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  • Help with SQL query (Calculate a ratio between two entitiess)

    - by Mestika
    Hi, I’m going to calculate a ratio between two entities but are having some trouble with the query. The principal is the same to, say a forum, where you say: A user gets points for every new thread. Then, calculate the ratio of points for the number of threads. Example: User A has 300 points. User A has started 6 thread. The point ratio is: 50:6 My schemas look as following: student(studentid, name, class, major) course(courseid, coursename, department) courseoffering(courseid, semester, year, instructor) faculty(name, office, salary) gradereport(studentid, courseid, semester, year, grade) The relations is a following: Faculity(name) = courseoffering(instructor) Student(studentid) = gradereport (studentid) Courseoffering(courseid) = course(courseid) Gradereport(courseid) = courseoffering(courseid) I have this query to select the faculty names there is teaching one or more students: SELECT COUNT(faculty.name) FROM faculty, courseoffering, gradereport, student WHERE faculty.name = courseoffering.instructor AND courseoffering.courseid = gradereport.courseid AND gradereport.studentid = student.studentid My problem is to find the ratio between the faculty members salary in regarding to the number of students they are teaching. Say, a teacher get 10.000 in salary and teaches 5 students, then his ratio should be 1:5. I hope that someone has an answer to my problem and understand what I'm having trouble with. Thanks Mestika

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  • Working with fields which can mutate or be new instances altogether

    - by dotnetdev
    Structs are usually used for immutable data, eg a phone number, which does not mutate, but instead you get a new one (eg the number 000 becoming 0001 would mean two seperate numbers). However, pieces of information like Name, a string, can either mutate (company abc changing its name to abcdef, or being given a new name like def). For fields like this, I assume they should reside in the mutable class and not an immutable structure? My way of structuring code is to have an immutable concept, like Address (any change is a new address completely), in a struct and then reference it from a class like Customer, since Customer always has an address. So I would put CompanyName, or Employer, in the class as it is mutable. But a name can either mutate and so be the same 1 instance, or a new name setup and while the company still owning the first name too. Would the correct pattern for assigning a new instance (eg a new company name but the old name still owned by the company) be?: string name = ""; string newName = new string(); newName = "new"; name = newName; And a mutation just the standard assignment pattern? Thanks

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  • IndexOutOfRangeException when a stream is a multiple of the buffer size

    - by dnord
    I don't have a lot of experience with streams and buffers, but I'm having to do it for a project, and I'm stuck on an exception being thrown when the stream I'm reading is a multiple of the buffer size I've chosen. Let me show you: My code starts by reading bufferSize (100, let's say) bytes from the stream: numberOfBytesRead = DataReader.GetBytes(0, index, output, 0, bufferSize); Then, I loop through a while loop: while (numberOfBytesRead == bufferSize) { BufferWriter.Write(output); BufferWriter.Flush(); index += bufferSize; numberOfBytesRead = DataReader.GetBytes(0, index, output, 0, bufferSize); } ... and, once we get to a non-bufferSize read, we know we've hit the end of the stream and can move on. But if the bufferSize is 100, and the stream is 200, we'll read positions 0-99, 100-199, and then the attempt to read 200-299 errors out. I'd like it if it returned 0, but it throws an error. What I'm doing to handle that is, well, a try-catch: catch (System.IndexOutOfRangeException) numberOfBytesRead = 0; ...which ends the loop, and successfully finishes the thing, but we all know I don't want to control code flow with error handling. Is there a better (more standard?) way to handle stream reading when the stream length is unknown? This seems like a small wrinkle in a fairly reasonable strategy for reading streams, but I just don't know if I've got it wrong or what. The specifics of this (which I've cleaned up a little bit for posting) are a MySqlDataReader hitting a LARGEBLOB column. It's working whenever the buffer is larger than the number of returned bytes, or when the number of returned bytes is not a multiple of bufferSize. Because we don't, in that case, throw an IndexOutOfRangeException.

