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• Modifying File while in use using Java

  - by Marquinio

  Hi all, I have this recurrent Java JAR program tasks that tries to modify a file every 60seconds. Problem is that if user is viewing the file than Java program will not be able to modify the file. I get the typical IOException. Anyone knows if there is a way in Java to modify a file currently in use? Or anyone knows what would be the best way to solve this problem? I was thinking of using the File canRead(), canWrite() methods to check if file is in use. If file is in use then I'm thinking of making a backup copy of data that could not be written. Then after 60 seconds add some logic to check if backup file is empty or not. If backup file is not empty then add its contents to main file. If empty then just add new data to main file. Of course, the first thing I will always do is check if file is in use. Thanks for all your ideas.

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• Passing session between jsf backing bean and model

  - by Rachel

  Background : I am having backing bean which has upload method that listen when file is uploaded. Now I pass this file to parser and in parser am doing validation check for row present in csv file. If validation fails, I have to log information and saving in logging table in database. My end goal : Is to get session information in logging bean so that I can get initialContext and make call to ejb to save data to database. What is happening : In my upload backing bean, am getting session but when i call parser, I do not pass session information as I do not want parser to be dependent on session as I want to unit test parser individually. So in my parser, I do not have session information, from parser am making call to logging bean(just a bean with some ejb methods) but in this logging bean, i need session because i need to get initial context. Question Is there a way in JSF, that I can get the session in my logging bean that I have in my upload backing bean? I tried doing: FacesContext ctx = FacesContext.getCurrentInstance(); HttpSession session = (HttpSession) ctx.getExternalContext().getSession(false); but session value was null, more generic question would be : How can I get session information in model bean or other beans that are referenced from backing beans in which we have session? Do we have generic method in jsf using which we can access session information throughout JSF Application?

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• Simplification / optimization of GPS track

  - by GreyCat

  I've got a GPS track, produces by gpxlogger(1) (supplied as a client for gpsd). GPS receiver updates its coordinates every 1 second, gpxlogger's logic is very simple, it writes down location (lat, lon, ele) and a timestamp (time) received from GPS every n seconds (n = 3 in my case). After writing down a several hours worth of track, gpxlogger saves several megabyte long GPX file that includes several thousands of points. Afterwards, I try to plot this track on a map and use it with OpenLayers. It works, but several thousands of points make using the map a sloppy and slow experience. I understand that having several thousands of points of suboptimal. There are myriads of points that can be deleted without losing almost anything: when there are several points making up roughly the straight line and we're moving with the same constant speed between them, we can just leave the first and the last point and throw anything else. I thought of using gpsbabel for such track simplification / optimization job, but, alas, it's simplification filter works only with routes, i.e. analyzing only geometrical shape of path, without timestamps (i.e. not checking that the speed was roughly constant). Is there some ready-made utility / library / algorithm available to optimize tracks? Or may be I'm missing some clever option with gpsbabel?

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• What is the best free cross-platform OpenGL GUI library for a video game?

  - by Jim Buck

  It must come with source. I've looked at these which look semi-promising: glgooey, guichan, and cegui. I've come across others that look more Windows-y than game-y, but that's not the direction I am looking to go in. I would like some simple functionality of typical controls (lists, dropdown box, etc.) but with support for graphical widgets that you would normally find in game frontends. Mouse clicking, dragging, dropping, etc. and sound effect hooks would be nice. (These libs often leave hooks for the external system to tell it when/where mouse events are occurring.) It would get rendered on top of what my own 3D engine is rendering for the game, so it must be able to play nicely with rendering code outside of the lib. The best criteria is whether or not a reasonable 2D game could be implemented just with the GUI library and minimal glue code. (By glue code, I mean init code, hooking up the mouse, and game logic.) I am creating a 3D game, but this criteria gives a pretty solid idea of what level of interactivity I would like in the GUI.

