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• How do I efficiently write a "toggle database value" function in AJAX?

  - by AmbroseChapel

  Say I have a website which shows the user ten images and asks them to categorise each image by clicking on buttons. A button for "funny", a button for "scary", a button for "pretty" and so on. These buttons aren't exclusive. A picture can be both funny and scary. The user clicks the "funny" button. An AJAX request is sent off to the database to mark that image as funny. The "funny" button lights up, by assigning a class in the DOM to mark it as "on". But the user made a mistake. They meant to hit the next button over. They should click "funny" again to turn it off, right? At this point I'm not sure whats the most efficient way to proceed. The database knows that the "funny" flag is set, but it's inefficient to query the database every time a button is clicked to say, is this flag set or not, then go on with a second database call to toggle it. Should I infer the state of the database flag from the DOM, i.e. if that button has the class "on" then the flag must be set, and branch at that point? Or would it be better to have a data structure in Javascript in the page which duplicates the state of each image in the database, so that every time I set the database flag to true, I also set the value in the Javascript data to true and so on?

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• efficiently determining if a polynomial has a root in the interval [0,T]

  - by user168715

  I have polynomials of nontrivial degree (4+) and need to robustly and efficiently determine whether or not they have a root in the interval [0,T]. The precise location or number of roots don't concern me, I just need to know if there is at least one. Right now I'm using interval arithmetic as a quick check to see if I can prove that no roots can exist. If I can't, I'm using Jenkins-Traub to solve for all of the polynomial roots. This is obviously inefficient since it's checking for all real roots and finding their exact positions, information I don't end up needing. Is there a standard algorithm I should be using? If not, are there any other efficient checks I could do before doing a full Jenkins-Traub solve for all roots? For example, one optimization I could do is to check if my polynomial f(t) has the same sign at 0 and T. If not, there is obviously a root in the interval. If so, I can solve for the roots of f'(t) and evaluate f at all roots of f' in the interval [0,T]. f(t) has no root in that interval if and only if all of these evaluations have the same sign as f(0) and f(T). This reduces the degree of the polynomial I have to root-find by one. Not a huge optimization, but perhaps better than nothing.

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• Hybrid EAV/CR model via WCF (and statically-typed language)?

  - by Pat

  Background I'm working on the architecture for a cloud-based LOB application, using Silverlight for the client, WCF, ASP.NET/C# for server and SQL Server for storage. The data model requires some flexibility per user (ability to add custom properties and define validation rules for them, for example), and a hybrid EAV/CR persistence model on the server side will suit nicely. Problem I need an efficient and maintainable technology and approach to handle the transformation from the persisted EAV model to/from WCF (and similarly allow the client to bind to the resulting data - DataGrid is a key UI element)? Admission: I don't yet know enough about WCF to understand if it supports ExpandoObject directly, but I suspect it will. Options I started off looking at WCF RIA services, but quickly discovered they're heavily dependent upon both static type data and compile-time code generation. Neither of these appeal. The options I'm considering include: Using WCF RIA services and pass the data over the network directly in EAV form (i.e. Dictionary), and handle the binding issue purely on the client side (like this) Using a dynamic language (probably IronPython) to handle both ends of the communication, with plumbing to generate the necessary CLR type data on the client to allow binding, and transform to/from EAV form on the server (spam preventer stopped me from posting a URL here, I'll try it in a comment). Dynamic LINQ (CreateClass() and friends), although I'm way out of my depth there and don't know what the limitations on that approach might be yet. I'm interested in comments on these approaches as well as alternative approaches that might solve the problem. Other Notes The Silverlight client will not be the only consumer of the service, making me slightly uncomfortable with option #1 above. While the data model is flexible, it's not expected to be modified heavily. For argument's sake, we could assume that we might have 25 distinct data models active at a given time, with something like 10-20 unique data fields/rules each. Modifications to the data model will happen infrequently (typically when a new user is initially configured).

