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  • Designing a chain of states

    - by devoured elysium
    I want to model a kind of FSM(Finite State Machine). I have a sequence of states (let's say, from StateA to StateZ). This sequence is called a Chain and is implemented internally as a List. I will add states by the order I want them to run. My purpose is to be able to make a sequence of actions in my computer (for example, mouse clicks). (I know this has been done a zillion times). So a state is defined as a: boolean Precondition() <- Checks to see if for this state, some condition is true. For example, if I want to click in the Record button of a program, in this method I would check if the program's process is running or not. If it is, go to the next state in the chain list, otherwise, go to what was defined as the fail state (generally is the first state of them all). IState GetNextState() <- Returns the next state to evaluate. If Precondition() was sucessful, it should yield the next state in the chain otherwise it should yield the fail state. Run() Simply checks the Precondition() and sets the internal data so GetNextState() works as expected. So, a naive approach to this would be something like this: Chain chain = new Chain(); //chain.AddState(new State(Precondition, FailState, NextState) <- Method structure chain.AddState(new State(new WinampIsOpenCondition(), null, new <problem here, I want to referr to a state that still wasn't defined!>); The big problem is that I want to make a reference to a State that at this point still wasn't defined. I could circumvent the problem by using strings when refrering to states and using an internal hashtable, but isn't there a clearer alternative? I could just pass only the pre-condition and failure states in the constructor, having the chain just before execution put in each state the correct next state in a public property but that seems kind of awkward.

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  • Fastest way to do a weighted tag search in SQL Server

    - by Hasan Khan
    My table is as follows ObjectID bigint Tag nvarchar(50) Weight float Type tinyint I want to get search for all objects that has tags 'big' or 'large' I want the objectid in order of sum of weights (so objects having both the tags will be on top) select objectid, row_number() over (order by sum(weight) desc) as rowid from tags where tag in ('big', 'large') and type=0 group by objectid the reason for row_number() is that i want paging over results. The query in its current form is very slow, takes a minute to execute over 16 million tags. What should I do to make it faster? I have a non clustered index (objectid, tag, type) Any suggestions?

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  • PHP string to object name.

    - by Smickie
    Ok I have a string... $a_string = "Product"; and I want to use this string in a call to a object like this: $this->$a_string->some_function(); How the dickens do I dynamically call that object? (don't think Im on php 5 mind)

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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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  • C# Linq: Can you merge DataContexts?

    - by Andreas Grech
    Say I have one database, and this database has a set of tables that are general to all Clients and some tables that are specific to certain clients. Now what I have in mind is creating a primary DataContext that includes only the tables that are general to all the clients, and then create separate DataContexts that contain only the tables that are specific to the client. Is there a way to kind of "merge" DataContexts so that it becomes one context? So for Client A, I need one DataContext that includes both the general tables and also the tables for that specific client (retrieved from two different DataContexts) ? [Update] What I think I can do is, from the Partial Class of the DataContext instead of letting my DataContext inherit from DataContext I make it inherit from MyDataContext; that way, the tables from MyDataContext and the other DataContext will be available in one DataContext class. What do you think about this approach? Of course with something like this you can only merge two datacontexts at once though...

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  • Better alternative to autonumber primary keys

    - by Comrad_Durandal
    I am looking for a better primary key than the autonumber data type, namely for the reason that it's limited to a long integer, when I really just need the field to reflect a number or text string that will never ever repeat, no matter HOW many records are added or deleted from the table. The problem is I am not sure how to implement something like turning the current date and time into a hexadecimal string and using that as a unique field I can use as a primary key. Am I just being too paranoid about running out of space?

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  • BackOffice Database Application FrontEnd - Program in C#/VB.Net or PHP?

