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  • What is design principle behind Servlets being Singleton

    - by Sandeep Jindal
    A servlet container "generally" create one instance of a servlet and different threads of the same instance to serve multiple requests. (I know this can be changed using deprecated SingleThreadModel and other features, but this is the usual way). I thought, the simple reason behind this is performance gain, as creating threads is better than creating instances. But it seems this is not the reason. On the other hand, creating instances have little advantage that developers never have to worry about thread safety. I am trying to understand the reason for this decision over the trade-off of thread-safety.

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  • Database Design: A proper table design for large number of column values.

    - by Jake
    I wish to perform an experiment many different times. After every trial, I am left with a "large" set of output statistics -- let's say, 1000. I would like to store the outputs of my experiments in a table, but what's the best way...? Option 1 Have a table with 1000 columns. Seems like a bad idea. What if the number of statistics one day exceeds the maximum number of columns? Option 2 Have a table with three columns. Let's say, ID, StatisticType, and StatisticValue. That way, you can have as many statistics as you want. However, reading a single experiments statistics becomes more complicated. Moreover, what if different statistics are different data types?? Any suggestions?

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  • Code Design Process?

    - by user156814
    I am going to be working on a project, a web application. I was reading 37signals getting real pamphlet online (http://gettingreal.37signals.com/), and I understand the recommended process to build the entire website. Brainstorm, sketch, HTML, code. They touch on each process lightly, but they never really talk much about the coding process (all they say is to keep code lean). I've been reading about different ways to go about it (top to bottom, bottom to top) but I dont know much about each way. I even read somewhere that one should write tests for the code before they actually write the code??? WHAT? What coding process should one follow when building an application. if its necessary, I'm using PHP and a framework.

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  • design question for transportation agency/workflow system

    - by George2
    Hello everyone, I am designing a transportation agency/workflow system, and it including 3 types of people, customer who requests to transport some stuff, drivers who deliver the stuff, and truck manager who manages transport source/destination truck coordination and communicates/organizes drivers. The system is expected to be a web site, and 3 kinds of people could use the web site to submit request, accept request, monitor status of specific stuff transportation, etc. The web site is more like an open agency or a workflow system. I am wondering whether there are any existing technologies, tools or projects (better to be open source, but not a must) which I could build my application faster based on? I prefer to use .Net technologies, but not a must. thanks in advance, George

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  • table design for storing large number of rows

    - by hyperboreean
    I am trying to store in a postgresql database some unique identifiers along with the site they have been seen on. I can't really decide which of the following 3 option to choose in order to be faster and easy maintainable. The table would have to provide the following information: the unique identifier which unfortunately it's text the sites on which that unique identifier has been seen The amount of data that would have to hold is rather large: there are around 22 millions unique identifiers that I know of. So I thought about the following designs of the table: id - integer identifier - text seen_on_site - an integer, foreign key to a sites table This approach would require around 22 mil multiplied by the number of sites. id - integer identifier - text seen_on_site_1 - boolean seen_on_site_2 - boolean ............ seen_on_site_n - boolean Hopefully the number of sites won't go past 10. This would require only the number of unique identifiers that I know of, that is around 20 millions, but it would make it hard to work with it from an ORM perspective. one table that would store only unique identifiers, like in: id - integer unique_identifier - text, one table that would store only sites, like in: id - integer site - text and one many to many relation, like: id - integer, unique_id - integer (fk to the table storing identifiers) site_id - integer (fk to sites table) another approach would be to have a table that stores unique identifiers for each site So, which one seems like a better approach to take on the long run?

