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  • Strange compiler complaint when using similar code

    - by Jason
    For a project, I have to ask the user for a file name, and I'm reading it in character by character using getchar. From the main, I call the function char *coursename= introPrint(); //start off to print the usage directions and get the first bit of input. That function is defined as char *introPrint(){ int size= 20; int c; int length=0; char buffer[size]; //instructions printout, cut for brevity //get coursename from user and return it while ( (c=getchar()) != EOF && (c != '\n') ){ buffer[length++]= c; if (length==size-1) break; } buffer[length]=0; return buffer; } This is basically identical code I wrote to ask the user for input, replace the character echo with asterisks, then print out the results. Here, though, I'm getting a function returns address of local variable warning for the return statement. So why am I getting no warnings from the other program, but trigger one for this code?

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  • jQuery class selector oddness

    - by x3sphere
    I'm using jQuery to change the background image of a button depending on the class associated with it on hover. It only works if I put the hover statements in separate functions, however. Why is this? Here's the NON working code, always evaluates to the .submit hover statement, even when that class is removed via the keyup event. $(function() { { $('.submit-getinfo').hover(function () { $(this).css( {backgroundPosition: "right bottom"} ); }, function() { $(this).css( {backgroundPosition: "right top"} ); //$(this).removeClass('submithover'); }); $('.submit').hover(function () { $(this).css( {backgroundPosition: "left bottom"} ); }, function() { $(this).css( {backgroundPosition: "left top"} ); //$(this).removeClass('submithover'); }); }}); Working code: $(function() { { $('.submit').hover(function () { $(this).css( {backgroundPosition: "left bottom"} ); }, function() { $(this).css( {backgroundPosition: "left top"} ); //$(this).removeClass('submithover'); }); }}); $('#test').bind('keyup', function() { if (url == 'devel') { $("#submit").addClass("submit-getinfo").removeClass("submit"); $('.submit-getinfo').hover(function () { $(this).css( {backgroundPosition: "right bottom"} ); }, function() { $(this).css( {backgroundPosition: "right top"} ); //$(this).removeClass('submithover'); }); } } ); I just fail to see why I have to put the hover statements in separate functions, instead of sticking both in the main DOM.

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  • :include and table aliasing

    - by dondo
    I'm suffering from a variant of the problem described here: ActiveRecord assigns table aliases for association joins fairly unpredictably. The first association to a given table keeps the table name. Further joins with associations to that table use aliases including the association names in the path... but it is common for app developers not to know about [other] joins at coding time. In my case I'm being bitten by a toxic mix of has_many and :include. Many tables in my schema have a state column, and the has_many wants to specify conditions on that column: has_many :foo, :conditions => {:state => 1}. However, since the state column appears in many tables, I disambiguate by explicitly specifying the table name: has_many :foo, :conditions => "this_table.state = 1". This has worked fine until now, when for efficiency I want to add an :include to preload a fairly deep tree of data. This causes the table to be aliased inconsistently in different code paths. My reading of the tickets referenced above is that this problem is not and will not be fixed in Rails 2.x. However, I don't see any way to apply the suggested workaround (to specify the aliased table name explicitly in the query). I'm happy to specify the table alias explicitly in the has_many statement, but I don't see any way to do so. As such, the workaround doesn't appear applicable to this situation (nor, I presume, in many 'named_scope' scenarios). Is there a viable workaround?

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  • What C# container is most resource-efficient for existence for only one operation?

    - by ccornet
    I find myself often with a situation where I need to perform an operation on a set of properties. The operation can be anything from checking if a particular property matches anything in the set to a single iteration of actions. Sometimes the set is dynamically generated when the function is called, some built with a simple LINQ statement, other times it is a hard-coded set that will always remain the same. But one constant always exists: the set only exists for one single operation and has no use before or after it. My problem is, I have so many points in my application where this is necessary, but I appear to be very, very inconsistent in how I store these sets. Some of them are arrays, some are lists, and just now I've found a couple linked lists. Now, none of the operations I'm specifically concerned about have to care about indices, container size, order, or any other functionality that is bestowed by any of the individual container types. I picked resource efficiency because it's a better idea than flipping coins. I figured, since array size is configured and it's a very elementary container, that might be my best choice, but I figure it is a better idea to ask around. Alternatively, if there's a better choice not out of resource-efficiency but strictly as being a better choice for this kind of situation, that would be nice as well.