    - by HK1
    I'm working on a project where there will be a MySQL database containing data that will mostly be displayed on the web using PHP. However, there is a need here for a back-office data entry application (linked to the same MySQL database) that is feature rich and easy to use. what I'm trying to understand is where we are at with web-based frontends. I find that there are still so many events and features that I can make use of in a Windows Desktop GUI written in something like C#, VB.Net or MS Access. I don't have a lot of experience programming UI for web but it's my impression that it's still more difficult and takes longer to get similar or the same functionality using non-MS web technologies (I dislike ASP.net, sorry) as compared to programming the desktop portion in a traditional desktop application language like C#, VB.Net, or MS Access. jQuery and jQuery UI are definately making things easier. Also, there's very rich online applications like Google Docs and Zoho but it's my impression that these are programmed by some of the top web UI programmers around, not to mention that it takes longer to write it and intensive testing to make it work in all of your target browsers. It also takes extra time and code to "block" browsers that don't meet the requirements. What programming language would you recommend? I know I may not have given enough information here but I'm not sure what I'm missing. If you have questions just leave a comment below so I can edit this post and answer the questions.

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  • Rails architecture questions

    - by justinbach
    I'm building a Rails site that, among other things, allows users to build their own recipe repository. Recipes are entered either manually or via a link to another site (think epicurious, cooks.com, etc). I'm writing scripts that will scrape a recipe from these sites given a link from a user, and so far (legal issues notwithstanding) that part isn't giving me any trouble. However, I'm not sure where to put the code that I'm writing for these scraper scripts. My first thought was to put it in the recipes model, but it seems a bit too involved to go there; would a library or a helper be more appropriate? Also, as I mentioned, I'm building several different scrapers for different food websites. It seems to me that the elegant way to do this would be to define an interface (or abstract base class) that determines a set of methods for constructing a recipe object given a link, but I'm not sure what the best approach would be here, either. How might I build out these OO relationships, and where should the code go?

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  • Does OOP make sense for small scripts?

    - by Fabian
    I mostly write small scripts in python, about 50 - 250 lines of code. I usually don't use any objects, just straightforward procedural programming. I know OOP basics and I have used object in other programming languages before, but for small scripts I don't see how objects would improve them. But maybe that is just my limited experience with OOP. Am I missing something by not trying harder to use objects, or does OOP just not make a lot of sense for small scripts?

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  • How would you organize this in asp.net mvc?

    - by chobo
    I have an asp.net mvc 2.0 application that contains Areas/Modules like calendar, admin, etc... There may be cases where more than one area needs to access the same Repo, so I am not sure where to put the Data Access Layers and Repositories. First Option: Should I create Data Access Layer files (Linq to SQL in my case) with their accompanying Repositories for each area, so each area only contains the Tables, and Repositories needed by those areas. The benefit is that everything needed to run that module is one place, so it is more encapsulated (in my mind anyway). The downside is that I may have duplicate queries, because other modules may use the same query. Second Option Or, would it be better to place the DAL and Repositories outside the Area's and treat them as Global? The advantage is I won't have any duplicate queries, but I may be loading a lot of unnecessary queries and DAL tables up for certain modules. It is also more work to reuse or modify these modules for future projects (though the chance of reusing them is slim to none :)) Which option makes more sense? If someone has a better way I'd love to hear it. Thanks!

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  • Best Practices & Considerations when writing HTML Emails

    - by Jonathan Sampson
    I've been developing websites for over a decade now, but quickly found that many of my habits in developing for the web are useless when developing for email clients. This has caused me an enormous amount of frustration, so I thought I would ask a question that would hopefully surface the best practices and necessary considerations for others like myself who may find themselves designing for gmail, outlook, etc. from time to time. Example: <style>...</style> vs inline CSS. In short: what transfers over from the web-world to the email-world, and what doesn't.

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  • How do i free objects in C#

    - by assassin
    Hi, Can anyone please tell me how I can free objects in C#? For example, I have an object: Object obj1 = new Object(); //Some code using obj1 //Here I would like to free obj1, after it is no longer required and also more importantly its scope is the full run time of the program. Thanks for all your help

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  • What is a good architecture for a Lift-JPA application?