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• Reasons for & against a Database

  - by dbemerlin

  Hi, i had a discussion with a coworker about the architecture of a program i'm writing and i'd like some more opinions. The Situation: The Program should update at near-realtime (+/- 1 Minute). It involves the movement of objects on a coordinate system. There are some events that occur at regular intervals (i.e. creation of the objects). Movements can change at any time through user input. My solution was: Build a server that runs continously and stores the data internally. The server dumps a state-of-the-program at regular intervals to protect against powerfailures and/or crashes. He argued that the program requires a Database and i should use cronjobs to update the data. I can store movement information by storing startpoint, endpoint and speed and update the position in the cronjob (and calculate collisions with other objects there) by calculating direction and speed. His reasons: Requires more CPU & Memory because it runs constantly. Powerfailures/Crashes might destroy data. Databases are faster. My reasons against this are mostly: Not very precise as events can only occur at full minutes (wouldn't be that bad though). Requires (possibly costly) transformation of data on every run from relational data to objects. RDBMS are a general solution for a specialized problem so a specialized solution should be more efficient. Powerfailures (or other crashes) can leave the Data in an undefined state with only partially updated data unless (possibly costly) precautions (like transactions) are taken. What are your opinions about that? Which arguments can you add for any side?

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• Debugging unexpected error message - possible memory management problem?

  - by Ben Packard

  I am trying to debug an application that is throwing up strange (to my untutored eyed) errors. When I try to simply log the count of an array... NSLog(@"Array has %i items", [[self startingPlayers] count]); ...I sometimes get an error: -[NSCFString count]: unrecognized selector sent to instance 0x1002af600 or other times -[NSConcreteNotification count]: unrecognized selector sent to instance 0x1002af600 I am not sending 'count' to any NSString or NSNotification, and this line of code works fine normally. A Theory... Although the error varies, the crash happens at predictable times, immediately after I have run through some other code where I'm thinking I might have a memory management issue. Is it possible that the object reference is still pointing to something that is meant to be destroyed? Sorry if my terms are off, but perhaps it's expecting the array at the address it calls 'count' on, but finds another previous object that shouldn't still be there (eg an NSString)? Would this cause the problem? If so, what is the most efficient way to debug and find out what is that address? Most of my debugging up until now involves inserting NSLogs, so this would be a good opportunity to learn how to use the debugger.

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• Printing out this week's dates in perl

  - by ABach

  Hi folks, I have the following loop to calculate the dates of the current week and print them out. It works, but I am swimming in the amount of date/time possibilities in perl and want to get your opinion on whether there is a better way. Here's the code I've written: #!/usr/bin/env perl use warnings; use strict; use DateTime; # Calculate numeric value of today and the # target day (Monday = 1, Sunday = 7); the # target, in this case, is Monday, since that's # when I want the week to start my $today_dt = DateTime->now; my $today = $today_dt->day_of_week; my $target = 1; # Create DateTime copies to act as the "bookends" # for the date range my ($start, $end) = ($today_dt->clone(), $today_dt->clone()); if ($today == $target) { # If today is the target, "start" is already set; # we simply need to set the end date $end->add( days => 6 ); } else { # Otherwise, we calculate the Monday preceeding today # and the Sunday following today my $delta = ($target - $today + 7) % 7; $start->add( days => $delta - 7 ); $end->add( days => $delta - 1 ); } # I clone the DateTime object again because, for some reason, # I'm wary of using $start directly... my $cur_date = $start->clone(); while ($cur_date <= $end) { my $date_ymd = $cur_date->ymd; print "$date_ymd\n"; $cur_date->add( days => 1 ); } As mentioned, this works - but is it the quickest/most efficient/etc.? I'm guessing that quickness and efficiency may not necessarily go together, but your feedback is very appreciated.

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• Random Pairings that don't Repeat

  - by Andrew Robinson

  This little project / problem came out of left field for me. Hoping someone can help me here. I have some rough ideas but I am sure (or at least I hope) a simple, fairly efficient solution exists. Thanks in advance.... pseudo code is fine. I generally work in .NET / C# if that sheds any light on your solution. Given: A pool of n individuals that will be meeting on a regular basis. I need to form pairs that have not previously meet. The pool of individuals will slowly change over time. For the purposes of pairing, (A & B) and (B & A) constitute the same pair. The history of previous pairings is maintained. For the purpose of the problem, assume an even number of individuals. For each meeting (collection of pairs) and individual will only pair up once. Is there an algorithm that will allow us to form these pairs? Ideally something better than just ordering the pairs in a random order, generating pairings and then checking against the history of previous pairings. In general, randomness within the pairing is ok.

