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• How is this algorithm, for finding maximum path on a Directed Acyclical Graph, called?

  - by Martín Fixman

  Since some time, I'm using an algorithm that runs in complexity O(V + E) for finding maximum path on a Directed Acyclical Graph from point A to point B, that consists on doing a flood fill to find what nodes are accessible from note A, and how many "parents" (edges that come from other nodes) each node has. Then, I do a BFS but only "activating" a node when I already had used all its "parents". queue <int> a int paths[] ; //Number of paths that go to note i int edge[][] ; //Edges of a int mpath[] ; //max path from 0 to i (without counting the weight of i) int weight[] ; //weight of each node mpath[0] = 0 a.push(0) while not empty(a) for i in edge[a] paths[i] += 1 a.push(i) while not empty(a) for i in children[a] mpath[i] = max(mpath[i], mpath[a] + weight[a]) ; paths[i] -= 1 ; if path[i] = 0 a.push(i) ; Is there any special name for this algorithm? I told it to an Informatics professor, he just called it "Maximum Path on a DAG", but it doesn't sound good when you say "I solved the first problem with a Fenwick Tree, the second with Dijkstra, and the third with Maximum Path".

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• What can cause my code to run slower when the server JIT is activated?

  - by durandai

  I am doing some optimizations on an MPEG decoder. To ensure my optimizations aren't breaking anything I have a test suite that benchmarks the entire codebase (both optimized and original) as well as verifying that they both produce identical results (basically just feeding a couple of different streams through the decoder and crc32 the outputs). When using the "-server" option with the Sun 1.6.0_18, the test suite runs about 12% slower on the optimized version after warmup (in comparison to the default "-client" setting), while the original codebase gains a good boost running about twice as fast as in client mode. While at first this seemed to be simply a warmup issue to me, I added a loop to repeat the entire test suite multiple times. Then execution times become constant for each pass starting at the 3rd iteration of the test, still the optimized version stays 12% slower than in the client mode. I am also pretty sure its not a garbage collection issue, since the code involves absolutely no object allocations after startup. The code consists mainly of some bit manipulation operations (stream decoding) and lots of basic floating math (generating PCM audio). The only JDK classes involved are ByteArrayInputStream (feeds the stream to the test and excluding disk IO from the tests) and CRC32 (to verify the result). I also observed the same behaviour with Sun JDK 1.7.0_b98 (only that ist 15% instead of 12% there). Oh, and the tests were all done on the same machine (single core) with no other applications running (WinXP). While there is some inevitable variation on the measured execution times (using System.nanoTime btw), the variation between different test runs with the same settings never exceeded 2%, usually less than 1% (after warmup), so I conclude the effect is real and not purely induced by the measuring mechanism/machine. Are there any known coding patterns that perform worse on the server JIT? Failing that, what options are available to "peek" under the hood and observe what the JIT is doing there?

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• Play 2.0 RESTful request post-processing

  - by virtualeyes

  In regard to this question I am curious how one can do post-request REST processing a la (crude): def postProcessor[T](content: T) = { request match { case Accepts.Json() => asJson(content) case Accepts.Xml() => asXml(content) case _ => content } } overriding onRouteRequest in Global config does not appear to provide access to body of the response, so it would seem that Action composition is the way to go to intercept the response and do post-processing task(s). Question: is this a good idea, or is it better to do content-type casting directly within a controller (or other class) method where the type to cast is known? Currently I'm doing this kind of thing everywhere: toJson( i18n("account not found") ) toJson( Map('orderNum-> orderNum) ) while I'd like the toJson/toXml conversion to happen based on accepts header post-request.

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• In MATLAB can I convert a java boolean to a MATLAB logical?

  - by Adrian

  In MATLAB I'm using a couple of java routines I've written to interface with a MyQSL database. One routine returns a boolean value result <1x1 java.lang.Boolean> >> result result = true When I then use it in a conditional statement I get an error message. >> if result, disp('result is true') end ??? Conversion to logical from java.lang.Boolean is not possible. Is there a way to use the java boolean class as a MATLAB logical type? Or do I have to resort to returning integer values from my java routines?

