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  • How to develop a menu for Linux apps

    - by Antonio Ciccia
    I want to create a python panel for Linux like pypanel or tint2 just for fun and to do practice with python development. Now the problem is: I want to create an auto-generated menu, but I don't know where to start. Where can I find all user's installed software in a Linux distro? I know I should look in the /usr/bin folder, but I don't know if it's really the best thing to do. Is there a way to filter installed apps to avoid dependecies programs?

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  • Functional Methods on Collections

    - by GlenPeterson
    I'm learning Scala and am a little bewildered by all the methods (higher-order functions) available on the collections. Which ones produce more results than the original collection, which ones produce less, and which are most appropriate for a given problem? Though I'm studying Scala, I think this would pertain to most modern functional languages (Clojure, Haskell) and also to Java 8 which introduces these methods on Java collections. Specifically, right now I'm wondering about map with filter vs. fold/reduce. I was delighted that using foldRight() can yield the same result as a map(...).filter(...) with only one traversal of the underlying collection. But a friend pointed out that foldRight() may force sequential processing while map() is friendlier to being processed by multiple processors in parallel. Maybe this is why mapReduce() is so popular? More generally, I'm still sometimes surprised when I chain several of these methods together to get back a List(List()) or to pass a List(List()) and get back just a List(). For instance, when would I use: collection.map(a => a.map(b => ...)) vs. collection.map(a => ...).map(b => ...) The for/yield command does nothing to help this confusion. Am I asking about the difference between a "fold" and "unfold" operation? Am I trying to jam too many questions into one? I think there may be an underlying concept that, if I understood it, might answer all these questions, or at least tie the answers together.

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  • What programming languages have you taught your children?

    - by Dubmun
    I'm a C# developer by trade but have had exposure to many languages (including Java, C++, and multiple scripting languages) over the course of my education and career. Since I code in the MS world for work I am most familiar with their stack and so I was excited when Small Basic was announced. I immediately started teaching my oldest to program in it but felt that something was missing from the experience. Being able to look up every command with the IDE's intellisense seemed to take something from the experience. Sure, it was easy to grasp but I found myself thinking that a little more challenge might be in order. I'm looking for something better and I would like to hear your experiences with teaching your children to program in whatever language you have chosen to do so in. What did you like and dislike? How fast did they pick it up? Were they challenged? Frustrated? Thank you very much!

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  • Materialized View does not import properly when importing a db for a second time in another schema [closed]

    - by marinus
    When I import a database with materialized view mv_mt in just one schema there are no errors. create materialized view mv_mt refresh complete next trunc( sysdate ) + 1 as SELECT sysdate, media_type.* from media_type; But when I try to import the same database to a copy in another schema in the same tablespace I get the following errors: IMP-00017: following statement failed with ORACLE error 1: "BEGIN DBMS_JOB.ISUBMIT(JOB=>438,WHAT=>'dbms_refresh.refresh(''"ALEXANDRA"" "."MV_MT"'');',NEXT_DATE=>TO_DATE('2012-07-02:14:22:36','YYYY-MM-DD:HH24:MI:" "SS'),INTERVAL=>'sysdate + 1 / 24 / 60 / 6 ',NO_PARSE=>TRUE); END;" IMP-00003: ORACLE error 1 encountered ORA-00001: unique constraint (SYS.I_JOB_JOB) violated ORA-06512: at "SYS.DBMS_JOB", line 100 ORA-06512: at line 1 IMP-00017: following statement failed with ORACLE error 23421: "BEGIN dbms_refresh.make('"ALEXANDRA"."MV_MT"',list=>null,next_date=>null," "interval=>null,implicit_destroy=>TRUE,lax=>FALSE,job=>438,rollback_seg=>NUL" "L,push_deferred_rpc=>TRUE,refresh_after_errors=>FALSE,purge_option => 1,par" "allelism => 0,heap_size => 0); END;" IMP-00003: ORACLE error 23421 encountered ORA-23421: job number 438 is not a job in the job queue ORA-06512: at "SYS.DBMS_SYS_ERROR", line 86 ORA-06512: at "SYS.DBMS_IJOB", line 793 ORA-06512: at "SYS.DBMS_REFRESH", line 86 ORA-06512: at "SYS.DBMS_REFRESH", line 62 ORA-06512: at line 1 IMP-00017: following statement failed with ORACLE error 23410: "BEGIN dbms_refresh.add(name=>'"ALEXANDRA"."MV_MT"',list=>'"ALEXANDRA"."MV" "_MT"',siteid=>0,export_db=>'ORCL01'); END;" IMP-00003: ORACLE error 23410 encountered ORA-23410: materialized view "ALEXANDRA"."MV_MT" is already in a refresh group ORA-06512: at "SYS.DBMS_SYS_ERROR", line 95 ORA-06512: at "SYS.DBMS_IREFRESH", line 484 ORA-06512: at "SYS.DBMS_REFRESH", line 140 ORA-06512: at "SYS.DBMS_REFRESH", line 125 ORA-06512: at line 1 Anyone any ideas?

