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  • Apache console accesses network drives, service does not?

    - by danspants
    I have an apache 2.2 server running Django. We have a network drive T: which we need constant access to within our Django app. When running Apache as a service, we cannot access this drive, as far as any django code is concerned the drive does not exist. If I add... <Directory "t:/"> Options Indexes FollowSymLinks MultiViews AllowOverride None Order allow,deny allow from all </Directory> to the httpd.conf file the service no longer runs, but I can start apache as a console and it works fine, Django can find the network drive and all is well. Why is there a difference between the console and the service? Should there be a difference? I have the service using my own log on so in theory it should have the same access as I do. I'm keen to keep it running as a service as it's far less obtrusive when I'm working on the server (unless there's a way to hide the console?). Any help would be most appreciated.

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  • Strange behavior while returning csv file from spring controller

    - by Fanooos
    I working in a spring application which have an action method that returns a CSV file. This action works fine but in some cases it throws a predefined exception (MyAppException). I have another method that is annotated @ExceptionHandler(MyAppException.class) In the exception handler method I return another csv file but with different contents. The code that returns the csv file is almost the same in the two methods. List<String[]> list= new ArrayList<String[]>(); list.add(new String[]{ integrationRequestErrorLog.getErrorMessage(), Long.toString(integrationRequestErrorLog.getId()), Integer.toString(integrationRequestErrorLog.getErrorCode()) }); CSVWriter writer = new CSVWriter(response.getWriter(), ','); writer.writeAll(list); writer.close(); the difference between the two method is the list of contents. In the first method the file is returned normally while in the exception handler method I have a strange behavior. The exception handler method works fine with Opera browser while it gives me a 404 with FireFox. Opera browser give me 404 also but it download the file while firefox does not? Really I do not understand what is the difference here.

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  • How to get Amazon s3 PHP SDK working?

    - by JakeRow123
    I'm trying to set up s3 for the first time and trying to run the sample file that comes with the PHP sdk that creates a bucket and attempts to upload some demo files to it. But this is the error I am getting: The difference between the request time and the current time is too large. I read on another question on SO that this is because Amazon determines a valid request by comparing the times between the server and the client, that the 2 must be within a 15 min span of one another. Now here is the problem. My laptop's time is 12:30AM June 8, 2012 at the moment. On my server I created a file called servertime.php and placed this code in that file: <?php print strftime('%c'); ?> and the output is: Fri Jun 8 00:31:22 2012 It looks like the day is correct but I don't know what to make of 00:31:22. In any case, how is it possible to always make sure the time between the client and server is within a 15 minute window of one another. What if I have a user in China who wishes to upload a file on my site which uses s3 for the cdn. Then the time difference would be over a day. How can I make sure all my user's times are within 15 minutes of my server time? What if the user is in the U.S. but the time on their machine is misconfigured. Basically how to get s3 bucket creation and upload to work?

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  • What is better: Developing a Web project in MVC or N -Tier Architecture?

    - by Starx
    I have asked a similar question before and got an convincing answer as well? http://stackoverflow.com/questions/2843311/what-is-difference-of-developing-a-website-in-mvc-and-3-tier-or-n-tier-architectu Due to the conclusion of this question I started developing projects in N-tier Architecture. Just about an hour ago, I asked another question, about what is the best design pattern to create interface? There the most voted answer is suggesting me to use MVC architecture. http://stackoverflow.com/questions/2930300/what-is-the-best-desing-pattern-to-design-the-interface-of-an-webpage Now I am confused, First post suggested me that both are similar, just a difference that in N-tier, the tier are physically and logically separated and one layer has access to the one above and below it but not all the layers. I think ASP.net used 3 Tier architecture while developing applications or Web applications. Where as frameworks like Zend, Symphony they use MVC. I just want to stick to a pattern that is best suitable for WebProject Development? May be this is a very silly confusion? But if someone could clear this confusion, that would be very greatful?

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  • Differences in accessing resources between Simulator and Device?

    - by Tony
    Is there some difference between the way that bundle resources can be accessed on the iPhone simulator versus a device (in my case, an iPad)? I am able to access a file on the former, but not the latter. NSString *filePath = [NSString stringWithFormat:@"%@%@",[[NSBundle mainBundle] bundlePath], @"/AppResources/html/pages/quickHelp.html"]; BOOL fileExists = [[NSFileManager defaultManager] fileExistsAtPath:filePath]; // fileExists == YES in the debugger on both the simulator and the device NSString *path = [NSString stringWithFormat:@"AppResources/html/pages/%@", contentsFileName]; NSString *pathForURL = [[NSBundle mainBundle] pathForResource:path ofType:@"html"]; NSURL *url = [NSURL fileURLWithPath:pathForURL isDirectory:NO]; The code above works fine in the simulator, but on the device pathForResource:path returns nil, so the last line throws a 'nil string parameter' exception. Am I missing something obvious? edit: Of course, in the above @"quickHelp" is being passed in the contentsFileName var. edit2: if it makes any difference, in my build settings "Base SDK" is set to "iPhone Device 4.0", and "iPhone OS Deployment Target" is set to "iPhone OS 3.1.3". Any other settings that might have an influence?

