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• Database Replication OOD Pattern

  - by MrOnigiri

  Greetings fellow overflowers, After reading on MSDN about correct strategies on how to perform database replication, and understanding their suggestion on Master-Subordinate Incremental Replication. It left me wondering, what OOD design pattern should I use on this... The main elements of this strategy are the Acquirer, the Manipulator and the Writer. The first fetches data from the database and passes on to the second which might perform simple transformations to the data, before handling it to the final element, the writer, that writes the desired data on the destination Database. I thought about using the Chain of Responsibility pattern, but the Acquirer, Manipulator and Writer don't share a common role among theme, so It makes no sense. Should these elements be written as separate classes, or methods inside my service? Of course I'll be creating a DB Helper class as well, but that doesn't constitutes a problem. Wondering what your opinions on this are! Thanks for your replies

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• Bidirectional one-to-many associations with indexed collections in NHibernate

  - by Jørn Schou-Rode

  Last summer, I asked a question regarding how to add new object to an IList mapped as a one-to-many with NHibernate. One of the answers let me to this paragraph in the documentation: Please note that NHibernate does not support bidirectional one-to-many associations with an indexed collection (list, map or array) as the "many" end, you have to use a set or bag mapping. While I am pretty sure I understand what this paragraph says, I have no idea why or how to work around this limitation. As I am now again working with a model that seems to require a "bidirectional one-to-many association with an index collection", I figured the time was right for follow-up questions: Why does NHibernate have this limitation on associations? It is my impression that the guys behind NHibernate are quite clever, so I assume there is a pretty good reason. What are the common workarounds for this shortcoming? Making the collection a non-indexed bag and adding an explicit Position property to the child class? Any better solutions?

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• SQL searching table fields with LIKE

  - by Tom Gullen

  Given your data stored somewhere in a database: Hello my name is Tom I like dinosaurs to talk about SQL. SQL is amazing. I really like SQL. We want to implement a site search, allowing visitors to enter terms and return relating records. A user might search for: Dinosaurs And the SQL: WHERE articleBody LIKE '%Dinosaurs%' Copes fine with returning the correct set of records. How would we cope however, if a user mispells dinosaurs? IE: Dinosores (Poor sore dino). How can we search allowing for error in spelling? We can associate common misspellings we see in search with the correct spelling, and then search on the original terms + corrected term, but this is time consuming to maintain. Any way programatically?

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• The fastest way to do a collection subtraction

  - by Tony

  I have two Sets. Set<B> b is the subset of Set<A> a. they're both very huge Sets. I want to subtract b from a , what's the best practice to do this common operation ? I've written to many codes like this , and I don't think it's efficient. what's your idea ? for(int i = 0 ; i < a.size(); i++) { for (int j=0 ; j < b.size() ;j++) { // do comparison , if found equals ,remove from a break; } } And I want to find an algorithm , not only applies to Sets, also works for Array.

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• What's the best way to calculate similarity between rows in a table based on association?

  - by André Pena

  Suppose each Person has a collection of favorite Books. So I have a table for: Person Book The association between Person and Book (joint table for MxN) I want to fetch the Persons that are similar to a Person1 based on the favorite Books overlaping. That is: The more books they have in common, the more they are similar. I don't have to use only SQL to solve this problem. I could use programming also. I'm using SQL Server 2008 and C#. What solution would you experts use?

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• Mootools not loading fast enough IE6

  - by Tom

  Very random and annoying problem with IE6. We keep our common JS files on a resources server so we only have to update them in one place. As well as our custom classes we also keep our build of mootools and more on the resources server and link to it in the head of our sites. This is fine in all the browsers accept IE6. In IE6 it seems to not loads the core quick enough from the external link before trying to process the mootools code in my site.js file. It will go wrong on the first line "windows.addEvent". If i put a mootools core in a folder where the site is though its fine. Does anyone know why it might be doing this and if so a way around it, but still keeping the files on the resources domain? Thanks Tom

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• Current state of client-side XSLT