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  • Switch front-end's of a website after X amount of hits

    - by Derek Adair
    Sorry about the title - not sure what to call this one. A client of mine would like to redirect users to different front-ends of his eCommerce site based on a hit-counter (possibly a timer?). important: -The content is moderately different in the two sites, enough to consider them two different websites. Knowing this client he will likely add more drastic content changes and other front-ends. So for this question consider the content to be -This site has a rather large back-end. With affiliate networking, multiple payment gateways, order-tracking, and several other features in the works. It is essential that these two front-ends have identical back-end functionality I know that if it was just a simple CSS swap this would be as simple as an if statement that ran off some kind of counter stored in a DB... but the different HTML markup is throwing me for a loop. Q: How can I serve two different front-ends (HTML/CSS) based on a hit counter? Also, I don't have any clue what to tag this one as...

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  • PHP variable equals true no matter what the value, even 0

    - by kaigoh
    This is the var_dump: object(stdClass)#27 (8) { ["SETTING_ID"]=> string(2) "25" ["SETTING_SOURCE"]=> string(2) "XV" ["SETTING_FLEET"]=> string(3) "313" ["SETTING_EXAM"]=> string(1) "A" ["SETTING_HIDE"]=> string(1) "0" ["SETTING_THRESHOLD"]=> string(1) "0" ["SETTING_COUNT"]=> string(8) "POSITIVE" ["SETTING_USAGE"]=> string(7) "MILEAGE" } The variable I am testing is SETTING_HIDE. This is being pulled from MySQL using the Code igniter framework. I don't know if it is just me being thick after a rather long day at work or what, but no matter what value the variable holds, any if statement made against it returns true, even when typecast as a boolean or a direct string comparison, ie. == "0" or == "1". Anyone with a fresh pair of eyes care to make me feel silly!?! :) Just to clarify: Have tried the following: if($examSetting->SETTING_HIDE == "1") { $showOnABC = "checked=\"checked\""; } if((bool)$examSetting->SETTING_HIDE) { $showOnABC = "checked=\"checked\""; } if($examSetting->SETTING_COUNT == "POSITIVE") further on in my code works perfectly.

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  • Runtime error in C code (strange double conversion)

    - by Miro Hassan
    I have a strange runtime error in my C code. The Integers comparison here works fine. But in the Decimals comparison, I always get that the second number is larger than the first number, which is false. I am pretty new to C and programming in general, so this is a complex application to me. #include <stdio.h> #include <stdbool.h> #include <stdlib.h> int choose; long long neLimit = -1000000000; long long limit = 1000000000; bool big(a,b) { if ((a >= limit) || (b >= limit)) return true; else if ((a <= neLimit) || (b <= neLimit)) return true; return false; } void largerr(a,b) { if (a > b) printf("\nThe First Number is larger ..\n"); else if (a < b) printf("\nThe Second Number is larger ..\n"); else printf("\nThe Two Numbers are Equal .. \n"); } int main() { system("color e && title Numbers Comparison && echo off && cls"); start:{ printf("Choose a Type of Comparison :\n\t1. Integers\n\t2. Decimals \n\t\t I Choose Number : "); scanf("%i", &choose); switch(choose) { case 1: goto Integers; break; case 2: goto Decimals; break; default: system("echo Please Choose a Valid Option && pause>nul && cls"); goto start; } } Integers: { system("title Integers Comparison && cls"); long x , y; printf("\nFirst Number : \t"); scanf("%li", &x); printf("\nSecond Number : "); scanf("%li", &y); if (big(x,y)) { printf("\nOut of Limit .. Too Big Numbers ..\n"); system("pause>nul && cls") ; goto Integers; } largerr(x,y); printf("\nFirst Number : %li\nSecond Number : %li\n",x,y); goto exif; } Decimals: { system("title Decimals Comparison && cls"); double x , y; printf("\nFirst Number : \t"); scanf("%le", &x); printf("\nSecond Number : "); scanf("%le", &y); if (big(x,y)) { printf("\nOut of Limit .. Too Big Numbers ..\n"); system("pause>nul && cls") ; goto Decimals; } largerr(x,y); goto exif; } exif:{ system("pause>nul"); system("cls"); main(); } }