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• How to extract data from F# list

  - by David White

  Following up my previous question, I'm slowly getting the hang of FParsec (though I do find it particularly hard to grok). My next newbie F# question is, how do I extract data from the list the parser creates? For example, I loaded the sample code from the previous question into a module called Parser.fs, and added a very simple unit test in a separate module (with the appropriate references). I'm using XUnit: open Xunit [<Fact>] let Parse_1_ShouldReturnListContaining1 () = let interim = Parser.parse("1") Assert.False(List.isEmpty(interim)) let head = interim.Head // I realise that I have only one item in the list this time Assert.Equal("1", ???) Interactively, when I execute parse "1" the response is: val it : Element list = [Number "1"] and by tweaking the list of valid operators, I can run parse "1+1" to get: val it : Element list = [Number "1"; Operator "+"; Number "1"] What do I need to put in place of my ??? in the snippet above? And how do I check that it is a Number, rather than an Operator, etc.?

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• bool as object vs string as object testing equality

  - by Ray Pendergraph

  I am relatively new to C# and I noticed something interesting today that I guess I have never noticed or perhaps I am missing something. Here is an NUnit test to give an example: object boolean1 = false; object booloan2 = false; Assert.That(boolean1 == booloan2); This unit test fails, but this one passes: object string1 = "string"; object string2 = "string"; Assert.That(string1 == string2); I'm not that surprised in and of itself that the first one fails seeing as boolean1 and boolean2 are different references. But it is troubling to me that the first one fails and the second one passes. I read (on MSDN somewhere) that some magic was done to the String class to facilitate this. I think my question really is why wasn't this behavior replicated in bool? As a note... if the boolean1 and 2 are declared as "bool" then there is no problem. Does anyone know the reason for these differences or why it was implemented that way? Can anyone think of a situation where you would want to reference a bool object for anything except its value?

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• jQuery: Main nav items selected depending on URL or page name

  - by Ricardo

  Ok, I've looked all over for a solution for this but so far I'm unable to find anything related to what I need to accomplish. What I need is very simple as far as logic goes. I have a nav bar like this one: <nav> <ul> <li><a href="download.shtml">Download</a></li> <li><a href="documentation.shtml">Documentation</a></li> <li><a href="contact.shtml">Contact</a></li> <li><a href="about.shtml">About</a></li> </ul> </nav> And the URLs of the site are straightforward: http://domain.net/download.shtml http://domain.net/documentation.shtml http://domain.net/contact.shtml http://domain.net/about.shtml Question: How can I detect which page/URL I'm on and add a class of .active to the corresponding nav item? The end result would be, for example if I'm in the Download page: <nav> <ul> <li><a href="download.shtml" class="active">Download</a></li> <li><a href="documentation.shtml">Documentation</a></li> <li><a href="contact.shtml">Contact</a></li> <li><a href="about.shtml">About</a></li> </ul> </nav> Thanks in advance for any help on this matter.

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• What is the best Design/Way to keep user connected ?

  - by Fasih Hansmukh

  Am working on a POC for self learning in which I want to keep my user connected in LIVE pattern. For example, A game in which 4 user can play at a time , here I need to keep this user connected to my game . M not good at Socket type of programming and love to do that in Services way.What i wana know is 'What is the best way of doing this'. According to my initial Brain Storming, I have decided that I will use SilverLight(In Browser Or Out of Browser) as Front end [I have no issue in that]. I m more concern in back end. Either I make an handler or make a WCF service or use full duplex service and use pooling mechanism for that. As a random thought I come up with a Timer type logic that will fire every after 10 seconds at clients end and get status like Is it now Its turn to roll a dice Home many user left (in case if some of them left) What are connected user status in game like there score/points ect and update game view according to this at his end Kindly place your best answers here that will help me to learn this. Regards and thanks in Advance EDIT: Starting Bounty as i need more feedback. FH

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• Is it possible to replace values in a queryset before sending it to your template?