    - by egervari
    I was wondering what is the best practice for a JPA model in Lift? I noticed that in the jpa demo application, there is just a Model object that is like a super object that does everything. I don't think this can be the most scalable approach, no? Is it is wise to still do the DAO pattern in Lift? For example, there's some code that looks a tad bloated and could be simplified across all model objects: Model.remove(Model.getReference(classOf[Author], someId)) Could be: AuthorDao.remove(someId) I'd appreciate any tips for setting up something that will work with the way Lift wants to work and is also easy to organize and maintain. Preferably from someone who has actually used JPA on a medium to large Lift site rather than just postulating what Spring does (we know how to do that) ;) The first phase of development will be around 30-40 tables, and will eventually get to over 100... we need a scalable, neat approach.

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  • How do I link ASP.NET membership/role users to tables in db?

    - by SnapConfig.com
    I am going to use forms authentication but I want to be able to link the asp.net users to some tables in the db for example If I have a class and students (as roles) I'll have a class students table. I'm planning to put in a Users table containing a simple int userid and ASP.NET username in there and put userid wherever I want to link the users. Does that sound good? any other options of modeling this? it does sound a bit convoluted?

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  • Error: Too Many Arguments Specified when Inserting Values from ASP.NET to SQL Server

    - by SidC
    Good Afternoon All, I have a wizard control that contains 20 textboxes for part numbers and another 20 for quantities. I want the part numbers and quantities loaded into the following table: USE [Diel_inventory] GO /****** Object: Table [dbo].[QUOTEDETAILPARTS] Script Date: 05/09/2010 16:26:54 ******/ SET ANSI_NULLS ON GO SET QUOTED_IDENTIFIER ON GO CREATE TABLE [dbo].[QUOTEDETAILPARTS]( [QuoteDetailPartID] [int] IDENTITY(1,1) NOT NULL, [QuoteDetailID] [int] NOT NULL, [PartNumber] [float] NULL, [Quantity] [int] NULL, CONSTRAINT [pkQuoteDetailPartID] PRIMARY KEY CLUSTERED ( [QuoteDetailPartID] ASC )WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY] ) ON [PRIMARY] GO ALTER TABLE [dbo].[QUOTEDETAILPARTS] WITH CHECK ADD CONSTRAINT [fkQuoteDetailID] FOREIGN KEY([QuoteDetailID]) REFERENCES [dbo].[QUOTEDETAIL] ([ID]) ON UPDATE CASCADE ON DELETE CASCADE GO Here's the snippet from my sproc for this insert: set @ID=scope_identity() Insert into dbo.QuoteDetailParts (QuoteDetailPartID, QuoteDetailID, PartNumber, Quantity) values (@ID, @QuoteDetailPartID, @PartNumber, @Quantity) When I run the ASPX page, I receive an error that there are too many arguments specified for my stored procedure. I understand why I'm getting the error, given the above table layout. However, I need help in structuring my insert syntax to look for values in all 20 PartNumber and Quantity field pairs. Thanks, Sid

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  • What is the best practice for accessing Model using MVVM pattern

    - by Dzenand
    I have a database that communicates with webservices with my Model (own thread) and exposes Data Objects. My UI application consists of different Views and ViewModels and Custom Controls. I'm using ServiceProvider (IServiceProvider) to access the Model and route the events to the UI thread. Communication between the ViewModels is handeled by a Messenger. Is this way to go? I was also wondering what is the best way to strucutre the DataObjects At the moment i have the DataObjects that have a hierarchy structure but does not support INotifyProperty though the children list are of type of ObservableCollection. I have no possiblity to implement notifypropertychange on the properties. I was wondering the best way of making them MVVM friendly. Implementing a partial class and adding all the properties or commands that are necessary or wrapping all the DataObjects and keep the Model list and MVVM list in sync. All thoughts and ideas are appreciated.