  - by Casey

  Last I heard, Blizzard was one of the few companies to put client-side XSLT into practice (2008). Is this still the case in 2011, or are more people now exploring this technique in production?  It seems that modern browsers (IE9, FF4, Chrome) and client processing power are primed to exploit this standard for tangible savings in server CPU power and bandwidth on large scale properties. Am I missing something? The negative aspects I'm aware of include * additional rendering time * additional assets required on uncached page load * additional layer of complexity * noticably less developer experience than server-side template techniques The benefits I perceive include * distributed template composition (offloaded on the client) * caching of common template fragments offloaded on the client * logical separation of document structure and data * well-documented web standard supported by all modern browsers Finally, although I know it's impossible to predict the future, I am curious to know opinions on whether or not client-side XSLT's day will come. With interest in HTML5 driving users to upgrade their browsers and developers to explore new techniques, I would say yes. How about you? Thanks in advance, Casey

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• Python key word arguments

  - by pythonic metaphor

  I have several layers of function calls, passing around a common dictionary of key word arguments: def func1(**qwargs): func2(**qwargs) func3(**qwargs) I would like to supply some default arguments in some of the subsequent function calls, something like this: def func1(**qwargs): func2(arg = qwargs.get("arg", default), **qwargs) func3(**qwargs) The problem with this approach is that if arg is inside qwargs, a TypeError is raised with "got multiple values for keyword argument". I don't want to set qwargs["arg"] to default, because then func3 gets this argument without warrant. I could make a copy.copy of the qwargs and set "arg" in the copy, but qwargs could have large data structures in it and I don't want to copy them (maybe copy.copy wouldn't, only copy.deepcopy?). What's the pythonic thing to do here?

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• DataAdapter Select string from base table schema?

  - by MattSlay

  When I built my .xsd, I had to choose the columns for each table, and it made a schema for the tables, right? So how can I get that Select string to use as a base Select command for new instances of dataadapters, and then just append a Where and OrderBy clause to it as needed? That would keep me from having to keep each DataAdapter's field list (for the same table) in synch with the schema of that table in the .xsd file. Isn't it common to have several DataAdapters that work on a certain table schema, but with different params in the Where and OrderBy clauses? Surely one does not have to maintain (or even redundently build) the field list part of the Select strings for half a dozen DataAdapters that all work off of the same table schema. I'm envisioning something like this pseudo code: BaseSelectString = MyTypedDataSet.JobsTable.GetSelectStringFromSchema() // Is there such a method or technique? WhereClause = " Where SomeField = @Param1 and SomeOtherField = @Param2" OrderByClause = " Order By Field1, Field2" SelectString=BaseSelectString + WhereClause + OrderByClause OleDbDataAdapter adapter = new OleDbDataAdapter(SelectString, MyConn)

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• django app organization

  - by iHeartDucks

  I have been reading some django tutorial and it seems like all the view functions have to go in a file called "views.py" and all the models go in "models.py". I fear that I might end up with a lot of view functions in my view.py file and the same is the case with models.py. Is my understanding of django apps correct? Django apps lets us separate common functionality into different apps and keep the file size of views and models to a minimum? For example: My project can contain an app for recipes (create, update, view, and search) and a friend app, the comments app, and so on. Can I still move some of my view functions to a different file? So I only have the CRUD in one single file?

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• my windows forms application throws filenotfoundexception when run on another machine

  - by user248785

  Hi, I have created a windows forms application using vs2008. when i copy the bin folder over to another machine and try to run it the applicaiton throws a filenotfoundexception error. Ive looked at the references files used in the project and each file points to either c:\Windows\Microsoft.NET\Framework\v2.0.50727... c:\Program Files\Reference Assemblies\Microsoft\Framework\v3.5... c:\Program Files\Common Files\Microsoft Shared\Visual Basic Power Packs\1.1... i have verified that these directories exist on the other machines that cause the error. the two machines that i have tried it on and that throw there error are Windows XP WITHOUT VS2008 installed and Windows 7 with VS2008 installed I tried on two machine that DID work which are Windows XP with VS2008 and and my development machine Windows 7 with VS2008 Could anyone provide me with some insight on this issue Thanks

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• Methods for ensuring security between users in multi-user applications

  - by Emilio

  I'm writing a multiuser application (.NET - C#) in which each user's data is separated from the others and there is no data that's common between users. It's critical to ensure that no user has access to another user's data. What are some approaches for implementing security at the database level and/or in the application architecture to to accomplish this? For example (and this is totally made up - I'm not suggesting it's a good or bad approach) including a userID column in all data tables might be an approach. I'm developing the app in C# (asp.net) and SQL Server 2008. I'm looking for options that are are either native in the tools I'm using or general patterns.