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  • Excel VBA creating a new column with formula

    - by Amatya
    I have an excel file with a column which has date data. I want the user to input a date of their choosing and then I want to create a new column that lists the difference in days between the two dates. The Macro that I have is working but I have a few questions and I would like to make it better. Link to MWE small data file is here. The user input date was 9/30/2013, which I stored in H20 Macro: Sub Date_play() Dim x As Date Dim x2 As Date Dim y As Variant x = InputBox(Prompt:="Please enter the Folder Report Date. The following formats are acceptable: 4 1 2013 or April 1 2013 or 4/1/2013") x2 = Range("E2") y = DateDiff("D", x2, x) MsgBox y 'Used DateDiff above and it works but I don't know how to use it to fill a column or indeed a cell. Range("H20").FormulaR1C1 = x Range("H1").FormulaR1C1 = "Diff" Range("H2").Formula = "=DATEDIF(E2,$H$20,""D"")" Range("H2").AutoFill Destination:=Range("H2:H17") Range("H2:H17").Select End Sub Now, could I have done this without storing the user input date in a particular cell? I would've preferred to use the variable "x" in the formula but it wasn't working for me. I had to store the user input in H20 and then use $H$20. What's the difference between the function Datedif and the procedure DateDiff? I am able to use the procedure DateDiff in my macro but I don't know how to use it to fill out my column. Is one method better than the other? Is there a better way to add columns to the existing sheet, where the columns include some calculations involving existing data on the sheet and some user inputs? There are tons of more complicated calculations I want to do next. Thanks

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  • crash when using stl vector at instead of operator[]

    - by Jamie Cook
    I have a method as follows (from a class than implements TBB task interface - not currently multithreading though) My problem is that two ways of accessing a vector are causing quite different behaviour - one works and the other causes the entire program to bomb out quite spectacularly (this is a plugin and normally a crash will be caught by the host - but this one takes out the host program as well! As I said quite spectacular) void PtBranchAndBoundIterationOriginRunner::runOrigin(int origin, int time) const // NOTE: const method { BOOST_FOREACH(int accessMode, m_props->GetAccessModes()) { // get a const reference to appropriate vector from member variable // map<int, vector<double>> m_rowTotalsByAccessMode; const vector<double>& rowTotalsForAccessMode = m_rowTotalsByAccessMode.find(accessMode)->second; if (origin != 129) continue; // Additional debug constrain: I know that the vector only has one non-zero element at index 129 m_job->Write("size: " + ToString(rowTotalsForAccessMode.size())); try { // check for early return... i.e. nothing to do for this origin if (!rowTotalsForAccessMode[origin]) continue; // <- this works if (!rowTotalsForAccessMode.at(origin)) continue; // <- this crashes } catch (...) { m_job->Write("Caught an exception"); // but its not an exception } // do some other stuff } } I hate not putting in well defined questions but at the moment my best phrasing is : "WTF?" I'm compiling this with Intel C++ 11.0.074 [IA-32] using Microsoft (R) Visual Studio Version 9.0.21022.8 and my implementation of vector has const_reference operator[](size_type _Pos) const { // subscript nonmutable sequence #if _HAS_ITERATOR_DEBUGGING if (size() <= _Pos) { _DEBUG_ERROR("vector subscript out of range"); _SCL_SECURE_OUT_OF_RANGE; } #endif /* _HAS_ITERATOR_DEBUGGING */ _SCL_SECURE_VALIDATE_RANGE(_Pos < size()); return (*(_Myfirst + _Pos)); } (Iterator debugging is off - I'm pretty sure) and const_reference at(size_type _Pos) const { // subscript nonmutable sequence with checking if (size() <= _Pos) _Xran(); return (*(begin() + _Pos)); } So the only difference I can see is that at calls begin instead of simply using _Myfirst - but how could that possibly be causing such a huge difference in behaviour?

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  • EXC_BAD_ACCESS in NSURLConnection: how to debug?

    - by baswell
    I have an iPhone app that downloads URLs. (PDFs to display) Easy: self.conn = [NSURLConnection connectionWithRequest:self.request delegate:self]; where self.conn is a retained property. For specific URLs, this throws EXC_BAD_ACCESS. The URL is valid and is constructed in the same way as URLs that do work. (90% of URLs are fine) These ones work: http://www.airservicesaustralia.com/publications/current/ersa/FAC_YARG_11-Mar-2010.pdf http://www.airservicesaustralia.com/publications/current/ersa/FAC_YARK_11-Mar-2010.pdf These don't: http://www.airservicesaustralia.com/publications/current/ersa/FAC_YAMK_11-Mar-2010.pdf http://www.airservicesaustralia.com/publications/current/ersa/FAC_YATN_11-Mar-2010.pdf Spot the difference? Yeah, me neither. Also no difference in response headers from the server for them. To clarify, the ones that work ALWAYS work, the ones that don't NEVER work. So not some random release/retain issue it seems. For the ones that don't work, none of the methods in my delegate are ever called, it fails hard before that. And with no error message, just EXC_BAD_ACCESS. Sooo.... Any way to debug what is going on inside NSURLConnection?