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  • What resources do you recommend for learning more about TCP/IP, networking, and related areas?

    - by mkelley33
    As a relatively-new Python programmer, I'm finding more and more that networking as it relates to the web and web development is becoming increasingly important to understand. When I was an active C# ASP.NET programmer making smaller websites with less responsibility this knowledge seemed less important, since there was often a "networking" guy performing any tasks beyond acquiring a domain name for a client. Which books, websites, presentations, articles, or other resources would you recommend so that I best understand what's happening between the time a user types a URL and receives the rendered HTML? Thanks!

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  • What are the consequences of immutable classes with references to mutable classes?

    - by glenviewjeff
    I've recently begun adopting the best practice of designing my classes to be immutable per Effective Java [Bloch2008]. I have a series of interrelated questions about degrees of mutability and their consequences. I have run into situations where a (Java) class I implemented is only "internally immutable" because it uses references to other mutable classes. In this case, the class under development appears from the external environment to have state. Do any of the benefits (see below) of immutable classes hold true even by only "internally immutable" classes? Is there an accepted term for the aforementioned "internal mutability"? Wikipedia's immutable object page uses the unsourced term "deep immutability" to describe an object whose references are also immutable. Is the distinction between mutability and side-effect-ness/state important? Josh Bloch lists the following benefits of immutable classes: are simple to construct, test, and use are automatically thread-safe and have no synchronization issues do not need a copy constructor do not need an implementation of clone allow hashCode to use lazy initialization, and to cache its return value do not need to be copied defensively when used as a field make good Map keys and Set elements (these objects must not change state while in the collection) have their class invariant established once upon construction, and it never needs to be checked again always have "failure atomicity" (a term used by Joshua Bloch) : if an immutable object throws an exception, it's never left in an undesirable or indeterminate state

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  • Is WCF suitable for writing an application which is shared among applications?

    - by RPK
    I have developed and deployed few ASP.NET applications. Sometimes I want to stop the users from either inserting or updating a record when: Maintenance is going on. Stop operations due to payment delay. In one of my recent application I have implemented this feature to first check the database operations for locked status. If any of the above condition fulfils, database operations like insert and update are not carried out. I now need this feature in all the old applications and the future applications I build. I want to know whether WCF is suitable in this scenario as I want to share methods or an independent locking application among various other applications. Is WCF appropriate for this type of scenario?

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  • Need help understanding a recursion example in Python

    - by Ali Mustafa
    Python is my first programming language, and I'm learning it from "How to Think Like a Computer Scientist". In Chapter 5 the author gives the following example on recursion: def factorial(n): if n == 0: return 1 else: recurse = factorial(n-1) result = n * recurse return result I understand that if n = 3, then the function will execute the second branch. But what I don't understand is what happens when the function enters the second branch. Can someone explain it to me?

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  • Which iPhone ad API has produced the highest revenue for you?

