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• Determining polygon intersection and containment

  - by Victor Liu

  I have a set of simple (no holes, no self-intersections) polygons, and I need to check that they don't intersect each other (one can be entirely contained in another; that is okay). I can check this by simply checking the per-vertex inside-ness of one polygon versus other polygons. I also need to determine the containment tree, which is the set of relationships that say which polygon contains any given polygon. Since no polygon can intersect any other, then any contained polygon has a unique container; the "next-bigger" one. In other words, if A contains B contains C, then A is the parent of B, and B is the parent of C, and we don't consider A the parent of C. The question: How do I efficiently determine the containment relationships and check the non-intersection criterion? I ask this as one question because maybe a combined algorithm is more efficient than solving each problem separately. The algorithm should take as input a list of polygons, given by a list of their vertices. It should produce a boolean B indicating if none of the polygons intersect any other polygon, and also if B = true, a list of pairs (P, C) where polygon P is the parent of child C. This is not homework. This is for a hobby project I am working on.

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• Create new or update existing entity at one go with JPA

  - by Alex R

  A have a JPA entity that has timestamp field and is distinguished by a complex identifier field. What I need is to update timestamp in an entity that has already been stored, otherwise create and store new entity with the current timestamp. As it turns out the task is not as simple as it seems from the first sight. The problem is that in concurrent environment I get nasty "Unique index or primary key violation" exception. Here's my code: // Load existing entity, if any. Entity e = entityManager.find(Entity.class, id); if (e == null) { // Could not find entity with the specified id in the database, so create new one. e = entityManager.merge(new Entity(id)); } // Set current time... e.setTimestamp(new Date()); // ...and finally save entity. entityManager.flush(); Please note that in this example entity identifier is not generated on insert, it is known in advance. When two or more of threads run this block of code in parallel, they may simultaneously get null from entityManager.find(Entity.class, id) method call, so they will attempt to save two or more entities at the same time, with the same identifier resulting in error. I think that there are few solutions to the problem. Sure I could synchronize this code block with a global lock to prevent concurrent access to the database, but would it be the most efficient way? Some databases support very handy MERGE statement that updates existing or creates new row if none exists. But I doubt that OpenJPA (JPA implementation of my choice) supports it. Event if JPA does not support SQL MERGE, I can always fall back to plain old JDBC and do whatever I want with the database. But I don't want to leave comfortable API and mess with hairy JDBC+SQL combination. There is a magic trick to fix it using standard JPA API only, but I don't know it yet. Please help.

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• Inserting javascript with jQuery .html

  - by Andrew Appleby

  I'm experiencing an issue with a website I'm working on, where I originally believed I could simply replace $("main").html('THIS') which was originally code for a flash object, with a new and improved HTML5/Javascript version. The original code: $("#main").html('<div style="height: 100%; width: 100%; overflow: hidden;"><object width="100%" height="100%" codebase="http://fpdownload.macromedia.com/pub/shockwave/cabs/flash/swflash.cab#version=8,0,0,0" classid="clsid:d27cdb6e-ae6d-11cf-96b8-444553540000">\ <param value="images/uploads/'+image_id+'.swf" name="movie">\ <param value="true" name="allowFullScreen">\ <param value="#737373" name="bgcolor">\ <param value="" name="FlashVars">\ <embed width="100%" height="100%" flashvars="" bgcolor="#737373" allowfullscreen="true" src="images/uploads/'+image_id+'.swf" type="application/x-shockwave-flash" pluginspage="http://www.macromedia.com/go/getflashplayer">\ </object></div>\ '); }); And my (failed) attempt at inserting my new code: $("#main").html('<script type="text/javascript">pano=new pano2vrPlayer("container");skin=new pano2vrSkin(pano);pano.readConfigUrl("xml/tablet_'+image_id+'.xml");hideUrlBar();</script>'); It doesn't even work when I just put , so I know it's gotta be the javascript itself. I've looked at the solutions out there, but I can't make sense in how to properly implement them here in the most efficient way. Your help is much appreciated, thanks!

