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• Useful links

  - by Madhan ayyasamy

  Difference between STI vs Polymorphic associationsSTI vs PolymorphicDifference between habtm vs has_many :throughhabtm vs throughCapistrano Guide linkCapistrano guideRails application without database stuffclass Car < ActiveRecord::Baseself.abstract = trueendAnother link: rails without databaseNamed scope useful linkNamed scopeDifference between http and https verbhttp vs httpsRails 2.3 useful guide websiterails 2.3 guide

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• using paperclip with secure and non-secure files

  - by crankharder

  First off, we have this namespaced/sti'd structure for our different types of 'Media' Media< Ar::Base Media::Local < Media Media::Local::Image < Media::Local Media::Local::Csv < Media::Local etc... etc.. This is excellent since a user can have many media, and how we display each piece of media is based on the class name and a co-responding partial. But what if we have some Csv's that need to be secure? That is, they can't reside inside of public. I really hate the idea of branching Media again and doing something like this: Media::Secure < Media Media::Secure::Image < Media::Secure Media::NotSecure < Media Media::NotSecure::Image < Media::NotSecure ...where Secure and NotSecure would have different params passed to has_attached_file. Now there are two classes that represent Image and it makes my view/helper system that much more complicated -- not to mention it feels very obtuse. What I would really like to do is be able to change where certain Paperclip::Attachment objects get saved before they get saved (e.g. anything uploaded through foo_secure_action) -- but I can't seem to make this work. Paperclip::Attachment has an @options hash with :path and :url, but changing those before it is saved doesn't have an effect on where it actually gets set. Even if this is possible, I'm not sure if it would have further consequences... I'm open to alternative ideas for structuring this data, but for the moment I like the idea of using STI for this situation.

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• Problem with Active Record

  - by kshchepelin

  Hello everyone. Lets assume we have a User model. And user can plan some activities. The number of types of activities is about 50. All activities have common properties, such as start_time, end_time, user_id, etc. But each of them has some unique properties. Now we have each activity living in its own table in DB. And thats why we have such terrible sql queries like SELECT * FROM `first_activities_table` WHERE (`first_activity`.`id` IN (17,18)) SELECT * FROM `second_activities_table` WHERE (`second_activity`.`id` = 17) ..... SELECT * FROM `n_activities_table` WHERE (`n_activity`.`id` = 44) About 50 queries. That's terrible. There are different ways to solve this. Choose the activity type with the biggest number of properties, create the table 'Activities' and have STI model. But this way we must name our columns in uncomfortable way and often the record in that table would have some NULL fields. Also STI model, but having columns, common for all of activity types and some blob column with serialized properties. But we have to do some search on activities - there can be a problem. And serialization is quite slow. Please help me dealing with this. Maybe my problem has quite different solution that will fit my needs. Thanks for help.

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• Call child's method or cast parent to child in Rails

  - by Brian

  I have some STI structure like following: class Box has_many :part,:class_name = "Part" end class Part def self.dosomething() end end class TypeA class TypeB assuming we have some codes like boxtypeA = Box.new. I am wondering if there is a way to make boxtypeA.part.dosomething() to call TypeA's method not Part's or TypeB's. I think basically what we need to do is to convert the part to TypeA, how can we achieve that? Thx in advance!

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• Call child's method or cast parent to child in Rails

  - by Brian

  I have some STI structure like following: class Box has_many :part,:class_name = "Part" end class Part def self.dosomething() end end class TypeA<Part def self.dosomething() end end class TypeB<Part def self.dosomething() end end assuming we have some codes like boxtypeA = Box.new. I am wondering if there is a way to make boxtypeA.part.dosomething() to call TypeA's method not Part's or TypeB's. I think basically what we need to do is to convert the part to TypeA, how can we achieve that? Thx in advance!

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• How to return children objects?

  - by keruilin

  I have -- what I think -- is a simple question. Here's my code: class Fruit < ActiveRecord::Base end class Apple < Fruit end class Kiwi < Fruit end Assume that I have all the STI setup correctly, and there are multiple types of Apple and Kiwi records in the table. From here... fruits = Fruit.find(:all) ...how do I return an array of just Apples from the fruits array?

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• How can I prevent Libre Office to start unexpected when I start other applications?

