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• Newbie, deciding Python or Erlang

  - by Joe

  Hi Guys, I'm a Administrator (unix, Linux and some windows apps such as Exchange) by experience and have never worked on any programming language besides C# and scripting on Bash and lately on powershell. I'm starting out as a service provider and using multiple network/server monitoring tools based on open source (nagios, opennms etc) in order to monitor them. At this moment, being inspired by a design that I came up with, to do more than what is available with the open source at this time, I would like to start programming and test some of these ideas. The requirement is that a server software that captures a stream of data and store them in a database(CouchDB or MongoDB preferably) and the client side (agent installed on a server) would be sending this stream of data on a schedule of every 10 minutes or so. For these two core ideas, I have been reading about Python and Erlang besides ruby. I do plan to use either Amazon or Rackspace where the server platform would run. This gives me the scalability needed when we have more customers with many servers. For that reason alone, I thought Erlang was a better fit(I could be totally wrong, new to this game) and I understand that Erlang has limited support in some ways compared to Ruby or Python. But also I'm totally new to the programming realm of things and any advise would be appreciated grately. Jo

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• Cannot rollback ransaction with Entity Framework

  - by Luca

  I have to do queries on uncommitted changes and I tried to use transactions, but I found that it do not work if there are exceptions. I made a simple example to reproduce the problem. I have a database with only one table called "Tabella" and the table has two fields: "ID" is a autogenerated integer, and "Valore" is an integer with a Unique constraint. Then I try to run this code: using (TransactionScope scope = new TransactionScope()) { Db1Container db1 = new Db1Container(); try { db1.AddToTabella(new Tabella() { Valore = 1 }); db1.SaveChanges(); } catch { } try { db1.AddToTabella(new Tabella() { Valore = 1 }); db1.SaveChanges(); //Unique constraint is violated here and an exception is thrown } catch { } try { db1.AddToTabella(new Tabella() { Valore = 2 }); db1.SaveChanges(); } catch { } //scope.Complete(); //NEVER called } //here everything should be rolled back Now if I look into the database it should contain no records because the transaction should rollback, instead I find two records!!!! One with Valore=1 and one with Valore=2. I am missing something? It looks like the second call to SaveChanges method rollback its own changes and "deletes" the transaction, then the third call to SaveChanges commits the changes of the first and the third insert (at this point it is like the transaction not exists). I also tried to use SaveChanges(false) method (even without calling AcceptAllChanges method), but with no success: I have the same behaviour. I do not want the transaction to be rolled back automatically by SaveChanges, because I want to correct the errors (for example by user interaction in the catch statement) and make a retry. Can someone help me with this? It seems like a "bug", and it is giving me a really big headache...

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• Status of VB6/ Best Desktop Application Language with Native Compilation

  - by Sandeep Jindal

  I was looking for a Desktop Application Programming Language with one of the biggest constraint: - “I need to output as native executable”. I explored multiple options: Java is not a very good option for desktop programming, but still you can use it. But Java to Exe is a problem. Only GCJ and Excelsior-Jet provides this. .Net platform does not support native compilation. Only very few expensive tools are available which can do the job. Python is not an option for native compilation. Right? VB6 is the option I am left with. From the above list, if I am correct, VB6 is the only and probably the best option I have. But VB6 itself has issues like: It is no more under development since There are questions on support of VB6 IDE with Vista Thus my questions are: From the list of programming language options, do you want to add any more? If VB6 is good/best option, looking at its development status, would you suggest using VB6 in this era?

