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• Speed/expensive of SQLite query vs. List.contains() for "in-set" icon on list rows

  - by kpdvx

  An application I'm developing requires that the app main a local list of things, let's say books, in a local "library." Users can access their local library of books and search for books using a remote web service. The app will be aware of other users of the app through this web service, and users can browse other users' lists of books in their library. Each book is identified by a unique bookId (represented as an int). When viewing books returned through a search result or when viewing another user's book library, the individual list row cells need to visually represent if the book is in the user's local library or not. A user can have at most 5,000 books in the library, stored in SQLite on the device (and synchronized with the remote web service). My question is, to determine if the book shown in the list row is in the user's library, would it be better to directly ask SQLite (via SELECT COUNT(*)...) or to maintain, in-memory, a List or int[] array of some sort containing the unique bookIds. So, on each row display do I query SQLite or check if the List or int[] array contains the unique bookId? Because the user can have at most 5,000 books, each bookId occupies 4 bytes so at most this would use ~ 20kB. In thinking about this, and in typing this out, it seems obvious to me that it would be far better for performance if I maintained a list or int[] array of in-library bookIds vs. querying SQLite (the only caveat to maintaining an int[] array is that if books are added or removed I'll need to grow or shrink the array by hand, so with this option I'll most likely use an ArrayList or Vector, though I'm not sure of the additional memory overhead of using Integer objects as opposed to primitives). Opinions, thoughts, suggestions?

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• C++ Printing: Printer jams, what am I doing wrong?

  - by Kleas

  I have a problem with printing in C++. As far as I know, this code used to work on my previous printer, but ever since I got another one (an HP C7280) it started giving problems. Whenever I try to print anything, even an empty page, the page JAMS the printer. I have to manualy remove the page from the printer. I have no clue why this is happening. Am I doing something wrong, is it a driver problem, are there better ways to print in C++? I am using Windows 7 64 bit, but this problem also presented itself when I was using Windows Vista 64 bit. I use the following code: PRINTDLG pd; ZeroMemory(&pd, sizeof(pd)); pd.lStructSize = sizeof(pd); pd.hwndOwner = mainWindow; pd.hDevMode = NULL; pd.hDevNames = NULL; pd.Flags = PD_USEDEVMODECOPIESANDCOLLATE | PD_RETURNDC; pd.nCopies = 1; pd.nMinPage = 1; pd.nMaxPage = 0xFFFF; if (PrintDlg(&pd)==TRUE) { DOCINFO di; di.cbSize = sizeof(DOCINFO); di.lpszDocName = "Rumitec en Roblaco Print"; di.lpszOutput = (LPTSTR)NULL; di.fwType = 0; // Start printing StartDoc(pd.hDC, &di); StartPage(pd.hDC); initPrinter(pd.hDC); // ... // Do some drawing // ... // End printing EndPage(pd.hDC); EndDoc(pd.hDC); DeleteDC(pd.hDC); } Am I doing something wrong? Alternatively, is there a better, easier, more modern way to do it?

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• "2d Search" in Solr or how to get the best item of the multivalued field 'items'?

  - by Karussell

  The title is a bit awkward but I couldn't found a better one. My problem is as follows: I have several users stored as documents and I am storing several key-value-pairs or items (which have an id) for each document. Now, if I apply highlighting I can get the first n items. If you have several hundreds of such items this highlighting is necessary and works nicely. But there are two problems: The highlighted text won't contain the id and so retrieving additional information of the highlighted item text is ugly. E.g. you need to store the id in the text so that the highlighter returns it. Adding the id to the hl.fl parameter does not help. You will not get the most relevant n-items. You will get the first n items ... So how can I find the best items of a documents with multiple such items? I will now add my own findings as answers, but as I will point out. Each of them has its drawbacks. Hopefully anyone of you can point me to a better solution.