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  • While loop not reading in the last item

    - by Gandalf StormCrow
    I'm trying to read in a multi line string then split it then print it .. here is the string : 1T1b5T!1T2b1T1b2T!1T1b1T2b2T!1T3b1T1b1T!3T3b1T!1T3b1T1b1T!5T1*1T 11X21b1X 4X1b1X When I split the string with ! I get this without the last line string : 1T1b5T 1T1b5T1T2b1T1b2T 1T2b1T1b2T1T1b1T2b2T 1T1b1T2b2T1T3b1T1b1T 1T3b1T1b1T3T3b1T 3T3b1T1T3b1T1b1T 1T3b1T1b1T5T1*1T 5T1*1T11X21b1X 11X21b1X Here is my code : import java.io.BufferedInputStream; import java.util.Scanner; public class Main { public static void main(String args[]) { Scanner stdin = new Scanner(new BufferedInputStream(System.in)); while (stdin.hasNext()) { for (String line : stdin.next().split("!")) { System.out.println(line); for (int i = 0; i < line.length(); i++) { System.out.print(line.charAt(i)); } } } } } Where did I make the mistake, why is not reading in the last line? After I read in all lines properly I should go trough each line if I encounter number I should print the next char the n times the number I just read, but that is long way ahead first I need help with this. Thank you UPDATE : Here is how the output should look like : 1T1b5T 1T2b1T1b2T 1T1b1T2b2T 1T3b1T1b1T 3T3b1T 1T3b1T1b1T 5T1*1T 11X21b1X 4X1b1X Here is a solution in C(my friend solved it not me), but I'd stil wanted to do it in JAVA : #include <stdio.h> int main (void) { char row[134]; for (;fgets (row,134,stdin)!=NULL;) { int i,j=0; for (i=0;row[i]!='\0';i++) { if (row[i]<='9'&&row[i]>='1') j+=(row[i]-'0'); else if ((row[i]<='Z'&&row[i]>='A')||row[i]=='*') for (;j;j--) printf ("%c",row[i]); else if (row[i]=='b') for (;j;j--) printf (" "); else if (row[i]=='!'||row[i]=='\n') printf ("\n"); } } return 0; }

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  • Problem with checkboxes, sql select statements & php

    - by smokey20
    I am trying to display some rows from a database table based on choices submitted by the user. Here is my form code <form action="choice.php" method="POST" > <input type="checkbox" name="variable[]" value="Apple">Apple <input type="checkbox" name="variable[]" value="Banana">Banana <input type="checkbox" name="variable[]" value="Orange">Orange <input type="checkbox" name="variable[]" value="Melon">Melon <input type="checkbox" name="variable[]" value="Blackberry">Blackberry From what I understand I am placing the values of these into an array called variable. Two of my columns are called receipe name and ingredients(each field under ingredients can store a number of fruits). What I would like to do is, if a number of checkboxes are selected then the receipe name/s is displayed. Here is my php code. <?php // Make a MySQL Connection mysql_connect("localhost", "*****", "*****") or die(mysql_error()); mysql_select_db("****") or die(mysql_error()); $variable=$_POST['variable']; foreach ($variable as $variablename) { echo "$variablename is checked"; } $query = "SELECT receipename FROM fruit WHERE $variable like ingredients"; $row = mysql_fetch_assoc($result); foreach ($_POST['variabble'] as $ingredients) echo $row[$ingredients] . '<br/>'; ?> I am very new to php and just wish to display the data, I do not need to perform any actions on it. I have tried many select statements but I cannot get any results to display. My db connection is fine and it does print out what variables are checked. Many thanks in advance.

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  • How to count children from different lists? [jQuery]

    - by Filip Breckx
    Hi, I'm trying to count the number of child elements a certain category has. This is the situation: <ul id="select_cat"> <li id="_1">Category 1 (<span>#</span>)</li> <li id="_2">Category 2 (<span>#</span>)</li> </ul> <ul id="cat_1> <li>Link 1</li> <li>Link 2</li> <li>Link 3</li> </ul> <ul id="cat_2"> <li>Link 1</li> <li>Link 2</li> </ul> So I want to count the number of children a category has. In this example the first cardinal sign should be 3, and the second should be 2. How can I do this, using jQuery. Check an example (not jQuery) Thanks!

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  • Is it possible to develop a remote desktop server application?

    - by Heshan Perera
    I just want to know whether it is possible to develop an Android application that will allow remotely controlling an Android phone in the same way that remote desktop, or team viewer allows control over desktop operating systems. Is it possible on an unrooted phone? The basic functionlit required to acompolish this is would be the ability to capture the frame buffer and programmatically invoke touch on the device. Any feedback on this matter would be highly appreciated.