  - by Issy

  Hi Guys, Wondering if it's possible to change a value returned from a queryset before sending it off to the template. Say for example you have a bunch of records Date | Time | Description 10/05/2010 | 13:30 | Testing... etc... However, based on the day of the week the time may change. However this is static. For example on a monday the time is ALWAYS 15:00. Now you could add another table to configure special cases but to me it seems overkill, as this is a rule. How would you replace that value before sending it to the template? I thought about using the new if tags (if day=1), but this is more of business logic rather then presentation. Tested this in a custom template tag def render(self, context): result = self.model._default_manager.filter(from_date__lte=self.now).filter(to_date__gte=self.now) if self.day == 4: result = result.exclude(type__exact=2).order_by('time') else: result = result.order_by('type') result[0].time = '23:23:23' context[self.varname] = result return '' However it still displays the results from the DB, is this some how related to 'lazy' evaluation of templates? Thanks! Update Responding to comments below: It's not stored wrong in the DB, its stored Correctly However there is a small side case where the value needs to change. So for example I have a From Date & To date, my query checks if todays date is between those. Now with this they could setup a from date - to date for an entire year, and the special cases (like mondays as an example) is taken care off. However if you want to store in the DB you would have to capture several more records to cater for the side case. I.e you would be capturing the same information just to cater for that 1 day when the time changes. (And the time always changes on the same day, and is always the same)

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• How do I generate reports in R?

  - by Maiasaura

  I've been struggling for a week now trying to figure out how to generate reports in R using either Sweave or Brew. I should say right at the beginning that I have never used Tex before but I understand the logic of it. I have read this document several times. However, I cannot even get a simple example to parse. Brew successfully converts a simple markup file (just a title and some text) to a .tex file (no error). But it never ever converts tex to a pdf. > library(tools) > library(brew) > brew("population.brew", "population.tex") > texi2dvi("population.tex", pdf = TRUE) The last step always fails with: Error in texi2dvi("population.tex", pdf = TRUE) : Running 'texi2dvi' on 'population.tex' failed. What am I doing wrong? The report I am trying to build is fairly simple. I have 157 different analysis to summarize. Each one has 4 plots, 1 table and a summary. I just want output plot 1,2,3,4 output table \pagebreak ... that's it. Can anyone help me get further? I use osx, don't have Tex installed. thanks

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• Decimal To Octal Converter, last digit issue

  - by Srishan Supertramp

  I tried making a C program to convert a user entered decimal number to octal. I wrote the C code with my own logic without any research of how other users try to do it. It works fine for the number 601 and some other numbers but for most numbers it returns the octal equivalent with the last digit being 1 less than it should be. For 75 it returns 112 instead of 113. I realize using printf with %o gets the job done but it's kind of defeating the purpose of learning to program. Here's my code: #include <stdio.h> #include <math.h> /* converting decimal to octal */ int main() { int n,x,y,p,s; printf("Enter a decimal number "); scanf("%d",&x); s=0;p=0; while (x!=0) { y=x%8; s=s+y*pow(10,p); x=(x-y)/8; p=p+1; } printf("the octal equivalent is: %d\n",s); getch(); return 0; }

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• What is the best / proper idiom in django for modifying a field during a .save() where you need to o

  - by MDBGuy

  Hi, say I've got: class LogModel(models.Model): message = models.CharField(max_length=512) class Assignment(models.Model): someperson = models.ForeignKey(SomeOtherModel) def save(self, *args, **kwargs): super(Assignment, self).save() old_person = #????? LogModel(message="%s is no longer assigned to %s"%(old_person, self).save() LogModel(message="%s is now assigned to %s"%(self.someperson, self).save() My goal is to save to LogModel some messages about who Assignment was assigned to. Notice that I need to know the old, presave value of this field. I have seen code that suggests, before super().save(), retrieve the instance from the database via primary key and grab the old value from there. This could work, but is a bit messy. In addition, I plan to eventually split this code out of the .save() method via signals - namely pre_save() and post_save(). Trying to use the above logic (Retrieve from the db in pre_save, make the log entry in post_save) seemingly fails here, as pre_save and post_save are two seperate methods. Perhaps in pre_save I can retrieve the old value and stick it on the model as an attribute? I was wondering if there was a common idiom for this. Thanks.