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  • Commercial web application--scalable database design

    - by Rob Campbell
    I'm designing a set of web apps to track scientific laboratory data. Each laboratory has several members, each of whom will access both their own data and that of their laboratory as a whole. Many typical queries will thus be expected to return records of multiple members (e.g. my mouse, joe's mouse and sally's mouse). I think I have the database fairly well normalized. I'm now wondering how to ensure that users can efficiently access both their own data and their lab's data set when it is mixed among (hopefully) a whole ton of records from other labs. What I've come up with so far is that most tables will end with two fields: user_id and labgroup_id. The WHERE clause of any SELECT statement will include the appropriate reference to one of the id fields ("...WHERE 'labroup_id=n..." or "...WHERE user_id=n..."). My questions are: Is this an approach that will scale to 10^6 or more records? If so, what's the best way to use these fields in a query so that it most efficiently searches the relevant subset of the database? e.g. Should the first step in querying be to create a temporary table containing just the labgroup's data? Or will indexing using some combination of the id, user_id, and labroup_id fields be sufficient at that scale? I thank any responders very much in advance.

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  • Database design MySQL using foreign keys

    - by dscher
    I'm having some a little trouble understanding how to handle the database end of a program I'm making. I'm using an ORM in Kohana, but am hoping that a generalized understanding of how to solve this issue will lead me to an answer with the ORM. I'm writing a program for users to manage their stock research information. My tables are basically like so: CREATE TABLE tags( id INT AUTO_INCREMENT NOT NULL PRIMARY KEY, tags VARCHAR(30), UNIQUE(tags) ) ENGINE=INNODB DEFAULT CHARSET=utf8; CREATE TABLE stock_tags( id INT AUTO_INCREMENT NOT NULL PRIMARY KEY, tag_id INT NOT NULL, stock_id INT NOT NULL, FOREIGN KEY (tag_id) REFERENCES tags(id), FOREIGN KEY(stock_id) REFERENCES stocks(id) ON DELETE CASCADE ) ENGINE=INNODB DEFAULT CHARSET=utf8; CREATE TABLE notes( id INT AUTO_INCREMENT NOT NULL, stock_id INT NOT NULL, notes TEXT NOT NULL, FOREIGN KEY (stock_id) REFERENCES stocks(id) ON DELETE CASCADE, PRIMARY KEY(id) ) ENGINE=INNODB DEFAULT CHARSET=utf8; CREATE TABLE links( id INT AUTO_INCREMENT NOT NULL, stock_id INT NOT NULL, links VARCHAR(2083) NOT NULL, FOREIGN KEY (stock_id) REFERENCES stocks(id) ON DELETE CASCADE, PRIMARY KEY(id) ) ENGINE=INNODB DEFAULT CHARSET=utf8; How would I get all the attributes of a single stock, including its links, notes, and tags? Do I have to add links, notes, and tags columns to the stocks table and then how do you call it? I know this differs using an ORM and I'd assume that I can use join tables in SQL. Thanks for any help, this will really help me understand the issue a lot better.

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  • What is the best schema design for child collection with a "primary" entity

    - by erg39
    Here is the scenario: You have a Persons table with a one-to-many relationship with an Addresses table, where one of the Address rows is the "primary" Address. Is it better in a normalized schema to Use a Persons.PrimaryAddressID to access the "primary" Address for a Person or Use an Addresses.IsPrimary bit column to reference the "primary" Address for a Person via Addresses.PersonID or Other and why?

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  • Android listing design problem with cursors

    - by Priyank
    Hi. I have a following situation in my android app. I have an app that fetches messages from inbox, sent items and drafts based on search keywords. I use to accomplish this by fetching cursors for each manually based on selection by user and then populating them in a custom data holder object. Filter those results based on given keywords and then manually render view with respective data. Someone suggested that I should use a custom Cursor adapter to bind view and my cursor data. So I tried doing that. Now what I am doing is this: Fetch individual cursors for inbox, sent items and drafts. Merge them into one using Merge cursor and then pass that back to my CursorAdapter implmentation. Now where or how do I filter my cursor data based on keywords; because now binding will ensure that they are directly rendered to view on list. Also, some post fetching operation like fetching sender's contact pic and all will be something that I do not want to move to adapter. If I do all this processing in adapter; it'll be heavy and ugly. How could I have designed it better such that it performs and the responsibilities are shared and distributed. Any ideas will be helpful.