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• Python PyQt Timer Firmata

  - by George Cullins

  Hello. I am pretty new to python and working with firmata I am trying to play around with an arduino . Here is what I want to happen: Set arduino up with an LED as a digital out Set potentiometer to analog 0 Set PyQt timer up to update potentiometer position in application Set a threshold in PyQt to turn LED on (Analog in has 1024bit resolution, so say 800 as the threshold) I am using this firmata library : Link Here is the code that I am having trouble with: import sys from PyQt4 import QtCore, QtGui from firmata import * # Arduino setup self.a = Arduino('COM3') self.a.pin_mode(13, firmata.OUTPUT) # Create timer self.appTimer = QtCore.QTimer(self) self.appTimer.start(100) self.appTimer.event(self.updateAppTimer()) def updateAppTimer(self): self.analogPosition = self.a.analog_read(self, 0) self.ui.lblPositionValue.setNum() I am getting the error message: Traceback (most recent call last): File "D:\Programming\Eclipse\IO Demo\src\control.py", line 138, in myapp = MainWindow() File "D:\Programming\Eclipse\IO Demo\src\control.py", line 56, in init self.appTimer.event(self.updateAppTimer()) File "D:\Programming\Eclipse\IO Demo\src\control.py", line 60, in updateAppTimer self.analogPosition = self.a.analog_read(self, 0) TypeError: analog_read() takes exactly 2 arguments (3 given) If I take 'self' out I get the same error message but that only 1 argument is given What is python doing implicitly that I am not aware of? Blockquote

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• MySQL Relational Database Foreign Key

  - by user623879

  To learn databasing, I am creating a movie database. To associate multiple directors with a movie, I have the following schema: movie(m_ID, ....) m_director(dirID, dirName)//dirID is a autoincrement primary key m_directs(dirID, m_ID) //dirID, m_ID are set as foreign Keys in the mysql database(InnoDB engine) I have a program that connects to the db that needs to add a movie to the database. I can easily add a new entry to the movie table and the m_director table, but I am having trouble adding a entry in the m_directs table. INSERT INTO m_director (dirName) VALUES("Jason Reitman"); INSERT INTO m_directs (dirID, m_ID) VALUES(LAST_INSERT_ID(), "tt0467406"); I am using this sql statement to insert a new director and add the association to the movie. I know the primary key of the movie, but I don't know the dirID, so I use LAST_INSERT_ID() to get the last id of the director just inserted. The problem I am having is that I get the following error: MySql.Data.MySqlClient.MySqlException (0x80004005): Cannot add or update a child row: a foreign key constraint fails (`siteproducts`. `m_directs`, CONSTRAINT `m_directs_ibfk_2` FOREIGN KEY (`dirID`) REFERENCES `m_directs` (`dirID`) ON DELETE CASCADE ON UPDATE CASCADE) Any ideas?

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• Don't Understand Sql Server Error

  - by Jonathan Wood

  I have a table of users (User), and need to create a new table to track which users have referred other users. So, basically, I'm creating a many-to-many relation between rows in the same table. So I'm trying to create table UserReferrals with the columns UserId and UserReferredId. I made both columns a compound primary key. And both columns are foreign keys that link to User.UserID. Since deleting a user should also delete the relationship, I set both foreign keys to cascade deletes. When the user is deleted, any related rows in UserReferrals should also delete. But this gives me the message: 'User' table saved successfully 'UserReferrals' table Unable to create relationship 'FK_UserReferrals_User'. Introducing FOREIGN KEY constraint 'FK_UserReferrals_User' on table 'UserReferrals' may cause cycles or multiple cascade paths. Specify ON DELETE NO ACTION or ON UPDATE NO ACTION, or modify other FOREIGN KEY constraints. Could not create constraint. See previous errors. I don't get this error. A cascading delete only deletes the row with the foreign key, right? So how can it cause "cycling cascade paths"? Thanks for any tips.

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• Decisions in teaching someone else to program: language selection