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• What data stucture should I use for BigInt class

  - by user1086004

  I would like to implement a BigInt class which will be able to handle really big numbers. I want only to add and multiply numbers, however the class should also handle negative numbers. I wanted to represent the number as a string, but there is a big overhead with converting string to int and back for adding. I want to implement addition as on the high school, add corresponding order and if the result is bigger than 10, add the carry to next order. Then I thought that it would be better to handle it as a array of unsigned long long int and keep the sign separated by bool. With this I'm afraid of size of the int, as C++ standard as far as I know guarantees only that int < float < double. Correct me if I'm wrong. So when I reach some number I should move in array forward and start adding number to the next array position. Is there any data structure that is appropriate or better for this? Thanks in advance.

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• Optimized 2D Tile Scrolling in OpenGL

  - by silicus

  Hello, I'm developing a 2D sidescrolling game and I need to optimize my tiling code to get a better frame rate. As of right now I'm using a texture atlas and 16x16 tiles for 480x320 screen resolution. The level scrolls in both directions, and is significantly larger than 1 screen (thousands of pixels). I use glTranslate for the actual scrolling. So far I've tried: Drawing only the on-screen tiles using glTriangles, 2 per square tile (too much overhead) Drawing the entire map as a Display List (great on a small level, way to slow on a large one) Partitioning the map into Display Lists half the size of the screen, then culling display lists (still slows down for 2-directional scrolling, overdraw is not efficient) Any advice is appreciated, but in particular I'm wondering: I've seen Vertex Arrays/VBOs suggested for this because they're dynamic. What's the best way to take advantage of this? If I simply keep 1 screen of vertices plus a bit of overdraw, I'd have to recopy the array every few frames to account for the change in relative coordinates (shift everything over and add the new rows/columns). If I use more overdraw this doesn't seem like a big win; it's like the half-screen display list idea. Does glScissor give any gain if used on a bunch of small tiles like this, be it a display list or a vertex array/VBO Would it be better just to build the level out of large textures and then use glScissor? Would losing the memory saving of tiling be an issue for mobile development if I do this (just curious, I'm currently on a PC)? This approach was mentioned here Thanks :)

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• Sorting by some field and fetching whole tree from DB

  - by Niaxon

  Hello everyone, I am trying to do file browser in a tree form and have a problem to sort it somehow. I use PHP and MySQL for that. I've created mixed (nested set + adjacency) table 'element' with the following fields: element_id, left_key, right_key, level, parent_id, element_name, element_type (enum: 'folder','file'), element_size. Let's not discuss right now that it is better to move information about element (name, type, size) into other table. Function to scan specified directory and fill table work correctly. Noteworthy, i am adding elements to tree in specific order: folders first and only files. After that i can easily fetch and display whole table on the page using simple query: SELECT * FROM element WHERE 1=1 ORDER BY left_key With the result of that query and another function i can generate correct html code (<ul><li>... and so on). Now back to the question (finally, huh?). I am struggling to add sorting functionality. For example i want to order my result by size. Here i need to keep in my mind whole hierarchy of tree and rule: folders first, files later. I believe i can do that by generating in PHP recursive query: SELECT * FROM element WHERE parent_id = {$parentId} ORDER BY element_type (so folders would be first), size (or name for example) After that for each result which is folder i will send another query to get it's content. Also it's possible to fetch whole tree by left_key and after that sort it in PHP as array but i guess that would be worse :) I wonder if there is better and more efficient way to do such thing?

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• What techniques can I employ to create a series of UI Elements from a collection of objects using WP

  - by elggarc

  I'm new to WPF and before I dive in solving a problem in completely the wrong way I was wondering if WPF is clever enough to handle something for me. Imagine I have a collection containing objects. Each object is of the same known type and has two parameters. Name (a string) and Picked (a boolean). The collection will be populated at run time. I would like to build up a UI element at run time that will represent this collection as a series of checkboxes. I want the Picked parameter of any given object in the collection updated if the user changes the selected state of the checkbox. To me, the answer is simple. I iterate accross the collection and create a new checkbox for each object, dynamically wiring up a ValueChanged event to capture when Picked should be changed. It has occured to me, however, that I may be able to harness some unknown feature of WPF to do this better (or "properly"). For example, could data binding be employed here? I would be very interested in anyone's thoughts. Thanks, E FootNote: The structure of the collection can be changed completely to better fit any chosen solution but ultimately I will always start from, and end with, some list of string and boolean pairs.