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  • Database Design Question

    - by deniz
    Hi, I am designing a database for a project. I have a table that has 10 columns, most of them are used whenever the table is accessed, and I need to add 3 more rows; View Count Thumbs Up (count) Thumbs Down (Count) which will be used on %90 of the queries when the table is accessed. So, my question is that whether it is better to break the table up and create new table which will have these 3 columns + Foreign ID, or just make it 13 columns and use no joins? Since these columns will be used frequently, I guess adding 3 more columns is better, but if I need to create 10 more columns which will be used %90 of the time, should I add them as well, or create a new table and use joins? I am not sure when to break the table if the columns are used very frequently. Do you have any suggestions? Thanks in advance,

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  • Good code architecture for this problem?

    - by RCIX
    I am developing a space shooter game with customizable ships. You can increase the strength of any number of properties of the ship via a pair of radar charts*. Internally, i represent each ship as a subclassed SpaceObject class, which holds a ShipInfo that describes various properties of that ship. I want to develop a relatively simple API that lets me feed in a block of relative strengths (from minimum to maximum of what the radar chart allows) for all of the ship properties (some of which are simplifications of the underlying actual set of properties) and get back a ShipInfo class i can give to a PlayerShip class (that is the object that is instantiated to be a player ship). I can develop the code to do the transformations between simplified and actual properties myself, but i would like some recommendations as to what sort of architecture to provide to minimize the pain of interacting with this translator code (i.e. no methods with 5+ arguments or somesuch other nonsense). Does anyone have any ideas? *=not actually implemented yet, but that's the plan.

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  • Table Design in mysql

    - by RIDDHI
    Hi everyone, I need to create one table, Description : i need to create table based on schedule like daily, weekly & monthly, columns are like : sno, startdate, enddate, day, scheduletype For example i ll take weekly data, for my point of view : From sunday to saturday (1 - 7 )Id i create.... So lots of posibilities are creates like (1,2)(1,3) ..(1,2,3)....up to n....this twise posibility only but that will created up to 7 posibility in one. so how can i store this posibility in mysql database? If any one have an issue get back to me... Thanks in advanced!!!! Riddhi

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  • Database Table design for Weekdays and Values

    - by Ved
    Guys, I would love to here your ideas on this. I am creating a table which will store weekly shift hours for employees. for example: Jon works 9:00am tp 9:00pm Monday , 10:00 AM to 5:00PM on Tuseday etc.... How should i go on designing this table. I thought of 2 options. (1) For every record I can have two lines for AM and PM and have columns for Monday to Sunday ID | ParentID | Type | Monday | Tuseday ......Sunday 1 | 1 | AM | 9:00 | 9:00 12:00 2 | 1 | PM | 9:00 | 5:00 02:00 3 | 2 | AM | 10:00 | 4 | 2 | PM | 10:00 | (2) I can save Preference in XML format in one column ID | Info 1 | |Hours|Monday|9:00 AM - 9:00PM|Monday|Tuseday........|Hours Any better ideas ? Thanks

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  • How to design websites for all display sizes

    - by katie bekell
    I like to use a lot of unique graphics on my pages, which often results in making different page sizes depending on available screen width/height. Here are two examples: http://www.uvm.edu/~areid/homesite/ - the image floats at the bottom of my screen but on a larger browser, the image floats near the middle making it look off. It looks best when the bottom of the window aligns with the bottom of the image www.stevenlebel.com - it loads two different pages depending on what monitor size is detected. This seems like a lot of redundant coding. My question is, how can I make sliced/Photoshop images transition well to different screen sizes. Does Photoshop allow you to make DIVS instead of tables? Can i make each of the slices created by Photoshop grow/shrink when the browser window size changes? If anyone has any input on creating websites like this I would be very interested to hear what they have to say. Thanks Katie

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  • Effecient data structure design