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  • Determine an elements position in a variable length grid of elements

    - by gaoshan88
    I have a grid of a variable number of elements. Say 5 images per row and a variable number of images. I need to determine which column (for lack of a better word) each image is in... i.e. 1, 2, 3, 4 or 5. In this grid, images 1, 6, 12 and 17 would be in column 1 while 4, 9 and 15 would be in column 4. 1 2 3 4 5 6 7 8 9 10 12 13 14 15 16 17 18 19 What I am trying to do is apply a background image to each element based on it's column position. An example of this hard coded and inflexible (and if I'm barking up the wrong tree here by all means tell me how you'd ideally accomplish this as it always bugs me when I see someone ask "How do I build a gold plated, solar powered jet pack to get to the top of this building?" when they really should be asking "Where's the elevator?"): switch (imgnum){ case "1" : case "6" : case "11" : value = "1"; break; case "2" : case "7" : case "12" : value = "2"; break; case "3" : case "8" : case "13" : value = "3"; break; case "4" : case "9" : case "14" : value = "4"; break; case "5" : case "10" : case "15" : value = "5"; break; default : value = ""; } $('.someclass > ul').css('background','url("/img/'+value+'.png") no-repeat');

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  • How can I find the jdbc connection timeout of a hibernate session

    - by StevenWilkins
    I currently have a long running thread which uses a hibernate session to perform many updates. We currently have our c3p0 connection timeout set to 20 minutes and it's timing out sometimes because of the number of updates we're performing. The solution I have is to periodically return the connection to the pool via closing the session (we have hibernate configured this way) and get a new one. Upping the timeout is not desirable because the same pool is used for the entire application. The problem is I don't know when to return the connection to the pool because I don't know what the timeout of the connection is. I know what the current setting is in our property file, but that can be changed without my knowledge at any time so it's fragile. Having a counter and returning the connection based on the number of updates I've performed is not ideal but could be my option of last resort. I have a hibernate session, how can I retrieve the connection timeout of the jdbc connection which backs the session? Using the SessionFactory and SessionFactoryImpl classes are perfectly acceptable.

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  • Retrieve the Value of An Integer Variable

    - by Abluescarab
    This is probably easily figured out (I feel very stupid right now), but I can't find a solution anywhere, for some reason. Perhaps I'm not searching for the right thing. And maybe it's in some beginner tutorial I haven't watched. Anyway, I was wondering how to retrieve the value of an integer variable in C++? I know you can use cin.getline() for string variables, but I received an error message when I attempted that with an integer variable (and rightfully so, I know it was wrong, but I was looking for a solution). My project is a Win32 console application. What I'm trying to do is ask a user to input a number, stored in the variable n. Then I take the value of n and perform various math functions with it. In my header file, I have string, windows, iostream, stdio, math, and fstream. Do I need to add another library? There's not much more to tell. I can post my code if I must. EDIT: cout << "TEST SINE"; cout << "\nPlease enter a number.\n\n"; cin >> n; break; Here's the code I'm trying to use. Is this all I need to do? If so, how do I incorporate the variable so I can test it using sin, cos, and tan? Yet again, thanks ahead of time.

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  • Lucene.Net: How can I add a date filter to my search results?