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• multiple models in Rails with a shared interface

  - by dfondente

  I'm not sure of the best structure for a particular situation in Rails. We have several types of workshops. The administration of the workshops is the same regardless of workshop type, so the data for the workshops is in a single model. We collect feedback from participants about the workshops, and the questionnaire is different for each type of workshop. I want to access the feedback about the workshop from the workshop model, but the class of the associated model will depend on the type of workshop. If I was doing this in something other than Rails, I would set up an abstract class for WorkshopFeedback, and then have subclasses for each type of workshop: WorkshopFeedbackOne, WorkshopFeedbackTwo, WorkshopFeedbackThree. I'm unsure how to best handle this with Rails. I currently have: class Workshop < ActiveRecord::Base has_many :workshop_feedbacks end class Feedback < ActiveRecord::Base belongs_to :workshop has_many :feedback_ones has_many :feedback_twos has_many :feedback_threes end class FeedbackOne < ActiveRecord::Base belongs_to :feedback end class FeedbackTwo < ActiveRecord::Base belongs_to :feedback end class FeedbackThree < ActiveRecord::Base belongs_to :feedback end This doesn't seem like to the cleanest way to access the feedback from the workshop model, as accessing the correct feedback will require logic investigating the Workshop type and then choosing, for instance, @workshop.feedback.feedback_one. Is there a better way to handle this situation? Would it be better to use a polymorphic association for feedback? Or maybe using a Module or Mixin for the shared Feedback interface? Note: I am avoiding using Single Table Inheritance here because the FeedbackOne, FeedbackTwo, FeedbackThree models do not share much common data, so I would end up with a large sparsely populated table with STI.

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• What stackoverflow questions bring out the best in you? [closed]

  - by Mark Robinson

  This question is to help me (us) ask better questions of this community to encourage better working together. What questions here bring out the best in you? I don't mean which are the best / most appropriate questions but which bring the best out of you? That is, it brings out your best thinking and most constructive behaviour. Consider, for example, questions that make you think or that are asked in a certain way. Or consider specific a question should be. Or more abstractly, questions asked on a certain day / time, ... So I'm not necessarily asking about specific subjects but rather how a question is asked. What inspires you to drop everything and start answering? This comes from my observing questions that get highest points - I’m graduating with a Computer Science degree but I don’t feel like I know how to program. is very positive but my first ever question caused a minor storm. Ironically, I'm nervous posting this question so please don't attack if this is inappropriate.

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• Caching queries in Django

  - by dolma33

  In a django project I only need to cache a few queries, using, because of server limitations, a cache table instead of memcached. One of those queries looks like this: Let's say I have a Parent object, which has a lot of Child objects. I need to store the result of the simple query parent.childs.all(). I have no problem with that, and everything works as expected with some code like key = "%s_children" %(parent.name) value = cache.get(key) if value is None: cache.set(key, parent.children.all(), CACHE_TIMEOUT) value = cache.get(key) But sometimes, just sometimes, the cache.set does nothing, and, after executing cache.set, cache.get(key) keeps returning None. After some test, I've noticed that cache.set is not working when parent.children.all().count() has higher values. That means that if I'm storing inside of key (for example) 600 children objects, it works fine, but it wont work with 1200 children. So my question is: is there a limit to the data that a key could store? How can I override it? Second question: which way is "better", the above code, or the following one? key = "%s_children" %(parent.name) value = cache.get(key) if value is None: value = parent.children.all() cache.set(key, value, CACHE_TIMEOUT) The second version won't cause errors if cache.set doesn't work, so it could be a workaround to my issue, but obviously not a solution. In general, let's forget about my issue, which version would you consider "better"?