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  • Inexplicably slow query in MySQL

    - by Brandon M.
    Given this result-set: mysql> EXPLAIN SELECT c.cust_name, SUM(l.line_subtotal) FROM customer c -> JOIN slip s ON s.cust_id = c.cust_id -> JOIN line l ON l.slip_id = s.slip_id -> JOIN vendor v ON v.vend_id = l.vend_id WHERE v.vend_name = 'blahblah' -> GROUP BY c.cust_name -> HAVING SUM(l.line_subtotal) > 49999 -> ORDER BY c.cust_name; +----+-------------+-------+--------+---------------------------------+---------------+---------+----------------------+------+----------------------------------------------+ | id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra | +----+-------------+-------+--------+---------------------------------+---------------+---------+----------------------+------+----------------------------------------------+ | 1 | SIMPLE | v | ref | PRIMARY,idx_vend_name | idx_vend_name | 12 | const | 1 | Using where; Using temporary; Using filesort | | 1 | SIMPLE | l | ref | idx_vend_id | idx_vend_id | 4 | csv_import.v.vend_id | 446 | | | 1 | SIMPLE | s | eq_ref | PRIMARY,idx_cust_id,idx_slip_id | PRIMARY | 4 | csv_import.l.slip_id | 1 | | | 1 | SIMPLE | c | eq_ref | PRIMARY,cIndex | PRIMARY | 4 | csv_import.s.cust_id | 1 | | +----+-------------+-------+--------+---------------------------------+---------------+---------+----------------------+------+----------------------------------------------+ 4 rows in set (0.04 sec) I'm a bit baffled as to why the query referenced by this EXPLAIN statement is still taking about a minute to execute. Isn't it true that this query only has to search through 449 rows? Anyone have any idea as to what could be slowing it down so much?

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  • Timestamps and Intervals: NUMTOYMINTERVAL SYSTDATE CALCULATION SQL QUERY

    - by MeachamRob
    I am working on a homework problem, I'm close but need some help with a data conversion I think. Or sysdate - start_date calculation The question is: Using the EX schema, write a SELECT statement that retrieves the date_id and start_date from the Date_Sample table (format below), followed by a column named Years_and_Months_Since_Start that uses an interval function to retrieve the number of years and months that have elapsed between the start_date and the sysdate. (Your values will vary based on the date you do this lab.) Display only the records with start dates having the month and day equal to Feb 28 (of any year). DATE_ID START_DATE YEARS_AND_MONTHS_SINCE_START 2 Sunday , February 28, 1999 13-8 4 Monday , February 28, 2005 7-8 5 Tuesday , February 28, 2006 6-8 Our EX schema that refers to this question is simply a Date_Sample Table with two columns: DATE_ID NUMBER NOT Null START_DATE DATE I Have written this code: SELECT date_id, TO_CHAR(start_date, 'Day, MONTH DD, YYYY') AS start_date , NUMTOYMINTERVAL((SYSDATE - start_date), 'YEAR') AS years_and_months_since_start FROM date_sample WHERE TO_CHAR(start_date, 'MM/DD') = '02/28'; But my Years and months since start column is not working properly. It's getting very high numbers for years and months when the date calculated is from 1999-ish. ie, it should be 13-8 and I'm getting 5027-2 so I know it's not correct. I used NUMTOYMINTERVAL, which should be correct, but don't think the sysdate-start_date is working. Data Type for start_date is simply date. I tried ROUND but maybe need some help to get it right. Something is wrong with my calculation and trying to figure out how to get the correct interval there. Not sure if I have provided enough information to everyone but I will let you know if I figure it out before you do. It's a question from Murach's Oracle and SQL/PL book, chapter 17 if anyone else is trying to learn that chapter. Page 559.

