a specific child class wich can be done using "x INSTANCE OF Entity" in WHERE clause. Now I need to put conditions specific for that child class but I get this error: "Class Person has no association named student_field_1" Person = Parent Class Employee = Child class Student = Child class is there any way yo cast of somehow tell Doctrine that the Person is actually a Student and to allow me to put Student fields in the WHERE?

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  • Polymorphic association inserts 0 instead of raising error when column is misconfigured as Integer

    - by zetetic
    Here's one that stumped me for a while, though in retrospect it should have been obvious. I was getting the error message NoMethodError: undefined method `constantize' for 0:Fixnum when accessing a model through a polymorphic association. Turns out the table on the belongs_to side of the association had an integer type column instead of a string. Easily fixed, but it seems like Rails ought to raise an error in this situation -- instead it happily adds the row with 0 in the type column.

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  • are you supposed to be able to "ping" specific pages of websites, or just the domain name?

    - by Bec
    (sorry, i think my jargon is a bit off there, not sure) I'm trying to work out what's going on with my podcasts not downloading properly, to see whether it was my pod-catching software or the connection i tried doing a ping on the podcast URL e.g. www.abc.net.au/rn/podcast/feeds/ockham.xml and it failed (i got "could not find host"), it works for the first part of it though www.abc.net.au I can get to the xml page in a web browser though, and ping doesn't work on the podcasts which have been downloading right either.

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  • Rails accepts_nested_attributes_for and build_attribute with polymorphic relationships

    - by SooDesuNe
    The core of this question is where build_attribute is required in a model with nested attribuites I'm working with a few models that are setup like: class Person < ActiveRecord::Base has_one :contact accepts_nested_attributes_for :contact, :allow_destroy=> true end class Contact < ActiveRecord::Base belongs_to :person has_one :address, :as=>:addressable accepts_nested_attributes_for :address, :allow_destroy=> true end class Address < ActiveRecord::Base belongs_to :addressable, :polymorphic=>true end I have to define the new method of people_controller like: def new @person = Person.new @person.build_contact @person.contact.build_address #!not very good encapsulation respond_to do |format| format.html # new.html.erb format.xml { render :xml => @person } end end Without @person.contact.build_address the address relationship on contact is NIL. I don't like having to build_address in people_controller. That should be handled by Contact. Where do I define this in Contact since the contacts_controller is not involved here?

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  • Rails can't render polymorphic associations to XML?

    - by ambertch
    When I render XML with an :include clause for a polymorphic association I have, it doesn't work. I end up with the XML returning the object pointers instead of the actual objects, like: <posts> #<Comment:0x102ed1540>#<Comment:0x102ecaa38>#<Comment:0x102ec7fe0>#<Comment:0x102ec3cd8> </posts> Yet as_json works! When I render JSON with :include clause, the associations are rendered correctly and I get something like: posts":[ {"type":"Comment","created_at":"2010-04-20T23:02:30-07:00","id":7,"content":"fourth comment"}, {"type":"Comment","created_at":"2010-04-20T23:02:26-07:00","id":6,"content":"third comment"}] My current workaround is using XML builder, but I'm not too comfortable with that in the long run. Does anyone happen to know about this issue? I'm kind of in a catch-22 because while XML doesn't render the associations, as_json doesn't render in a kosher json format (returns an array rather than a list of hashes as proper json should) and the deserializer I'm using on the client side would require modification to parse the json correctly.

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  • Polymorphic functions with parameters from a class hierarchy

    - by myahya
    Let's say I have the following class hierarchy in C++: class Base; class Derived1 : public Base; class Derived2 : public Base; class ParamType; class DerivedParamType1 : public ParamType; class DerivedParamType2 : public ParamType; And I want a polymorphic function, func(ParamType), defined in Base to take a parameter of type DerivedParamType1 for Derived1 and a parameter of type DerivedParamType2 for Derived2. How would this be done without pointers, if possible?

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  • Polymorphic Behavior in VB6

    - by Tom Tresansky
    I recently noticed the CallByName keyword in VB6. Since this takes a object, procedure name, "call type" and arguments array, can this be used to "fake" some types of polymorphic behavior? I can make 2 classes, class A and B, each with the same method Foo, and do: Dim list As New Collection Dim instanceA As New ClassA Dim instanceB As New ClassB Dim current As Object Call list.Add(instanceA) Call list.Add(instanceB) For Each current in list Call CallByName(current, "methodName", vbMethod) Next Anyone done this before? Problems? Horrible idea or genius idea? Implications? Unintended consequences?