  - by Dinah

  My friend would like for me to guide her into learning programming. She's already proven enormous aptitude for thinking like a programmer but is scared of the idea of programming since in her mind it's relegated to some magical realm accessible only to smart people and trained computer scientists (ironically, I am neither but that's beside the point). My main question is the age-old and irritating question: which language should I chose? I've limited it down to these: PHP: dead simple to start with and I remember enough of the language to answer all novice questions. However, I can think of a million reasons why I wouldn't recommend this as a first language. The most diplomatic of which is that there's no desktop app option to which I would feel comfortable subjecting a novice. Python: supposed to be wonderful for beginners and generally everything I've heard about it screams that this is the correct choice. That's the problem: everything I've heard about it. I don't know it yet and have a lot of projects going on right now so I don't feel like learning it yet -- but I'm going to be the tech-support when any little thing goes wrong. I know there are tons of online resources but in the frustration of the moment, it's always going to be just me. C#: this is the language I'm most comfortable with so I know I can be good tech support. I also love this language and its versatility and community. The big drawback here is that I remember when I first learned it after doing mainly PHP, Perl, and JavaScript and I found the experience overwhelming. You are simultaneously learning: programming concepts, C# syntax, strong typing, OOP, and a complex powerful IDE with a bazillion options and buttons all over it.

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• Error C2451: Illegal conditional expression of type 'UnaryOp<E1, Op>' in ostream - visual studio 9

  - by Steven Hill

  I am getting a repeated error with VS 9. The code compiles under GNU C++, but I want debug with the VS IDE. Any idea what could be causing this error. Error 13 error C2451: conditional expression of type 'UnaryOp' is illegal \Microsoft Visual Studio 9.0\VC\include\ostream 512 //unary constraint template class UnaryOp : public Constraint { public: const E1& e1; UnaryOp(const E1& _e1); bool Satisfiable() const; Bool SatisfiableAux() const; void Print (std::ostream& os) const; UnaryOp* clone () const; //operator bool () const { return true; } }; template std::ostream& operator<<(std::ostream& os, const UnaryOp& unop); UnaryOp code that uses ostream: template INLINE void UnaryOp::Print (std::ostream& os) const { os << *this; } template INLINE std::ostream& operator<<(std::ostream& os, const UnaryOp& unop) { return os << Op::name << unop.e1; } ostream line with error: _Myt& __CLR_OR_THIS_CALL put(_Elem _Ch) { // insert a character ios_base::iostate _State = ios_base::goodbit; const sentry _Ok(*this); 512 if (!_Ok) _State |= ios_base::badbit; else { // state okay, insert character _TRY_IO_BEGIN

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• What is the best "forgot my password" method?

  - by Edward Tanguay

  I'm programming a community website. I want to build a "forgot my password" feature. Looking around at different sites, I've found they employ one of three options: send the user an email with a link to a unique, hidden URL that allows him to change his password (Gmail and Amazon) send the user an email with a new, randomly generated password (Wordpress) send the user his current password (www.teach12.com) Option #3 seems the most convenient to the user but since I save passwords as an MD5 hash, I don't see how option #3 would be available to me since MD5 is irreversible. This also seems to be insecure option since it means that the website must be saving the password in clear text somewhere, and at the least the clear-text password is being sent over insecure e-mail to the user. Or am I missing something here? So if I can't do option #1, option #2 seems to be the simplest to program since I just have to change the user's password and send it to him. Although this is somewhat insecure since you have to have a live password being communicated via insecure e-mail. However, this could also be misused by trouble-makers to pester users by typing in random e-mails and constantly changing passwords of various users. Option #1 seems to be the most secure but requires a little extra programming to deal with a hidden URL that expires etc., but it seems to be what the big sites use. What experience have you had using/programming these various options? Are there any options I've missed?

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• How to use an OSGi service from a web application?

  - by Jaime Soriano

  I'm trying to develop a web application that is going to be launched from a HTTP OSGi service, this application needs to use other OSGi service (db4o OSGi), for what I need a reference to a BundleContext. I have tried two different approaches to get the OSGi context in the web application: Store the BundleContext of the Activator in an static field of a class that the web service can import and use. Use FrameworkUtil.getBundle(this.getClass()).getBundleContext() (being this an instance of MainPage, a class of the web application). I think that first option is completely wrong, but anyway I'm having problems with the class loaders in both options. In the second one it raises a LinkageError: java.lang.LinkageError: loader constraint violation: loader (instance of org/apache/felix/framework/ModuleImpl$ModuleClassLoader) previously initiated loading for a different type with name "com/db4o/ObjectContainer" Also tried with Equinox and I have a similar error: java.lang.LinkageError: loader constraint violation: loader (instance of org/eclipse/osgi/internal/baseadaptor/DefaultClassLoader) previously initiated loading for a different type with name "com/db4o/ObjectContainer" The code that provokes the exception is: ServiceReference reference = context.getServiceReference(Db4oService.class.getName()); Db4oService service = (Db4oService)context.getService(reference); database = service.openFile("foo.db"); The exception is raised in the last line, database class is ObjectContainer, if I change the type of this variable to Object exception is not raised, but It's not useful as an Object :)