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• MySQL query against pseudo-key-value pair data in WordPress custom query

  - by andrevr

  I'm writing a custom WordPress query to use some of the data which the Woothemes Diarise theme creates. Diarise is an event planner theme with calendar blah, blah... and uses custom fields to store the event start and end dates in WP custom fields in the *wp_postmeta* table, which implements a key-value store. So for each post in the "event" category, there are 2 records in *wp_postmeta*, named *event_start_date* and *event_end_date* that I'm interested in. The task is to compare a tourist's arrival and departure dates with the start and end dates of events, yielding a what's on list of events available. We thought we'd killed it with a grand flash of logic, that goes like this: Disregard any event that ends before the tourist arrives, and any that begin after the departure date. I wrote this query: SELECT wposts.* FROM wp_posts wposts LEFT JOIN wp_postmeta wpostmeta ON wposts.ID = wpostmeta.post_id LEFT JOIN wp_term_relationships ON (wposts.ID = wp_term_relationships.object_id) LEFT JOIN wp_term_taxonomy ON (wp_term_relationships.term_taxonomy_id = wp_term_taxonomy.term_taxonomy_id) WHERE wp_term_taxonomy.taxonomy = 'category' AND wp_term_taxonomy.term_id IN(3,4) AND ( wpostmeta.meta_key = 'event_start_date' AND NOT ( concat(subst(wpostmeta.meta_value,7,4),'-',subst(wpostmeta.meta_value,4,2),'-',subst(wpostmeta.meta_value,1,2) > '2010-07-31' ) ) AND ( wpostmeta.meta_key = 'event_end_date' AND NOT ( concat(subst(wpostmeta.meta_value,7,4),'-',subst(wpostmeta.meta_value,4,2),'-',subst(wpostmeta.meta_value,1,2) < '2010-05-01' ) ) ) ORDER BY wpostmeta.meta_value ASC And, of course it returns no records. The problem I believe is in the dual reference to wpostmeta.meta_key, but how to get around that?

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• Magento: Attribute always returns default value in catalog view, works fine in product view

  - by colinodell

  I've created a new Yes/No attribute for products. I've extended the Product model to do some custom logic and the custom functions are working everywhere. When I initially tried getting the custom attribute value, I ran into some issue. Magento wasn't loading it for me, so calls to $product-getMyAttributeName() did nothing. In the product views, I got it working with this additional function: public function getAttrVal($attr_name) { return $this->getResource()->getAttribute($attr_name)->getFrontend()->getValue($this); } So that worked great when viewing a product on the frontend. It would fetch the assigned value if set, or the default if not. When I view any Category (grid of all products in that category), the same exact code is being executed. But my getAttrVal() function always returns the default value, even if I've explicitly set this value for my product. I can't, for the life of me, figure out why the attribute loads correctly in the Product view but the Category view always grabs the default value, despite running the same exact code. Any thoughts?

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• Total Average Week using a Parameter

  - by Jose

  I have a crystal report that shows sales volumes called week to date volume. It shows current week, previous week, and average week. The report prompts for a date parameter and I extract the week number to get current week and previous week volumes. Did it this way because Mngmt wants to be able to run report whenever. My problem is for Average Week I cant figure out how to get the number of weeks to divide by for my average. Report originates from June 1st, 2010. Right now I have: DATEPART("ww", {?date}) - DATEPART("ww", DATE(2010, 6, 1)) This returns 2 right now which is perfect, so i divide my total by 2. This code will work until the end of the year then I'm hooped. Any idea how I can make this a little more dynamic. I was thinking a counter somehow, just can't get the logic down because the date parameter will keep changing, meaning I cant increase my counter by 1 after each week??? Cheers.