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• Bulletin board - Database optimisation

  - by andrew

  This question is a follow on from this Question The project and problem The project I am currently working on is a bulletin board for a large non-profit organisation. The bulletin board will be used to allow inter-office communication within the organisation. I am building the application and have been having trouble extracting the results that I need from my database because I don't think it is properly normalized and because of limitations in my knowledge of relational database theory and mysql. I would appreciate input into the design of the board in general and in particular, ways that the database structure can be improved to facilitate efficient queries and help me develop this application and future application faster Business Logic The bulletin board will be used in the following way Posting bulletins and responses to bulletins Employees or 'users' in offices around the country will be able to post messages to the bulletin board.Bulletins must be posted to a location and categorised- i'll call these "bulletins". Users will be able to post any number of replies to any one bulletin and users will be able to reply to their own bulletin - i'll call these 'replies'. Rating bulletins and replies Users will be able to either 'like' or 'dislike' a bulletin or a reply and the total number of likes or dislikes will be shown for each bulletin or reply. Viewing the bulletin board and responses Bulletins can be displayed chronologically. Users can sort bulletins chronologically or chronologically by the latest reply to that bulletin(let me know if you need more explanation) When a particular bulletin is selected, replies to that bulletin will be displayed chronologically @PerformanceDBA - edited 10:34 est 28/12/10I have begun implementing the data model. I assume that the 6th data model is the physical model because it contains the associative tables. I am going to post any questions that I have below. I will put up a database dump once I am done. I will then put up a list of all the queries that I need to run on the database and begin writing them. I hope you had a good Christmas. I'm in Canada and there's snow! Implementation of Physical model

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• Refactoring - Speed increase

  - by Michael G

  How can I make this function more efficient. It's currently running at 6 - 45 seconds. I've ran dotTrace profiler on this specific method, and it's total time is anywhere between 6,000ms to 45,000ms. The majority of the time is spent on the "MoveNext" and "GetEnumerator" calls. and example of the times are 71.55% CreateTableFromReportDataColumns - 18, 533* ms - 190 calls -- 55.71% MoveNext - 14,422ms - 10,775 calls What can I do to speed this method up? it gets called a lot, and the seconds add up: private static DataTable CreateTableFromReportDataColumns(Report report) { DataTable table = new DataTable(); HashSet<String> colsToAdd = new HashSet<String> { "DataStream" }; foreach (ReportData reportData in report.ReportDatas) { IEnumerable<string> cols = reportData.ReportDataColumns.Where(c => !String.IsNullOrEmpty(c.Name)).Select(x => x.Name).Distinct(); foreach (var s in cols) { if (!String.IsNullOrEmpty(s)) colsToAdd.Add(s); } } foreach (string col in colsToAdd) { table.Columns.Add(col); } return table; }

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• Web development scheme for staging and production servers using Git Push

  - by ServAce85

  I am using git to manage a dynamic website (PHP + MySQL) and I want to send my files from my localhost to my staging and development servers in the most efficient and hassle-free way. I am currently convinced that the best way for me to approach this problem is to use this git branching model to organize my local git repo. From there, I will use the release branches to push to my staging server for testing. Once I am happy that the release code works on the staging server, I can then merge with my master branch and push that to my production server. Pushing to Staging Server: As noted in many introductory git posts, I could run into problems pushing into a non-bare repo, so, as suggested in this response, I plan to push the release branch to a bare repo on the server and have a post-receive hook that clones the bare repo to a non-bare repo that also acts as the web-hosted directory. Pushing to Production Server: Here's my newest source of confusion... In the response that I cited above, it made me curious as to why @Paul states that it's a completely different story when pushing to a live, development server. I guess I don't see the problem. Would it be safe and hassle-free to follow the same steps as above, but for the master branch? Where are the potential pit-falls? Config Files: With respect to configuration files that are unique to each environment (.htaccess, config.php, etc), it seems simplest to .gitignore each of those files in their respective repos on their respective servers. Can you see anything immediately wrong with this? Better solutions? Accessing Data: Finally, as I initially stated, the site uses MySQL databases to store data. How would you suggest I access that data (for testing purposes) from the staging server and localhost? I realize that I may have asked way too many questions for a single post, but since they're all related to the best way to set up this development scheme, I thought it was necessary.