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• Swing layout with miglayout and nested panels

  - by Jazzepi

  I have a Swing program using SwingLayout. The structure of the Swing components looks like this. JFrame JPanel (Cardlayout) JPanel (Miglayout) - Main panel Jpanel (Flowlayout) - Checkbox Panel JPanel (Flowlayout) - Option Panel My problem right now is that I'm not sure how to prevent the checkbox panel from growing. I don't want it to "push" out the column that it's in to the right. I want Wraplayout (which works fine on the option panel) to wrap the content of the checkbox panel when it grows too big. This is the view of it from the Windowsbuilder GUI inside of Eclipse. The panel with the label "sites" in it is the Checkbox Panel. Directly to the right of the Checkbox panel is the Option panel. The big panel containing both of them is the main panel. http://i.imgur.com/S7Njo.png This is what happens when I add too many checkboxes http://i.imgur.com/f2SZz.png My main problem is that I don't understand why setting "grow 0" on the column constraint for the first column in mainpanel doesn't prevent it from growing when the component inside gets too big as I add new checkboxes to the site panel (the site panel can have an arbitrary number of checkboxes). This is my miglayout for the main panel. mainPanel.setLayout(new MigLayout("", "[][grow]", "[][][][][][][][grow]")); Here are my component constraints for when I add the checkbox panel siteCheckBoxPanel = new JPanel(); mainPanel.add(siteCheckBoxPanel, "cell 0 0,alignx left,gapx 0px,aligny center"); siteCheckBoxPanel.setLayout(new FlowLayout(FlowLayout.CENTER, 5, 5)); I've also tried it without flow layout, and that doesn't fix anything. Any insight you could provide would be great! I'm also happy to provide more information if people have questions. FYI I've also tried "grow 0" on both the column and row constraint for the cell that the Checkbox Panel is inside.

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• Merge replication server side foreign key violation from unpublished table

  - by Reiste

  We are using SQL Server 2005 Merge Replication with SQL CE 3.5 clients. We are using partitions with filtering for the separate subscriptions, and nHibernate for the ORM mapping. There is automatic ID range management from SQL Server for the subscriptions. We have a table, Item, and a table with a foreign key to Item - ItemHistory. Both of these are replicated down, filtered according to the subscription. Item has a column called UserId, and is filtered per subscription with this filter: WHERE UserId IN (SELECT... [complicated subselect]...) ItemHistory hangs off Item in the publication filter articles. On the server, we have a table ItemHistoryExport, which has a foreign key to ItemHistory. ItemHistoryExport is not published. Entries in the Item and ItemHistory tables are never deleted, on the server or the client. However, the "ownership" of items (and hence their ItemHistories) MAY change, which causes them to be moved from one client subscription/partition to another from time to time. When we sync, we occasionally get the following error: A row delete at '48269404 - 4108383dbb11' could not be propagated to 'MyServer\MyInstance.MyDatabase'. This failure can be caused by a constraint violation. The DELETE statement conflicted with the REFERENCE constraint "FK_ItemHistoryExport_ItemHistory". The conflict occurred in database "MyDatabase", table "dbo.ItemHistoryExport", column 'ItemHistoryId'. Can anyone help us understand why this happens? There shouldn't ever be a delete happening on the server side.