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  • Adding a ActionPerformed Array to a String Array

    - by user267490
    Hey, Before you guys ask, yes I've searched online for the answer, but everything I found just leaves a lil confuse and nothing is recent so asking in those forums won't really help. My problems is this: I have an array that holds my name for a menu. String[] fontColor = new String[] {"Red", "Blue", "Green"}; for (int i = 0; i < fontColors.length; i++) { JMenuItem fontC = new JMenuItem(fontColors[i]); fontC.addActionListener(new fontColorAction()); changeFontColor.add(fontC); } Then I have an array that holds my color change in a class called fontColorAction in that class I have another array that does the same thing as my string array except all thats in the statement is textarea.setForeground(colorArr[i]); that will set the setForeground() in order, but now how do I successfully attact the action listner in my class to my menuItems? my class looks like this private class fontColorAction implements ActionListener { Color[] colorArr - new Color[] {"Color.RED","Color.BLUE","Color.GREEN"}; public void actionPerformed(ActionEvent e){ for(i = 0; i < collorArr.length; i++){ textarea.setForeground(colorArr[i]); } } }

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  • How do I stop Ant from hanging after executing a java program that attempted to interrupt a thread (and failed) and continued?

    - by Zugwalt
    I have Ant build and execute a java program. This program tries to do something that sometimes hangs, so we execute it in a thread. actionThread.start(); try { actionThread.join(10000); } catch (InterruptedException e) { System.out.println("InterruptedException: "+e.getMessage()); } if (actionThread.isAlive()) { actionThread.interrupt(); System.out.println("Thread timed out and never died"); } The ant call looks like this: <java fork="true" failonerror="yes" classname="myPackage.myPathName" classpath="build"> <arg line=""/> <classpath> <pathelement location="bin" /> <fileset dir="lib"> <include name="**/*.jar"/> </fileset> </classpath> </java> And when this runs I see the "Thread timed out and never died" statement, and I also see the main program finish execution, but then Ant just hangs. Presumably it is waiting for the child threads to finish, but they never will. How can I have Ant be done once it is done executing main() and just kill or ignore dead threads?

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  • transforming 1d (1column) into 5d(5column) matrix through copy paste or other

    - by Curious
    Ex. I want to take the column with 12345..... and order 5 columns across as seen. next 5 numbers in column will be next row. However my code creates a 4 row gap in between each successive row. I dont know what additional logic (possibly if then statement) I can embed into do loop to may make it cleaner. I am new to this, so showing as much sample code to learn the syntax would be most beneficial. thanks in advance. Below is the Result of my code. VBA code is below result. 1 1 2 3 4 5 2 3 4 5 6 6 7 8 9 10 7 8 9 10 11 11 12 13 14 15 12 13 14 15 16 16 17 17 Sub Working_Code() ' Working_Code Macro Do ActiveCell.Select Selection.Copy ActiveCell.Offset(0, 5).Select ActiveSheet.Paste ActiveCell.Offset(1, -5).Select Selection.Copy ActiveCell.Offset(-1, 6).Select ActiveSheet.Paste ActiveCell.Offset(2, -6).Select Selection.Copy ActiveCell.Offset(-2, 7).Select ActiveSheet.Paste ActiveCell.Offset(3, -7).Select Selection.Copy ActiveCell.Offset(-3, 8).Select ActiveSheet.Paste ActiveCell.Offset(4, -8).Select Selection.Copy ActiveCell.Offset(-4, 9).Select ActiveSheet.Paste ActiveCell.Offset(5, -9).Select Loop Until IsEmpty(ActiveCell.Offset(0, -1)) End Sub

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  • LINQ to SQL - Lightweight O/RM?