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• Implementation of MVC with SQLite and NSURLConnection, use cases?

  - by user324723

  I'm interested in knowing how others have implemented/designed database & web services in their iphone app and how they simplified it for the entire application. My application is dependent on these services and I can't figure out a efficient way to use them together due to the (semi)complexity of my requirements. My past attempts on combining them haven't been completely successful or at least optimal in my mind. I'm building a database driven iphone app that uses a relational database in sqlite and consumes web services based on missing content or user interaction. Like this hasn't been done before...right? Since I am using a relational database - any web services consumed requires normalization, parsing the result and persisting it to the database before it can be displayed in a table view controller. The applications UI consists of nested(nav controller) table views where a user can select a cell and be taken to the next table view where it attempts to populate the table views data source from the database. If nothing exists in the database then it will send a request via web services to download its content, thus download - parse - persist - query - display. Since the user has the ability to request a refresh of this data it still requires the same process. Quickly describing what I've implemented and tried to run with - 1st attempt - Used a singleton web service class that handled sending web service requests, parsing the result and returning it to the table view controller via delegate protocols. Once the controller received that data it would then be responsible for persisting it to the database and re-returning the result. I didn't like the idea of only preventing the case where the app delegate selector doesn't exists(released) causing the app to crash. 2nd attempt - Used NSNotificationCenter for easy access to both database and web services but later realized it was more complex due to adding and removing observers per view(which isn't advised anyways).

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• Calculate the year for ending month/day?

  - by Dave Jarvis

  Given: Start Year Start Month & Start Day End Month & End Day What SQL statement results in TRUE if a date lands between the Start and End days? 1st example: Start Date = 11-22 End Date = 01-17 Start Year = 2009 Specific Date = 2010-01-14 TRUE 2nd example: Start Date = 11-22 End Date = 11-16 Start Year = 2009 Specific Date = 2010-11-20 FALSE 3rd example: Start Date = 02-25 End Date = 03-19 Start Year = 2004 Specific Date = 2004-02-29 TRUE I was thinking of using the MySQL functions datediff and sign plus a CASE condition to determine whether the year wraps, but it seems rather expensive. Am looking for a simple, efficient calculation. Update 1 The problem is the end date cannot simply use the year. The year must be increased if the end month/day combination happens before the start date. The start date is easy: Start Date = date( concat_ws( '-', year, Start Month, Start Day ) ) The end date is not so simple. Update 2 Here is what I was thinking about for obtaining the end year: end_year = case sign( diff( date( concat_ws( year, start_month, start_day ) ), date( concat_ws( year, end_month, end_day ) ) ) ) when -1 then Start_Year + 1 else Start_Year end case Then wrap that expression (once syntactically correct) inside of another date, followed by BETWEEN statement. Update 3 To clear up some confusion: there is no end year. The end year must be calculated. Thank you!