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• python interactive mode module import issue

  - by Jeff

  I believe I have what would be called a scope issue, perhaps name space. Not too sure I'm new to python. I'm trying to make a module that will search through a list using regular expressions. I'm sure there is a better way of doing it but this error that I'm getting is bugging me and I want to understand why. here's my code: class relist(list): def __init__(self, l): list.__init__(self, l) def __getitem__(self, rexp): r = re.compile(rexp) res = filter(r.match, self) return res if __name__ == '__main__': import re listl = [x+y for x in 'test string' for y in 'another string for testing'] print(listl) test = relist(listl) print('----------------------------------') print(test['[s.]']) When I run this code through the command line it works the way I expect it to; however when I run it through python interactive mode I get the error >>> test['[s.]'] Traceback (most recent call last): File "<stdin>", line 1, in <module> File "relist.py", line 8, in __getitem__ r = re.compile(rexp) NameError: global name 're' is not defined While in the interactive mode I do import re and I am able to use the re functions, but for some reason when I'm trying to execute the module it doesn't work. Do I need to import re into the scope of the class? I wouldn't think so because doesn't python search through other scopes if it's not found in the current one? I appreciate your help, and if there is a better way of doing this search I would be interested in knowing. Thanks

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• How can i design a DB where the user can define the fields and types of a detail table in a M-D rela

  - by Simon

  My application has one table called 'events' and each event has approx 30 standard fields, but also user defined fields that could be any name or type, in an 'eventdata' table. Users can define these event data tables, by specifying x number of fields (either text/double/datetime/boolean) and the names of these fields. This 'eventdata' (table) can be different for each 'event'. My current approach is to create a lookup table for the definitions. So if i need to query all 'event' and 'eventdata' per record, i do so in a M-D relaitionship using two queries (i.e. select * from events, then for each record in 'events', select * from 'some table'). Is there a better approach to doing this? I have implemented this so far, but most of my queries require two distinct calls to the DB - i cannot simply join my master 'events' table with different 'eventdata' tables for each record in in 'events'. I guess my main question is: can i join my master table with different detail tables for each record? E.g. SELECT E.*, E.Tablename FROM events E LEFT JOIN 'E.tablename' T ON E._ID = T.ID If not, is there a better way to design my database considering i have no idea on how many user defined fields there may be and what type they will be.

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• Why would one want to use the public constructors on Boolean and similar immutable classes?

  - by Robert J. Walker

  (For the purposes of this question, let us assume that one is intentionally not using auto(un)boxing, either because one is writing pre-Java 1.5 code, or because one feels that autounboxing makes it too easy to create NullPointerExceptions.) Take Boolean, for example. The documentation for the Boolean(boolean) constructor says: Note: It is rarely appropriate to use this constructor. Unless a new instance is required, the static factory valueOf(boolean) is generally a better choice. It is likely to yield significantly better space and time performance. My question is, why would you ever want to get a new instance in the first place? It seems like things would be simpler if constructors like that were private. For example, if they were, you could write this with no danger (even if myBoolean were null): if (myBoolean == Boolean.TRUE) It'd be safe because all true Booleans would be references to Boolean.TRUE and all false Booleans would be references to Boolean.FALSE. But because the constructors are public, someone may have used them, which means that you have to write this instead: if (Boolean.TRUE.equals(myBoolean)) But where it really gets bad is when you want to check two Booleans for equality. Something like this: if (myBooleanA == myBooleanB) ...becomes this: if ( (myBooleanA == null && myBooleanB == null) || (myBooleanA == null && myBooleanA.equals(myBooleanB)) ) I can't think of any reason to have separate instances of these objects which is more compelling than not having to do the nonsense above. What say you?

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• Need some ideas on how to acomplish this in Java (parsing strings)

  - by Matt

  Sorry I couldn't think of a better title, but thanks for reading! My ultimate goal is to read a .java file, parse it, and pull out every identifier. Then store them all in a list. Two preconditions are there are no comments in the file, and all identifiers are composed of letters only. Right now I can read the file, parse it by spaces, and store everything in a list. If anything in the list is a java reserved word, it is removed. Also, I remove any loose symbols that are not attached to anything (brackets and arithmetic symbols). Now I am left with a bunch of weird strings, but at least they have no spaces in them. I know I am going to have to re-parse everything with a . delimiter in order to pull out identifiers like System.out.print, but what about strings like this example: Logger.getLogger(MyHash.class.getName()).log(Level.SEVERE, After re-parsing by . I will be left with more crazy strings like: getLogger(MyHash getName()) log(Level SEVERE, How am I going to be able to pull out all the identifiers while leaving out all the trash? Just keep re-parsing by every symbol that could exist in java code? That seems rather lame and time consuming. I am not even sure if it would work completely. So, can you suggest a better way of doing this?