  - by brubaker

  I am on Ubuntu 11.10/64bit with Gnome 3. Regards [update] I trying to say that when I start an application like Nautilus LibreOffice starts as well. Sometimes this also happens when I open a document with a totally different extension i.e. a .html doc. I checked if and which plugins are installed to Firefox: OpenOffice.org Plug-in File: libnpsoplugin.so Version: OpenOffice.org Plug-in handles all its documents MIME Type Description Suffixes application/vnd.stardivision.calc StarCalc 3.0 - 5.0 sdc application/vnd.stardivision.chart StarChart 3.0 - 5.0 sds application/vnd.stardivision.draw StarDraw 3.0 - 5.0 sda application/vnd.stardivision.impress StarImpress 3.0 - 5.0 sdd application/vnd.stardivision.impress-packed StarImpress-packed 3.0 - 5.0 sdp application/vnd.stardivision.math StarMath 3.0 - 5.0 smf application/vnd.stardivision.writer StarWriter Template 3.0 - 5.0 vor application/vnd.stardivision.writer-global StarWriter Global 3.0 - 5.0 sgl application/vnd.staroffice.writer StarWriter 3.0 - 5.0 sdw application/vnd.sun.xml.calc StarOffice 6.0/7 Spreadsheet sxc application/vnd.sun.xml.calc.template StarOffice 6.0/7 Spreadsheet Template stc application/vnd.sun.xml.draw StarOffice 6.0/7 Drawing sxd application/vnd.sun.xml.draw.template StarOffice 6.0/7 Drawing Template std application/vnd.sun.xml.impress StarOffice 6.0/7 Presentation sxi application/vnd.sun.xml.impress.template StarOffice 6.0/7 Presentation Template sti application/vnd.sun.xml.math StarOffice 6.0/7 Formula sxm application/vnd.sun.xml.writer StarOffice 6.0/7 Text Document sxw application/vnd.sun.xml.writer.global StarOffice 6.0/7 Master Document sxg application/vnd.sun.xml.writer.template StarOffice 6.0/7 Text Document Template stw application/vnd.oasis.opendocument.text OpenDocument Text odt application/vnd.oasis.opendocument.text-template OpenDocument Text Template ott application/vnd.oasis.opendocument.text-master OpenDocument Master Document odm application/vnd.oasis.opendocument.text-web HTML Document Template oth application/vnd.oasis.opendocument.spreadsheet OpenDocument Spreadsheet ods application/vnd.oasis.opendocument.spreadsheet-template OpenDocument Spreadsheet Template ots application/vnd.oasis.opendocument.graphics OpenDocument Drawing odg application/vnd.oasis.opendocument.graphics-template OpenDocument Drawing Template otg application/vnd.oasis.opendocument.presentation OpenDocument Presentation odp application/vnd.oasis.opendocument.presentation-template OpenDocument Presentation Template otp application/vnd.oasis.opendocument.formula OpenDocument Formula odf

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• Rails single table inheritance/subclass find condition in parent

  - by slythic

  Hi all, I have a table called Users (class User < ActiveRecord::Base) and a subclass/STI of it for Clients (class Client < User). Client "filtering" works as expected, in other words Client.find(:all) works to find all the clients. However, for users I need to filter the result to only find users that are NOT clients (where type is null or blank). I've tried the following in my index controller but no matter what I put for the type it returns all users regardless of type. User.find(:all, :conditions => { :type => nil }, :order => 'name') Any clue on how to get this condition to work? Thanks!

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• named_scope or find_by_sql?

  - by keruilin

  I have three models: User Award Trophy The associations are: User has many awards Trophy has many awards Award belongs to user Award belongs to trophy User has many trophies through awards Therefore, user_id is a fk in awards, and trophy_id is a fk in awards. In the Trophy model, which is an STI model, there's a trophy_type column. I want to return a list of users who have been awarded a specific trophy -- (trophy_type = 'GoldTrophy'). Users can be awarded the same trophy more than once. (I don't want distinct results.) Can I use a named_scope? How about chaining them? Or do I need to use find_by_sql? Either way, how would I code it?