    - by Sway
    Hi there, I need to match a series of user inputed words against a large dictionary of words (to ensure the entered value exists). So if the user entered: "orange" it should match an entry "orange' in the dictionary. Now the catch is that the user can also enter a wildcard or series of wildcard characters like say "or__ge" which would also match "orange" The key requirements are: * this should be as fast as possible. * use the smallest amount of memory to achieve it. If the size of the word list was small I could use a string containing all the words and use regular expressions. however given that the word list could contain potentially hundreds of thousands of enteries I'm assuming this wouldn't work. So is some sort of 'tree' be the way to go for this...? Any thoughts or suggestions on this would be totally appreciated! Thanks in advance, Matt

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  • Design pattern to integrate Rails with a Comet server

    - by empire29
    I have a Ruby on Rails (2.3.5) application and an APE (Ajax Push Engine) server. When records are created within the Rails application, i need to push the new record out on applicable channels to the APE server. Records can be created in the rails app by the traditional path through the controller's create action, or it can be created by several event machines that are constantly monitoring various inputstream and creating records when they see data that meets a certain criteria. It seems to me that the best/right place to put the code that pushes the data out to the APE server (which in turn pushes it out to the clients) is in the Model's after_create hook (since not all record creations will flow through the controller's create action). The final caveat is I want to push a piece of formatted HTML out to the APE server (rather than a JSON representation of the data). The reason I want to do this is 1) I already have logic to produce the desired layout in existing partials 2) I don't want to create a javascript implementation of the partials (javascript that takes a JSON object and creates all the HTML around it for presentation). This would quickly become a maintenance nightmare. The problem with this is it would require "rendering" partials from within the Model (which im having trouble doing anyhow because they don't seem to have access to Helpers when they're rendered in this manner). Anyhow - Just wondering what the right way to go about organizing all of this is. Thanks

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  • Dependency Injection & Singleton Design pattern

    - by SysAdmin
    How do we identify when to use dependency injection or singleton pattern. I have read in lot of websites where they say "Use Dependency injection over singleton pattern". But I am not sure if I totally agree with them. For my small or medium scale projects I definitely see the use of singleton pattern straightforward. For example Logger. I could use Logger.GetInstance().Log(...) But, instead of this, why do I need to inject every class I create, with the logger's instance?.

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  • java api design - NULL or Exception

    - by srini.venigalla
    Is it better to return a null value or throw an exception from an API method? Returning a null requires ugly null checks all over, and cause a major quality problem if the return is not checked. Throwing an exception forces the user to code for the faulty condition, but since Java exceptions bubble up and force the caller code to handle them, in general, using custom exceptions may be a bad idea (specifically in java). Any sound and practical advice?

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  • Useful design patterns when dealing with spring 3 controllers

    - by Mat Banik
    Recently I was overlooking my controllers and they are bit of mess. I'd like to organize they way I set returning views Do more elegant mesageSource massaging back to the users and account for i18n Security checking, what user can access an what they can't Consistent way of calling the service layer And somehow bring consistency to the debugging lines. Do better job with error handling and serving it to the user. I'm already on mission to do security logging with AOP :) I'm just looking for patterns I could implement to help me to do all of the above. Or just some general advice in case no patterns apply, or advice on something I didn't mention but is common practice.

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  • MVC & Design patterns in C++

    - by theunanonim
    I have an assignment (university level) in C++ The application that was done so far: - MVC agenda - the views are command-line - Agenda contains a list of contacts - a contact may be a friend or an acquiantance - Agenda may contain also a Company that is a contact and may contain other contacts (sorry the code is already too big as I tried to keep the MVC aspect of the application, and I can't post it here or request your time to study it..) To do: - implement factory method pattern - implement observer pattern - implement strategy pattern - implement visitor pattern The evaluation will depend on the number of added patterns and places they have been added. Am I an idiot or this is the stupidies possible assignement ? If not, please help me with some basic tips.. which one where ? Best Regards. P.S. Sorry for my English

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  • SQL Server many-to-many design recommendation

    - by Jean-Philippe Brabant
    I have a SQL Server database with two table : Users and Achievements. My users can have multiple achievements so it a many-to-many relation. At school we learned to create an associative table for that sort of relation. That mean creating a table with a UserID and an AchivementID. But if I have 500 users and 50 achievements that could lead to 25 000 row. As an alternative, I could add a binary field to my Users table. For example, if that field contained 10010 that would mean that this user unlocked the first and the fourth achievements. Is their other way ? And which one should I use.