    - by rockinthesixstring
    I've got my searcher working really well, however it does tend to return results that are obsolete. My site is much like NerdDinner whereby events in the past become irrelevant. I'm currently indexing like this Public Function AddIndex(ByVal searchableEvent As [Event]) As Boolean Implements ILuceneService.AddIndex Dim writer As New IndexWriter(luceneDirectory, New StandardAnalyzer(), False) Dim doc As Document = New Document doc.Add(New Field("id", searchableEvent.ID, Field.Store.YES, Field.Index.UN_TOKENIZED)) doc.Add(New Field("fullText", FullTextBuilder(searchableEvent), Field.Store.YES, Field.Index.TOKENIZED)) doc.Add(New Field("user", If(searchableEvent.User.UserName = Nothing, "User" & searchableEvent.User.ID, searchableEvent.User.UserName), Field.Store.YES, Field.Index.TOKENIZED)) doc.Add(New Field("title", searchableEvent.Title, Field.Store.YES, Field.Index.TOKENIZED)) doc.Add(New Field("location", searchableEvent.Location.Name, Field.Store.YES, Field.Index.TOKENIZED)) doc.Add(New Field("date", searchableEvent.EventDate, Field.Store.YES, Field.Index.UN_TOKENIZED)) writer.AddDocument(doc) writer.Optimize() writer.Close() Return True End Function Notice how I have a "date" index that stores the event date. My search then looks like this ''# code omitted Dim reader As IndexReader = IndexReader.Open(luceneDirectory) Dim searcher As IndexSearcher = New IndexSearcher(reader) Dim parser As QueryParser = New QueryParser("fullText", New StandardAnalyzer()) Dim query As Query = parser.Parse(q.ToLower) ''# We're using 10,000 as the maximum number of results to return ''# because I have a feeling that we'll never reach that full amount ''# anyways. And if we do, who in their right mind is going to page ''# through all of the results? Dim topDocs As TopDocs = searcher.Search(query, Nothing, 10000) Dim doc As Document = Nothing ''# loop through the topDocs and grab the appropriate 10 results based ''# on the submitted page number While i <= last AndAlso i < topDocs.totalHits doc = searcher.Doc(topDocs.scoreDocs(i).doc) IDList.Add(doc.[Get]("id")) i += 1 End While ''# code omitted I did try the following, but it was to no avail (threw a NullReferenceException). While i <= last AndAlso i < topDocs.totalHits If Date.Parse(doc.[Get]("date")) >= Date.Today Then doc = searcher.Doc(topDocs.scoreDocs(i).doc) IDList.Add(doc.[Get]("id")) i += 1 End If End While I also found the following documentation, but I can't make heads or tails of it http://lucene.apache.org/java/1_4_3/api/org/apache/lucene/search/DateFilter.html

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  • [LaTeX] positions of page numbers, position of chapter headings, chapters AND Table of Contents, Ref

    - by kaikanmonaco
    I am writing my PhD thesis (120+ pages) in latex, the deadline is approaching and I am struggling with layout problems. I am using the documentstyle book. I am posting both problems in this one thread because I am not sure if the solution might be related to both problems or not. Problems are: 1.) The page numbers are mostly located on the top-right of each page (this is correct and where I want them to be). However, only on the first page of chapters and on the first page of what I call "special chapters", the page number is located bottom-centered. With "special chapters" I mean: List of Contents, List of Figures, List of Tables, References, Index. My university will not accept the thesis like this. The page number must ALWAYS be top-right one each page, even if the page is the first page of a chapter or the first page of something like the List of Contents. How can I fix this? 2.) On the first page of chapters and "special chapters" (List of Contents...), the chapter title is located far too low on the page. This is the standard layout of LaTeX with documentstyle book I think. However, the chapter title must start at the very top of the page! I.e. the same height as the normal text on the pages that follow. I mean the chapter title, not the header. I.e., if there is a chapter called "Chapter 1 Dynamics of foobar under mechanical stress" then that text has to start from the top the page, but right now it starts several centimeters below the top. How can I fix this? Have tried all kinds of things to no effect, I'd be very thankful for a solution! Thanks.

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  • Load Testing Java Web Application - find TPS / Avg transaction response time

    - by Steve
    I would like to build my own load testing tool in Java with the goal of being able to load test a web application I am building throughout the development cycle. The web application will be receiving server to server HTTP Post requests and I would like to find its starting transaction per second (TPS) capacity along with the avgerage response time. The Post request and response messages will be in XML (I dont' think that's really applicable though :) ). I have written a very simple Java app to send transactions and count how many transactions it was able to send in one second (1000 ms) however I don't think this is the best way to load test. Really what I want is to send any number of transactions at exactly the same time - i.e. 10, 50, 100 etc. Any help would be appreciated! Oh and here is my current test app code: Thread[] t = new Thread[1]; for (int a = 0; a < t.length; a++) { t[a] = new Thread(new MessageLoop()); } startTime = System.currentTimeMillis(); System.out.println(startTime); for (int a = 0; a < t.length; a++) { t[a].start(); } while ((System.currentTimeMillis() - startTime) < 1000 ) { } if ((System.currentTimeMillis() - startTime) > 1000 ) { for (int a = 0; a < t.length; a++) { t[a].interrupt(); } } long endTime = System.currentTimeMillis(); System.out.println(endTime); System.out.println("Total time: " + (endTime - startTime)); System.out.println("Total transactions: " + count); private static class MessageLoop implements Runnable { public void run() { try { //Test Number of transactions while ((System.currentTimeMillis() - startTime) < 1000 ) { // SEND TRANSACTION HERE count++; } } catch (Exception e) { } } }

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  • Is there a simple automatic backup system for Visual Studio projects?