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• Implementing arrays using a stack

  - by Zack

  My programming language has no arrays, no lists, no pointers, no eval and no variable variables. All it has: Ordinary variables like you know them from most programming languages: They all have an exact name and a value. One stack. Functions provided are: push (add element to top), pop (remove element from top, get value) and empty (check if stack is empty) My language is turing-complete. (Basic arithmetics, conditional jumps, etc implemented) That means, it must be possible to implement some sort of list or array, right? But I have no idea how... What I want to achieve: Create a function which can retrieve and/or change an element x of the stack. I could easily add this function in the implementation of my language, in the interpreter, but I want to do it in my programming language. "Solution" one (Accessing an element x, counting from the stack top) Create a loop. Pop off the element from the stack top x times. The last element popped of is element number x. I end up with a destroyed stack. Solution two: Do the same as above, but store all popped off values in a second stack. Then you could move all elements back after you are done. But you know what? I don't have a second stack!

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• How do you pass .net objects values around in F#?

  - by Russell

  I am currently learning F# and functional programming in general (from a C# background) and I have a question about using .net CLR objects during my processing. The best way to describe my problem will be to give an example: let xml = new XmlDocument() |> fun doc -> doc.Load("report.xml"); doc let xsl = new XslCompiledTransform() |> fun doc -> doc.Load("report.xsl"); doc let transformedXml = new MemoryStream() |> fun mem -> xsl.Transform(xml.CreateNavigator(), null, mem); mem This code transforms an XML document with an XSLT document using .net objects. Note XslCompiledTransform.Load works on an object, and returns void. Also the XslCompiledTransform.Transform requires a memorystream object and returns void. The above strategy used is to add the object at the end (the ; mem) to return a value and make functional programming work. When we want to do this one after another we have a function on each line with a return value at the end: let myFunc = new XmlDocument("doc") |> fun a -> a.Load("report.xml"); a |> fun a -> a.AppendChild(new XmlElement("Happy")); a Is there a more correct way (in terms of functional programming) to handle .net objects and objects that were created in a more OO environment? The way I returned the value at the end then had inline functions everywhere feels a bit like a hack and not the correct way to do this. Any help is greatly appreciated!

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• If I wanted to make a Pac-Man Game?

  - by SoulBeaver

  I am immediately placing this as a community wiki thing. I don't want to ask for help in programming yet or have even a specific question about programming, but rather the process and the resources needed to make such a game. To put it simply: My college friend and I decided to give ourselves a really big challenge to further our skills in programming. In six months time we want to show ourselves a Pac-Man game. Pac-Man will be AI-controlled like the Ghosts and whichever Pac-Man lives the longest after a set of tries wins. This isn't like anything we've done so far. The goal here, for me, isn't to create a perfect game, but to try and complete it, learn a whole bunch in the process. Even if I don't finish in the time, which is a good possibility, I would want to have at least tried this. So my question is this: How should I start preparing myself? I already have started vector math, matrices, all that fun stuff. My desired platform would be DirectX 9.0c; is that advisable? Keep in mind that this is not a preference just for this project, but I wish to have some kind of future in graphics develepment, so I want to pick a platform that is future-safe. As for the game development in general, what should I take into consideration? I have never done a real game before, so any and all advise to development of mid-scale projects( if this would be a mid-scale project ) is greatly appreciated. My main concerns are the pit-falls and demotivators. Sorry if the question is so vague. If it doesn't belong here, then I will remove it. Otherwise, any and all advise regarding making larger projects is greatly appreciated.

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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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• How to put foreign key constraints on a computed fields in sql server?

  - by Asaf R

  Table A has a computed field called Computed1. It's persisted and not null. Also, it always computes to an expression which is char(50). It's also unique and has a unique key constraint on it. Table B has a field RefersToComputed1, which should refer to a valid Computed1 value. Trying to create a foreign key constraint on B's RefersToComputed1 that references A' Computed1 leads to the following error: Error SQL01268: .Net SqlClient Data Provider: Msg 1753, Level 16, State 0, Line 1 Column 'B.RefersToComputed1' is not the same length or scale as referencing column 'A.Computed1' in foreign key 'FK_B_A'. Columns participating in a foreign key relationship must be defined with the same length and scale. Q: Why is this error created? Are there special measures needed for foreign keys for computed columns, and if so what are they? Summary: The specific problem rises from computed, char based, fields being varchar. Hence, Computed1 is varchar(50) and not char(50). It's best to have a cast surrounding a computed field's expression to force it to a specific type. Credit goes to Cade Roux for this tip.