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• How do I best run a search on Date when it is not a :has_many association?

  - by Angela

  I have a number of activities that have a calculated scheduled date. The activities, for example, Email, have a email.days method which is the days from a Contact.start_date on which it should be sent. This means contact.start_date + email.days yields a date on which email is sent to contact. I would like to use link_to around the date, so I can see all the emails and associated contacts that are to be scheduled on that date. However, this "date" is not an attribute or an associate, so I'm not linking to a model's view. It's calculated. So: 1) What should the actual "format" of the date that gets passed in the URl be? What is the method to do the consistent conversion? 2) How do I (find) all instances, because this "date" is not an actual attribute, is it a calculated value which changes depending on the two associated models of Contact and Email. Thanks.

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• IGrouping and Casting in Linq

  - by FiveTools

  I have the following query: var groupCats = from g in groups group g by g.Value into grouped select new { GroupCategory = grouped.Key, Categories = GetCategories(grouped.Key, child) }; This works fine. In the anonymous type returned GroupCategory is a string, and Categories are an Enumerable - what is the proper way to declare this instead of using 'var'? I tried: IGrouping<string,string> groupCats = from g in groups group g by g.Value into grouped select new { GroupCategory = grouped.Key, Categories = GetCategories(grouped.Key, child) }; and IGrouping<string,Enumerable<string>> groupCats = from g in groups group g by g.Value into grouped select new { GroupCategory = grouped.Key, Categories = GetCategories(grouped.Key, child) }; In both instances I get: Cannot implicity convert type....An explicit conversion exists (are you missing a cast) How do I cast this?

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• Presentation Issue in an Unordered List

  - by phreeskier

  I'm having an issue with correctly presenting items in an unordered list. The labels are floating left and the related spans that are long in length are wrapping and showing below the label. I need a solution that keeps the related spans in their respective columns. In other words, I don't want long spans to show under the labels. What property can I take advantage of so that I get the desired layout in all of the popular browsers, including IE6? Thanks in advance for the help. My code is as follows: <ul> <li> <label>Name</label> <span><%= Html.Encode(Model.Name) %></span> </li> <li> <label>Entity</label> <span><%= Html.Encode(Model.Entity) %></span> </li> <li> <label>Phone</label> <span><%= Html.Encode(Model.Phone) %></span> </li> </ul> My CSS styling is as follows: ul { display:block; list-style-type:none; margin:0; padding:0; } ul li label { float:left; width:100px; }

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• Pointer incrementing query

  - by Craig

  I have been looking at this piece of code, and it is not doing what I expect. I have 3 globals. int x, y, *pointer, z; Inside of main I declare them. x = 10; y = 25; pointer = &x; now at this point &x is 0x004A144 &y is 0x004A138 pointer is pointing to 0x004A144 Now when I increment: y = *++pointer; it points to 0x004A148, this is the address y should be at shouldn't it? The idea is that incrementing the pointer to 'x' should increment it to point at y, but it doesn't seem to want to declare them in in order like I expect. If this a VS2005 / 2008 problem? Or maybe an Express problem? This isn't really homework, as I have done it a couple of years ago but I was revising on my pointer stuff and I tried this again. But this time I am getting unexpected results. Does anyone have opinions on this? *UPDATE sorry should be more clear, 'thought' on declaration 'y' should be at 148, and that incrementing the pointer pointing to x should increment 'pointer' to 148 (which it does), but that isn't where y is. Why isn't y declaring where it should be.

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• Weird MySQL behavior, seems like a SQL bug