    - by CoffeeAddict
    I've heard from some that LINQ to SQL is good for lightweight apps. But then I see LINQ to SQL being used for Stackoverflow, and a bunch of other .coms I know (from interviewing with them). Ok, so is this true? for an e-commerce site that's bringing in millions and you're typically only doing basic CRUDs most the time with the exception of an occasional stored proc for something more complex, is LINQ to SQL complete enough and performance-wise good enough or able to be tweaked enough to run happily on an e-commerce site? I've heard that you just need to tweak performance on the DB side when using LINQ to SQL for a better approach. So there are really 2 questions here: 1) Meaning/scope/definition of a "Lightweight" O/RM solution: What the heck does "lightweight" mean when people say LINQ to SQL is a "lightweight O/RM" and is that true??? If this is so lightweight then why do I see a bunch of huge .coms using it? Is it good enough to run major .coms (obviously it looks like it is) and what determines what the context of "lightweight" is...it's such a generic statement. 2) Performance: I'm working on my own .com and researching different O/RMs. I'm not really looking at the Entity Framework (yet), just want to figure out the LINQ to SQL basics here and determine if it will be efficient enough for me. The problem I think is you can't tweak or control the SQL it generates...

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  • PHP OO vs Procedure with AJAX

    - by vener
    I currently have a AJAX heavy(almost everything) intranet webapp for a business. It is highly modularized(components and modules ala Joomla), with plenty of folders and files. ~ 80-100 different viewing pages (each very unique in it's own sense) on last count and will likely to increase in the near future. I based around the design around commands and screens, the client request a command and sends the required data and receives the data that is displayed via javascript on the screen. That said, there are generally two types of files, a display files with html, javascript, and a little php for templating. And also a php backend file with a single switch statement with actions such as, save, update and delete and maybe other function. There is very little code reuse. Recently, I have been adding an server sided undo function that requires me to reuse some code. So, I took the chance to try out OOP but I notice that some functions are so simple, that creating a class, retrieving all the data then update all the related rows on the database seems like overkill for a simple action as speed is quite critical. Also I noticed there is only one class in an entire file. So, what if the entire php is a class. So, between creating a class and methods, and using global variables and functions. Which is faster?

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  • Named Range Breaks Code

    - by Daniel
    I have one workbook with several sheets. I populate the listboxes (pulling static data from cells) on the 2nd sheet, click a button and it runs fine. When I populate the listboxes with a named range, the listbox populates the way I want, but I get an error because the code thinks that I didn't select anything in the listbox, even though I did. So it passes through "" instead of "title". Is this a common issue? The named range isn't a problem because it passes through the data to the listbox and I know it's selecting data because as soon as the listbox loses focus, it spits out the contents of the cell into cell A1. What's even stranger is that I have the contents of the listbox set to Msg1. So A1 gets populated with Msg1 (what I actually selected in the listbox). But when I try and use Msg1 in the code, it tells me that Msg1 is "". Again, this only happens when I use the dynamic named range, not with static data in cells K1:K9. Private Function strEndSQL1 As String Dim strSQL As String strSQL = "" 'Create SQL statement strSQL = "FROM (SELECT * FROM dbo.Filter WHERE ID = " & TextBox1.Text & " And Source IN (" & Msg1 & ")) a FULL OUTER JOIN " strSQL = strSQL & "(SELECT * FROM dbo.Filters WHERE ID = " & TextBox2.Text & " And Source IN (" & Msg1 & ")) b " strSQL = strSQL & "ON a.Group = b.Group strEndSQL = strSQL End Function

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  • Write to PDF using PHP from android device