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• help me reason about F# threads

  - by Kevin Cantu

  In goofing around with some F# (via MonoDevelop), I have written a routine which lists files in a directory with one thread: let rec loop (path:string) = Array.append ( path |> Directory.GetFiles ) ( path |> Directory.GetDirectories |> Array.map loop |> Array.concat ) And then an asynchronous version of it: let rec loopPar (path:string) = Array.append ( path |> Directory.GetFiles ) ( let paths = path |> Directory.GetDirectories if paths <> [||] then [| for p in paths -> async { return (loopPar p) } |] |> Async.Parallel |> Async.RunSynchronously |> Array.concat else [||] ) On small directories, the asynchronous version works fine. On bigger directories (e.g. many thousands of directories and files), the asynchronous version seems to hang. What am I missing? I know that creating thousands of threads is never going to be the most efficient solution -- I only have 8 CPUs -- but I am baffled that for larger directories the asynchronous function just doesn't respond (even after a half hour). It doesn't visibly fail, though, which baffles me. Is there a thread pool which is exhausted? How do these threads actually work?

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• Two radically different queries against 4 mil records execute in the same time - one uses brute force.

  - by IanC

  I'm using SQL Server 2008. I have a table with over 3 million records, which is related to another table with a million records. I have spent a few days experimenting with different ways of querying these tables. I have it down to two radically different queries, both of which take 6s to execute on my laptop. The first query uses a brute force method of evaluating possibly likely matches, and removes incorrect matches via aggregate summation calculations. The second gets all possibly likely matches, then removes incorrect matches via an EXCEPT query that uses two dedicated indexes to find the low and high mismatches. Logically, one would expect the brute force to be slow and the indexes one to be fast. Not so. And I have experimented heavily with indexes until I got the best speed. Further, the brute force query doesn't require as many indexes, which means that technically it would yield better overall system performance. Below are the two execution plans. If you can't see them, please let me know and I'll re-post then in landscape orientation / mail them to you. Brute-force query: Index-based exception query: My question is, based on the execution plans, which one look more efficient? I realize that thing may change as my data grows.

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• Oracle - UPSERT with update not executed for unmodified values

  - by Buthrakaur

  I'm using following update or insert Oracle statement at the moment: BEGIN UPDATE DSMS SET SURNAME = :SURNAME, FIRSTNAME = :FIRSTNAME, VALID = :VALID WHERE DSM = :DSM; IF (SQL%ROWCOUNT = 0) THEN INSERT INTO DSMS (DSM, SURNAME, FIRSTNAME, VALID) VALUES (:DSM, :SURNAME, :FIRSTNAME, :VALID); END IF; END; This runs fine except that the update statement performs dummy update if the data is same as the parameter values provided. I would not mind the dummy update in normal situation, but there's a replication/synchronization system build over this table using triggers on tables to capture updated records and executing this statement frequently for many records simply means that I'd cause huge traffic in triggers and the sync system. Is there any simple method how to reformulate this code that the update statement wouldn't update record if not necessary without using following IF-EXISTS check code which I find not sleek enough and maybe also not most efficient for this task? DECLARE CNT NUMBER; BEGIN SELECT COUNT(1) INTO CNT FROM DSMS WHERE DSM = :DSM; IF SQL%FOUND THEN UPDATE DSMS SET SURNAME = :SURNAME, FIRSTNAME = :FIRSTNAME, VALID = :VALID WHERE DSM = :DSM AND (SURNAME != :SURNAME OR FIRSTNAME != :FIRSTNAME OR VALID != :VALID); ELSE INSERT INTO DSMS (DSM, SURNAME, FIRSTNAME, VALID) VALUES (:DSM, :SURNAME, :FIRSTNAME, :VALID); END IF; END;

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• Fastest XML parser for small, simple documents in Java

  - by Varkhan

  I have to objectify very simple and small XML documents (less than 1k, and it's almost SGML: no namespaces, plain UTF-8, you name it...), read from a stream, in Java. I am using JAXP to process the data from my stream into a Document object. I have tried Xerces, it's way too big and slow... I am using Dom4j, but I am still spending way too much time in org.dom4j.io.SAXReader. Does anybody out there have any suggestion on a faster, more efficient implementation, keeping in mind I have very tough CPU and memory constraints? [Edit 1] Keep in mind that my documents are very small, so the overhead of staring the parser can be important. For instance I am spending as much time in org.xml.sax.helpers.XMLReaderFactory.createXMLReader as in org.dom4j.io.SAXReader.read [Edit 2] The result has to be in Dom format, as I pass the document to decision tools that do arbitrary processing on it, like switching code based on the value of arbitrary XPaths, but also extracting lists of values packed as children of a predefined node. [Edit 3] In any case I eventually need to load/parse the complete document, since all the information it contains is going to be used at some point. (This question is related to, but different from, http://stackoverflow.com/questions/373833/best-xml-parser-for-java )

