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• CQRS - The query side

  - by mattcodes

  A lot of the blogsphere articles related to CQRS (command query repsonsibility) seperation seem to imply that all screens/viewmodels are flat. e.g. Name, Age, Location Of Birth etc.. and thus the suggestion that implementation wise we stick them into fast read source etc.. single table per view mySQL etc.. and pull them out with something like primitive SqlDataReader, kick that nasty nhibernate ORM etc.. However, whilst I agree that domain models dont mapped well to most screens, many of the screens that I work with are more dimensional, and Im sure this is pretty common in LOB apps. So my question is how are people handling screen where by for example it displays a summary of customer details and then a list of their orders with a [more detail] link etc.... I thought about keeping with the straight forward SQL query to the Query Database breaking off the outer join so can build a suitable ViewModel to View but it seems like overkill? Alternatively (this is starting to feel yuck) in CustomerSummaryView table have a text/big (whatever the type is in your DB) column called Orders, and the columns for the Order summary screen grid are seperated by , and rows by |. Even with XML datatype it still feeel dirty. Any thoughts on an optimal practice?

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• MVC pattern and State Machine

  - by topright

  I think of a game as a state machine. Game States separate I/O processing, game logic and rendering into different classes: while (game_loop) { game->state->io_events(this); game->state->logic(this); game->state->rendering(); } You can easily change a game state in this approach. MVC separation works in more complex way: while (game_loop) { game->cotroller->io_events(this); game->model->logic(this); game->view->rendering(); } So changing Game States becomes error prone task (switch 3 MVC objects, not 1). What are practical ways of combining these 2 concepts?

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• How do we greatly optimize our MySQL database (or replace it) when using joins?

  - by jkaz

  Hi there, This is the first time I'm approaching an extremely high-volume situation. This is an ad server based on MySQL. However, the query that is used incorporates a lot of JOINs and is generally just slow. (This is Rails ActiveRecord, btw) sel = Ads.find(:all, :select = '*', :joins = "JOIN campaigns ON ads.campaign_id = campaigns.id JOIN users ON campaigns.user_id = users.id LEFT JOIN countries ON countries.campaign_id = campaigns.id LEFT JOIN keywords ON keywords.campaign_id = campaigns.id", :conditions = [flashstr + "keywords.word = ? AND ads.format = ? AND campaigns.cenabled = 1 AND (countries.country IS NULL OR countries.country = ?) AND ads.enabled = 1 AND campaigns.dailyenabled = 1 AND users.uenabled = 1", kw, format, viewer['country'][0]], :order = order, :limit = limit) My questions: Is there an alternative database like MySQL that has JOIN support, but is much faster? (I know there's Postgre, still evaluating it.) Otherwise, would firing up a MySQL instance, loading a local database into memory and re-loading that every 5 minutes help? Otherwise, is there any way I could switch this entire operation to Redis or Cassandra, and somehow change the JOIN behavior to match the (non-JOIN-able) nature of NoSQL? Thank you!

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• Suggest Cassandra data model for an existing schema

  - by Andriy Bohdan

  Hello guys! I hope there's someone who can help me suggest a suitable data model to be implemented using nosql database Apache Cassandra. More of than I need it to work under high loads and large amounts of data. Simplified I have 3 types of objects: Product Tag ProductTag Product: key - string key name - string .... - some other fields Tag: key - string key name - unique tag words ProductTag: product_key - foreign key referring to product tag_key - foreign key referring to tag rating - this is rating of tag for this product Each product may have 0 or many tags. Tag may be assigned to 1 or many products. Means relation between products and tags is many-to-many in terms of relational databases. Value of "rating" is updated "very" often. I need to be run the following queries Select objects by keys Select tags for product ordered by rating Select products by tag order by rating Update rating by product_key and tag_key The most important is to make these queries really fast on large amounts of data, considering that rating is constantly updated.

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• Why use SQL database?