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• Rails: RESTful Find, Initialize, or Create

  - by Andrew

  I have an app that has Cities in it. I'm looking for some suggestions on how to RESTfully structure a controller so that I can lookup, initialize, and create city records via AJAX requests. For instance: Given a text field city_name A user enters the name of a City, like "Paris, France" The app checks this location to see if there is such a city in the database already If there is, it returns the city object If there is not, it returns a new record initialized with the name "Paris" and the country "France", and prompts the user to confirm they want to add this city to the database If the user says "Yes" the record is saved. If not the record is discarded and the form is cleared. Now, my first approach was to change the Create action to use find_or_create, so that an AJAX post to cities_path would result in either returning the existing city or creating it and returning it. That works ok... However, it would be better to setup controller actions that would take a string input, find , or else initialize and return, then only create if the user confirms the generated record is correct. The ideal scenario would put this all in one action so AJAX request can go to that url, the server responds with JSON objects, and javascript can handle things from there. I'd like to keep all the user-interaction logic client side, and also minimize the number of requests it takes to achieve this. Any suggestions on the cleanest, most RESTful way to accomplish this?

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• Real Time Progress Indicator

  - by jignesh

  I am trying to get the real time progress indicator. In the code snippet below,i am trying to set the width of DIV on the basis of the Number of Items retrieve from the Web Service Call Back Function. for (i = 0; i < data.length; i++) { table += '<tr>'; table += '<td>' + data[i].ItemId + '</td>'; table += '<td></td>'; table += '<td>' + data[i].Name + '</td>'; table += '<td>' + data[i].Unit + '</td>'; table += '<td><input type=text value=' + data[i].Quantity + '></td>'; table += '<td>' + data[i].Brands + '</td>'; table += '<td><img border=0 src=../images/Delete_icon.gif></td>'; table += '</tr>'; $('#divProgressIndicator').width((100 * (i / data.length)) + '%'); } As shown in the code above,after the for loop is executed i only see the divProgressIndicator filled with the background color and I am not able to see the progress. Can I achieve this in a for loop or i need to use some thing else. Regards

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• How to DRY on CRUD parts of my Rails app?

  - by kolrie

  I am writing an app which - similarly to many apps out there - is 90% regular CRUD things and 10% "juice", where we need nasty business logic and more flexibility and customization. Regarding this 90%, I was trying to stick to the DRY principle as much as I can. As long as controllers go, I have found resource_controller to really work, and I could get rid of all the controllers on that area, replacing them with a generic one. Now I'd like to know how to get the same with the views. On this app I have an overall, application.html.erb layout and then I must have another layout layer, common for all CRUD views and finally a "core" part: On index.html.erb all I need to generate a simple table with the fields and labels I indicate. For new and edit, also generic form edition, indicating labels and fields (with a possibility of providing custom fields if needed). I am not sure I will need show, but if I do it would be the same as new and edit. What plugins and tools (or even articles and general pointer) would help me to get that done? Thanks, Felipe.

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• Spawning a thread in python

  - by morpheous

  I have a series of 'tasks' that I would like to run in separate threads. The tasks are to be performed by separate modules. Each containing the business logic for processing their tasks. Given a tuple of tasks, I would like to be able to spawn a new thread for each module as follows. from foobar import alice, bob charles data = getWorkData() # these are enums (which I just found Python doesn't support natively) :( tasks = (alice, bob, charles) for task in tasks # Ok, just found out Python doesn't have a switch - @#$%! # yet another thing I'll need help with then ... switch case alice: #spawn thread here - how ? alice.spawnWorker(data) No prizes for guessing I am still thinking in C++. How can I write this in a Pythonic way using Pythonic 'enums' and 'switch'es, and be able to run a module in a new thread. Obviously, the modules will all have a class that is derived from a ABC (abstract base class) called Plugin. The spawnWorker() method will be declared on the Plugin interface and defined in the classes implemented in the various modules. Maybe, there is a better (i.e. Pythonic) way of doing all this?. I'd be interested in knowing

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• Django: returning a selection of fields from a model based on their values?