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• Exporting dataset to Excel file with multiple sheets in ASP.NET

  - by engg

  In C# ASP.NET 3.5 web application, I need to export multiple datatables (or a dataset) to an Excel 2007 file with multiple sheets, and then provide the user with 'Open/Save' dialog box, WITHOUT saving the Excel file on the web server. I have used Excel Interop before. I have been reading that it's not efficient and is not the best approach to achieve this and there are more ways to do it, 2 of them being: 1) Converting data in datatables to an XML string that Excel understands 2) Using OPEN XML SDK 2.0. It looks like OPEN XML SDK 2.0 is better, please let me know. Are there any other ways to do it? I don't want to use any third-party tools. If I use OPEN XML SDK, it creates an excel file, right? I don't want to save it on the (Windows 2003) server hard drive (I don't want to use Server.MapPath, these Excel files are dynamically created, and they are not required on the server, once client gets them). I directly want to prompt the user to open/save it. I know how to do it when the 'XML string' approach is used. Please help. Thank you.

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• Python IOError: Not a gzipped file (Gzip and Blowfish Encrypt/Compress)

  - by notbad.jpeg

  I'm having some problems with python's built-in library gzip. Looked through almost every other stack question about it, and none of them seem to work. MY PROBLEM IS THAT WHEN I TRY TO DECOMPRESS I GET THE IOError I'm Getting: Traceback (most recent call last): File "mymodule.py", line 61, in return gz.read() File "/usr/lib/python2.7/gzip.py", line 245, readself._read(readsize) File "/usr/lib/python2.7/gzip.py", line 287, in _readself._read_gzip_header() File "/usr/lib/python2.7/gzip.py", line 181, in _read_gzip_header raise IOError, 'Not a gzipped file'IOError: Not a gzipped file This is my code to send it over SMB, it might not make sense why i do things, but it's normally in a while loop and memory efficient, I just simplified it. buffer = cStringIO.StringIO(output) #output is from a subprocess call small_buffer = cStringIO.StringIO() small_string = buffer.read() #need a string to write to buffer gzip_obj = gzip.GzipFile(fileobj=small_buffer,compresslevel=6, mode='wb') gzip_obj.write(small_string) compressed_str = small_buffer.getvalue() blowfish = Blowfish.new('abcd', Blowfish.MODE_ECB) remainder = '|'*(8 - (len(compressed_str) % 8)) compressed_str += remainder encrypted = blowfish.encrypt(compressed_str) #i send it over smb, then retrieve it later Then this is the code that retrieves it: #buffer is a cStringIO object filled with data from smb retrieval decrypter = Blowfish.new('abcd', Blowfish.MODE_ECB) value = buffer.getvalue() decrypted = decrypter.decrypt(value) buff = cStringIO.StringIO(decrypted) buff.seek(0) gz = gzip.GzipFile(fileobj=buff) return gz.read() Here's the problem return gz.read()

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• mysql subselect alternative

  - by Arnold

  Hi, Lets say I am analyzing how high school sports records affect school attendance. So I have a table in which each row corresponds to a high school basketball game. Each game has an away team id and a home team id (FK to another "team table") and a home score and an away score and a date. I am writing a query that matches attendance with this seasons basketball games. My sample output will be (#_students_missed_class, day_of_game, home_team, away_team, home_team_wins_this_season, away_team_wins_this_season) I now want to add how each team did the previous season to my analysis. Well, I have their previous season stored in the game table but i should be able to accomplish that with a subselect. So in my main select statement I add the subselect: SELECT COUNT(*) FROM game_table WHERE game_table.date BETWEEN 'start of previous season' AND 'end of previous season' AND ( (game_table.home_team = team_table.id AND game_table.home_score > game_table.away_score) OR (game_table.away_team = team_table.id AND game_table.away_score > game_table.home_score)) In this case team-table.id refers to the id of the home_team so I now have all their wins calculated from the previous year. This method of calculation is neither time nor resource intensive. The Explain SQL shows that I have ALL in the Type field and I am not using a Key and the query times out. I'm not sure how I can accomplish a more efficient query with a subselect. It seems proposterously inefficient to have to write 4 of these queries (for home wins, home losses, away wins, away losses). I am sure this could be more lucid. I'll absolutely add color tomorrow if anyone has questions

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• jdbc query - date ranges as parameters