  - by martinthenext

  I'm not quite sure stackoverflow is a place for such a general question, but let's give it a try. Being exposed to the need of storing application data somewhere, I've always used MySQL or sqlite, just because it's always done like that. As it seems like the whole world is using these databases, most of all software products, frameworks, etc. It is rather hard for a beginning developer like me to ask a question - why? Ok, say we have some object-oriented logic in our application, and objects are related to each other somehow. We need to map this logic to the storage logic, so we need relations between database objects too. This leads us to using relational database and I'm ok with that - to put it simple, our database rows sometimes will need to have references to other tables' rows. But why do use SQL language for interaction with such a database? SQL query is a text message. I can understand this is cool for actually understanding what it does, but isn't it silly to use text table and column names for a part of application that no one ever seen after deploynment? If you had to write a data storage from scratch, you would have never used this kind of solution. Personally, I would have used some 'compiled db query' bytecode, that would be assembled once inside a client application and passed to the database. And it surely would name tables and colons by id numbers, not ascii-strings. In the case of changes in table structure those byte queries could be recompiled according to new db schema, stored in XML or something like that. What are the problems of my idea? Is there any reason for me not to write it myself and to use SQL database instead?

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• GRAPH PROBLEM: find an algorithm to determine the shortest path from one point to another in a recta

  - by newba

  I'm getting such an headache trying to elaborate an appropriate algorithm to go from a START position to a EXIT position in a maze. For what is worth, the maze is rectangular, maxsize 500x500 and, in theory, is resolvable by DFS with some branch and bound techniques ... 10 3 4 7 6 3 3 1 2 2 1 0 2 2 2 4 2 2 5 2 2 1 3 0 2 2 2 2 1 3 3 4 2 3 4 4 3 1 1 3 1 2 2 4 2 2 1 Output: 5 1 4 2 Explanation: Our agent looses energy every time he gives a step and he can only move UP, DOWN, LEFT and RIGHT. Also, if the agent arrives with a remaining energy of zero or less, he dies, so we print something like "Impossible". So, in the input 10 is the initial agent's energy, 3 4 is the START position (i.e. column 3, line 4) and we have a maze 7x6. Think this as a kind of labyrinth, in which I want to find the exit that gives the agent a better remaining energy (shortest path). In case there are paths which lead to the same remaining energy, we choose the one which has the small number of steps, of course. I need to know if a DFS to a maze 500x500 in the worst case is feasible with these limitations and how to do it, storing the remaining energy in each step and the number of steps taken so far. The output means the agent arrived with remaining energy= 5 to the exit pos 1 4 in 2 steps. If we look carefully, in this maze it's also possible to exit at pos 3 1 (column 3, row 1) with the same energy but with 3 steps, so we choose the better one. With these in mind, can someone help me some code or pseudo-code? I have troubles working this around with a 2D array and how to store the remaining energy, the path (or number of steps taken)....

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• I cannot grok MVC, what it is, and what it is not?

  - by Hao

  I cannot grok what MVC is, what mindset or programming model should I acquire so MVC stuff can instantly "lightbulb" on my head? If not instantly, what simple programs/projects should I try to do first so I can apply the neat things MVC brings to programming. OOP is intuitive and easier, object is all around us, and the benefits of code reuse using OOP-paradigm instantly click to anyone. You can probably talk to anybody about OOP in a few minutes and lecture some examples and they would get it. While OOP somehow raise the intuitiveness aspect of programming, MVC seems to do the opposite. I'm getting negative thoughts that some future employers(or even clients) would look down upon me for not using MVC technology. Though I probably get the skinnable aspect of MVC, but when I try to apply it to my own project, I don't know where to start. And also some programmers even have diverging views on how to accomplish MVC properly. Take this for instance from Jeff's post about MVC: The view is simply how you lay the data out, how it is displayed. If you want a subset of some data, for example, my opinion is that is a responsibility of the model. So maybe some programmers use MVC, but they somehow inadvertently use the View or the Controller to extract a subset of data. Why we can't have a definitive definition of what and how to accomplish MVC properly? And also, when I search for MVC .NET programs, most of it applies to web programs, not desktop apps, this intrigue me further. My guess is, this is most advantageous to web apps, there's not much problem about intermixed view(html) and controller(program code) in desktop apps.

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• Algorithm to represent Decision tables

  - by driveBy

  What would be the best algorithm to use if you wanted to store Decision tables in code, i've looked at the Adjacency matrix and Binary tree would anyone consider this to be the right direction? What other choices to I have?