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• Using Full-Text Search in SQL Server 2005 across multiple tables, columns

  - by crisgomez

  Hi, I have a problem, I created a full text search query which return a record(s), in which the paramater I have supplied match(es) in every fields(full-text indexed) of multiple tables. The problem is , when the user.id is equal to ceritification.AId it returns a records eventhough it was not satisfied with the parameter supplied. For this example I supplied a value "xandrick" which return an Id=184, but the problem is it returns two ids which is 184 and 154.What is the best way to return an ID(s) that satisfied of the supplied given value? User table Id Firstname Lastname Middlename Email AlternativeEmail 154 Gregorio Honasan Pimentel [email protected] [email protected] 156 Qwerty Qazggf fgfgf [email protected]. [email protected] 184 Xandrick Flores NULL [email protected] null Certification table Id AID Certification School 12 184 sdssd AMA 13 43 web-based and framework 2 Asian development foundation college 16 184 hjhjhj STI 17 184 rrrer PUP 18 154 vbvbv AMA SELECT DISTINCT Users.Id FROM Users INNER JOIN Certification on Users.Id=Certification.aid LEFT JOIN FREETEXTTABLE (Users,(Firstname,Middlename,Lastname,Email,AlternativeEmail), 'xandrick' )as ftUsr ON Users.Id=ftUsr.[KEY] LEFT JOIN FREETEXTTABLE (Certification,(Certification,School), 'xandrick' )as ftCert ON Certification.Id=ftCert.[KEY]

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• Rails Multiple Table Inheritance question

  - by Tony

  I am starting to implement an MTI solution and have a basic question. I have 3 physical models - SMSNotifications, EmailNotifications, TwitterNotifications and they are subclasses of notification. At times in my code, I want to say Notifications.find(:all)so that I can get a set of results sorted by their creation time. Then I want to do things based on their subclass. What is the way to write Notifications.find(:all) and have Rails look through the subclass tables and combine the results? Right now Rails still thinks I have a physical Notifications table which goes against my MTI design. I am also considering the possibility that I should be using STI instead. I would probably have 10 empty columns per row but if getting all notifications requires a query for each type of notification, then I feel like this could be a big issue. Thanks!

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• Rails Model for Playlist that can contain tracks and albums using polymorphism

  - by philk

  I struggle to find a model how to store a playlist with different type of items on it in Rails. Consider I have class Track end class Album has_many :tracks end class PlaylistItem belongs_to :playable belongs_to :playlist end class Playable belongs_to :playable, :polymorph => true end class Playlist has_many :playlist_items end I think I can use a polymorphic model "Playable" here since the Playlist can contain Tracks, Albums and maybe in the future also Movies. Also I would like to use STI for Track and Albums since they share some common attributes like title and length but also have totally different attributes. I modeled it like described here but it does not work. Anybody any idea how to model a Playlist that can contain many items of different kind?

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• How to override the attr_protected?

  - by KandadaBoggu

  I have STI implementation as follows: class Automobile < ActiveRecord::Base end class Car < Automobile end class Truck < Automobile end class User < ActiveRecord::Base has_many :automobiles accepts_nested_attributes_for :automobiles end I am creating a list of automobiles for a user. For each automobile, the UI sets the type field and the properties associated with the automobile.While form submission, the type field is ignored as it is a protected attribute. How do I work around this issue? Is there a declarative way to unprotect a protected attribute?

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• Rails object inheritence with belongs_to

  - by Rabbott

  I have a simple has_many/belongs_to relationship between Report and Chart. The issue I'm having is that my Chart model is a parent that has children. So in my Report model I have class Report < ActiveRecord::Base has_many :charts end And my Chart model is a parent, where Pie, Line, Bar all inherit from Chart. I'm not sure where the belongs_to :report belongs within the chart model, or children of chart model. I get errors when I attempt to access chart.report because the object is of type "Class" undefined local variable or method `report' for #< Class:0x104974b90 The Chart model uses STI so its pulling say.. 'Pie' from the chart_type column in the charts table.. what am I missing?

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• This is right way for database?

  - by ciss

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

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• Torchlight Black Screen and doesn't show up