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  • Java - Calling all methods of a class

    - by Thomas Eschemann
    I'm currently working on an application that has to render several Freemarker templates. So far I have a Generator class that handles the rendering. The class looks more or less like this: public class Generator { public static void generate(…) { renderTemplate1(); renderTemplate2(); renderTemplate3(); } private static void render(…) { // renders the template } private static void renderTemplate1() { // Create config object for the rendering // and calls render(); }; private static void renderTemplate1() { // Create config object for the rendering // and calls render(); }; … } This works, but it doesn't really feel right. What I would like to do is create a class that holds all the renderTemplate...() methods and then call them dynamically from my Generator class. This would make it cleaner and easier to extend. I was thinking about using something like reflection, but it doesn't really feel like a good solution either. Any idea on how to implement this properly ?

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  • 0/1 Knapsack with irrational weights

    - by user356106
    Consider the 0/1 knapsack problem. The standard Dynamic Programming algorithm applies only when the capacity as well as the weights to fill the knapsack with are integers/ rational numbers. What do you do when the capacity/weights are irrational? The issue is that we can't memoize like we do for integer weights because we may need potentially infinite decimal places for irrational weights - leading to an infinitely large number of columns for the Dynamic Programming Table . Is there any standard method for solving this? Any comments on the complexity of this problem? Any heuristics? What about associated recurrences like (for example): f(x)=1, for x< sqrt(2) f(x)=f(x-sqrt(2))+sqrt(3)

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  • What strategies are efficient to handle concurrent reads on heterogeneous multi-core architectures?

    - by fabrizioM
    I am tackling the challenge of using both the capabilities of a 8 core machine and a high-end GPU (Tesla 10). I have one big input file, one thread for each core, and one for the the GPU handling. The Gpu thread, to be efficient, needs a big number of lines from the input, while the Cpu thread needs only one line to proceed (storing multiple lines in a temp buffer was slower). The file doesn't need to be read sequentially. I am using boost. My strategy is to have a mutex on the input stream and each thread locks - unlocks it. This is not optimal because the gpu thread should have a higher precedence when locking the mutex, being the fastest and the most demanding one. I can come up with different solutions but before rush into implementation I would like to have some guidelines. What approach do you use / recommend ?

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  • Table with unequal rows in XUL layout

    - by Michael
    Trying to get something similar for Firefox extension using XUL. The most difficult part is the grid with unequal number of rows. I tried <grid> but it didn't work well. Also don't want to use HTML inside of XUL. Any ideas how to build such table?

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  • Stupid java question: Is it a method?

    - by Stefan
    Hello, I'm no Java guy, so I ask myself what this means: public Button(Light light) { this.light = light; } Is Button a method? I ask myself, because it takes an input parameter light. But if it was a method, why would it begin with a capital letter and has no return data type? Here comes the full example: public class Button { private Light light; public Button(Light light) { this.light = light; } public void press() { light.turnOn(); } } I know, this question is really trivial. However, I have nothing to do with Java and haven't found a description for the Button thing above. I'm just interested.

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  • ruby on rails has_many through relationship