    - by Brent Mitchell
    I am trying to write to a pdf file on php server. I have sent variables to the server, create the pdf document, then have my phone download the document to view on device. The variables seem not to write on the php file. I have my code below public void postData() { try { Calculate calc = new Calculate(); HttpClient mClient = new DefaultHttpClient(); StringBuilder sb=new StringBuilder("myurl.com/pdf.php"); HttpPost mpost = new HttpPost(sb.toString()); String value = "1234"; List nameValuepairs = new ArrayList(1); nameValuepairs.add(new BasicNameValuePair("id",value)); mpost.setEntity(new UrlEncodedFormEntity(nameValuepairs)); } catch (UnsupportedEncodingException e) { Log.w(" error ", e.toString()); } catch (Exception e) { Log.w(" error ", e.toString()); } } And my php code to write the variable "value" onto the pdf document: //code to reverse the string if($_POST[] != null) { $reversed = strrev($_POST["value"]); $this->SetFont('Arial','u',50); $this->Text(52,68,$reversed); } I am just trying to write the variable in a random spot, but the variable the if statement is always null and I do not know why. Thanks. Sorry if it is a little sloppy.

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  • Problems with variadic function (C)

    - by morpheous
    I have the following function from some legacy code that I am maintaining. long getMaxStart(long start, long count, const myStruct *s1, ...) { long i1, maxstart; myStruct *s2; va_list marker; maxstart = start; /*BUGFIX: 003 */ /*(va_start(marker, count);*/ va_start(marker, s1); for (i1 = 1; i1 <= count; i1++) { s2 = va_arg(marker, myStruct *); /* <- s2 is assigned null here */ maxstart = MAX(maxstart, s2->firstvalid); /* <- SEGV here */ } va_end(marker); return (maxstart); } When the function is called with only one myStruct argument, it causes a SEGV. The code compiled and run without crashing on an XP, when I compiled it using VS2005. I have now moved the code to Ubuntu Karmic and I am having problems with the stricter compiler on Linux. Is anyone able to spot what is causing the parameter not to be read correctly in the var_arg() statement? I am compiling using gcc version 4.4.1

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  • What is wrong with this Asynchronus task?

    - by bluebrain
    the method onPostExecute simply was not executed, I have seen 16 at LogCat but I can not see 16 in LogCAT. I tried to debug it, it seemed that it goes to the first line of the class (package line) after return statement. private class Client extends AsyncTask<Integer, Void, Integer> { protected Integer doInBackground(Integer... params) { Log.e(TAG,10+""); try { socket = new Socket(target, port); Log.e(TAG,11+""); oos = new ObjectOutputStream(socket.getOutputStream()); Log.e(TAG,14+""); ois = new ObjectInputStream(socket.getInputStream()); Log.e(TAG,15+""); } catch (UnknownHostException e) { e.printStackTrace(); } catch (IOException e) { e.printStackTrace(); } Log.e(TAG,16+""); return 1; } protected void onPostExecute(Integer result) { Log.e(TAG,13+""); try { Log.e(TAG,12+""); oos.writeUTF(key); Log.e(TAG,13+""); if (ois.readInt() == OKAY) { isConnected = true; Log.e(TAG,14+""); }else{ Log.e(TAG,15+""); isConnected = false; } } catch (IOException e) { e.printStackTrace(); isClosed = true; } } }

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  • Concatenate an each loop inside another

    - by Lothar
    I want to to concatenate the results of a jquery each loop inside of another but am not getting the results I expect. $.each(data, function () { counter++; var i = 0; var singlebar; var that = this; tableRow = '<tr>' + '<td>' + this.foo + '</td>' + $.each(this.bar, function(){ singlebar = '<td>' + that.bar[i].baz + '</td>'; tableRow + singlebar; }); '</tr>'; return tableRow; }); The portion inside the nested each does not get added to the string that is returned. I can console.log(singlebar) and get the expected results in the console but I cannot concatenate those results inside the primary each loop. I have also tried: $.each(this.bar, function(){ tableRow += '<td>' + that.bar[i].baz + '</td>'; }); Which also does not add the desired content. How do I iterate over this nested data and add it in the midst of the table that the primary each statement is building?