  - by Daniel Magliola

  I'm getting a very strange behavior in MySQL, which looks like some kind of weird bug. I know it's common to blame the tried and tested tool for one's mistakes, but I've been going around this for a while. I have 2 tables, I, with 2797 records, and C, with 1429. C references I. I want to delete all records in I that are not used by C, so i'm doing: select * from i where id not in (select id_i from c); That returns 0 records, which, given the record counts in each table, is physically impossible. I'm also pretty sure that the query is right, since it's the same type of query i've been using for the last 2 hours to clean up other tables with orphaned records. To make things even weirder... select * from i where id in (select id_i from c); DOES work, and brings me the 1297 records that I do NOT want to delete. So, IN works, but NOT IN doesn't. Even worse: select * from i where id not in ( select i.id from i inner join c ON i.id = c.id_i ); That DOES work, although it should be equivalent to the first query (i'm just trying mad stuff at this point). Alas, I can't use this query to delete, because I'm using the same table i'm deleting from in the subquery. I'm assuming something in my database is corrupt at this point. In case it matters, these are all MyISAM tables without any foreign keys, whatsoever, and I've run the same queries in my dev machine and in the production server with the same result, so whatever corruption there might be survived a mysqldump / source cycle, which sounds awfully strange. Any ideas on what could be going wrong, or, even more importantly, how I can fix/work around this? Thanks! Daniel

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• Problem using SQLDataReader with Sybase ASE

  - by John K.

  We're developing a reporting application that uses asp.net-mvc (.net 4). We connect through DDTEK.Sybase middleware to a Sybase ASE 12.5 database. We're having a problem pulling data into a datareader (from a stored procedure). The stored procedure computes values (approximately 50 columns) by doing sums, counts, and calling other stored procedures. The problem we're experiencing is... certain (maybe 5% of the columns) come back with NULL or 0. If we debug and copy the SQL statement being used for the datareader and run it inside another SQL tool we get all valid values for all columns. conn = new SybaseConnection { ConnectionString = ConfigurationManager.ConnectionStrings[ConnectStringName].ToString() }; conn.Open(); cmd = new SybaseCommand { CommandTimeout = cmdTimeout, Connection = conn, CommandText = mainSql }; reader = cmd.ExecuteReader(); // AT THIS POINT IMMEDIATELY AFTER THE EXECUTEREADER COMMAND // THE READER CONTAINS THE BAD (NULL OR 0) DATA FOR THESE COLUMNS. DataTable schemaTable = reader.GetSchemaTable(); // AT THIS POINT WE CAN VIEW THE DATATABLE FOR THE SCHEMA AND IT APPEARS CORRECT // THE COLUMNS THAT DON'T WORK HAVE SPECIFICATIONS IDENTICAL TO THE COLUMNS THAT DO WORK Has anyone had problems like this using Sybase and ADO? Thanks, John K.

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• Seaching for an element in a circular sorted array

  - by guirgis

  I wanted to share this with you, i had this problem in a google interview. we want to search for a given element in a circular sorted array in complexity not greater than O(Log n). ex: search for 13 in {5,9,13,1,3}. My idea was to convert the circular array into a regular sorted array then do a binary search on the resulting array, but my problem was the algorithm i came up was stupid that it takes O(n) in the worst case: for(i = 1; i < a.length; i++){ if (a[i] < a[i-1]){ minIndex = i; break; } } then the corresponding index of ith element will be determined from the following relation: (i + minInex - 1) % a.length it is clear that my conversion (from circular to regular) algorithm may take O(n), so we need a better one, any suggestions?

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• Typical Hadoop setup for remote job submission

  - by Artii

  So I am still a bit new to hadoop and am currently in the process of setting up a small test cluster on Amazonaws. So my question relates to some tips on the structuring of the cluster so it is possible to work submit jobs from remote machines. Currently I have 5 machines. 4 are basically the Hadoop cluster with the NameNodes, Yarn etc. One machine is used as a manager machine( Cloudera Manager). I am gonna describe my thinking process on the setup and if anyone can chime in the points I am not clear with, that would be great. I was thinking what was the best setup for a small cluster. So I decided to expose only one manager machine and probably use that to submit all the jobs through it. The other machines will see each other etc, but not be accessible from the outside world. I am have conceptual idea on how to do this,but I am not sure how to properly go about doing this though, if anyone could point me in the right direction that would great. Also another big point is, I want to be able to submit jobs to the cluster through exposed machine from a client machine (might be Windows). I am not so clear on this setup as well. Do I need to have Hadoop installed on the machine in order to use the normal hadoop commands, and to write/submit jobs say from Eclipse or something similar. So to sum it up my questions are, Is this an ok setup for a small test cluster How can I go about using one exposed machine to submit/route jobs to the cluster, without having any of the Hadoop nodes on it. How do I setup a client machine to submit jobs to a remote cluster, and an example on how to do it on Windows. Also if there are any reason not to use Windows as a client machine in this setup. Thanks I would greatly appreciate any advice or help on this.