  - by pstanton

  Hi all, I'd like to write a single JDBC statement that can handle the equivalent of any number of NOT BETWEEN date1 AND date2 where clauses. By single query, i mean that the same SQL string will be used to create the JDBC statements and then have different parameters supplied. This is so that the underlying frameworks can efficiently cache the query (i've been stung by that before). Essentially, I'd like to find a query that is the equivalent of SELECT * FROM table WHERE mydate NOT BETWEEN ? AND ? AND mydate NOT BETWEEN ? AND ? AND mydate NOT BETWEEN ? AND ? AND mydate NOT BETWEEN ? AND ? and at the same time could be used with fewer parameters: SELECT * FROM table WHERE mydate NOT BETWEEN ? AND ? or more parameters SELECT * FROM table WHERE mydate NOT BETWEEN ? AND ? AND mydate NOT BETWEEN ? AND ? AND mydate NOT BETWEEN ? AND ? AND mydate NOT BETWEEN ? AND ? AND mydate NOT BETWEEN ? AND ? AND mydate NOT BETWEEN ? AND ? AND mydate NOT BETWEEN ? AND ? AND mydate NOT BETWEEN ? AND ? AND mydate NOT BETWEEN ? AND ? AND mydate NOT BETWEEN ? AND ? AND mydate NOT BETWEEN ? AND ? I will consider using a temporary table if that will be simpler and more efficient. thanks for the help!

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• C# String.Replace with a start/index (Added my (slow) implementation)

  - by Chris T

  I'd like an efficient method that would work something like this EDIT: Sorry I didn't put what I'd tried before. I updated the example now. // Method signature, Only replaces first instance or how many are specified in max public int MyReplace(ref string source,string org, string replace, int start, int max) { int ret = 0; int len = replace.Length; int olen = org.Length; for(int i = 0; i < max; i++) { // Find the next instance of the search string int x = source.IndexOf(org, ret + olen); if(x > ret) ret = x; else break; // Insert the replacement source = source.Insert(x, replace); // And remove the original source = source.Remove(x + len, olen); // removes original string } return ret; } string source = "The cat can fly but only if he is the cat in the hat"; int i = MyReplace(ref source,"cat", "giraffe", 8, 1); // Results in the string "The cat can fly but only if he is the giraffe in the hat" // i contains the index of the first letter of "giraffe" in the new string The only reason I'm asking is because my implementation I'd imagine getting slow with 1,000s of replaces.

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• Alternative to Galileo GWS

  - by Anton Gogolev

  Please note that this Galileo is absolutely not related to Java. Galileo is basically a set of web services which can be used to book airline tickets. Originally, it was supposed to be used via Galileo Desktop, whereby operators would enter various commands to perform required operations. For example, SA*AZ610J20JULFCOJFK will "Display seat availability map for specified flight and class". Granted, humans can get used to it and be very efficient, but here comes a problem of integrating this with other systems. For that, folks at TravelPort basically slapped a SOAP interface to this system (which must have been written in COBOL or something), without even thinking about actually embracing XML. For example, it can contain <Ind1>N</Ind1> <Ind2>N</Ind2> <Ind3>N</Ind3> ... <Ind72>N</Ind72> <!-- Yes! 72! --> or, better yet <Text>P/RU/4xxx24528/RU/11MAY67/M/23DEC12/AxxxxxxV/MxxxM</Text> In light of this, my question is as follows: are there any sane airline tickets booking systems we can integrate with? Or are there companies which have products that can abstract away all this?

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• What is a data structure for quickly finding non-empty intersections of a list of sets?

  - by Andrey Fedorov

  I have a set of N items, which are sets of integers, let's assume it's ordered and call it I[1..N]. Given a candidate set, I need to find the subset of I which have non-empty intersections with the candidate. So, for example, if: I = [{1,2}, {2,3}, {4,5}] I'm looking to define valid_items(items, candidate), such that: valid_items(I, {1}) == {1} valid_items(I, {2}) == {1, 2} valid_items(I, {3,4}) == {2, 3} I'm trying to optimize for one given set I and a variable candidate sets. Currently I am doing this by caching items_containing[n] = {the sets which contain n}. In the above example, that would be: items_containing = [{}, {1}, {1,2}, {2}, {3}, {3}] That is, 0 is contained in no items, 1 is contained in item 1, 2 is contained in itmes 1 and 2, 2 is contained in item 2, 3 is contained in item 2, and 4 and 5 are contained in item 3. That way, I can define valid_items(I, candidate) = union(items_containing[n] for n in candidate). Is there any more efficient data structure (of a reasonable size) for caching the result of this union? The obvious example of space 2^N is not acceptable, but N or N*log(N) would be.