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  • Custom ADO.NET provider to intercept and modify sql queries.

    - by Faisal
    Our client has an application that stores blobs in database which has now grown enough to impact the performance of SQL Server. To overcome this issue, we are planning to offload all blobs to file system and leave the path of file in a new column in user table. Like if user has a table docs with columns id, name and content (blob); we would ask him to add a new column 'filepath' in this table. Our client is willing to make this change in this database. But when it comes to changing the sql queries to read and write into this table, they are not ready to accep this. Actually, they don't want any change that results in recompilation and deployment. Now we are planning to write a custom ADO.NET provider that will intercept the select queries add a column 'filepath' at the end of the select statement retieve the result set and modify the 'content' column value based on 'filepath' value Is there any use case that you think will certainly fail with this approach? I know this sounds dirty but do we have a better way?

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  • Is it possible to shuffle a 2D matrix while preserving row AND column frequencies?

    - by j_random_hacker
    Suppose I have a 2D array like the following: GACTG AGATA TCCGA Each array element is taken from a small finite set (in my case, DNA nucleotides -- {A, C, G, T}). I would like to randomly shuffle this array somehow while preserving both row and column nucleotide frequencies. Is this possible? Can it be done efficiently? [EDIT]: By this I mean I want to produce a new matrix where each row has the same number of As, Cs, Gs and Ts as the corresponding row of the original matrix, and where each column has the same number of As, Cs, Gs and Ts as the corresponding column of the original matrix. Permuting the rows or columns of the original matrix will not achieve this in general. (E.g. for the example above, the top row has 2 Gs, and 1 each of A, C and T; if this row was swapped with row 2, the top row in the resulting matrix would have 3 As, 1 G and 1 T.) It's simple enough to preserve just column frequencies by shuffling a column at a time, and likewise for rows. But doing this will in general alter the frequencies of the other kind. My thoughts so far: If it's possible to pick 2 rows and 2 columns so that the 4 elements at the corners of this rectangle have the pattern XY YX for some pair of distinct elements X and Y, then replacing these 4 elements with YX XY will maintain both row and column frequencies. In the example at the top, this can be done for (at least) rows 1 and 2 and columns 2 and 5 (whose corners give the 2x2 matrix AG;GA), and for rows 1 and 3 and columns 1 and 4 (whose corners give GT;TG). Clearly this could be repeated a number of times to produce some level of randomisation. Generalising a bit, any "subrectangle" induced by a subset of rows and a subset of columns, in which the frequencies of all rows are the same and the frequencies of all columns are the same, can have both its rows and columns permuted to produce a valid complete rectangle. (Of these, only those subrectangles in which at least 1 element is changed are actually interesting.) Big questions: Are all valid complete matrices reachable by a series of such "subrectangle rearrangements"? I suspect the answer is yes. Are all valid subrectangle rearrangements decomposable into a series of 2x2 swaps? I suspect the answer is no, but I hope it's yes, since that would seem to make it easier to come up with an efficient algorithm. Can some or all of the valid rearrangements be computed efficiently? This question addresses a special case in which the set of possible elements is {0, 1}. The solutions people have come up with there are similar to what I have come up with myself, and are probably usable, but not ideal as they require an arbitrary amount of backtracking to work correctly. Also I'm concerned that only 2x2 swaps are considered. Finally, I would ideally like a solution that can be proven to select a matrix uniformly at random from the set of all matrices having identical row frequencies and column frequencies to the original. I know, I'm asking for a lot :)

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  • What are the benefits of `while(condition) { //work }` and `do { //work } while(condition)`?