    - by Kyle Humfeld
    This isn't a technical question, but more of a request for advice and empirical/anecdotal data. I'm nearly done writing a free app for iPhone, and I'm at the stage where I'm going to put ads into the app. I've had mixed success in the past with iAd (their fill rates have been atrocious recently, and their payouts have cut by about 75% over the past 4 months or so), and would like to know how much ad revenue you, the community, has seen from the various ad APIs you've used for your iPhone apps. This isn't a request for opinion, i.e. which is 'better', only what kinds of numbers you're seeing. I don't need absolute figures, but 'iAd pays x% higher than AdMob, and y% lower than AdSense' would be extremely helpful to me as I make my decision as to which ad API to integrate into my App. Also, have you had any experience or success with integrating multiple ad APIs into the same app? That's something I'm considering doing in my current iAd-filled apps (particularly my iPad app, which has yet to receive a single impression after nearly 60,000 requests)... something like: 1) Request-from-iAd 2) if that fails, request-from-adSense 3) if that fails, request-from-adMob 4) if that fails, ... etc.

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  • Which iPhone ad API has produced the highest revenue for you?

    - by Kyle Humfeld
    This isn't a technical question, but more of a request for advice and empirical/anecdotal data. I'm nearly done writing a free app for iPhone, and I'm at the stage where I'm going to put ads into the app. I've had mixed success in the past with iAd (their fill rates have been atrocious recently, and their payouts have cut by about 75% over the past 4 months or so), and would like to know how much ad revenue you, the community, has seen from the various ad APIs you've used for your iPhone apps. This isn't a request for opinion, i.e. which is 'better', only what kinds of numbers you're seeing. I don't need absolute figures, but 'iAd pays x% higher than AdMob, and y% lower than AdSense' would be extremely helpful to me as I make my decision as to which ad API to integrate into my App. Also, have you had any experience or success with integrating multiple ad APIs into the same app? That's something I'm considering doing in my current iAd-filled apps (particularly my iPad app, which has yet to receive a single impression after nearly 60,000 requests)... something like: 1) Request-from-iAd 2) if that fails, request-from-adSense 3) if that fails, request-from-adMob 4) if that fails, ... etc.

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  • Releasing an open source project without getting embarrassed

    - by Hopeful
    I've been working by myself on a fairly large open source project for quite a while and it's nearing the point where I'd like to release it. However, I'm self-taught and I don't really know anyone who could adequately review my project. A few years ago, I had released a small bit of code which pretty much got ripped apart (in a critical sense) on the forum where I released it. Even though the code worked, the criticism was accurate but brutal. It prompted me to begin searching for best practices for everything and in the end I feel that it made me a much better developer. I've gone over everything in my project so many times trying to make it perfect that I've lost count. I believe in my project and think it has the potential to help a lot of people and I feel like I've done some cool things in interesting ways with it. Still, because I'm self-taught, I can't help but wonder what gaps exist in my self-education. The way my code was ripped apart last time isn't something I'd like to repeat. I think my two biggest fears with releasing my project that I've poured countless hours into are being absolutely embarrassed because I missed some patently obvious things because of my self-education or, worse, releasing it to the sound of crickets. Is there anyone who has been in a similar situation? I'm not afraid of constructive criticism, so long as it is constructive and not just a rant on how I screwed up. I know there is a code review site on StackExchange, but it's not really set up for large projects and I didn't feel like the community there is large enough yet to get good feedback if I were to post parts of my project piecemeal (I tried with one file). What can I do to give my project at least some measure of success without getting embarrassed or devestated in the process?

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  • Web application framework for embedded systems?

    - by datenwolf
    I'm currently developing the software for a measurement and control system. In addition to the usual SCPI interface I'd also give it a nice HTTP frontend. Now I don't want to reinvent the wheel all over again. I already have a simple HTTPD running, but I don't want to implement all the other stuff. So what I'm looking for is a web application toolkit targeted at embedded system development. In particular this has to run on a ARM Cortex-M4, and I have some 8k of RAM available for this. It must be written in C. Is there such a thing or do I have to implement this myself?

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  • Design patterns to avoiding breaking the SRP while performing heavy data logging

    - by Kazark
    A class that performs both computations and data logging seems to have at least two responsibilities. Given a system for which the specifications require heavy data logging, what kind of design patterns or architectural patterns can be used to avoid bloating all the classes with logging calls every time they compute something? The decorator pattern be used (e.g. Interpolator decorated to LoggingInterpolator), but it seems that would result in a situation hardly more desirable in which almost every major class would need to be decorated with logging.