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• Finding Common Phrases in MS SQL TEXT Column

  - by regex

  Hello All, Short Desc: I'm curious to see if I can use SQL Analysis services or some other MS SQL service to mine some data for me that will show commonalities between SQL TEXT fields in a dataset. Long Desc I am looking at a subset of data that consists of about 10,000 rows of TEXT blobs which are used as a notes column in a issue tracking (ticketing) software. I would like to use something out of the box (without having to build something) that might be able to parse through all of the rows and find commonly used byte sequences in the "Notes" column. In other words, I want to find commonly used phrases (two to three word phrases, so 9 - 20 character sections of the TEXT blob). This will help me better determine if associate's notes contain similar phrases (troubleshooting techniques) that we could standardize in our troubleshooting process flow. Closing Note I'd really rather not build an application to do this as my method will probably not be the most efficient way to do it. Hopefully all this makes sense. Please let me know in the comments if anything needs clarification. Thanks in advance for your help.

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• Implementing Model-level caching

  - by Byron

  I was posting some comments in a related question about MVC caching and some questions about actual implementation came up. How does one implement a Model-level cache that works transparently without the developer needing to manually cache, yet still remains efficient? I would keep my caching responsibilities firmly within the model. It is none of the controller's or view's business where the model is getting data. All they care about is that when data is requested, data is provided - this is how the MVC paradigm is supposed to work. (Source: Post by Jarrod) The reason I am skeptical is because caching should usually not be done unless there is a real need, and shouldn't be done for things like search results. So somehow the Model itself has to know whether or not the SELECT statement being issued to it worthy of being cached. Wouldn't the Model have to be astronomically smart, and/or store statistics of what is being most often queried over a long period of time in order to accurately make a decision? And wouldn't the overhead of all this make the caching useless anyway? Also, how would you uniquely identify a query from another query (or more accurately, a resultset from another resultset)? What about if you're using prepared statements, with only the parameters changing according to user input? Another poster said this: I would suggest using the md5 hash of your query combined with a serialized version of your input arguments. This would require twice the number of serialization options. I was under the impression that serialization was quite expensive, and for large inputs this might be even worse than just re-querying. And is the minuscule chance of collision worth worrying about? Conceptually, caching in the Model seems like a good idea to me, but it seems in practicality the developer should have direct control over caching and write it into the controller. Thoughts/ideas? Edit: I'm using PHP and MySQL if that helps to narrow your focus.

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• FIFO dequeueing in python?

  - by Aaron Ramsey

  hello again everybody— I'm looking to make a functional (not necessarily optimally efficient, as I'm very new to programming) FIFO queue, and am having trouble with my dequeueing. My code looks like this: class QueueNode: def __init__(self, data): self.data = data self.next = None def __str__(self): return str(self.data) class Queue: def__init__(self): self.front = None self.rear = None self.size = 0 def enqueue(self, item) newnode = QueueNode(item) newnode.next = None if self.size == 0: self.front = self.rear = newnode else: self.rear = newnode self.rear.next = newnode.next self.size = self.size+1 def dequeue(self) dequeued = self.front.data del self.front self.size = self.size-1 if self.size == 0: self.rear = None print self.front #for testing if I do this, and dequeue an item, I get the error "AttributeError: Queue instance has no attribute 'front'." I guess my function doesn't properly assign the new front of the queue? I'm not sure how to fix it though. I don't really want to start from scratch, so if there's a tweak to my code that would work, I'd prefer that—I'm not trying to minimize runtime so much as just get a feel for classes and things of that nature. Thanks in advance for any help, you guys are the best.

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• Simple description of worker and I/O threads in .NET

  - by Konstantin

  It's very hard to find detailed but simple description of worker and I/O threads in .NET What's clear to me regarding this topic (but may not be technically precise): Worker threads are threads that should employ CPU for their work; I/O threads (also called "completion port threads") should employ device drivers for their work and essentially "do nothing", only monitor the completion of non-CPU operations. What is not clear: Although method ThreadPool.GetAvailableThreads returns number of available threads of both types, it seems there is no public API to schedule work for I/O thread. You can only manually create worker thread in .NET? It seems that single I/O thread can monitor multiple I/O operations. Is it true? If so, why ThreadPool has so many available I/O threads by default? In some texts I read that callback, triggered after I/O operation completion is performed by I/O thread. Is it true? Isn’t this a job for worker thread, considering that this callback is CPU operation? To be more specific – do ASP.NET asynchronous pages user I/O threads? What exactly is performance benefit in switching I/O work to separate thread instead of increasing maximum number of worker threads? Is it because single I/O thread does monitor multiple operations? Or Windows does more efficient context switching when using I/O threads?