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• SDL side-scroller scrolls inconsistantly

  - by SDLFunTimes

  So I'm working on an upgrade from my previous project (that I posted here for code review) this time implementing a repeating background (like what is used on cartoons) so that SDL doesn't have to load really big images for a level. There's a strange inconsistency in the program, however: the first time the user scrolls all the way to the right 2 less panels are shown than is specified. Going backwards (left) the correct number of panels is shown (that is the panels repeat the number of times specified in the code). After that it appears that going right again (once all the way at the left) the correct number of panels is shown and same going backwards. Here's some selected code and here's a .zip of all my code constructor: Game::Game(SDL_Event* event, SDL_Surface* scr, int level_w, int w, int h, int bpp) { this->event = event; this->bpp = bpp; level_width = level_w; screen = scr; w_width = w; w_height = h; //load images and set rects background = format_surface("background.jpg"); person = format_surface("person.png"); background_rect_left = background->clip_rect; background_rect_right = background->clip_rect; current_background_piece = 1; //we are displaying the first clip rect_in_view = &background_rect_right; other_rect = &background_rect_left; person_rect = person->clip_rect; background_rect_left.x = 0; background_rect_left.y = 0; background_rect_right.x = background->w; background_rect_right.y = 0; person_rect.y = background_rect_left.h - person_rect.h; person_rect.x = 0; } and here's the move method which is probably causing all the trouble: void Game::move(SDLKey direction) { if(direction == SDLK_RIGHT) { if(move_screen(direction)) { if(!background_reached_right()) { //move background right background_rect_left.x += movement_increment; background_rect_right.x += movement_increment; if(rect_in_view->x >= 0) { //move the other rect in to fill the empty space SDL_Rect* temp; other_rect->x = -w_width + rect_in_view->x; temp = rect_in_view; rect_in_view = other_rect; other_rect = temp; current_background_piece++; std::cout << current_background_piece << std::endl; } if(background_overshoots_right()) { //sees if this next blit is past the surface //this is used only for re-aligning the rects when //the end of the screen is reached background_rect_left.x = 0; background_rect_right.x = w_width; } } } else { //move the person instead person_rect.x += movement_increment; if(get_person_right_side() > w_width) { //person went too far right person_rect.x = w_width - person_rect.w; } } } else if(direction == SDLK_LEFT) { if(move_screen(direction)) { if(!background_reached_left()) { //moves background left background_rect_left.x -= movement_increment; background_rect_right.x -= movement_increment; if(rect_in_view->x <= -w_width) { //swap the rect in view SDL_Rect* temp; rect_in_view->x = w_width; temp = rect_in_view; rect_in_view = other_rect; other_rect = temp; current_background_piece--; std::cout << current_background_piece << std::endl; } if(background_overshoots_left()) { background_rect_left.x = 0; background_rect_right.x = w_width; } } } else { //move the person instead person_rect.x -= movement_increment; if(person_rect.x < 0) { //person went too far left person_rect.x = 0; } } } } without the rest of the code this doesn't make too much sense. Since there is too much of it I'll upload it here for testing. Anyway does anyone know how I could fix this inconsistency?

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• Most Astonishing Violation of the Principle of Least Astonishment

  - by Adam Liss

  The Principle of Least Astonishment suggests that a system should operate as a user would expect it to, as much as possible. In other words, it should never "astonish" the user with unexpected behavior. In your experience as the "astonishee," what types of systems are the worst offenders, and if you were the project manager, how would you correct the problem? Bonus if your answer describes how you'd retrain the developers!

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• Perl vs Python: implementation of algorithms to deal with advanced data structures

  - by user350571

  I'm learning perl and everytime I search for perl stuff in the internet I get some random page with people saying that perl should die because code written in it looks like a lesson in steganography. Then they say that python is clean and stuff like that. Now, I know that those comparisons are always stupid and made by fellows that feel that languages are a extension of their boring personality so, let me ask instead: can you give me the implementation of a widely known algorithm to deal with a data structure like red-black trees in both languages so I can compare?

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• O(log n) algorithm for computing rank of union of two sorted lists?

  - by Eternal Learner

  Given two sorted lists, each containing n real numbers, is there a O(log?n) time algorithm to compute the element of rank i (where i coresponds to index in increasing order) in the union of the two lists, assuming the elements of the two lists are distinct? I can think of using a Merge procedure to merge the 2 lists and then find the A[i] element in constant time. But the Merge would take O(n) time. How do we solve it in O(log n) time?