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• Storing DateTime (UTC) vs. storing DateTimeOffset

  - by Frederico

  I usually have an "interceptor" that right before reading/writing from/to the database does datetime conversion (from UTC to localtime, and from localtime to utc), so I can use DateTime.Now (derivations and comparisions) throughout the system without worrying about timezones. Regarding serialization and moving data between computers, there is no need to bother, as the datetime is always UTC. Should I continue storing my dates (SQL 2008 - datetime) in UTC format or should I instead store it using DateTimeOffset (SQL 2008 - datetimeoffset)? UTC Dates in the database (datetime type) have been working and known for so long, why change it? What are the advantages? I have already looked into articles like this one, but I'm not 100% convinced though. Any thoughts?

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• Horizontally-centering an absolute position to match a relative position

  - by Chris Vandevelde

  I'm trying to make a div box, containing various elements, fixed at the top of the page once the page has been scrolled so that the box would normally be out of view, but scroll normally until that point (like the behaviour at http://perldoc.perl.org/perl.html). The conditionally-fixed part is pretty simple to implement (set the position to "fixed" once the user has scrolled past a certain point, and "static" once it's scrolled back up), but I'm having trouble with the positioning and dimensions; it screws up if I'm not specifying an absolute position (if I'm using % or "auto", rather than px, em, cm, etc.) or it, confusingly, left-aligns if the box is less than the width of the page. I can understand why, more or less, I'm just trying to fix it. My strategy right now is to have an invisible DIV hold the place of the box and use Prototype's clonePosition() function to hold its position, but it doesn't seem to work for some reason. Neither does copying the margin from one element to the other. Any ideas? Bonus points and eternal gratitude if you can come up with an idea that will adjust itself with the browser window (like auto margins) without setting an onresize event.

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• Converting an AWT application to SWT/JFace

  - by data

  I am currently toying with the idea of converting a small/medium sized project from AWT to SWT, although Swing is not totally out of the picture yet. I was thinking about converting the main window to an SWT_AWT bridge object, but I have no idea how the semantics for this work. After that, I plan to update dialog for dialog, but not necessarily within one release. Is this possible? Has someone done a conversion like this and can give me some hints? Is there maybe even a tutorial somewhere out there? Is there maybe even a tool that can automate parts of this? I have tried googling, but to no avail. Update: One additional thing is: Currently, this is a netbeans project. Might be of help or not, I don't know.

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• how to copy char * into a string and visa versa

  - by user295030

  If i pass a char * into a function. I want to then take that char * convert it to a std::string and once I get my result convert it back to char * from a std::string to show the result. I don't know how to do this for conversion ( I am not talking const char * but just char *) I am not sure how to manipulate the value of the pointer I send in. so steps i need to do take in a char * convert it into a string. take the result of that string and put it back in the form of a char * return the result such that the value should be available outside the function and not get destroyed. If possible can i see how it could be done via reference vs a pointer (whose address I pass in by value however I can still modify the value that pointer is pointing to. so even though the copy of the pointer address in the function gets destroyed i still see the changed value outside. thanks!

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• How to have multiple instances of jQuery plugin on single page?

  - by James Skidmore

  I'm writing a simple jQuery plugin, but I'm having trouble being able to use multiple instances on a page. For instance, here is a sample plugin to illustrate my point: (function($) { $.fn.samplePlugin = function(options) { if (typeof foo != 'undefined') { alert('Already defined!'); } else { var foo = 'bar'; } }; })(jQuery); And then if I do this: $(document).ready(function(){ $('#myDiv').samplePlugin({}); // does nothing $('#myDiv2').samplePlugion({}); // alerts "Already defined!" }); This is obviously an over-simplified example to get across the point. So my question is, how do I have two separate instances of the plugin? I'd like to be able to use it across multiple instances on the same page. I'm guessing that part of the problem might be with defining the variables in a global scope. How can I define them unique to that instance of the plugin then? Thank you for your guidance!