  - by AP257

  I am working with some data over which I have little control. I'd like to return ONLY the fields of my model that aren't certain 'uninteresting' values (e.g. '0', 'X' or '-'), and access them individually in the template. My model is like this: class Manors(models.Model): structidx = models.IntegerField(primary_key=True, verbose_name="ID") hills = models.CharField(max_length=100, null=True, blank=True, verbose_name="Number of fields") In my template, I return a QuerySet of Manors, and I'd like to output something like this if the hills field isn't uninteresting: {% for manor in manors %} {% if manor.hills %}<li>Hills blah blah: {{ manor.hills }}</li>{% endif %} {% endfor %} I want to avoid too much logic in the template. Ideally, the manor object would simply not return with the uninteresting fields attached, then I could just do {% if manor.hills %}. I tried writing a model method that returns a dictionary of the interesting values, like this: def get_field_dictionary(self): interesting_fields = {} for field in Manors._meta.fields: if field.value_to_string(self) != "N" and field.value_to_string(self) != "0" and field.value_to_string(self) != "-" and field.value_to_string(self) != "X": interesting_fields[field.name] = field.value_to_string(self) return interesting_fields But I don't know how to access individual values of the dictionary in the template: {% if manor.get_field_dictionary['hills'] %}<li>Hills blah blah: {{ manor.get_field_dictionary['hills'] }}</li>{% endif %} gives a TemplateSyntaxError. Is there a better way to do this?

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• How to know which image is being viewed in UIScrollView? Also, is it possible to loop scrolling for

  - by bruin

  This is what I'm trying to do, and I'm not sure if it's possible using UIScrollView. First, I don't care about zooming, all I care is that the user is able to scroll through images just like the Photo App, this I got. But how do I know which image he is viewing while using UIScrollView? For instance, if he stops on the 3rd image out of 10 images in the view, how do I know he's on that image? I can't find a way to access the index (is this accessible)?? Also, bonus question, once the user scrolls to the last image, I don't want the scrolling to stop but I want it to loop so that image 1 comes after image 10. And vice versa, if you scroll left passed image 1, you'll see image 10. I'm not asking for the logic, I can do this in an array very simply, I just don't know how to access (if it's even possible) the indexing of the images in the scroll view. If it's not, does anyone have a solution to do this? thanks in advance!

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• ISO C90 forbids mixed declarations and code sscanf

  - by Need4Sleep

  I'm getting a strange error attempting to compile my unit test code,. For some reason the compiler treats my sscanf call as a mixed declaration? I don't quite understand, here is the entire error: cc1: warnings being treated as errors /home/brlcad/brlcad/src/libbn/tests/bn_complex.c: In function 'main': /home/brlcad/brlcad/src/libbn/tests/bn_complex.c:53: error: ISO C90 forbids mixed declarations and code make[2]: *** [src/libbn/tests/CMakeFiles/tester_bn_complex.dir/bn_complex.c.o] Error 1 make[1]: *** [src/libbn/tests/CMakeFiles/tester_bn_complex.dir/all] Error 2 make: *** [all] Error 2 int main(int argc, char *argv[]) { double expRe1, expIm2, expSqRe1, expSqIm2; double actRe1, actIm2, actSqRe1, actSqIm2; actRe1 = actIm2 = actSqRe1 = actSqIm2 = expRe1 = expIm2 = expSqRe1 = expSqIm2 = 0.0; bn_complex_t com1,com2; //a struct that holds two doubles if(argc < 5) bu_exit(1, "ERROR: Invalid parameters[%s]\n", argv[0]); sscanf(argv[1], "%lf,%lf", &com1.re, &com1.im); /* Error is HERE */ sscanf(argv[2], "%lf,%lf", &com2.re, &com2.im); sscanf(argv[3], "%lf,%lf", &expRe1, &expIm2); sscanf(argv[4], "%lf,%lf", &expSqRe1, &expSqIm2); test_div(com1, com2, &actRe1, &actIm2); test_sqrt(com1,com2, &actSqRe1, &actSqIm2); if((fabs(actRe1 - expRe1) < 0.00001) || (fabs(actIm2 - expIm2) < 0.00001)){ printf("Division failed...\n"); return 1; } if((fabs(actSqRe1 - expSqRe1) < 0.00001) || (fabs(actSqIm2 - expSqIm2) < 0.00001)){ printf("Square roots failed...\n"); return 1; } return 0; }