  - by Lelouch Reyiz

  When I open it in full screen I get a black screen that covers whole screen,in windowed mode middle of screen.Here is a video: https://copy.com/fvrGw7QIJ8Z0 Terminal Output: alperen@alperen-Inspiron-N5010 /usr/local/games/Torchlight $ ./Torchlight.bin.x86_64 Creating resource group General Creating resource group Internal Creating resource group Autodetect SceneManagerFactory for type 'DefaultSceneManager' registered. Registering ResourceManager for type Material Registering ResourceManager for type Mesh Registering ResourceManager for type Skeleton MovableObjectFactory for type 'ParticleSystem' registered. OverlayElementFactory for type Panel registered. OverlayElementFactory for type BorderPanel registered. OverlayElementFactory for type TextArea registered. Registering ResourceManager for type Font ArchiveFactory for archive type FileSystem registered. ArchiveFactory for archive type Zip registered. FreeImage version: 3.13.1 This program uses FreeImage, a free, open source image library supporting all common bitmap formats. See http://freeimage.sourceforge.net for details Supported formats: bmp,ico,jpg,jif,jpeg,jpe,jng,koa,iff,lbm,mng,pbm,pbm,pcd,pcx,pgm,pgm,png,ppm,ppm,ras,tga,targa,tif,tiff,wap,wbmp,wbm,psd,cut,xbm,xpm,gif,hdr,g3,sgi,exr,j2k,j2c,jp2,pfm,pct,pict,pic,bay,bmq,cr2,crw,cs1,dc2,dcr,dng,erf,fff,hdr,k25,kdc,mdc,mos,mrw,nef,orf,pef,pxn,raf,raw,rdc,sr2,srf,arw,3fr,cine,ia,kc2,mef,nrw,qtk,rw2,sti,drf,dsc,ptx,cap,iiq,rwz DDS codec registering Registering ResourceManager for type HighLevelGpuProgram Registering ResourceManager for type Compositor MovableObjectFactory for type 'Entity' registered. MovableObjectFactory for type 'Light' registered. MovableObjectFactory for type 'BillboardSet' registered. MovableObjectFactory for type 'ManualObject' registered. MovableObjectFactory for type 'BillboardChain' registered. MovableObjectFactory for type 'RibbonTrail' registered. Loading library lib64/OGRE/RenderSystem_GL Installing plugin: GL RenderSystem OpenGL Rendering Subsystem created. Plugin successfully installed Loading library lib64/OGRE/Plugin_ParticleFX Installing plugin: ParticleFX Particle Emitter Type 'Point' registered Particle Emitter Type 'Box' registered Particle Emitter Type 'Ellipsoid' registered Particle Emitter Type 'Cylinder' registered Particle Emitter Type 'Ring' registered Particle Emitter Type 'HollowEllipsoid' registered Particle Affector Type 'LinearForce' registered Particle Affector Type 'ColourFader' registered Particle Affector Type 'ColourFader2' registered Particle Affector Type 'ColourImage' registered Particle Affector Type 'ColourInterpolator' registered Particle Affector Type 'Scaler' registered Particle Affector Type 'Rotator' registered Particle Affector Type 'DirectionRandomiser' registered Particle Affector Type 'DeflectorPlane' registered Plugin successfully installed Loading library lib64/OGRE/Plugin_OctreeSceneManager Installing plugin: Octree & Terrain Scene Manager Plugin successfully installed *-*-* OGRE Initialising *-*-* Version 1.6.5 (Shoggoth) terminate called after throwing an instance of 'std::out_of_range' what(): basic_string::substr Error: signal: 6 ./Torchlight.bin.x86_64(_ZN10LinuxUtils13crash_handlerEi+0x25)[0x17eb6f5] /lib/x86_64-linux-gnu/libc.so.6(+0x37000)[0x7fc647877000] /lib/x86_64-linux-gnu/libc.so.6(gsignal+0x39)[0x7fc647876f89] /lib/x86_64-linux-gnu/libc.so.6(abort+0x148)[0x7fc64787a398] /usr/lib/x86_64-linux-gnu/libstdc++.so.6(_ZN9__gnu_cxx27__verbose_terminate_handlerEv+0x155)[0x7fc6481826b5] /usr/lib/x86_64-linux-gnu/libstdc++.so.6(+0x5e836)[0x7fc648180836] /usr/lib/x86_64-linux-gnu/libstdc++.so.6(+0x5e863)[0x7fc648180863] /usr/lib/x86_64-linux-gnu/libstdc++.so.6(+0x5eaa2)[0x7fc648180aa2] /usr/lib/x86_64-linux-gnu/libstdc++.so.6(_ZSt20__throw_out_of_rangePKc+0x67)[0x7fc6481d25d7] /usr/lib/x86_64-linux-gnu/libstdc++.so.6(+0xbe3d3)[0x7fc6481e03d3] ./Torchlight.bin.x86_64(_ZN11CFileSystem21buildMassiveDataGroupEv+0x453)[0x1617805] ./Torchlight.bin.x86_64(_ZN11CFileSystemC1Eb+0x14be)[0x16145ae] ./Torchlight.bin.x86_64(_ZN22CMasterResourceManagerC1EP9CSettings+0x41a)[0xfe1d0a] ./Torchlight.bin.x86_64(_ZN5CGame5setupEb+0x79a)[0x73ceaa] ./Torchlight.bin.x86_64(_ZN5CGame5beginEPv+0x28d)[0x73b839] ./Torchlight.bin.x86_64(main+0x649)[0x146dbe4] /lib/x86_64-linux-gnu/libc.so.6(__libc_start_main+0xf5)[0x7fc647861ec5] ./Torchlight.bin.x86_64[0x739ca9]