    - by Shaharyar
    I found myself confronted with an interview question where the goal was to write a sorting algorithm that sorts an array of unsorted int values: int[] unsortedArray = { 9, 6, 3, 1, 5, 8, 4, 2, 7, 0 }; Now I googled and found out that there are so many sorting algorithms out there! Finally I could motivate myself to dig into Bubble Sort because it seemed pretty simple to start with. I read the sample code and came to a solution looking like this: static int[] BubbleSort(ref int[] array) { long lastItemLocation = array.Length - 1; int temp; bool swapped; do { swapped = false; for (int itemLocationCounter = 0; itemLocationCounter < lastItemLocation; itemLocationCounter++) { if (array[itemLocationCounter] > array[itemLocationCounter + 1]) { temp = array[itemLocationCounter]; array[itemLocationCounter] = array[itemLocationCounter + 1]; array[itemLocationCounter + 1] = temp; swapped = true; } } } while (swapped); return array; } I clearly see that this is a situation where the do { //work } while(cond) statement is a great help to be and prevents the use of another helper variable. But is this the only case that this is more useful or do you know any other application where this condition has been used?

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  • Accessing variables with different scope in C++

    - by Portablejim
    With #include <iostream> using namespace std; int a = 1; int main() { int a = 2; if(true) { int a = 3; cout << a << " " << ::a // Can I access a = 2 here? << " " << ::a << endl; } cout << a << " " << ::a << endl; } having the output 3 1 1 2 1 Is there a way to access the 'a' equal to 2 inside the if statement where there is the 'a' equal to 3, with the output 3 2 1 2 1 Note: I know this should not be done (and the code should not get to the point where I need to ask). This question is more "can it be done".

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  • RoR ActiveRecord f.select nil method error

    - by sellis6688
    Whenever I use an f.select statement to determine assignment_id(or student_id), and I should get a validation error, I get this error instead of the validation message: You have a nil object when you didn't expect it! You might have expected an instance of Array. The error occurred while evaluating nil.collect Extracted source (around line #11): 8: </p> 9: <p> 10: <%= f.label 'Assignment:' %><br /> 11: <%= f.select(:assignment_id, @assignments.collect {|p| [p.ass_num, p.id]})%> 12: </p> 13: <p> 14: <%= f.label 'First Student:' %><br /> My grades model: class Grade < ActiveRecord::Base has_and_belongs_to_many :students belongs_to :assignment validates_presence_of :score, :assignment_id, :student_id validates_numericality_of :score, :greater_than_or_equal_to => 0, :less_than_or_equal_to => 100, :allow_nil => true validates_uniqueness_of :student_id, :scope => :assignment_id end If I use a text_field, I don't get the error... but there's far too many students for that. Neither @assignments nor @students are nil. Any suggestions?

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  • Selecting row in SSMS causes Entity Framework 4 to Fail

    - by Eric J.
    I have a simple Entity Framework 4 unit test that creates a new record, saves it, attempts to find it, then deletes it. All works great, unless... ... I open up SQL Server Management Studio while stopped at a breakpoint in the unit test and execute a SELECT statement that returns the row I just created (not SELECT FOR UPDATE, not WITH (updlock), no transaction, just a plain SELECT). If I do that before attempting to find the row I just created, I don't find the row. If I instead do that after finding the row but before deleting the row, I do find the row but get an OptimisticConcurrencyException. This is consistently repeatable. Unit Test: [TestMethod()] public void CreateFindDeleteActiveParticipantsTest() { // Setup this test Participant utPart = CreateUTParticipant(); ctx.Participants.AddObject(utPart); ctx.SaveChanges(); // External SELECT Point #1: // part is null // Find participant Participant part = ParticipantRepository.Find(UT_SURVEY_ID, UT_TOKEN); Assert.IsNotNull(part, "Expected to find a participant"); // External SELECT Point #2: // SaveChanges throws OptimisticConcurrencyException // Cleanup this test ctx.Participants.DeleteObject(utPart); ctx.SaveChanges(); }

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