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  • error: polymorphic expression with default arguments

    - by 0__
    This following bugs me: trait Foo[ A ] class Bar[ A ]( set: Set[ Foo[ A ]] = Set.empty ) This yields <console>:8: error: polymorphic expression cannot be instantiated to expected type; found : [A]scala.collection.immutable.Set[A] required: Set[Foo[?]] class Bar[ A ]( set: Set[ Foo[ A ]] = Set.empty ) ^ It is quite annoying that I have to repeat the type parameter in Set.empty. Why does the type inference fail with this default argument? The following works: class Bar[ A ]( set: Set[ Foo[ A ]] = { Set.empty: Set[ Foo[ A ]]}) Please note that this has nothing to do with Set in particular: case class Hallo[ A ]() class Bar[ A ]( hallo: Hallo[ A ] = Hallo.apply ) // nope Strangely not only this works: class Bar[ A ]( hallo: Hallo[ A ] = Hallo.apply[ A ]) ...but also this: class Bar[ A ]( hallo: Hallo[ A ] = Hallo() ) // ???

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  • Hibernate - Persisting polymorphic joins

    - by Marty Pitt
    Hi I'm trying to understand how to best implement a polymorphic one-to-many in hibernate. Eg: @MappedSuperclass public class BaseEntity { Integer id; // etc... } @Entity public class Author extends BaseEntity {} @Entity public class Post extends BaseEntity {} @Entity public class Comment extends BaseEntity {} And now, I'd like to also persist audit information, with the following class: @Entity public class AuditEvent { @ManyToOne // ? BaseEntity entity; } What is the appropriate mapping for auditEvent.entity? Also, how will Hibernate actually persist this? Would a series of join tables be generated (AuditEvent_Author , AuditEvent_Post, AuditEvent_Comment), or is there a better way? Note, I'd rather not have my other entity classes expose the other side of the join (eg., List<AuditEvent> events on BaseEntity) - but if that's the cleanest way to implement, then it will suffice.

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  • Polymorphic associations in Rails

    - by Newy
    Say I have two models, Apples and Oranges, and they are both associated with a description in a Text model. Text is a separate class as I'd like to keep track of the different revisions. Is the following correct? Is there a better way to do this? [Apple] has_one :text, :as => :targit, :order => 'id DESC' has_many :revisions, :class_name => 'Text', :as => :targit, :order => 'id', :dependent => :destroy [Text] belongs_to :targit, :polymorphic => true

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  • Rails: using find method to access joined tables for polymorphic relationships

    - by DJTripleThreat
    Ok, I have a generic TimeSlot model that deals with a start_at and an end_at for time spans. A couple models derive from this but I'm referring to one in this question: AppointmentBlock which is a collection of Appointments. I want to validate an AppointmentBlock such that no other AppointmentBlocks have been scheduled for a particular Employee in the same time frame. Since AppointmentBlock has a polymorphic association with TimeSlot, you have to access the AppointmentBlock's start_at and end_at through the TimeSlot like so: appt_block.time_slot.start_at This means that I need to have some kind of join in my :conditions for my find() method call. Here is my code so far: #inside my appointment_block.rb model validate :employee_not_double_booked def employee_not_double_booked unless self.employee_id # this find's condition is incorrect because I need to join time_slots to get access # to start_at and end_at. How can I do this? blocks = AppointmentBlock.find(:first, :conditions => ['employee_id = ? and (start_at between ? and ? or end_at between ? and ?)', self.employee_id, self.time_slot.start_at, self.time_slot.end_at, self.time_slot.start_at, self.time_slot.end_at]) # pseudo code: # collect a list of appointment blocks that end after this # apointment block starts or start before this appointment # block ends that are also associated with this appointment # blocks assigned employee # if the count is great then 0 the employee has been double # booked. # if a block was found that means this employee is getting # double booked so raise an error errors.add "AppointmentBlock", "has already been scheduled during this time" if blocks end end Since AppointmentBlock doesn't have a start_at or an end_at how can I join with the time_slots table to get those conditions to work?

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  • Setting up podcasting for a non-tech user

    - by Force Flow
    I have a user who wants to start making podcasts, but they only have basic skills when it comes to technology. So, I was trying to get a process together that would be easy for them to follow. To upload files (the mp3's and rss feed files), I have an explorer shortcut for their FTP space. To record the podcast, I was going to either use audacity or PodProducer. For the RSS feed, I was looking for a podcast RSS generator of some sort. In my search for this, I've come across a lot of dead links and a lot of paid tools, so I haven't come up with anything too useful. Is there a free, reliable webservice or windows-based tool available that folks like to use?

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