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• Any book on designing and implementing a CRPG engine?

  - by Fabzter

  Hi! First, let me tell you, I am not really interested in making my own rpg engine (at least not in the near future, hehe), but I do feel like I want to understand the internals of how a rpg engine works. Why? Well, because I like to read about programming and design, It keeps me motivated and excited, and because I know I will learn a lot, for, even when I have been programming for some years now, I never stop considering myself an ignorant... there are simply SO many things involving a game engine (specially rpg ones, like branching storylines, and items and economics!) I'm eager to know. I've been searching (and thus, finding) lots of info online, but it is never focused in what I'm interested (most of it talks about the mathematics and AI algorithms implementation, which I know quite well), which is the design of overall structure, patterns, scripting engine, decision engine... damn, so many things I can't even imagine, since I've never done any game programming. I hope you know have an idea of how I feel, and how I want to learn for the sake of learning, and why would I want you to tell me if you know if there exist books touching the topics that interest me the most.

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• What's the fastest way to bulk insert a lot of data in SQL Server (C# client)

  - by Andrew

  I am hitting some performance bottlenecks with my C# client inserting bulk data into a SQL Server 2005 database and I'm looking for ways in which to speed up the process. I am already using the SqlClient.SqlBulkCopy (which is based on TDS) to speed up the data transfer across the wire which helped a lot, but I'm still looking for more. I have a simple table that looks like this: CREATE TABLE [BulkData]( [ContainerId] [int] NOT NULL, [BinId] [smallint] NOT NULL, [Sequence] [smallint] NOT NULL, [ItemId] [int] NOT NULL, [Left] [smallint] NOT NULL, [Top] [smallint] NOT NULL, [Right] [smallint] NOT NULL, [Bottom] [smallint] NOT NULL, CONSTRAINT [PKBulkData] PRIMARY KEY CLUSTERED ( [ContainerIdId] ASC, [BinId] ASC, [Sequence] ASC )) I'm inserting data in chunks that average about 300 rows where ContainerId and BinId are constant in each chunk and the Sequence value is 0-n and the values are pre-sorted based on the primary key. The %Disk time performance counter spends a lot of time at 100% so it is clear that disk IO is the main issue but the speeds I'm getting are several orders of magnitude below a raw file copy. Does it help any if I: Drop the Primary key while I am doing the inserting and recreate it later Do inserts into a temporary table with the same schema and periodically transfer them into the main table to keep the size of the table where insertions are happening small Anything else? -- Based on the responses I have gotten, let me clarify a little bit: Portman: I'm using a clustered index because when the data is all imported I will need to access data sequentially in that order. I don't particularly need the index to be there while importing the data. Is there any advantage to having a nonclustered PK index while doing the inserts as opposed to dropping the constraint entirely for import? Chopeen: The data is being generated remotely on many other machines (my SQL server can only handle about 10 currently, but I would love to be able to add more). It's not practical to run the entire process on the local machine because it would then have to process 50 times as much input data to generate the output. Jason: I am not doing any concurrent queries against the table during the import process, I will try dropping the primary key and see if that helps. ~ Andrew

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• Good Learning Method for Objective-C?

  - by Josh Kahane

  Hi I know this must be asked a millions times and can't be easy to answer as there is o definitive method, but any help would be appreciated, thanks. I have been playing around with all sorts of things in Xcode and with Objective-C, however I can't seem to find a good way of learning things in an efficient way. I have bought the book 'Programming in Objective-C 2.0' and its great but just lays down the basics it seems. I want to learn in the 2D game development direction, then of course 3D after nailing that, if thats the right thing to do? I am 17 currently in year 13, last year of school/A Levels and am almost definitely taking a gap year. Any good, well known reputable courses online or offline (real world)? This is my first programming language, and I am absolutely serious about learning this. One last question, is when learning things online, I have in the past started building a feature and learning a certain aspect in programming only to find out after adding more its slows down the app or its to inefficient. Is the key to use a certain method in a certain situation (being os many ways to do the same thing) or use any of those methods and refine it in your app to make it run smoothly? Sorry, its hard for me to know when I have little experience, thus far. Sorry for rambling on! I would appreciate any help, thank you!