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• Lucene raise document score if sibling entity matches query

  - by Pitagoras

  I have the following design situation. I use hibernate search (lucene in the back). Tha application manages ITEMs which have title, description and tags. These are full text indexed. On the other hand, we have COLLECTION of ITEMs. The user can create a COLLECTION and add as many ITEMs as she wants. ITEMs can also belong to many COLLECTIONs. I have a boosted query so that search terms that appear in the tags are more important than in the title, and lastly in the description. But I need an additional matching criteria: for a given ITEM, it whould rank better if other documents in some COLLECTION where the ITEM belongs, also match the query. This is like to say: the title/tags/description of "fellow" items (i.e. items in some shared collection) make the item rank better. I was thinking that adding an ITEM to a COLLECTION would add something like "extra tags" to every other ITEM in the collection, being these extra tags the elements to match in the added ITEM. I feel a more clever solution lucene-wise should exists. Any ideas/pointers are welcome. Thanks.

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• Determining presence of prototype with correct return type

  - by R..

  Here's a random problem in C black magic I just came up with: Write a function that returns 1 if malloc has been prototyped to return a pointer type and 0 if malloc has a return type of int (either implicitly or due to wrong prototype), without invoking any implementation-defined or undefined behavior. I believe it's solvable, but I haven't worked out the solution. Note that calling the function cannot be necessary and in fact is not possible since calling a function with the incorrect prototype is undefined behavior. I have some ideas for ingredients but I think it makes for a better puzzle (and possibly more diverse ideas) if I leave them out for now. I don't need the solution for any immediate use, but it could be handy in configure scripts and such. Update: A better example of the usefulness (with strdup instead of malloc): #undef strdup #define strdup(x) (strdup_has_proto ? strdup((x)) : my_strdup((x))) i.e. being able to implement X_has_proto as an expression at the source level could be a portable way to use functions which a system might or might not have, and fall back on a local replacement, without needing any separate configure step.

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• Suggestions on how to implement a UI Element to display a long image in iPhone.

  - by Tattat

  I want to display a long image on iPhone. The user can swipe left or right to see difficult parts of the image. I want to spite the long image into different parts... for example, a long long image is 1000* 100; I want to display 100*100 for each time. When the image is loaded, it shows from x:0 to x:100. When user swipe right, it becomes x:101, x:200. When the user swipe left, it back to x:0, x:100, when the user continue to swipe right, it show x:201, x:300. I am thinking how to implement this specified imageView. I have two ideas now. First, make my own imageView, which super class is UIImageView, and overriding the swipe left, swipe right method. Second, make my own UIView. just implement the user swipe left/right action. Which way you think is better, or any better ideas on implement this? thz u.

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• Building a structure/object in a place other than the constructor

  - by Vishal Naidu

  I have different types of objects representing the same business entity. UIObject, PowershellObject, DevCodeModelObject, WMIObject all are different representation to the same entity. So say if the entity is Animal then I have AnimalUIObject, AnimalPSObject, AnimalModelObject, AnimalWMIObject, etc. Now the implementations of AnimalUIObject, AnimalPSObject, AnimalModelObject are all in separate assemblies. Now my scenario is I want to verify the contents of business entity Animal irrespective of the assembly it came from. So I created a GenericAnimal class to represent the Animal entity. Now in GenericAnimal I added the following constructors: GenericAnimal(AnimalUIObject) GenericAnimal(AnimalPSObject) GenericAnimal(AnimalModelObject) Basically I made GenericAnimal depend on all the underlying assemblies so that while verifying I deal with this abstraction. Now the other approach to do this is have GenericAnimal with an empty constructor an allow these underlying assemblies to have a Transform() method which would build the GenericAnimal. Both approaches have some pros and cons: The 1st approach: Pros: All construction logic is in one place in one class GenericAnimal Cons: GenericAnimal class must be touched every-time there is a new representation form. The 2nd approach: Pros: construction responsibility is delegated to the underlying assembly. Cons: As construction logic is spread accross assemblies, tomorrow if I need to add a property X in GenericAnimal then I have to touch all the assemblies to change the Transform method. Which approach looks better ? or Which would you consider a lesser evil ? Is there any alternative way better than the above two ?