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• Java-Eclipse-Spring 3.1 - the fastest way to get familiar with this set

  - by Leron

  I, know almost all of you at some point of your life as a programmer get to the point where you know (more or less) different technologies/languages/IDEs and a times come when you want to get things together and start using them once - more efficient and second - more closely to the real life situation where in fact just knowing Java, or some experience with Eclipse doesn't mean nothing, and what makes you a programmer worth something is the ability to work with the combination of 2 or more combinations. Having this in mind here is my question - what do you think is the optimal way of getting into Java+Eclipse+Spring3.1 world. I've read, and I've read a lot. I started writing real code but almost every step is discovering the wheel again and again, wondering how to do thing you know are some what trivial, but you've missed that one article where this topic was discussed and so on. I don't mind for paying for a good tutorial like for example, after a bit of research I decided that instead of losing a lot of time getting the different parts together I'd rather pay for the videos in http://knpuniversity.com/screencast/starting-in-symfony2-tutorial and save myself a lot of time (I hope) and get as fast as possible to writing a real code instead of wondering what do what and so on. But I find it much more difficult to find such sources of info especially when you want something more specific as me and that's the reason to ask this question. I know a lot of you go through the hard way, and I won't give up if I have to do the same, but to be honest I really hope to get post with good tutorials on the subject (paid or not) because in my situation time is literally money. Thanks Leron

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• C#. How to pass message from unsafe callback to managed code?

  - by maxima120

  Is there a simple example of how to pass messages from unsafe callback to managed code? I have a proprietary dll which receives some messages packed in structs and all is coming to a callback function. The example of usage is as follows but it calls unsafe code too. I want to pass the messages into my application which is all managed code. *P.S. I have no experience in interop or unsafe code. I used to develop in C++ 8 yrs ago but remember very little from that nightmarish times :) P.P.S. The application is loaded as hell, the original devs claim it processes 2mil messages per sec.. I need a most efficient solution.* static unsafe int OnCoreCallback(IntPtr pSys, IntPtr pMsg) { // Alias structure pointers to the pointers passed in. CoreSystem* pCoreSys = (CoreSystem*)pSys; CoreMessage* pCoreMsg = (CoreMessage*)pMsg; // message handler function. if (pCoreMsg->MessageType == Core.MSG_STATUS) OnCoreStatus(pCoreSys, pCoreMsg); // Continue running return (int)Core.CALLBACKRETURN_CONTINUE; } Thank you.

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• Fast serarch of 2 dimensional array

  - by Tim

  I need a method of quickly searching a large 2 dimensional array. I extract the array from Excel, so 1 dimension represents the rows and the second the columns. I wish to obtain a list of the rows where the columns match certain criteria. I need to know the row number (or index of the array). For example, if I extract a range from excel. I may need to find all rows where column A =”dog” and column B = 7 and column J “a”. I only know which columns and which value to find at run time, so I can’t hard code the column index. I could use a simple loop, but is this efficient ? I need to run it several thousand times, searching for different criteria each time. For r As Integer = 0 To UBound(myArray, 0) - 1 match = True For c = 0 To UBound(myArray, 1) - 1 If not doesValueMeetCriteria(myarray(r,c) then match = False Exit For End If Next If match Then addRowToMatchedRows(r) Next The doesValueMeetCriteria function is a simple function that checks the value of the array element against the query requirement. e.g. Column A = dog etc. Is it more effiecent to create a datatable from the array and use the .select method ? Can I use Linq in some way ? Perhaps some form of dictionary or hashtable ? Or is the simple loop the most effiecent ? Your suggestions are most welcome.