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  • Database design: objects with different attributes

    - by Álvaro G. Vicario
    I'm designing a product database where products can have very different attributes depending on their type, but attributes are fixed for each type and types are not manageable at all. E.g.: magazine: title, issue_number, pages, copies, close_date, release_date web_site: name, bandwidth, hits, date_from, date_to I want to use InnoDB and enforce database integrity as much as the engine allows. What's the recommended way to handle this? I hate those designs where tables have 100 columns and most of the values are NULL so I thought about something like this: product_type ============ product_type_id INT product_type_name VARCHAR product ======= product_id INT product_name VARCHAR product_type_id INT -> Foreign key to product_type.product_type_id valid_since DATETIME valid_to DATETIME magazine ======== magazine_id INT title VARCHAR product_id INT -> Foreign key to product.product_id issue_number INT pages INT copies INT close_date DATETIME release_date DATETIME web_site ======== web_site_id INT name VARCHAR product_id INT -> Foreign key to product.product_id bandwidth INT hits INT date_from DATETIME date_to DATETIME This can handle cascaded product deletion but... Well, I'm not fully convinced...

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  • Request for advice about class design, inheritance/aggregation

    - by Lasse V. Karlsen
    I have started writing my own WebDAV server class in .NET, and the first class I'm starting with is a WebDAVListener class, modelled after how the HttpListener class works. Since I don't want to reimplement the core http protocol handling, I will use HttpListener for all its worth, and thus I have a question. What would the suggested way be to handle this: Implement all the methods and properties found inside HttpListener, just changing the class types where it matters (ie. the GetContext + EndGetContext methods would return a different class for WebDAV contexts), and storing and using a HttpListener object internally Construct WebDAVListener by passing it a HttpListener class to use? Create a wrapper for HttpListener with an interface, and constrct WebDAVListener by passing it an object implementing this interface? If going the route of passing a HttpListener (disguised or otherwise) to the WebDAVListener, would you expose the underlying listener object through a property, or would you expect the program that used the class to keep a reference to the underlying HttpListener? Also, in this case, would you expose some of the methods of HttpListener through the WebDAVListener, like Start and Stop, or would you again expect the program that used it to keep the HttpListener reference around for all those things? My initial reaction tells me that I want a combination. For one thing, I would like my WebDAVListener class to look like a complete implementation, hiding the fact that there is a HttpListener object beneath it. On the other hand, I would like to build unit-tests without actually spinning up a networked server, so some kind of mocking ability would be nice to have as well, which suggests I would like the interface-wrapper way. One way I could solve this would be this: public WebDAVListener() : WebDAVListener(new HttpListenerWrapper()) { } public WebDAVListener(IHttpListenerWrapper listener) { } And then I would implement all the methods of HttpListener (at least all those that makes sense) in my own class, by mostly just chaining the call to the underlying HttpListener object. What do you think? Final question: If I go the way of the interface, assuming the interface maps 1-to-1 onto the HttpListener class, and written just to add support for mocking, is such an interface called a wrapper or an adapter?

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  • Design pattern: polymorphisim for list of objects

    - by ziang
    Suppose I have a class A, and A1, A2 inherits from A. There are 2 functions: List<A1> getListA1(){...} List<A2> getListA2(){...} Now I want to do something similar to both A1 and A2 in another function public void process(List<A>){...} If I want to pass the instance of either ListA1 or ListA2, of course the types doesn't match because the compiler doesn't allow the coercion from List< A1 to List< A. I can't do something like this: List<A1> listA1 = getListA1(); List<A> newList = (List<A>)listA1; //this is not allowed. So what is the best approach to the process()? Is there any way to do it in a universal way rather than write the similar code to both List and List?

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