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• How to parse mathematical expressions involving parentheses

  - by Rob P.

  Please forgive my title, I really don't know how to phrase it better. This isn't a school assignment or anything, but I realize it's a mostly academic question. But, what I've been struggling to do is parse 'math' text and come up with an answer. For Example - I can figure out how to parse '5 + 5' or '3 * 5' - but I fail when I try to correctly chain operations together. (5 + 5) * 3 It's mostly just bugging me that I can't figure it out. If anyone can point me in a direction, I'd really appreciate it. EDIT Thanks for all of the quick responses. I'm sorry I didn't do a better job of explaining. First - I'm not using regular expressions. I also know there are already libraries available that will take, as a string, a mathematical expression and return the correct value. So, I'm mostly looking at this because, sadly, I don't "get it". Second - What I've tried doing (is probably misguided) but I was counting '(' and ')' and evaluating the deepest items first. In simple examples, this worked; but my code is not pretty and more complicated stuff crashes. When I 'calculated' the lowest level, I was modifying the string. So... (5 + 5) * 3 Would turn into 10 * 3 Which would then evaluate to 30 But it just felt 'wrong'. I hope that helps clarify things. I'll certainly check out the links provided.

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• To NOLOCK or NOT to NOLOCK, that is the question

  - by Limey

  Hi all, This is really more of a discussion than a specific question about nolock. I took over an app recently that almost every query (and there are lots of them) has the nolock option on them. Now I am pretty new to SQL server (used Oracle for 10 years) but yet I find this pretty disturbing. So this weekend I was talking with one of my friends who runs a rather large ecommerce site (name will be withheld to protect the guilty) and he says he has to do this with all of his SQL servers cause he will always end in deadlocks. Is this just a huge short fall with SQL server? Is this just a failure in the DB design (mine is not 3rd level, but its close) Is anybody out there running an SQL server app without nolocks? These are issues that Oracle handles better with more grandulare recordlocks. Is SQL server just not able to handle big loads? Is there some better workaround than reading uncommited data? I would love to hear what people think. Thanks

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• How do I access a <form> that is not the master page <form>?

  - by VBCSharp

  Winforms developer converting to web developer. I know the part about the Master Page having the tag, what is not clear is if I can or can not have another in one of my content pages. I have been seeing both answers doing searches. I see yes you can if only one has runat=server. The thing is I have a that contains several radio buttons on a web page that has a master page. I have a .js file that has a function if I send the name into it, it will loop thru the controls in the form to see which one is selected and return the desired date horizon(MTD, QTD, YTD, etc.). When I run this on a non master page web page it works fine. However, when I run on a web page that has a master page I can't seem to get to the element. I tried getElementByID, I tried looping through the page elements, etc. Maybe I am going about this incorrectly and I hope someone can straighten me out. Here is the code from my .js file that may help explain what I am trying to do a little better. var frmDateRanges = document.getElementById(formFieldName); var chosen; var len = frmDateRanges.DateRanges.length; for(i=0;i<len;i++) { if(frmDateRanges.DateRanges[i].checked) { chosen = frmDateRanges.DateRanges[i].value; } } where formFieldName is an arguement that is passed into the function and DateRanges is the name value given to the radio buttons. In the button I call this function I have: onclick ="FunctionCall('frmDateRanges')" FunctionCall is just for description purposes, 'frmDateRanges' is the name and id given to the form action="" Thanks for the help as I am stumped at this point. If there is a better way to do this please let me know that as well.

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• Is a web-server (e.g servlets) a good solution for an IM server?