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• MySQL use certain columns, based on other columns

  - by Rabbott

  I have this query: SELECT COUNT(articles.id) AS count FROM articles, xml_documents, streams WHERE articles.xml_document_id = xml_documents.id AND xml_documents.stream_id = streams.id AND articles.published_at BETWEEN '2010-01-01' AND '2010-04-01' AND streams.brand_id = 7 Which just uses the default equajoin by specifying three tables in csv format in the FROM clause.. What I need to do is group this by a value found within articles.source (raw xml).. so it could turn into this: SELECT COUNT(articles.id) AS count, ExtractValue(articles.source, "/article/media_type") AS media_type FROM articles, xml_documents, streams WHERE articles.xml_document_id = xml_documents.id AND xml_documents.stream_id = streams.id AND articles.published_at BETWEEN '2010-01-01' AND '2010-04-01' AND streams.brand_id = 7 GROUP BY media_type which works fine, the problem is, I'm using rails, and using STI for the xml_documents table. The articles.source that is provided to the ExtractValue method will be of a couple different formats.. So what I need to be able to do is use "/article/media_type" IF xml_documents.type = 'source one' and use "/article/source" if xml_documents.type = 'source two' This is just because the two document types format their XML differently, but I don't want to have to run multiple queries to retrieve this information.. It would be nice if one could use a ternary operator, but i don't think this is possible.. EDIT At this Point I am looking at making a temp table, or simply using UNION to place multiple result sets together..

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• rails: has_many :through validation?

  - by ramonrails

  Rails 2.1.0 (Cannot upgrade for now due to several constraints) I am trying to achieve this. Any hints? A project has many users through join model A user has many projects through join model Admin class inherits User class. It also has some Admin specific stuff. Admin like inheritance for Supervisor and Operator Project has one Admin, One supervisor and many operators. Now I want to 1. submit data for project, admin, supervisor and operator in a single project form 2. validate all and show errors on the project form. Project has_many :projects_users ; has_many :users, :through => :projects_users User has_many :projects_users ; has_many :projects, :through => :projects_users ProjectsUser = :id integer, :user_id :integer, :project_id :integer, :user_type :string ProjectUser belongs_to :project, belongs_to :user Admin < User # User has 'type:string' column for STI Supervisor < User Operator < User Is the approach correct? Any and all suggestions are welcome.

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• how to store/model users/faceboook users/linkedin users, etc, with ActiveRecord?

  - by crankharder

  My app has "normal" users: those which come through a typical signup page facebook(FB) users: those which come from Facebook connect "FB-normal" users: a user that can log with both email/password * FB connect Further, there's the a slew of other openID-ish login methods (I don't think openID itself will be acceptable since it doesn't link up the accounts and allow the 3rd party specific features (posting to twitter, adding a FB post, etc etc)) So, how do I model this? Right now we have User class with #facebook_user? defined -- but it gets messy with the "FB-normal" users - plus all the validations become very tricky and hard to interpret. Also, there are methods like #deliver_password_reset! which make no sense in the context for facebook-only users. (this is lame) I've thought out STI (User::Facebook, User::Normal, User::FBNormal, etc.) This makes validations super slick, but it doesn't scale to other connection types, and all the permutations between them... User::FacebookLinkedInNormal(wtf?) Doing this with a bunch of modules I think would suck a lot. Any other ideas?