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• Best way to randomly select rows *per* column in SQL Server

  - by LesterDove

  A search of SO yields many results describing how to select random rows of data from a database table. My requirement is a bit different, though, in that I'd like to select individual columns from across random rows in the most efficient/random/interesting way possible. To better illustrate: I have a large Customers table, and from that I'd like to generate a bunch of fictitious demo Customer records that aren't real people. I'm thinking of just querying randomly from the Customers table, and then randomly pairing FirstNames with LastNames, Address, City, State, etc. So if this is my real Customer data (simplified): FirstName LastName State ========================== Sally Simpson SD Will Warren WI Mike Malone MN Kelly Kline KS Then I'd generate several records that look like this: FirstName LastName State ========================== Sally Warren MN Kelly Malone SD Etc. My initial approach works, but it lacks the elegance that I'm hoping the final answer will provide. (I'm particularly unhappy with the repetitiveness of the subqueries, and the fact that this solution requires a known/fixed number of fields and therefore isn't reusable.) SELECT FirstName = (SELECT TOP 1 FirstName FROM Customer ORDER BY newid()), LastName= (SELECT TOP 1 LastNameFROM Customer ORDER BY newid()), State = (SELECT TOP 1 State FROM Customer ORDER BY newid()) Thanks!

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• question about MySQL database migration

  - by WilliamLou

  Hi there: If I have a MySQL database with several tables on a live server, now I would like to migrate this database to another server. Of course, the migration I mean here involves some database tables, for example: add some new columns to several tables, add some new tables etc.. Now, the only method I can think of is to use some php/python(two scripts I know) script, connect two databases, dump the data from the old database, and then write into the new database. However, this method is not efficient at all. For example: in old database, table A has 28 columns; in new database, table A has 29 columns, but the extra column will have default value 0 for all the old rows. My script still needs to dump the data row by row and insert each row into the new database. Is there any tools or a better method than writing a script yourself? Here, I dont need to worry about multithread writing problems etc.., I mean the old database will be down (not open to public usage etc.., only for upgrade ) for a while. Thanks!!

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• Database design and foreign keys: Where should they be added in related tables?

  - by Carvell Fenton

  I have a relatively simple subset of tables in my database for tracking something called sessions. These are academic sessions (think offerings of a particular program). The tables to represent a sessions information are: sessions session_terms session_subjects session_mark_item_info session_marks All of these tables have their own primary keys, and are like a tree, in that sessions have terms, terms have subjects, subjects have mark items, etc. So each on would have at least its "parent's" foreign key. My question is, design wise is it a good idea to include the sessions primary key in the other tables as a foreign key to easily select related session items, or is that too much redundency? If I include the session foreign key (or all parent foreign keys from tables up the heirarchy) in all the tables, I can easily select all the marks for a session. As an example, something like SELECT mark FROM session_marks WHERE sessionID=... If I don't, then I would have to combine selects with something like WHERE something IN (SELECT... Which approach is "more correct" or efficient? Thanks in advance!

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• Running an existing LINQ query against a dynamic object (DataTable like)

  - by TomTom

  Hello, I am working on a generic OData provider to go against a custom data provider that we have here. Thsi is fully dynamic in that I query the data provider for the table it knows. I have a basic storage structure in place so far based on the OData sample code. My problem is: OData supports queries and expects me to hand in an IQueryable implementation. On the lowe rside, I dont have any query support. Not a joke - the provider returns tables and the WHERE clause is not supported. Performance is not an issue here - the tables are small. It is ok to sort them in the OData provider. My main problem is this. I submit a SQL statement to get out the data of a table. The result is some sort of ADO.NET data reader here. I need to expose an IQueryable implementation for this data to potentially allow later filtering. Any ide ahow to best touch that? .NET 3.5 only (no 4.0 planned for some time). I was seriously thinking of creating dynamic DTO classes for every table (emitting bytecode) so I can use standard LINQ. Right now I am using a dictionary per entry (not too efficient) but I see no real way to filter / sort based on them.