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• Tail recursion and memoization with C#

  - by Jay

  I'm writing a function that finds the full path of a directory based on a database table of entries. Each record contains a key, the directory's name, and the key of the parent directory (it's the Directory table in an MSI if you're familiar). I had an iterative solution, but it started looking a little nasty. I thought I could write an elegant tail recursive solution, but I'm not sure anymore. I'll show you my code and then explain the issues I'm facing. Dictionary<string, string> m_directoryKeyToFullPathDictionary = new Dictionary<string, string>(); ... private string ExpandDirectoryKey(Database database, string directoryKey) { // check for terminating condition string fullPath; if (m_directoryKeyToFullPathDictionary.TryGetValue(directoryKey, out fullPath)) { return fullPath; } // inductive step Record record = ExecuteQuery(database, "SELECT DefaultDir, Directory_Parent FROM Directory where Directory.Directory='{0}'", directoryKey); // null check string directoryName = record.GetString("DefaultDir"); string parentDirectoryKey = record.GetString("Directory_Parent"); return Path.Combine(ExpandDirectoryKey(database, parentDirectoryKey), directoryName); } This is how the code looked when I realized I had a problem (with some minor validation/massaging removed). I want to use memoization to short circuit whenever possible, but that requires me to make a function call to the dictionary to store the output of the recursive ExpandDirectoryKey call. I realize that I also have a Path.Combine call there, but I think that can be circumvented with a ... + Path.DirectorySeparatorChar + .... I thought about using a helper method that would memoize the directory and return the value so that I could call it like this at the end of the function above: return MemoizeHelper( m_directoryKeyToFullPathDictionary, Path.Combine(ExpandDirectoryKey(database, parentDirectoryKey)), directoryName); But I feel like that's cheating and not going to be optimized as tail recursion. Any ideas? Should I be using a completely different strategy? This doesn't need to be a super efficient algorithm at all, I'm just really curious. I'm using .NET 4.0, btw. Thanks!

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• mysql image disable print download

  - by Vish

  Hi, We use a Flex AIR client and a WAMP server. Tiff images are stored in MySQL. Currently, I can download the image from AIR client and it prompts for a download dialog. Things are fine till this point. We got a new requirement. Requirement is that only some users can print the image which gets downloaded. For other users, they should not be able to print the tiff image. Wondering how to accomplish this. One idea, not sure if its efficient, is to convert the image requested to pdf at the server side, disable print option there(hope there are API's available) and send back the pdf. Please let me know btter ideas. Also, is there a way to prevent file download dialog from popping up everytime the file is requested for download? Can we just get the file stream to the client and manipulate it to open with a particular viewer or write it to pdf... Please help.

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• N-gram split function for string similarity comparison

  - by Michael

  As part of excersise to better understand F# which I am currently learning , I wrote function to split given string into n-grams. 1) I would like to receive feedback about my function : can this be written simpler or in more efficient way? 2) My overall goal is to write function that returns string similarity (on 0.0 .. 1.0 scale) based on n-gram similarity; Does this approach works well for short strings comparisons , or can this method reliably be used to compare large strings (like articles for example). 3) I am aware of the fact that n-gram comparisons ignore context of two strings. What method would you suggest to accomplish my goal? //s:string - target string to split into n-grams //n:int - n-gram size to split string into let ngram_split (s:string, n:int) = let ngram_count = s.Length - (s.Length % n) let ngram_list = List.init ngram_count (fun i -> if( i + n >= s.Length ) then s.Substring(i,s.Length - i) + String.init ((i + n) - s.Length) (fun i -> "#") else s.Substring(i,n) ) let ngram_array_unique = ngram_list |> Seq.ofList |> Seq.distinct |> Array.ofSeq //produce tuples of ngrams (ngram string,how much occurrences in original string) Seq.init ngram_array_unique.Length (fun i -> (ngram_array_unique.[i], ngram_list |> List.filter(fun item -> item = ngram_array_unique.[i]) |> List.length) )