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• Great examples of self-paced labs and exercises

  - by Mayo

  It is probably a safe bet that many of us are what they call Tactile / Kinesthetic Learners meaning that we learn best when we are physically doing something as opposed to listening to an online tutorial or reading a book. My goal with this question is to derive a list of books or online resources that serve as superb examples of self-paced programming labs and exercises. For example, I was extremely impressed with the SportsStore exercise in Steven Sanderson's Pro ASP.NET MVC Framework. The exercise spanned multiple chapters and gradually introduced new topics. I was also impressed with the materials associated with the Windows Azure Boot Camp. The demos and lab materials, accessible through the website, allow us to practice and reinforce what we can read about in articles and books. Please list any examples you might have, one per submission, below. The question is language/platform agnostic. Suggestions can be generic or specific to a given technology (PHP, SQL Server, Azure, Flash, Objective C, etc.). I only ask that the answers pertain to labs and exercises that relate to programming. My hope is that the best answers will float to the top allowing developers to review the top answers and find another programming topic that can be learned through example.

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• IntegrityError: foreign key violation upon delete

  - by Lukasz Korzybski

  I have Order and Shipment model. Shipment has a foreign key to Order. class Order(...): ... class Shipment() order = m.ForeignKey('Order') ... Now in one of my views I want do delete order object along with all related objects. So I invoke order.delete(). I have Django 1.0.4, PostgreSQL 8.4 and I use transaction middleware, so whole request is enclosed in single transaction. The problem is that upon order.delete() I get: ... File "/usr/local/lib/python2.6/dist-packages/django/db/backends/__init__.py", line 28, in _commit return self.connection.commit() IntegrityError: update or delete on table "main_order" violates foreign key constraint "main_shipment_order_id_fkey" on table "main_shipment" DETAIL: Key (id)=(45) is still referenced from table "main_shipment". I checked in connection.queries that proper queries are executed in proper order. First shipment is deleted, after that django executes delete on order row: {'time': '0.000', 'sql': 'DELETE FROM "main_shipment" WHERE "id" IN (17)'}, {'time': '0.000', 'sql': 'DELETE FROM "main_order" WHERE "id" IN (45)'} Foreign key have ON DELETE NO ACTION (default) and is initially deferred. I don't know why I get foreign key constraint violation. I also tried to register pre_delete signal and manually delete shipment objects before delete on order is called, but it resulted in the same error. I can change ON DELETE behaviour for this key in Postgres but it would be just a hack, I wonder if anyone has a better idea what's going on here. There is also a small detail, my Order model inherits from Cart model, so it actually doesn't have id field but cart_ptr_id and after DELETE on order is executed there is also DELETE on cart, but it seems unrelated? to the shipment-order problem so I simplified it in the example.

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• Generic object to object mapping with parametrized constructor

  - by Rody van Sambeek

  I have a data access layer which returns an IDataRecord. I have a WCF service that serves DataContracts (dto's). These DataContracts are initiated by a parametrized constructor containing the IDataRecord as follows: [DataContract] public class DataContractItem { [DataMember] public int ID; [DataMember] public string Title; public DataContractItem(IDataRecord record) { this.ID = Convert.ToInt32(record["ID"]); this.Title = record["title"].ToString(); } } Unfortanately I can't change the DAL, so I'm obliged to work with the IDataRecord as input. But in generat this works very well. The mappings are pretty simple most of the time, sometimes they are a bit more complex, but no rocket science. However, now I'd like to be able to use generics to instantiate the different DataContracts to simplify the WCF service methods. I want to be able to do something like: public T DoSomething<T>(IDataRecord record) { ... return new T(record); } So I'd tried to following solutions: Use a generic typed interface with a constructor. doesn't work: ofcourse we can't define a constructor in an interface Use a static method to instantiate the DataContract and create a typed interface containing this static method. doesn't work: ofcourse we can't define a static method in an interface Use a generic typed interface containing the new() constraint doesn't work: new() constraint cannot contain a parameter (the IDataRecord) Using a factory object to perform the mapping based on the DataContract Type. does work, but: not very clean, because I now have a switch statement with all mappings in one file. I can't find a real clean solution for this. Can somebody shed a light on this for me? The project is too small for any complex mapping techniques and too large for a "switch-based" factory implementation.