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• template files evaluation in python

  - by saminny

  I am trying to use python for translating a set of templates to a set of configuration files based on values taken from a main configuration file. However, I am having certain issues. Consider the following example of a template file. file1.cfg.template %(CLIENT1)s %(HOST1)s %(PORT1)d C %(COMPID1)s %(CLIENT2)s %(HOST2)s %(PORT2)d C %(COMPID2)s This file contains an entry for each client. There are hundreds of config files like this and I don't want to have logic for each type of config file. Python should do the replacements and generate config files automatically given a set of global values read from a main xml config file. However, in the above example, if CLIENT2 does not exist, how do I delete that line? I expect Python would generate the config file using something like this: os.open("file1.cfg.template").read() % myhash where myhash is hash of configuration parameters from the main config file which may not contain CLIENT2 at all. In the case it does not contain CLIENT2, I want that line to disappear from the file. Is it possible to insert some 'IF' block in the file and have python evaluate it? Thanks for your help. Any suggestions most welcome.

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• How do you use stl's functions like for_each?

  - by thomas-gies

  I started using stl containers because they came in very handy when I needed functionality of a list, set and map and had nothing else available in my programming environment. I did not care much about the ideas behind it. STL documentations were only interesting up to the point where it came to functions, etc. Then I skipped reading and just used the containers. But yesterday, still being relaxed from my holidays, I just gave it a try and wanted to go a bit more the stl way. So I used the transform function (can I have a little bit of applause for me, thank you). From an academic point of view it really looked interesting and it worked. But the thing that boroughs me is that if you intensify the use of those functions, you need 10ks of helper classes for mostly everything you want to do in your code. The hole logic of the program is sliced in tiny pieces. This slicing is not the result of god coding habits. It's just a technical need. Something, that makes my life probably harder not easier. And I learned the hard way, that you should always choose the simplest approach that solves the problem at hand. And I can't see what, for example, the for_each function is doing for me that justifies the use of a helper class over several simple lines of code that sit inside a normal loop so that everybody can see what is going on. I would like to know, what you are thinking about my concerns? Did you see it like I do when you started working this way and have changed your mind when you got used to it? Are there benefits that I overlooked? Or do you just ignore this stuff as I did (and will go an doing it, probably). Thanks. PS: I know that there is a real for_each loop in boost. But I ignore it here since it is just a convenient way for my usual loops with iterators I guess.

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• What's the best way to "shuffle" a table of database records?

  - by Darth

  Say that I have a table with a bunch of records, which I want to randomly present to users. I also want users to be able to paginate back and forth, so I have to perserve some sort of order, at least for a while. The application is basically only AJAX and it uses cache for already visited pages, so even if I always served random results, when the user tries to go back, he will get the previous page, because it will load from the local cache. The problem is, that if I return only random results, there might be some duplicates. Each page contains 6 results, so to prevent this, I'd have to do something like WHERE id NOT IN (1,2,3,4 ...) where I'd put all the previously loaded IDs. Huge downside of that solution is that it won't be possible to cache anything on the server side, as every user will request different data. Alternate solution might be to create another column for ordering the records, and shuffle it every insert time unit here. The problem here is, I'd need to set random number out of a sequence to every record in the table, which would take as many queries as there are records. I'm using Rails and MySQL if that's of any relevance.

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