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  • Do people in non-English-speaking countries code in English?

    - by Damovisa
    With over 100 answers to this question it's highly likely that your answer has already been posted. Please don't post an answer unless you have something new to say I've heard it said (by coworkers) that everyone "codes in English" regardless of where they're from. I find that difficult to believe, however I wouldn't be surprised if, for most programming languages, the supported character set is relatively narrow. Have you ever worked in a country where English is not the primary language? If so, what did their code look like? Edit: Code samples would be great, by the way...

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  • Optimizing MySQL -

    - by Josh
    I've been researching how to optimize MySQL a bit, but I still have a few questions. MySQL Primer Results http://pastie.org/private/lzjukl8wacxfjbjhge6vw Based on this, the first problem seems to be that the max_connections limit is too low. I had a similar problem with Apache initially, the max connection limit was set to 100, and the web server would frequently lock up and take an excruciatingly long time to deliver pages. Raising the connection limit to 512 fixed this issue, and I read that raising the connection limit on MySQL to match this was considered good practice. Being that MySQL has actually been "locking up" recently as well (connections have been refused entirely for a few minutes at a time at random intervals) I'm assuming this is the main cause of the issue. However, as far as table cache goes, I'm not sure what I should set this as. I've read that setting this too high can hinder performance further, so should I raise this to right around 551, 560, 600, or do something else? Lastly, as far as raising the join_buffer_size value goes, this doesn't even seem to be included in Debian's my.cnf file by default. Assuming there's not much I can do about adding indexes, should I look into raising this? Any suggested values? Any suggestions in general here would be appreciated as well. Edit: Here's the number of open tables the MySQL server is reporting. I believe this value is related to my question (Opened_tables: 22574)

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  • Writing a new programming language - when and how to bootstrap datastructures?

    - by OnResolve
    I'm in the process of writing my own programming language which, thus far, has been going great in terms of what I set out to accomplish. However, now, I'd like to bootstrap some pre-existing data structures and/or objects. My problem is that I'm not really sure on how to begin. When the compiler begins do I splice in these add-ins so their part of the scope of the application? If I make these in some core library, my concern is how I distribute the library in addition to the compiler--or are they part of the compiler? I get that there are probably a number of plausible ways to approach this, but I'm having trouble with the setting my direction. If it helps, the language is on top of the .NET core (i.e it compiles to CLR code). Any help or suggestions are very much appreciated!

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  • What GUI tools are available for which DVCS?

    - by Macneil
    When I worked at Sun, we used a DVC system called Forte SCCS/Teamware, which used the old SCCS file format, but was a true distributed source code revision control system. One nice feature is that it had strong GUI support: You could bringover and putback changes by simply clicking and dragging. It would draw trees/graphs showing how workspaces relate to each other. You also could have a graph view to display a single file's complete history, which might have had several branches and merges. Allowing you to compare any two points. It also had a strong visual merge tool, to let you accept changes from one of two conflicting files. Naturally, many of the current DVCSs have command line support for these operations, but I'm looking for GUI support in order to use this in a lower-level undergraduate course I'll be teaching. I'm not saying the Forte Teamware solution was perfect, but it did seem to be ahead of the curve. Unfortunately, it's not a viable option to use for my class. Question: What support do the current DVCSs have with regards to GUIs? Do any of them work on Windows, and not just Linux? Are they "ready for prime-time" or still works in progress? Are these standalone or built as plug-ins, e.g., for Eclipse? Note: To help keep this discussion focused I'm only interested in GUI tools. And not a meta-discussion if GUI tools should be used in teaching.

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  • Link between tests and user stories

    - by Sardathrion
    I have not see these links explicitly stated in the Agile literature I have read. So, I was wondering if this approach was correct: Let a story be defined as "In order to [RESULT], [ROLE] needs to [ACTION]" then RESULT generates system tests. ROLE generates acceptance tests. ACTION generates component and unit tests. Where the definitions are the ones used in xUnit Patterns which to be fair are fairly standard. Is this a correct interpretation or did I misunderstand something?