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• Cheapest way of binding local variable to closure

  - by mmotorny

  I believe following to be a cheapest way of binding local variable to closure: void ByRValueReference(A&& a) { } std::function<void ()> CreateClosureByRValueReference() { A a; std::function<void ()> f = std::bind(&ByRValueReference, std::move(a)); // !!! return f; } However, it does not compile under Clang 3.1: error: no viable conversion from '__bind<void (*)(A &&), A>' to 'std::function<void ()>' and gcc 4.6.1: /usr/include/c++/4.6/functional:1778:2: error: no match for call to ‘(std::_Bind<void (*(A))(A&&)>) ()’ Am I violating the standard or it's just broken standard libraries?

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• php and mysql listing databases and looping through results

  - by Jacksta

  Beginner help needed :) I am doign an example form a php book which lists tables in databases. I am getting an error on line 36: $db_list .= "$table_list"; <?php //connect to database $connection = mysql_connect("localhost", "admin_cantsayno", "cantsayno") or die(mysql_error()); //list databases $dbs = @mysql_list_dbs($connection) or die(mysql_error()); //start first bullet list $db_list = "<ul>"; $db_num = 0; //loop through results of functions while ($db_num < mysql_num_rows($dbs)) { //get database names and make each a list point $db_names[$db_num] = mysql_tablename($dbs, $db_num); $db_list .= "<li>$db_names[$db_num]"; //get table names and make another list $tables = @mysql_list_tables($db_names[$db_num]) or die(mysql_error()); $table_list = "<ul>"; $table_num = 0; //loop through results of function while ($table_num < mysql_num_rows($tables)){ //get table names and make each bullet point $table_names[$table_num] = mysql_tablename($tables, $table_num); $table_list .= "<li>$table_names[$table_num]"; $table_num++; } //close inner bullet list and increment number to continue $table_list .= "</ul>" $db_list .= "$table_list"; $db_num++; } //close outer bullet list $db_list .= "</ul>"; ?> <html> <head> <title>MySQL Tables</title> </head> <body> <p><strong>Data bases and tables on local host</strong></p> <? echo "$db_list"; ?> </body>

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• Problem Rewriting URL's from HTTPS to HTTP using IIS7 URL Rewriter, when using Webforms ReturnURL=

  - by theminesgreg

  I took Jeff's Re-write rules from this post and the HTTP to HTTPS conversion works great. However, going back to HTTP is giving me problems because of the ReturnUrl= in the URL (I'm using webforms). Here's an example of the url: https://localhost/Login.aspx?ReturnUrl=%2f Here's the rewrite rule I'm using: <rule name="HTTPS to HTTP redirect for all other pages" stopProcessing="true"> <match url="^login\.aspx$" ignoreCase="true" negate="true" /> <conditions> <add input="{SERVER_PORT}" pattern="^443$" /> </conditions> <action type="Redirect" redirectType="Found" url="http://{HTTP_HOST}{REQUEST_URI}" /> </rule> Here's the resulting re-written URL: http://localhost/,/ Has anyone found a work around for this?

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• Unicode data from NSData to NSString

  - by Jeff

  So if I have NSData from an HTTP request, then I do something like this: NSString *test = [[NSString alloc] initWithData:data encoding:NSUTF8StringEncoding]; This will result in null if the data contains weird unicode data (title is from reddit): {"title":"click..¦¦me..and..then¦¦________ ¦¦check¦¦_.your...¦¦.__...¦¦____ ¦¦....¦¦¦¦¦¦¦¦¦¦¦¦¦¦....¦¦____ ¦¦¦¦¦¦....¦¦¦¦¦¦....¦¦¦¦¦¦____ ¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦____ ....¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦______ ........¦¦..._recently....¦¦________ ....¦¦....viewed....links....¦¦_____"}, How would I convert the data to a string? Ideally, it would best if the string wasn't null so I could parse it as JSON, but even a lossy conversion is fine with me in these cases. I'm not familiar with unicode (naive American I am), so any enlightenment about that would be a nice bonus :)

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• ARC, worth it or not?