    - by Jelly Amma
    Hello, I'm using Visual Studio 2008 Express and I would like Visual Studio (or perhaps an Add-in) to save my whole project to some sort of auto-incrementing archive or whatever would help me recover from disasters. I don't have much need for SVN or complex versioning systems. I'm just looking for something simple and lean. Any help would be much appreciated. Jenny PS : I looked into the built-in AutoRecover feature but it doesn't seem to save more than a few files.

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  • Dynamic GUI Framework Designing

    - by user575715
    There is a Scenario to be developed for a 3-tier Application .We need to design a Framework or a utility sort of thing . In tradional aspect of GUI Designing , either we tend to create a static gui page and code the elements on it along with other properties of the elements such as (disabled/enabled,image source,name ,id ,which function to be called under onclick event.) or we tend to drag and drop the elements from the control pallete provided by variety of gui frameworks. Certain things i need to design a POC so that we can develop this concept. 1) There must a utility ,such that during creation of screen layout , that screen should be saved in the database(RDBMS) with a screen number. 2) All the Events related to that control should be saved in some other table which will be dynamically mapped during the calling of screen number by the user. 3) When the user call that screen ,a generic function should be invoked which'll call the screen file from the database and apply all the properties ,events,etc at runtime and the final output will be displayed to the user. This POC will help the us to customised the screens according to our usage.also all the code will seperated which can easily be used for some other development process. Thanks Amit Kalra

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  • Why JEE is widely used in complicated projects?

    - by cane
    Hi. Yesterday me and my friend we've had nice conversation about IT and he asked me WHY JEE is so widely used when it comes to build complicated IT systems? From my point of view advantages are easily visible, but he is IT manager with a lot of Micro$oft experience (and little Java exp.), so I would like to hear your voice. And I'll give him a link of course. I don't want new .NET - JAVA war - just - why JEE :) Thanks, orsonek

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  • In Perl, how can I wait for threads to end in parallel?

    - by Pmarcoen
    I have a Perl script that launches 2 threads,one for each processor. I need it to wait for a thread to end, if one thread ends a new one is spawned. It seems that the join method blocks the rest of the program, therefore the second thread can't end until everything the first thread does is done which sort of defeats its purpose. I tried the is_joinable method but that doesn't seem to do it either. Here is some of my code : use threads; use threads::shared; @file_list = @ARGV; #Our file list $nofiles = $#file_list + 1; #Real number of files $currfile = 1; #Current number of file to process my %MSG : shared; #shared hash $thr0 = threads->new(\&process, shift(@file_list)); $currfile++; $thr1 = threads->new(\&process, shift(@file_list)); $currfile++; while(1){ if ($thr0->is_joinable()) { $thr0->join; #check if there are files left to process if($currfile <= $nofiles){ $thr0 = threads->new(\&process, shift(@file_list)); $currfile++; } } if ($thr1->is_joinable()) { $thr1->join; #check if there are files left to process if($currfile <= $nofiles){ $thr1 = threads->new(\&process, shift(@file_list)); $currfile++; } } } sub process{ print "Opening $currfile of $nofiles\n"; #do some stuff if(some condition){ lock(%MSG); #write stuff to hash } print "Closing $currfile of $nofiles\n"; } The output of this is : Opening 1 of 4 Opening 2 of 4 Closing 1 of 4 Opening 3 of 4 Closing 3 of 4 Opening 4 of 4 Closing 2 of 4 Closing 4 of 4

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  • string auto splitting in each loop - jquery