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• For the professional programmers - do you still write code for fun at home ? [closed]

  - by Led

  Possible Duplicate: Do you ever code just for fun? I've been working as a 'professional' coder for about 11 years. (I've just turned 33.) When I talk to my collegues, I find that most of them actually don't program any more in their spare time - 8 (or 10 :)) hours a day at their job is enough for them. A difference between me and them might be that I was always programming for fun (demoscene stuff etc.) which is why I got into the field, while most of them picked up programming later on (at university or whatever). When I get home my head is always full of ideas, so usually I have a hobby-project going on. Is it weird to spend 8 hours a day programming, and then get home, have dinner, and do some more ? For me the reasons are just - ideas : trying stuff - wanting to develop something all by myself, so when it's finished I can claim it as my own victory How about you ? And if you do, do you have other reasons to do so ? Edit: And if you've got sparetime projects, it might be fun to tell us a bit about it :) Spamming a link to your site/hobbyproject won't be frowned upon here ! Edit2: Vote for this if you want to encourage companies to make monitors that'll give you a nice tan ! ;-)

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• How to make an entity out of a join table without primary key

  - by tputkonen

  I'm trying to generate JPA entities out of an existing database having an "interesting" design. Database has a table called UserSet, which can have links to several other UserSets. There is a one to many relation between UserSets and LinkedUserSets. LinkedUserSets also has one to one relation to UserSets. I tried to generate a JPA Entity out of the database structure using Dali JPA Tools. The resulting entity Linkeduserset misses @Id or @EmbeddedId annotation and thus failes to compile. As the resulting entity contains only two @JoinColumns (which cannot be marked as @Id), I have not so far found a way around this issue. Database structure can not be modified in any way. Is there a way to overcome this somehow? Relevant pars of create table statements: CREATE TABLE `LinkedUserSets` ( `UsrSetID` INT(11) NOT NULL DEFAULT '0' , `ChildID` INT(11) NOT NULL DEFAULT '0' , CONSTRAINT `fk_LinkedUserSets_UserSet1` FOREIGN KEY (`UsrSetID` ) REFERENCES `UserSet` (`UsrSetID` )); CREATE TABLE `UserSet` ( `UsrSetID` INT(11) NOT NULL AUTO_INCREMENT , PRIMARY KEY (`UsrSetID`), CONSTRAINT `fk_UserSet_LinkedUserSets1` FOREIGN KEY (`UsrSetID` ) REFERENCES `LinkedUserSets` (`ChildID` )); Generated entities: @Entity @Table(name="linkedusersets") public class Linkeduserset { //bi-directional many-to-one association to Userset @ManyToOne @JoinColumn(name="UsrSetID") private Userset userset1; //bi-directional one-to-one association to Userset @OneToOne @JoinColumn(name="ChildID") private Userset userset2; } @Entity @Table(name="userset") public class Userset { private static final long serialVersionUID = 1L; @Id @Column(name="UsrSetID") private int jngSetID; //bi-directional many-to-one association to Linkeduserset @OneToMany(mappedBy="userset1") private Set<Linkeduserset> linkedusersets; //bi-directional one-to-one association to Linkeduserset @OneToOne(mappedBy="userset2") private Linkeduserset linkeduserset; } Error message: Entity "Linkeduserset" has no Id or EmbeddedId

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