  - by MSK

  When I moved to Objective C (iOS) from C++ (and little Java) I had hard time understanding memory management in iOS. But now all this seems natural and I know retain, autorelease, copy and release stuff. After reading about ARC, I am wondering is there more benefits of using ARC or it is just that you dont have to worry about memory management. Before moving to ARC I wanted to know how worth is moving to ARC. XCode has "Convert to Objective C ARC" menu. Is the conversion is that simple (nothing to worry about)? Does it help me in reducing my apps memory foot-print, memory leaks etc (somehow ?) Does it has much testing impact on my apps ? What are non-obvious advantages? Any Disadvantage os moving to it?

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• JSON parse data in javascript from php

  - by Stefania

  I'm trying to retrieve data in a javascript file from a php file using json. $items = array(); while($r = mysql_fetch_array($result)) { $rows = array( "id_locale" => $r['id_locale'], "latitudine" => $r['lat'], "longitudine" => $r['lng'] ); array_push($items, array("item" => $rows)); } ECHO json_encode($items); and in the javascript file I try to recover the data using an ajax call: $.ajax({ type:"POST", url:"Locali.php", success:function(data){ alert("1"); //var obj = jQuery.parseJSON(idata); var json = JSON.parse(data); alert("2"); for (var i=0; i<json.length; i++) { point = new google.maps.LatLng(json[i].item.latitudine,json[i].item.longitudine); alert(point); } } }) The first alert is printed, the latter does not, it gives me error: Unexpected token <.... but I do not understand what it is. Anyone have any idea where am I wrong? I also tried to recover the data with jquery but with no positive results.

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• Creation of Objects: Constructors or Static Factory Methods

  - by Rachel

  I am going through Effective Java and some of my things which I consider as standard are not suggested by the book, for instance creation of object, I was under the impression that constructors are the best way of doing it and books says we should make use of static factory methods, I am not able to few some advantages and so disadvantages and so am asking this question, here are the benefits of using it. Advantages: One advantage of static factory methods is that, unlike constructors, they have names. A second advantage of static factory methods is that, unlike constructors, they are not required to create a new object each time they’re invoked. A third advantage of static factory methods is that, unlike constructors, they can return an object of any subtype of their return type. A fourth advantage of static factory methods is that they reduce the verbosity of creating parameterized type instances. I am not able to understand this advantage and would appreciate if someone can explain this point Disadvantages: The main disadvantage of providing only static factory methods is that classes without public or protected constructors cannot be subclassed. A second disadvantage of static factory methods is that they are not readily distinguishable from other static methods.I am not getting this point and so would really appreciate some explanation. Reference: Effective Java, Joshua Bloch, Edition 2, pg: 5-10 Also, How to decide to use whether to go for Constructor or Static Factory Method for Object Creation ?

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• Recursion in prepared statements

  - by Rob

  I've been using PDO and preparing all my statements primarily for security reasons. However, I have a part of my code that does execute the same statement many times with different parameters, and I thought this would be where the prepared statements really shine. But they actually break the code... The basic logic of the code is this. function someFunction($something) { global $pdo; $array = array(); static $handle = null; if (!$handle) { $handle = $pdo->prepare("A STATEMENT WITH :a_param"); } $handle->bindValue(":a_param", $something); if ($handle->execute()) { while ($row = $handle->fetch()) { $array[] = someFunction($row['blah']); } } return $array; } It looked fine to me, but it was missing out a lot of rows. Eventually I realised that the statement handle was being changed (executed with different param), which means the call to fetch in the while loop will only ever work once, then the function calls itself again, and the result set is changed. So I am wondering what's the best way of using PDO prepared statements in a recursive way. One way could be to use fetchAll(), but it says in the manual that has a substantial overhead. The whole point of this is to make it more efficient. The other thing I could do is not reuse a static handle, and instead make a new one every time. I believe that since the query string is the same, internally the MySQL driver will be using a prepared statement anyway, so there is just the small overhead of creating a new handle on each recursive call. Personally I think that defeats the point. Or is there some way of rewriting this?

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