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• Help with active record relations

  - by Christian Fazzini

  class CreateActivities < ActiveRecord::Migration def self.up create_table :activities do |t| t.references :user t.references :media t.integer :artist_id t.string :type t.timestamps end end def self.down drop_table :activities end end class Fan < Activity belongs_to :user, :counter_cache => true end class Activity < ActiveRecord::Base belongs_to :user belongs_to :media belongs_to :artist, :class_name => 'User', :foreign_key => 'artist_id' end class User < ActiveRecord::Base has_many :activities has_many :fans end I tried changing my activity model too, without any success: class Activity < ActiveRecord::Base has_many :activities, :class_name => 'User', :foreign_key => 'user_id' has_many :activities, :class_name => 'User', :foreign_key => 'artist_id' end One thing to note. Activity is an STI. Fan inherits from Activity. In console, I do: # Create a fan object. User is a fan of himself fan = Fan.new => #<Fan id: nil, user_id: nil, media_id: nil, artist_id: nil, type: "Fan", comment: nil, created_at: nil, updated_at: nil> # Assign a user object fan.user = User.first => #<User id: 1, genre_id: 1, country_id: 1, .... # Assign an artist object fan.artist_id = User.first.id => 1 # Save the fan object fan.save! => true Activity.last => #<Fan id: 13, user_id: 1, media_id: nil, artist_id: 1, type: "Fan", comment: nil, created_at: "2010-12-30 08:41:25", updated_at: "2010-12-30 08:41:25"> Activity.last.user => #<User id: 1, genre_id: 1, country_id: 1, ..... But... Activity.last.artist => nil Why is Activity.last.artist returning nil?

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• Modules vs. Classes and their influence on descendants of ActiveRecord::Base

  - by Chris

  Here's a Ruby OO head scratcher for ya, brought about by this Rails scenario: class Product < ActiveRecord::Base has_many(:prices) # define private helper methods end module PrintProduct attr_accessor(:isbn) # override methods in ActiveRecord::Base end class Book < Product include PrintProduct end Product is the base class of all products. Books are kept in the products table via STI. The PrintProduct module brings some common behavior and state to descendants of Product. Book is used inside fields_for blocks in views. This works for me, but I found some odd behavior: After form submission, inside my controller, if I call a method on a book that is defined in PrintProduct, and that method calls a helper method defined in Product, which in turn calls the prices method defined by has_many, I'll get an error complaining that Book#prices is not found. Why is that? Book is a direct descendant of Product! More interesting is the following.. As I developed this hierarchy PrintProduct started to become more of an abstract ActiveRecord::Base, so I thought it prudent to redefine everything as such: class Product < ActiveRecord::Base end class PrintProduct < Product end class Book < PrintProduct end All method definitions, etc. are the same. In this case, however, my web form won't load because the attributes defined by attr_accessor (which are "virtual attributes" referenced by the form but not persisted in the DB) aren't found. I'll get an error saying that there is no method Book#isbn. Why is that?? I can't see a reason why the attr_accessor attributes are not found inside my form's fields_for block when PrintProduct is a class, but they are found when PrintProduct is a Module. Any insight would be appreciated. I'm dying to know why these errors are occurring!

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• multiple models in Rails with a shared interface

  - by dfondente

  I'm not sure of the best structure for a particular situation in Rails. We have several types of workshops. The administration of the workshops is the same regardless of workshop type, so the data for the workshops is in a single model. We collect feedback from participants about the workshops, and the questionnaire is different for each type of workshop. I want to access the feedback about the workshop from the workshop model, but the class of the associated model will depend on the type of workshop. If I was doing this in something other than Rails, I would set up an abstract class for WorkshopFeedback, and then have subclasses for each type of workshop: WorkshopFeedbackOne, WorkshopFeedbackTwo, WorkshopFeedbackThree. I'm unsure how to best handle this with Rails. I currently have: class Workshop < ActiveRecord::Base has_many :workshop_feedbacks end class Feedback < ActiveRecord::Base belongs_to :workshop has_many :feedback_ones has_many :feedback_twos has_many :feedback_threes end class FeedbackOne < ActiveRecord::Base belongs_to :feedback end class FeedbackTwo < ActiveRecord::Base belongs_to :feedback end class FeedbackThree < ActiveRecord::Base belongs_to :feedback end This doesn't seem like to the cleanest way to access the feedback from the workshop model, as accessing the correct feedback will require logic investigating the Workshop type and then choosing, for instance, @workshop.feedback.feedback_one. Is there a better way to handle this situation? Would it be better to use a polymorphic association for feedback? Or maybe using a Module or Mixin for the shared Feedback interface? Note: I am avoiding using Single Table Inheritance here because the FeedbackOne, FeedbackTwo, FeedbackThree models do not share much common data, so I would end up with a large sparsely populated table with STI.