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• Passing data between ViewControllers versus doing local Fetch in each VC

  - by Tofrizer

  Hi All, I'm developing an iPhone app using Core Data and I'm looking for some general advice and recommendations on whether its acceptable to pass data between ViewControllers versus doing a local fetch in each ViewController as you navigate to it. Ordinarily I would say it all depends on various factors (e.g. performance etc) but the passing data approach is so prevalent in my app and I'm spooked by all the stories about Apple rejecting apps because of not conforming to their standard guidelines. So let me put another way -- is it non-standard to pass data between VC's? The reason I pass data so much is because each ViewController is just another view on to data present in my object model / graph. Once I have a handle on my first object in the first view controller (which I of course do have to fetch), I can use the existing object composition / relationships to drill down into the next level of detail into data and so I just pass these objects to the next VC. Separately, one possible downside with this passing-data-to-each-VC approach is I don't benefit from (what I perceive to be) the optimisation/benefits that NSFetchedResultsController provides in terms of efficient memory usage and section handling. My app is read-only but I do have one table with 5000 rows and I'm curious if I am missing out on NSFetchedResultsController benefits. Any thoughts on this as well? Can I somehow still benefit from NSFetchedResultsController goodness without having to do a full fetch (as I would have already passed in the data from my previous VC)? Thanks a lot.

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• How to do this Python / MySQL manipulation (match) more efficiently?

  - by NJTechie

  Following is my data : Company Table : ID Company Address City State Zip Phone 1 ABC 123 Oak St Philly PA 17542 7329878901 2 CDE 111 Joe St Newark NJ 08654 3 GHI 211 Foe St Brick NJ 07740 7321178901 4 JAK 777 Wall Ocean NJ 07764 7322278901 5 KLE 87 Ilk St Plains NY 07654 7376578901 6 AB 1 W.House SField PA 87656 7329878901 Branch Office Table : ID Address City State Zip Phone 1 323 Alk St Philly PA 17542 7329832221 1 171 Joe St Newark NJ 08654 3 287 Foe St Brick NJ 07740 7321178901 3 700 Wall Ocean NJ 07764 7322278901 1 89 Blk St Surrey NY 07154 7376222901 File to be Matched (In MySQL): ID Company Address City State Zip Phone 1 ABC 123 Oak St Philly PA 17542 7329878901 2 AB 171 Joe St Newark NJ 08654 3 GHI 211 Foe St Brick NJ 07740 7321178901 4 JAK 777 Wall Ocean NJ 07764 7322278901 5 K 87 Ilk St Plains NY 07654 7376578901 Resulting File : ID Company Address City State Zip Phone appendedID 1 ABC 123 Oak St Philly PA 17542 7329878901 [Original record, field always empty] 1 ABC 171 Joe St Newark NJ 08654 1 [Company Table] 1 ABC 323 Alk St Philly PA 17542 7329832221 1 [Branch Office Table] 1 AB 1 W.House SField PA 87656 7329878901 6 [Partial firm and State, Zip match] 2 CDE 111 Joe St Newark NJ 08654 3 GHI 211 Foe St Brick NJ 07740 7321178901 3 GHI 700 Wall Ocean NJ 07764 7322278901 3 3 GHI 287 Foe St Brick NJ 07740 7321178901 3 4 JAK 777 Wall Ocean NJ 07764 7322278901 5 KLE 87 Ilk St Surrey NY 07654 7376578901 5 KLE 89 Blk St Surrey NY 07154 7376222901 5 Requirement : 1) I have to match each firm on the 'File to be Matched' to that of Company and Branch Office tables (MySQL). 2) If there are multiple exact/partial matches, then the ID from Company, Branch Office table is inserted as a new row in the resulting file. 3) Not all the firms will be matched perfectly, in that case I have to match on partial Company names (like 5/8th of the company name) and any of the address fields and insert them in the resulting file. Please help me out in the most efficient solution for this problem.

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• Java: split a List into two sub-Lists?

  - by Chris Conway

  What's the simplest, most standard, and/or most efficient way to split a List into two sub-Lists in Java? It's OK to mutate the original List, so no copying should be necessary. The method signature could be /** Split a list into two sublists. The original list will be modified to * have size i and will contain exactly the same elements at indices 0 * through i-1 as it had originally; the returned list will have size * len-i (where len is the size of the original list before the call) * and will have the same elements at indices 0 through len-(i+1) as * the original list had at indices i through len-1. */ <T> List<T> split(List<T> list, int i); [EDIT] List.subList returns a view on the original list, which becomes invalid if the original is modified. So split can't use subList unless it also dispenses with the original reference (or, as in Marc Novakowski's answer, uses subList but immediately copies the result).

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