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  • RMS java web framework

    - by Kamil Tomšík
    We're currently reconsidering technologies and frameworks to get more agile with "simple" RMS CRUD-based projects. In short, short-living things like this Right now we have custom extension on top of SmartGWT but after some time it has proven not to be enough flexible. I also personally dislike that java-js compilation process and the whole GWT codebase. Not only its ugly designed, it also makes certain low-level js things very complicated if not completely impossible. So what I'm looking for is: closest to web as possible, like JSF or possibly Tapestry, it is very important to be able get "low" and weave framework if necessary. Happens more often than we thought. datagrid capable - Ext.js & PrimeFaces looks pretty good, Vaadin does too. db-schema generators (optional, no matter in which way) If it were only on me, I'd probably stick to Ext.js + custom rest-based java solution, possibly generated from database schema (not sure about concrete tooling yet) I only does have experience with vanilla Ext.js, vanilla GWT and JSF 2.0 / Seam, so it kinda hard for me to judge or even propose other frameworks. What would be your proposition? What are the problems you've faced, what was your solution and how hard do you think it was to deal with them in "big picture"?

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  • Which design better when use foreign key instead of a string to store a list of id

    - by Kien Thanh
    I'm building online examination system. I have designed to table, Question and GeneralExam. The table GeneralExam contains info about the exam like name, description, duration,... Now I would like to design table GeneralQuestion, it will contain the ids of questions belongs to a general exam. Currently, I have two ideas to design GeneralQuestion table: It will have two columns: general_exam_id, question_id. It will have two columns: general_exam_id, list_question_ids (string/text). I would like to know which designing is better, or pros and cons of each designing. I'm using Postgresql database.

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  • Design review for application facing memory issues

    - by Mr Moose
    I apologise in advance for the length of this post, but I want to paint an accurate picture of the problems my app is facing and then pose some questions below; I am trying to address some self inflicted design pain that is now leading to my application crashing due to out of memory errors. An abridged description of the problem domain is as follows; The application takes in a “dataset” that consists of numerous text files containing related data An individual text file within the dataset usually contains approx 20 “headers” that contain metadata about the data it contains. It also contains a large tab delimited section containing data that is related to data in one of the other text files contained within the dataset. The number of columns per file is very variable from 2 to 256+ columns. The original application was written to allow users to load a dataset, map certain columns of each of the files which basically indicating key information on the files to show how they are related as well as identify a few expected column names. Once this is done, a validation process takes place to enforce various rules and ensure that all the relationships between the files are valid. Once that is done, the data is imported into a SQL Server database. The database design is an EAV (Entity-Attribute-Value) model used to cater for the variable columns per file. I know EAV has its detractors, but in this case, I feel it was a reasonable choice given the disparate data and variable number of columns submitted in each dataset. The memory problem Given the fact the combined size of all text files was at most about 5 megs, and in an effort to reduce the database transaction time, it was decided to read ALL the data from files into memory and then perform the following; perform all the validation whilst the data was in memory relate it using an object model Start DB transaction and write the key columns row by row, noting the Id of the written row (all tables in the database utilise identity columns), then the Id of the newly written row is applied to all related data Once all related data had been updated with the key information to which it relates, these records are written using SqlBulkCopy. Due to our EAV model, we essentially have; x columns by y rows to write, where x can by 256+ and rows are often into the tens of thousands. Once all the data is written without error (can take several minutes for large datasets), Commit the transaction. The problem now comes from the fact we are now receiving individual files containing over 30 megs of data. In a dataset, we can receive any number of files. We’ve started seen datasets of around 100 megs coming in and I expect it is only going to get bigger from here on in. With files of this size, data can’t even be read into memory without the app falling over, let alone be validated and imported. I anticipate having to modify large chunks of the code to allow validation to occur by parsing files line by line and am not exactly decided on how to handle the import and transactions. Potential improvements I’ve wondered about using GUIDs to relate the data rather than relying on identity fields. This would allow data to be related prior to writing to the database. This would certainly increase the storage required though. Especially in an EAV design. Would you think this is a reasonable thing to try, or do I simply persist with identity fields (natural keys can’t be trusted to be unique across all submitters). Use of staging tables to get data into the database and only performing the transaction to copy data from staging area to actual destination tables. Questions For systems like this that import large quantities of data, how to you go about keeping transactions small. I’ve kept them as small as possible in the current design, but they are still active for several minutes and write hundreds of thousands of records in one transaction. Is there a better solution? The tab delimited data section is read into a DataTable to be viewed in a grid. I don’t need the full functionality of a DataTable, so I suspect it is overkill. Is there anyway to turn off various features of DataTables to make them more lightweight? Are there any other obvious things you would do in this situation to minimise the memory footprint of the application described above? Thanks for your kind attention.