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• What is required to use LODSB in assembly?

  - by Harvey

  What is the minimum set of steps required to use LODSB to load a relative address to a string in my code? I have the following test program that I'm using PXE to boot. I boot it two ways: via pxelinux.0 and directly. If I boot it directly, my program prints both strings. If I boot via pxelinux.0, it only prints the first string. Why? Working technique (for both): Set the direction flag to increment, cld Set ds to cs Put the address (from start) of string in si Add the starting offset to si Non-working technique (just for pxelinux): Calculate a new segment address based on (((cs << 4) + offset) >> 4) Set ds to that. (either A000 or 07C0) text here to fix bug in markdown // Note: If you try this code, don't forget to set // the "#if 0" below appropriately! .text .globl start, _start start: _start: _start1: .code16 jmp real_start . = _start1 + 0x1fe .byte 0x55, 0xAA // Next sector . = _start1 + 0x200 jmp real_start test1_str: .asciz "\r\nTest: 9020:fe00" test2_str: .asciz "\r\nTest: a000:0000" real_start: cld // Make sure %si gets incremented. #if 0 // When loaded by pxelinux, we're here: // 9020:fe00 ==> a000:0000 // This works. movw $0x9020, %bx movw %bx, %ds movw $(test1_str - _start1), %si addw $0xfe00, %si call print_message // This does not. movw $0xA000, %bx movw %bx, %ds movw $(test2_str - _start1), %si call print_message #else // If we are loaded directly without pxelinux, we're here: // 0000:7c00 ==> 07c0:0000 // This works. movw $0x0000, %bx movw %bx, %ds movw $(test1_str - _start1), %si addw $0x7c00, %si call print_message // This does, too. movw $0x07c0, %bx movw %bx, %ds movw $(test2_str - _start1), %si call print_message #endif // Hang the computer sti 1: jmp 1b // Prints string DS:SI (modifies AX BX SI) print_message: pushw %ax jmp 2f 3: movb $0x0e, %ah /* print char in AL */ int $0x10 /* via TTY mode */ 2: lodsb (%si), %al /* get token */ cmpb $0, %al /* end of string? */ jne 3b popw %ax ret .balign 0x200 Here's the compilation: /usr/bin/ccache gcc -Os -fno-stack-protector -fno-builtin -nostdinc -DSUPPORT_SERIAL=1 -DSUPPORT_HERCULES=1 -DSUPPORT_GRAPHICS=1 -DHAVE_CONFIG_H -I. -Wall -ggdb3 -Wmissing-prototypes -Wunused -Wshadow -Wpointer-arith -falign-jumps=1 -falign-loops=1 -falign-functions=1 -Wundef -g -c -o ds_teststart_exec-ds_teststart.o ds_test.S /usr/bin/ccache gcc -g -o ds_teststart.exec -nostdlib -Wl,-N -Wl,-Ttext -Wl,8000 ds_teststart_exec-ds_teststart.o objcopy -O binary ds_teststart.exec ds_teststart

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• Problem with bootstrap loader and kernel