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• Are there any libraries for parsing "number expressions" like 1,2-9,33- in Java

  - by mihi

  Hi, I don't think it is hard, just tedious to write: Some small free (as in beer) library where I can put in a String like 1,2-9,33- and it can tell me whether a given number matches that expression. Just like most programs have in their print range dialogs. Special functions for matching odd or even numbers only, or matching every number that is 2 mod 5 (or something like that) would be nice, but not needed. The only operation I have to perform on this list is whether the range contains a given (nonnegative) integer value; more operations like max/min value (if they exist) or an iterator would be nice, of course. What would be needed that it does not occupy lots of RAM if anyone enters 1-10000000 but the only number I will ever query is 12345 :-) (To implement it, I would parse a list into several (min/max/value/mod) pairs, like 1,10,0,1 for 1-10 or 11,33,1,2 for 1-33odd, or 12,62,2,10 for 12-62/10 (i. e. 12, 22, 32, ..., 62) and then check each number for all the intervals. Open intervals by using Integer.MaxValue etc. If there are no libs, any ideas to do it better/more efficient?)

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• Saving multiple items per single database cell...

  - by eugeneK

  Hi, i have a countries list. Each user can check multiple countries. Once saved, this "user country list" will be used to get whether other users fit into countries certain user chose. Question is what would be the most efficient approach to this problem... I have one, one to save user selection as delimited list like Canada,USA,France ... in single varchar(max) field but problem with it would be that once user from Germany enters page i perform this check on. To search for Germany i would be needed to get all items and un-delimit each field to check against value or to use sql 'like' which again is pretty damn slow.. If you have better solution or some tips i would be glad to hear. Just to make sure, many users will have their own selections of countries from which and only they want to have users to land on their page. While millions of users will reach those pages. So the faster approach will be the better. technology, MSSQL and ASP.NET thanks

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• Is there any benefit to my rather quirky character sizing convention?

  - by Paul Alan Taylor

  I love things that are a power of 2. I celebrated my 32nd birthday knowing it was the last time in 32 years I'd be able to claim that my age was a power of 2. I'm obsessed. It's like being some Z-list Batman villain, except without the colourful adventures and a face full of batarangs. I ensure that all my enum values are powers of 2, if only for future bitwise operations, and I'm reasonably assured that there is some purpose (even if latent) for doing it. Where I'm less sure, is in how I define the lengths of database fields. Again, I can't help it. Everything ends up being a power of 2. CREATE TABLE Person ( PersonID int IDENTITY PRIMARY KEY ,Firstname varchar(64) ,Surname varchar(128) ) Can any SQL super-boffins who know about the internals of how stuff is stored and retrieved tell me whether there is any benefit to my inexplicable obsession? Is it more efficient to size character fields this way? Can anyone pop in with an "actually, what you're doing works because ....."? I suspect I'm just getting crazier in my older age, but it'd be nice to know that there is some method to my madness.

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• how to synchronize database table and directory with php

  - by twmulloy

  hello, I have a directory with files and a database table with what should be the same files. I would like to be able to synchronize the database table with the directory. What would be the most efficient way to do this? or would I realistically only be able to do this in a brute manner? Here's my approach: 1. retrieve all of the files in the directory as array 2. retrieve all of the filenames in the database table as array 3. loop through the file values in the directory array and use in_array() on the database table array to verify the filename is in that array, and if not then start building an array to insert the missing filenames. run db query to add each missing file row to database table 4. loop through directory array and use in_array() on the directory array and anything not found in the directory array will just be deleted from the table. Is there a better way to go about this? or something better for this in php than in_array()?