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• Oracle analytic functions for "the atatrbute from the row with the max date"

  - by tpdi

  I'm refactoring a colleague's code, and I have several cases where he's using a cursor to get "the latest row that matches some predicate": His technique is to write the join as a cursor, order it by the date field descending, open the cursor, get the first row, and close the cursor. This requires calling a cursor for each row of the result set that drives this, which is costly for many rows. I'd prefer to be able to join, but what something cheaper than a correlated subquery: select a.id_shared_by_several_rows, a.foo from audit_trail a where a.entry_date = (select max(a.entry_date) from audit_trail b where b.id_shared_by_several_rows = a.id_shared_by_several_rows ); I'm guessing that since this is a common need, there's an Oracle analytic function that does this?

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• How are integers converted to strings under the hood?

  - by CrazyJugglerDrummer

  I suppose the real question is how to convert base2/binary to base10. The most common application of this would probably be in creating strings for output: turning a chunk of binary numerical data into an array of characters. How exactly is this done? my guess: Seeing as there probably isn't a string predefined for each numerical value, I'm guessing that the computer goes through each bit of the integer from right to left, each time incrementing the appropriate values in the char array/base10 notation places. If we take the number 160 in binary (10100000), it would know that a 1 in the 8th place means 128, so it places 1 into the third column, 2 in the second, and 8 in the third. The 1 in the 6th column means 32, and it would add those values to the second and first place, carrying over if needed. After this it's an easy conversion to actual char codes.

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• Java Swing: how to add an image to a JPanel ?

  - by Leonel

  I have a JPanel to which I'd like to add JPEG and PNG images that I generate on the fly. All the examples I've seen so far in the Swing Tutorials, specially in the Swing examples use ImageIcons. I'm generating these images as byte arrays, and they are usually larger than the common icon they use in the examples, at 640x480. Is there any (performance or other) problem in using the ImageIcon class to display an image that size in a JPanel ? What's the usual way of doing it ? How to add an image to a JPanel without using the ImageIcon class ? Edit: A more careful examination of the tutorials and the API shows that you cannot add an ImageIcon directly to a JPanel. Instead, they achieve the same effect by setting the image as an icon of a JLabel. This just doesn't fill right...

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• How do I debug random Timeout::Error: execution expired

  - by ChrisH

  We are using Rails 2.3.5 and have been experiencing seemingly random Timeout::Error: execution expired errors. The errors reported by Hoptoad are not consistently in any particular controller and show up everywhere from user sessions to account settings to some of our core functionality controllers. The vast majority of requests do not Timeout but there are enough to cause concern. Is this normal? If so, what are some things to look at to decrease the occurance? If not, has anyone run into this and what are some common problems that can trigger an error like this.

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• Confused by Perl grep function

  - by titaniumdecoy

  I don't understand the last line of this function from Programming Perl 3e. Here's how you might write a function that does a kind of set intersection by returning a list of keys occurring in all the hashes passed to it: @common = inter( \%foo, \%bar, \%joe ); sub inter { my %seen; for my $href (@_) { while (my $k = each %$href) { $seen{$k}++; } } return grep { $seen{$_} == @_ } keys %seen; } I understand that %seen is a hash which maps each key to the number of times it was encountered in any of the hashes provided to the function.

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• Illustration for code presentation

  - by Lasse V. Karlsen

  I got an odd request, and I fear it will be closed as off-topic. So be it, but it's worth a shot. I'm creating a presentation about dependency injection and inversion of control, and I thought I'd make the point of interchangeable parts that serve a common purpose, but has different implementations, by showing an image I've seen before. Basically the image is of a man or a woman, but the image is split up into four parts: Head Torso uhm... not sure the name of this part, stomach, etc. Legs Possibly a fifth with feet and for each part you can choose among a few variants, creating odd people in the process. ie. a man torso with a woman head. But, I can't find such an image now of course. Does anyone know of such an image and can provide me with an url?

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• reference other projects in visual studio for win32 projects

  - by Vineel Kumar Reddy

  Hi All I am working with win32 API and my language of choice is pure C and no C++. Assume I have a project A that is present in Solution S in visual studio I want to add another project B(which has some common utility functions) in to S Now I want to reference Project B in Project A... So that I can use those utility functions from Project B source code level. I dont want it be used against dll of Project B assume project B contains some math related functions and i want to call the functions from Project A or project B contains come data structures and i want to make use of them in Project A How to achieve this.... thanks in advance

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• Code reading: where can i read great, modern, and well-documented C++ code?