    - by BennyB
    Hi i'm having a little trouble with a has_many through relationship for my app and was hoping to find some help. So i've got Users & Lectures. Lectures are created by one user but then other users can then "join" the Lectures that have been created. Users have their own profile feed of the Lectures they have created & also have a feed of Lectures friends have created. This question however is not about creating a lecture but rather "Joining" a lecture that has been created already. I've created a "lecturerelationships" model & controller to handle this relationship between Lectures & the Users who have Joined (which i call "actives"). Users also then MUST "Exit" the Lecture (either by clicking "Exit" or navigating to one of the header navigation links). I'm grateful if anyone can work through some of this with me... I've got: Users.rb model Lectures.rb model Users_controller Lectures_controller then the following model lecturerelationship.rb class lecturerelationship < ActiveRecord::Base attr_accessible :active_id, :joinedlecture_id belongs_to :active, :class_name => "User" belongs_to :joinedlecture, :class_name => "Lecture" validates :active_id, :presence => true validates :joinedlecture_id, :presence => true end lecturerelationships_controller.rb class LecturerelationshipsController < ApplicationController before_filter :signed_in_user def create @lecture = Lecture.find(params[:lecturerelationship][:joinedlecture_id]) current_user.join!(@lecture) redirect_to @lecture end def destroy @lecture = Lecturerelationship.find(params[:id]).joinedlecture current_user.exit!(@user) redirect_to @user end end Lectures that have been created (by friends) show up on a users feed in the following file _activity_item.html.erb <li id="<%= activity_item.id %>"> <%= link_to gravatar_for(activity_item.user, :size => 200), activity_item.user %><br clear="all"> <%= render :partial => 'shared/join', :locals => {:activity_item => activity_item} %> <span class="title"><%= link_to activity_item.title, lecture_url(activity_item) %></span><br clear="all"> <span class="user"> Joined by <%= link_to activity_item.user.name, activity_item.user %> </span><br clear="all"> <span class="timestamp"> <%= time_ago_in_words(activity_item.created_at) %> ago. </span> <% if current_user?(activity_item.user) %> <%= link_to "delete", activity_item, :method => :delete, :confirm => "Are you sure?", :title => activity_item.content %> <% end %> </li> Then you see I link to the the 'shared/join' partial above which can be seen in the file below _join.html.erb <%= form_for(current_user.lecturerelationships.build(:joinedlecture_id => activity_item.id)) do |f| %> <div> <%= f.hidden_field :joinedlecture_id %> </div> <%= f.submit "Join", :class => "btn btn-large btn-info" %> <% end %> Some more files that might be needed: config/routes.rb SampleApp::Application.routes.draw do resources :users do member do get :following, :followers, :joined_lectures end end resources :sessions, :only => [:new, :create, :destroy] resources :lectures, :only => [:create, :destroy, :show] resources :relationships, :only => [:create, :destroy] #for users following each other resources :lecturerelationships, :only => [:create, :destroy] #users joining existing lectures So what happens is the lecture comes in my activity_feed with a Join button option at the bottom...which should create a lecturerelationship of an "active" & "joinedlecture" (which obviously are supposed to be coming from the user & lecture classes. But the error i get when i click the join button is as follows: ActiveRecord::StatementInvalid in LecturerelationshipsController#create SQLite3::ConstraintException: constraint failed: INSERT INTO "lecturerelationships" ("active_id", "created_at", "joinedlecture_id", "updated_at") VALUES (?, ?, ?, ?) Also i've included my user model (seems the error is referring to it) user.rb class User < ActiveRecord::Base attr_accessible :email, :name, :password, :password_confirmation has_secure_password has_many :lectures, :dependent => :destroy has_many :lecturerelationships, :foreign_key => "active_id", :dependent => :destroy has_many :joined_lectures, :through => :lecturerelationships, :source => :joinedlecture before_save { |user| user.email = email.downcase } before_save :create_remember_token validates :name, :presence => true, :length => { :maximum => 50 } VALID_EMAIL_REGEX = /\A[\w+\-.]+@[a-z\d\-.]+\.[a-z]+\z/i validates :email, :presence => true, :format => { :with => VALID_EMAIL_REGEX }, :uniqueness => { :case_sensitive => false } validates :password, :presence => true, :length => { :minimum => 6 } validates :password_confirmation, :presence => true def activity # This feed is for "My Activity" - basically lectures i've started Lecture.where("user_id = ?", id) end def friendactivity Lecture.from_users_followed_by(self) end # lECTURE TO USER (JOINING) RELATIONSHIPS def joined?(selected_lecture) lecturerelationships.find_by_joinedlecture_id(selected_lecture.id) end def join!(selected_lecture) lecturerelationships.create!(:joinedlecture_id => selected_lecture.id) end def exit!(selected_lecture) lecturerelationships.find_by_joinedlecture_id(selected_lecture.id).destroy end end Thanks for any and all help - i'll be on here for a while so as mentioned i'd GREATLY appreciate someone who may have the time to work through my issues with me...

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