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• What's the difference between these LINQ queries ?

  - by SnAzBaZ

  I use LINQ-SQL as my DAL, I then have a project called DB which acts as my BLL. Various applications then access the BLL to read / write data from the SQL Database. I have these methods in my BLL for one particular table: public IEnumerable<SystemSalesTaxList> Get_SystemSalesTaxList() { return from s in db.SystemSalesTaxLists select s; } public SystemSalesTaxList Get_SystemSalesTaxList(string strSalesTaxID) { return Get_SystemSalesTaxList().Where(s => s.SalesTaxID == strSalesTaxID).FirstOrDefault(); } public SystemSalesTaxList Get_SystemSalesTaxListByZipCode(string strZipCode) { return Get_SystemSalesTaxList().Where(s => s.ZipCode == strZipCode).FirstOrDefault(); } All pretty straight forward I thought. Get_SystemSalesTaxListByZipCode is always returning a null value though, even when it has a ZIP Code that exists in that table. If I write the method like this, it returns the row I want: public SystemSalesTaxList Get_SystemSalesTaxListByZipCode(string strZipCode) { var salesTax = from s in db.SystemSalesTaxLists where s.ZipCode == strZipCode select s; return salesTax.FirstOrDefault(); } Why does the other method not return the same, as the query should be identical ? Note that, the overloaded Get_SystemSalesTaxList(string strSalesTaxID) returns a record just fine when I give it a valid SalesTaxID. Is there a more efficient way to write these "helper" type classes ? Thanks!

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• What is the proper way to use a Logger in a Serializable Java class?

  - by Tim Visher

  I have the following (doctored) class in a system I'm working on and Findbugs is generating a SE_BAD_FIELD warning and I'm trying to understand why it would say that before I fix it in the way that I thought I would. The reason I'm confused is because the description would seem to indicate that I had used no other non-serializable instance fields in the class but bar.model.Foo is also not serializable and used in the exact same way (as far as I can tell) but Findbugs generates no warning for it. import bar.model.Foo; import java.io.File; import java.io.Serializable; import java.util.List; import org.slf4j.Logger; import org.slf4j.LoggerFactory; public class Demo implements Serializable { private final Logger logger = LoggerFactory.getLogger(this.getClass()); private final File file; private final List<Foo> originalFoos; private Integer count; private int primitive = 0; public Demo() { for (Foo foo : originalFoos) { this.logger.debug(...); } } ... } My initial blush at a solution is to get a logger reference from the factory right as I use it: public DispositionFile() { Logger logger = LoggerFactory.getLogger(this.getClass()); for (Foo foo : originalFoos) { this.logger.debug(...); } } That doesn't seem particularly efficient, though. Thoughts?

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• Right way to return proxy model instance from a base model instance in Django ?

  - by sotangochips

  Say I have models: class Animal(models.Model): type = models.CharField(max_length=255) class Dog(Animal): def make_sound(self): print "Woof!" class Meta: proxy = True class Cat(Animal): def make_sound(self): print "Meow!" class Meta: proxy = True Let's say I want to do: animals = Animal.objects.all() for animal in animals: animal.make_sound() I want to get back a series of Woofs and Meows. Clearly, I could just define a make_sound in the original model that forks based on animal_type, but then every time I add a new animal type (imagine they're in different apps), I'd have to go in and edit that make_sound function. I'd rather just define proxy models and have them define the behavior themselves. From what I can tell, there's no way of returning mixed Cat or Dog instances, but I figured maybe I could define a "get_proxy_model" method on the main class that returns a cat or a dog model. Surely you could do this, and pass something like the primary key and then just do Cat.objects.get(pk = passed_in_primary_key). But that'd mean doing an extra query for data you already have which seems redundant. Is there any way to turn an animal into a cat or a dog instance in an efficient way? What's the right way to do what I want to achieve?

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