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• Codechef practice question help needed - find trailing zeros in a factorial

  - by manugupt1

  I have been working on this for 24 hours now, trying to optimize it. The question is how to find the number of trailing zeroes in factorial of a number in range of 10000000 and 10 million test cases in about 8 secs. The code is as follows: #include<iostream> using namespace std; int count5(int a){ int b=0; for(int i=a;i>0;i=i/5){ if(i%15625==0){ b=b+6; i=i/15625; } if(i%3125==0){ b=b+5; i=i/3125; } if(i%625==0){ b=b+4; i=i/625; } if(i%125==0){ b=b+3; i=i/125; } if(i%25==0){ b=b+2; i=i/25; } if(i%5==0){ b++; } else break; } return b; } int main(){ int l; int n=0; cin>>l; //no of test cases taken as input int *T = new int[l]; for(int i=0;i<l;i++) cin>>T[i]; //nos taken as input for the same no of test cases for(int i=0;i<l;i++){ n=0; for(int j=5;j<=T[i];j=j+5){ n+=count5(j); //no of trailing zeroes calculted } cout<<n<<endl; //no for each trialing zero printed } delete []T; } Please help me by suggesting a new approach, or suggesting some modifications to this one.

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• How to Manage project in this scenario

  - by vijay.shad

  Hi All, I am working on a web application which has got good amount of static or pre-login pages. These pages can have some simple forms as well where we would like to capture the visitor's details. Post login, I have got my main application. I am confused about the development and deployment architecture of my application. Post login part of my application has a release cycle of 1-2 months while pre-login pages are to be updated on a weekly basis. It is difficult to make a release of pre-login pages as the overall war also contains post-login application & which sometimes is not release ready. Currently, I have got both these parts bundled in the single war project. Please help me by letting me know the best practices whereby I can achieve following: Manage the releases of these two parts independently. I am using Maven. So is there a way I can share the resources, such as CSS, images etc between these two parts. Header and footer of my application is going to be same on pre-login & post-login pages. I was thinking of deploying these apps as two war files in my tomcat container. But then how will I manage the common resources like Css, images etc. Rgds Vijay

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• Need help choosing database server

  - by The Pretender

  Good day everyone. Recently I was given a task to develop an application to automate some aspects of stocks trading. While working on initial architecture, the database dilemma emerged. What I need is a fast database engine which can process huge amounts of data coming in very fast. I'm fairly experienced in general programming, but I never faced a task of developing a high-load database architecture. I developed a simple MSSQL database schema with several many-to-many relationships during one of my projects, but that's it. What I'm looking for is some advice on choosing the most suitable database engine and some pointers to various manuals or books which describe high-load database development. Specifics of the project are as follows: OS: Windows NT family (Server 2008 / 7) Primary platform: .NET with C# Database structure: one table to hold primary items and two or three tables with foreign keys to the first table to hold additional information. Database SELECT requirements: Need super-fast selection by foreign keys and by combination of foreign key and one of the columns (presumably DATETIME) Database INSERT requirements: The faster the better :) If there'll be significant performance gain, some parts can be written in C++ with managed interfaces to the rest of the system. So once again: given all that stuff I just typed, please give me some advice on what the best database for my project is. Links or references to some manuals and books on the subject are also greatly appreciated. EDIT: I'll need to insert 3-5 rows in 2 tables approximately once in 30-50 milliseconds and I'll need to do SELECT with 0-2 WHERE clauses queries with similar rate.

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• Synonym for "Many-to-Many" relationship (relational databases)

  - by Byron

  What's a synonym for a "many-to-many" relationship? I've finished writing an object-relational mapper but I'm still stumped as to what to name the function that adds that relation. addParent() and addChild() seemed quite logical for the many-to-one/one-to-many and addSuperclass() for one-to-one inheritance, but addManyToMany() would sound quite unintuitive to an object-oriented programmer. addSibling() or addCousin() doesn't really make sense either. Any suggestions? And before you dismiss this as a non-programming question, please remember that consistent naming schemes and encapsulation are pretty integral to programming :)

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• Why is it bad to use boolean flags in databases? And what should be used instead?

  - by David Chanin

  I've been reading through some of guides on database optimization and best practices and a lot of them suggest not using boolean flags at all in the DB schema (ex http://forge.mysql.com/wiki/Top10SQLPerformanceTips). However, they never provide any reason as to why this is bad. Is it a peformance issue? is it hard to index or query properly? Furthermore, if boolean flags are bad, what should you use to store boolean values in a database? Is it better to store boolean flags as an integer and use a bitmask? This seems like it would be less readable.