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  • Python: Future as a major programming language?

    - by chrisw
    After reading some Python material and seeing some Python code a few years back I decided to give it a whirl. I decided to start with Python to solve the problems on Project Euler and was throughly impressed with the language. Since then I've went on to learn Django, and now use it primarily for my web applications. I would love to have a career programming in this language, however I fear the future of the language is currently in a state of uncertainness. With Google and other major companies embracing it there may be some hope, what are your thoughts on Python, do you see many job opportunities out there?

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  • Eclipse vs. Aptana

    - by RPK
    I know that Eclipse is a universal IDE and variety of plugins are available to scale it. What is the difference between: The original Eclipse IDE, Aptana and NetBeans. I looked into Wikipedia and came to know that the latter two originate from the main Eclipse. For Aptana specially, what was the need to reproduce a new variant that resembles too much with its base IDE? If your preferred choice is Eclipse itself, what makes it unique as compared to the other two.

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  • Setter Validation can affect performance?

    - by TiagoBrenck
    Whitin a scenario where you use an ORM to map your entities to the DB, and you have setter validations (nullable, date lower than today validation, etc) every time the ORM get a result, it will pass into the setter to instance the object. If I have a grid that usually returns 500 records, I assume that for each record it passes on all validations. If my entity has 5 setter validations, than I have passed in 2.500 validations. Does those 2.500 validations will affect the performance? If was 15.000 validation, it will be different? In my opinion, and according to this answer (http://stackoverflow.com/questions/4893558/calling-setters-from-a-constructor/4893604#4893604), setter validation is usefull than constructors validation. Is there a way to avoid unecessary validation, since I am safe that the values I send to DB when saving the entity wont change until I edit it on my system?

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  • Designing a Database Application with OOP

    - by Tim C
    I often develop SQL database applications using Linq, and my methodology is to build model classes to represent each table, and each table that needs inserting or updating gets a Save() method (which either does an InsertOnSubmit() or SubmitChanges(), depending on the state of the object). Often, when I need to represent a collection of records, I'll create a class that inherits from a List-like object of the atomic class. ex. public class CustomerCollection : CoreCollection<Customer> { } Recently, I was working on an application where end-users were experiencing slowness, where each of the objects needed to be saved to the database if they met a certain criteria. My Save() method was slow, presumably because I was making all kinds of round-trips to the server, and calling DataContext.SubmitChanges() after each atomic save. So, the code might have looked something like this foreach(Customer c in customerCollection) { if(c.ShouldSave()) { c.Save(); } } I worked through multiple strategies to optimize, but ultimately settled on passing a big string of data to a SQL stored procedure, where the string has all the data that represents the records I was working with - it might look something like this: CustomerID:34567;CurrentAddress:23 3rd St;CustomerID:23456;CurrentAddress:123 4th St So, SQL server parses the string, performs the logic to determine appropriateness of save, and then Inserts, Updates, or Ignores. With C#/Linq doing this work, it saved 5-10 records / s. When SQL does it, I get 100 records / s, so there is no denying the Stored Proc is more efficient; however, I hate the solution because it doesn't seem nearly as clean or safe. My real concern is that I don't have any better solutions that hold a candle to the performance of the stored proc solution. Am I doing something obviously wrong in how I'm thinking about designing database applications? Are there better ways of designing database applications?

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