  - by baol

  Reading code is one of the best ways to learn new idioms, tricks, and techniques. Sadly it's very common to find badly written C++ code. Some use C++ as it was C, others as if it was Java, some just shoot in their feet. I believe gtkmm is a good example of C++ design, but a binding could not be the better code to read (you need to know the C library behind that). Boost libraries (at least the one I read) tend to be less readable than I'd like. Can you mention open source projects (or other projects which source is freely readable) that are good example of readable, modern, well-documented, and auto-contained, C++ code to learn from? (I believe that one project per answer will be better, and I'd include the motivation that led you to selecting that one.)

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• How do you handle descriptive database table names and their effect on foreign key names?

  - by Carvell Fenton

  Hello, I am working on a database schema, and am trying to make some decisions about table names. I like at least somewhat descriptive names, but then when I use suggested foreign key naming conventions, the result seems to get ridiculous. Consider this example: Suppose I have table session_subject_mark_item_info And it has a foreign key that references sessionSubjectID in the session_subjects table. Now when I create the foreign key name based on fk_[referencing_table]__[referenced_table]_[field_name] I end up with this maddness: fk_session_subject_mark_item_info__session_subjects_sessionSubjectID Would this type of a foreign key name cause me problems down the road, or is it quite common to see this? Also, how do the more experienced database designers out there handle the conflict between descriptive naming for readability vs. the long names that result? I am using MySQL and MySQL Workbench if that makes any difference. Thanks!

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• UML Class Relationships

  - by 01010011

  Hi, I would like to confirm whether I am on the right track when identifying common UML class relationships. For example, is the relationship between: 1 a stackoverflow member and his/her stackoverflow user account categorized as a composition relationship or an aggregation relationship? At first I thought it was an association because this member "has a" account. However on second thought, I am thinking its composition because each "part" (user account) belongs to only one whole (user) at a time, meaning for as long as I am logged into stackoverflow, I have to use this one and only account until I log off. If I log back onto stackoverflow with a different account then its composition again. Do you agree? 2 a database and a person's user account an aggregation relationship? I think so because 1 database (the whole) can store 0...* number of user accounts (the parts) but another database can store the same user accounts. Finally, can anyone recommend a website that specializes in designing code using UML? Thanks in advance

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• Ensure connection to a POSPrinter connected via COM

  - by Alexander

  Hi, I need to make sure that the connection to a POS printer is successful before writing data to the database and then printing a receipt. The POSprinter is normally of type BTP 2002NP but may differ. The common thing is that they are all connected via COM-port and NOT usb, so no drivers installed at all on the client. Can I send some kind of "ping" on a COM-port and check if a device is connected and turned on? Any help or suggestions are very much appreciated. Additional information, the application is developed in VB.net and Visual Studio 2008

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• Good input validation loop using cin - C++

  - by Alex

  Hi there, I'm in my second OOP class, and my first class was taught in C#, so I'm new to C++ and currently I am practicing input validation using cin. So here's my question: Is this loop I constructed a pretty good way of validating input? Or is there a more common/accepted way of doing it? Thanks! Code: int taxableIncome; int error; // input validation loop do { error = 0; cout << "Please enter in your taxable income: "; cin >> taxableIncome; if (cin.fail()) { cout << "Please enter a valid integer" << endl; error = 1; cin.clear(); cin.ignore(80, '\n'); } }while(error == 1);

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• HASH reference error with HTTP::Message::decodable

  - by scarba05

  Hi, I'm getting an "Can't use an undefined value as a HASH reference" error trying to call HTTP::Message::decodable() using Perl 5.10 / libwww installed on Debian Lenny OS using the aptitude package manager. I'm really stuck so would appreciate some help please. Here's the error: Can't use an undefined value as a HASH reference at (eval 2) line 1. at test.pl line 4 main::__ANON__('Can\'t use an undefined value as a HASH reference at enter code here`(eval 2)...') called at (eval 2) line 1 HTTP::Message::__ANON__() called at test.pl line 6 Here's the code: use strict; use HTTP::Request::Common; use Carp; $SIG{ __DIE__ } = sub { Carp::confess( @_ ) }; print HTTP::Message::decodable();

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