  - by John

  I'm looking at a new app, broadly speaking an IM application with a strong client-server model - all communications go through a server so they can be logged centrally. The server will be Java in some form, clients could at this point be anything from a .NET Desktop app to Flex/Silverlight, to a simple web-interface using JS/AJAX. I had anticipated doing the server using standard J2EE so I get a thread-safe, multi-user server for 'free'... to make things simple let's say using Servlets (but in practice SpringMVC would be likely). This all seemed very neat but I'm concerned if the stateless nature of Servlets is the best approach. If my memory of servlets (been a year or two) is right, each time a client sent a HTTP request, typically a new message entered by the user, the servlet could not assume it had the user/chat in memory and might have to get it from the DB... regardless it has to look it up. Then it either has to use some PUSH system to inform other members of the chat, or cache that there are new messages, for other clients who poll the server using AJAX or similar - and when they poll it again has to lookup the chat, including new messages, and send the new data. I'm wondering if a better system would be the server is running core Java, and implements a socket-based communication with clients. This allows much more immediate data transfer and is more flexible if say the IM client included some game you could play. But then you're writing a custom server and sockets don't sound very friendly to a browser-based client on current browsers. Am I missing some big piece of the puzzle here, it kind of feels like I am? Perhaps a better way to ask the question would simply be "if the client was browser-based using HTML/JS and had to run on IE7+,FF2+ (i.e no HTML5), how would you implement the server?" edit: if you are going to suggest using XMPP, I have been trying to get my head around this in another question, so please consider if that's a more appropriate place to discuss this specifically.

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• Most efficient way to make an activity log

  - by Nathan

  I am making a "recent activity" tab to profiles on my site and I also am going to have a log for moderators to see everything that happens on the site. This would require making an activity log of some sort. I just don't know what would be better. I have 2 options: Make a table called "activity" and then every time someone does something, add a record to it with the type of action, user id, timestamp, etc. Problem: table could get very long. Join all 3 tables (questions, answers, answer_comments) and then somehow show all these on the page in the order in which the action was taken. Problem: this would be extremely hard because I have no clue how I could make it say "John commented on an answer on Question Title Here" by just joining 3 tables. Does anyone know of a better way of making an activity log in this situation? I am using PHP and MySQL. If this is either too inefficient or hard I will probably just forget the Recent Activity tab on profiles but I still need an activity log for moderators. Here's some SQL that I started making for option 2, but this would not work because there is no way of detecting whether the action is a comment, question, or answer when I echo the info in a while loop: SELECT q.*, a.*, ac.* FROM questions q JOIN answers a ON a.questionid = q.qid JOIN answer_comments ac ON c.answerid = a.ans_id WHERE q.user = $userid AND a.userid = $userid AND ac.userid = $userid ORDER BY q.created DESC, a.created DESC, ac.created DESC Thanks in advance for any help!

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• Double join with habtm in ActiveRecord

  - by Daniel Huckstep

  I have a weird situation involving the need of a double inner join. I have tried the query I need, I just don't know how to make rails do it. The Data Account (has_many :sites) Site (habtm :users, belongs_to :account) User (habtm :sites) Ignore that they are habtm or whatever, I can make them habtm or has_many :through. I want to be able to do @user.accounts or @account.users Then of course I should be able to do @user.accounts < @some_other_account And then have @user.sites include all the sites from @some_other_account. I've fiddled with habtm and has_many :through but can't get it to do what I want. Basically I need to end up with a query like this (copied from phpmyadmin. Tested and works): SELECT accounts.* FROM accounts INNER JOIN sites ON sites.account_id = accounts.id INNER JOIN user_sites ON sites.id = user_sites.site_id WHERE user_sites.user_id = 2 Can I do this? Is it even a good idea to have this double join? I am assuming it would work better if users had the association with accounts to begin with, and then worry about getting @user.sites instead, but it works better for many other things if it is kept the way it is (users <- sites).

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• C++: Static variable inside a constructor, are there any drawbacks or side effects?

  - by doc

  What I want to do: run some prerequisite code whenever instance of the class is going to be used inside a program. This code will check for requiremts etc. and should be run only once. I found that this can be achieved using another object as static variable inside a constructor. Here's an example for a better picture: class Prerequisites { public: Prerequisites() { std::cout << "checking requirements of C, "; std::cout << "registering C in dictionary, etc." << std::endl; } }; class C { public: C() { static Prerequisites prerequisites; std::cout << "normal initialization of C object" << std::endl; } }; What bothers me is that I haven't seen similar use of static variables so far. Are there any drawbacks or side-effects or am I missing something? Or maybe there is a better solution? Any suggestions are welcome.

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