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• Evenly select N elems from array

  - by ninuhadida

  Hi, I need to evenly select n elements from an array. I guess the best way to explain is by example. say I have: array [0,1,2,3,4] and I need to select 3 numbers.. 0,3,4. of course, if the array length <= n, I just need to return the whole array. I'm pretty sure there's a defined algorithm for this, been trying to search, and I took a look at Introduction to algorithms but couldn't find anything that met my needs (probably overlooked it) The problem I'm having is that I can't figure out a way to scale this up to any array [ p..q ], selecting N evenly elements. note: I can't just select the even elements from the example above.. A couple other examples; array[0,1,2,3,4,5,6], 3 elements ; I need to get 0,3,6 array[0,1,2,3,4,5], 3 elements ; I need to get 0, either 2 or 3, and 5

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• What open source database platform is most easily transferred from my personal machine into a window

  - by Tom

  I would like eventual interaction with MS Dynamics SL and/or MindTouch Core (running on WMware) for eventual intranet and/or internet display. I guess I am asking for front and back end recommendations for a database I am constructing, but since this is my first major project I would greatly appreciate any help and advice. I would also love an opportunity to learn a new language so the code base could be in any language. I do have a few more related questions for discussion; What is the viability of using Google hosting to provide the service to the public for free? Should I implement plone or another CMS if I have a large amount of output? Is there a structuring questionnaire or standards publication I could reference? Does UML diagramming provide additional options for portability? Thank you.

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• CSS and Page Size and Horizontal Scrollbar

  - by Steve

  When I added some CSS stuff to my page, the page got wider and and horizontal appeared even the content is very minimal and does not require to scroll. How can I remove it. I used the following to remove it but it appears as a hack and I am just playing around with CSS, so is there a proper way to do this

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• Algorithm for max integer in an array of integers

  - by gagneet

  Explain which algorithm you would use to implement a function that takes an array of integers and returns the maximum integer in the collection, assuming that the length of the array is less than 1000. Would you use Bubble Sort or Merge Sort and Why? Also, what happens to the above algorithm choice, if the array length is greater than 1000?

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• iphone: caching and updating xml fields

  - by pJosh

  Thanks for your help. Here I have another question. I get the data through XMLParsing, now I want to store it in iphone's cache, and the XML Fields are updates every 12 hours.how can i check that XML Fields are change or not? and how can I store the data in iphone's cache memory so that evry it does not has to interact with web. Can anybody please help me???

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• How to maintain an ordered table with Core Data (or SQL) with insertions/deletions?

  - by Jean-Denis Muys

  This question is in the context of Core Data, but if I am not mistaken, it applies equally well to a more general SQL case. I want to maintain an ordered table using Core Data, with the possibility for the user to: reorder rows insert new lines anywhere delete any existing line What's the best data model to do that? I can see two ways: 1) Model it as an array: I add an int position property to my entity 2) Model it as a linked list: I add two one-to-one relations, next and previous from my entity to itself 1) makes it easy to sort, but painful to insert or delete as you then have to update the position of all objects that come after 2) makes it easy to insert or delete, but very difficult to sort. In fact, I don't think I know how to express a Sort Descriptor (SQL ORDER BY clause) for that case. Now I can imagine a variation on 1): 3) add an int ordering property to the entity, but instead of having it count one-by-one, have it count 100 by 100 (for example). Then inserting is as simple as finding any number between the ordering of the previous and next existing objects. The expensive renumbering only has to occur when the 100 holes have been filled. Making that property a float rather than an int makes it even better: it's almost always possible to find a new float midway between two floats. Am I on the right track with solution 3), or is there something smarter?

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• Why eGet() in EMF returns Object rather than EObject?

  - by Gabriel Šcerbák

  I am working on some code using the EMF framework in Java, but it is really hard to use, e.g. I cannot implement OCL-like query API on top of EMF which would be type-safe. One of the reasons is that eGet() for a EStructuralFeature return just an Object, not EObject. So anything I would write must use much of null checking, type checking and type casting which is unsafe, not performant and cannot be generalized in a reusable way. Why doesn't EMF generate dummy implementations with EObject wrappers for arbitrary Object value? Implementing the EObject and hence the EClass interfaces even with simple throw UnsupportedOperationException is really a pain (the APIs are too big). The same holds for the eContainer() method which makes navigatinng the model upwards painful.

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• Working with foreigh keys - cannot insert

  - by Industrial

  Hi everyone! Doing my first tryouts with foreign keys in a mySQL database and are trying to do a insert, that fails for this reason: Integrity constraint violation: 1452 Cannot add or update a child row: a foreign key constraint fails Does this mean that foreign keys restrict INSERTS as well as DELETES and/or UPDATES on each table that is enforced with foreign keys relations? Thanks!

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