  - by dboarman-FissureStudios

  We are working on a project to learn how to write a kernel and learn the ins and outs. We have a bootstrap loader written and it appears to work. However we are having a problem with the kernel loading. I'll start with the first part: bootloader.asm: [BITS 16] [ORG 0x0000] ; ; all the stuff in between ; ; the bottom of the bootstrap loader datasector dw 0x0000 cluster dw 0x0000 ImageName db "KERNEL SYS" msgLoading db 0x0D, 0x0A, "Loading Kernel Shell", 0x0D, 0x0A, 0x00 msgCRLF db 0x0D, 0x0A, 0x00 msgProgress db ".", 0x00 msgFailure db 0x0D, 0x0A, "ERROR : Press key to reboot", 0x00 TIMES 510-($-$$) DB 0 DW 0xAA55 ;************************************************************************* The bootloader.asm is too long for the editor without causing it to chug and choke. In addition, the bootloader and kernel do work within bochs as we do get the message "Welcome to our OS". Anyway, the following is what we have for a kernel at this point. kernel.asm: [BITS 16] [ORG 0x0000] [SEGMENT .text] ; code segment mov ax, 0x0100 ; location where kernel is loaded mov ds, ax mov es, ax cli mov ss, ax ; stack segment mov sp, 0xFFFF ; stack pointer at 64k limit sti mov si, strWelcomeMsg ; load message call _disp_str mov ah, 0x00 int 0x16 ; interrupt: await keypress int 0x19 ; interrupt: reboot _disp_str: lodsb ; load next character or al, al ; test for NUL character jz .DONE mov ah, 0x0E ; BIOS teletype mov bh, 0x00 ; display page 0 mov bl, 0x07 ; text attribute int 0x10 ; interrupt: invoke BIOS jmp _disp_str .DONE: ret [SEGMENT .data] ; initialized data segment strWelcomeMsg db "Welcome to our OS", 0x00 [SEGMENT .bss] ; uninitialized data segment Using nasm 2.06rc2 I compile as such: nasm bootloader.asm -o bootloader.bin -f bin nasm kernel.asm -o kernel.sys -f bin We write bootloader.bin to the floppy as such: dd if=bootloader.bin bs=512 count=1 of/dev/fd0 We write kernel.sys to the floppy as such: cp kernel.sys /dev/fd0 As I stated, this works in bochs. But booting from the floppy we get output like so: Loading Kernel Shell ........... ERROR : Press key to reboot Other specifics: OpenSUSE 11.2, GNOME desktop, AMD x64 Any other information I may have missed, feel free to ask. I tried to get everything in here that would be needed. If I need to, I can find a way to get the entire bootloader.asm posted somewhere. We are not really interested in using GRUB either for several reasons. This could change, but we want to see this boot successful before we really consider GRUB.

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• MBR Booting from DOS

  - by eflukx

  For a project I would like to invoke the MBR on the first harddisk directly from DOS. I've written a small assembler program that loads the MBR in memory at 0:7c00h an does a far jump to it. I've put my util on a bootable floppy. The disk (HD0, 0x80) i'm trying to boot has a TrueCrypt boot loader on it. It shows up the TrueCrypt screen, but after typing in the password it crashes the system. When I run my little utlility (w00t.com) on a normal WinXP machine it seams to crash immedealty. Apparently I'm forgetting some crucial stuff the BIOS normally does, my guess is it's something trivial. Can someone with better bare-metal DOS and BIOS experience help me out? Heres my code: .MODEL tiny .386 _TEXT SEGMENT USE16 INCLUDE BootDefs.i ORG 100h start: ; http://vxheavens.com/lib/vbw05.html ; Before DOS has booted the BIOS stores the amount of usable lower memory ; in a word located at 0:413h in memory. We going to erase this value because ; we have booted dos before loading the bootsector, and dos is fat (and ugly). ; fake free memory ;push ds ;push 0 ;pop ds ;mov ax, TC_BOOT_LOADER_SEGMENT / 1024 * 16 + TC_BOOT_MEMORY_REQUIRED ;mov word ptr ds:[413h], ax ;ax = memory in K ;pop ds ;lea si, memory_patched_msg ;call print ;mov ax, cs mov ax, 0 mov es, ax ; read first sector to es:7c00h (== cs:7c00) mov dl, 80h mov cl, 1 mov al, 1 mov bx, 7c00h ;load sector to es:bx call read_sectors lea si, mbr_loaded_msg call print lea si, jmp_to_mbr_msg call print ;Set BIOS default values in environment cli mov dl, 80h ;(drive C) xor ax, ax mov ds, ax mov es, ax mov ss, ax mov sp, 0ffffh sti push es push 7c00h retf ;Jump to MBR code at 0:7c00h ; Print string print: xor bx, bx mov ah, 0eh cld @@: lodsb test al, al jz print_end int 10h jmp @B print_end: ret ; Read sectors of the first cylinder read_sectors: mov ch, 0 ; Cylinder mov dh, 0 ; Head ; DL = drive number passed from BIOS mov ah, 2 int 13h jnc read_ok lea si, disk_error_msg call print read_ok: ret memory_patched_msg db 'Memory patched', 13, 10, 7, 0 mbr_loaded_msg db 'MBR loaded', 13, 10, 7, 0 jmp_to_mbr_msg db 'Jumping to MBR code', 13, 10, 7, 0 disk_error_msg db 'Disk error', 13, 10, 7, 0 _TEXT ENDS END start

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