    - by sluggerdog
    I have the following jquery code that is looping through the returned json data, for some reason is it splitting the suburb by a space when being assigned as the value but not as the text, I cannot work out why this is happening. MY CODE $.each(data , function( index, obj ) { $.each(obj, function( key, value ) { var suburb = $.trim(value['mcdl01']); var number = $.trim(value['mcmcu']); $("#FeedbackBranchName").append("<option value=" + suburb + ">" + suburb + " (" + number + ")</option>"); }); }); SAMPLE RETURNED RESULTS <option **value="AIRLIE" beach=""**>AIRLIE BEACH (4440)</option> <option value="ASHMORE">ASHMORE (4431)</option> <option **value="BANYO" commercial=""**>BANYO COMMERCIAL (4432)</option> <option value="BEENLEIGH">BEENLEIGH (4413)</option> <option value="BERRIMAH">BERRIMAH (4453)</option> <option **value="BOWEN" hills=""**>BOWEN HILLS (4433)</option> Notice how for AIRLEE BEACH, BANYO COMMERICAL AND BOWN HILLS the second word has been separated out from the value attribute but it's fine at the text level. Anyone have any idea why this might happen? Thanks

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  • Big-O for GPS data

    - by HH
    A non-critical GPS module use lists because it needs to be modifiable, new routes added, new distances calculated, continuos comparisons. Well so I thought but my team member wrote something I am very hard to get into. His pseudo code int k =0; a[][] <- create mapModuleNearbyDotList -array //CPU O(n) for(j = 1 to n) // O(nlog(m)) for(i =1 to n) for(k = 1 to n) if(dot is nearby) adj[i][j]=min(adj[i][j], adj[i][k] + adj[k][j]); His ideas transformations of lists to tables His worst case time complexity is O(n^3), where n is number of elements in his so-called table. Exception to the last point with Finite structure: O(mlog(n)) where n is number of vertices and m is an arbitrary constants Questions about his ideas why to waste resources to transform constantly-modified lists to table? Fast? only point where I to some extent agree but cannot understand the same upper limits n for each for-loops -- perhaps he supposed it circular why does the code take O(mlog(n)) to proceed in time as finite structure? The term finite may be wrong, explicit?

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  • Stop Visual Studio from appending numbers to the end of new controls

    - by techturtle
    I am wondering if there is any way to stop Visual Studio 2010 from appending a number to the end of the ID on new controls I create. For example, when I add a new TextBox, I would prefer that it do this: <asp:TextBox ID="TextBox" runat="server"> <asp:TextBox ID="TextBox" runat="server"> <asp:TextBox ID="TextBox" runat="server"> Instead of this: <asp:TextBox ID="TextBox1" runat="server"> <asp:TextBox ID="TextBox2" runat="server"> <asp:TextBox ID="TextBox3" runat="server"> It would make it easier to rename them appropriately, so I don't have to arrow/mouse over and delete the number each time. As I was writing this, the "Questions that may already have your answer" suggested this: How do I prevent Visual Studio from renaming my controls? which admittedly was the biggest part of my annoyance, but that appears to turn off putting in an ID="" field altogether, not just for pasted controls. It would still be helpful to turn off the numbering for new, non-pasted controls and have it not rename pasted ones as well. At the moment I'm working with ASP.NET, but it would be nice if it there was a way to do it for WinForms as well. Before anyone suggests it, I do know that allowing it to append the numbers prevents name conflicts should I not rename them appropriately. However, I would much rather have it fail to compile so I know to fix the issue now (if I forget to name something properly) rather than find random "TextBox1" items lying around in the code later on.

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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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  • Designing model/database for distance between any two locations (that may change)

    - by Yo Ludke
    We should create a web app which has a number of events each with a location (created as user-generated content, so the number of events will be increasingly large). The distance between any events should be available, for example to determine the top 5 closest events and such things. Users may change the locations of events. How should one design the database/model for this (in a scalable way)? I was thinking of doing it with a "distance table" (like so http://www.deutschland-tourist.info/images/entfernungstabelle.gif). Then every time, if a location changes, one row and one column have to be recalculated (this should be done with a delayed job, because it is not important to have the changes instantly). Possible problems in Scaling: Database to large (n² items for n events), too much calculation to be done. For example we should see if this is okay for 10.000 users. If each has created just one event, then this would be 100 million integers... Do you think this would be a good way to do it efficiently? How could one realize such a distance table with an rails model? Is it possible with a SQL databse? Would you start other approaches?

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