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  • objective C underscore property vs self

    - by user1216838
    I'm was playing around with the standard sample split view that gets created when you select a split view application in Xcode, and after adding a few fields i needed to add a few fields to display them in the detail view. and something interesting happend in the original sample, the master view sets a "detailItem" property in the detail view and the detail view displays it. - (void)setDetailItem:(id) newDetailItem { if (_detailItem != newDetailItem) { _detailItem = newDetailItem; // Update the view. [self configureView]; } i understand what that does and all, so while i was playing around with it. i thought it would be the same if instead of _detailItem i used self.detailItem, since it's a property of the class. however, when i used self.detailItem != newDetailItem i actually got stuck in a loop where this method is constantly called and i cant do anything else in the simulator. my question is, whats the actual difference between the underscore variables(ivar?) and the properties? i read some posts here it seems to be just some objective C convention, but it actually made some difference.

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  • Clarification/explanation of RegisterClientScriptInclude method

    - by mpminnich
    I've been looking on the Internet for a fairly clear explanation of the different methods of registering javascript in an asp.net application. I think I have a basic understating of the difference between registerStartupScript and registerClientScriptBlock (the main difference being where in the form the script is inserted). I'm not sure I understand what the RegisterClientScriptInclude method does or when it is used. From what I can gather, it is used to register an external .js file. Does this then make any and all javascript functions in that file available to the aspx page it was registered on? For example, if it was registered in the onLoad event of a master page, would all pages using that master page be able to use the javascript functions in the .js file? What problems would arise when trying to use document.getElementById in this case, if any? Also, when it is necessary/advantageous to use multiple .js files and register them separately? I appreciate any help you can give. If you know of any really good resources I can use to get a thorough understanding of this concept, I'd appreciate it!

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  • jQuery : how to determine that a div is scrolled down

    - by subtenante
    I have a div with defined height, and overflow:scroll;. Its content is too long so scrollbars appear. Now for the ichy part. Some of its inner HTML strangely appears all the time (to be precise, the footer of a table generated by the tableFilter plugin). I'd like to make this footer disappear when it is not needed (it actually appears out of the containing <div>'s border). I resolved to make it disappear but setting its z-index to -1000. But I want to make it appear when the containing <div> is totally scrolled down. How can I know the user has scrolled at the bottom ? Using the help from answers below, I used scrollTop attribute but the difference between scrollTop and innerHeight is the size of the scrollbar plus some unidentified delta. A scrollbar is 16 pixels high in most browsers under Windows, but I get a difference of 17 in Firefox and something like 20 in IE, where my <div> content's borders seems to be rendered bigger. A way (actually two ways...) to compute the scrollbar size has been given there.

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  • Not crawling the same content twice

    - by sirrocco
    I'm building a small application that will crawl sites where the content is growing (like on stackoverflow) the difference is that the content once created is rarely modified. Now , in the first pass I crawl all the pages in the site. But next, the paged content of that site - I don't want to re-crawl all of it , just the latest additions. So if the site has 500 pages, on the second pass if the site has 501 pages then I would only crawl the first and second pages. Would this be a good way to handle the situation ? In the end, the crawled content will end up in lucene - creating a custom search engine. So, I would like to avoid crawling multiple times the same content. Any better ideas ? EDIT : Let's say the site has a page : Results that will be accessed like so : Results?page=1 , Results?page=2 ...etc I guess that keeping a track of how many pages there were at the last crawl and just crawl the difference would be enough. ( maybe using a hash of each result on the page - if I start running into the same hashes - I should stop)

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  • Linq-to-sql join/where?

    - by Curtis White
    I've the following table structures Users id Types id isBool UsersTypes userid types I want to select all the UserTypes based on id and isBool. I tried this query var q = from usertype in usertypes from type in types where type.isBool == false where userstypes.user == id select usertype; But this did not work as expected. My questions are: Why? Is there any difference in using the join on syntax vs where, where vs where cond1 && cond2? My understanding is query optimizer will optimize. Is there any difference in using where cond1 == var1 && cond2 == var2 with and without the parenthesis? This seems peculiar that it is possible to build this without parenthesis What type of query do I need in this case? I can see that I could do a subquery or use a group but not 100% sure if it is required. An example might be helpful. I'm thinking a subquery may be required in this case.

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  • How do I use Haml in a view in my new plugin?

    - by Eric
    I'm creating a new plugin for a jruby on rails application that will eventually be turned into a gem. Inside my plugin I have controllers, helpers and views. For my views I'd like to use Haml. The problem is that I can't seem to get it to recognize that they are haml templates. Is it even possible to do this? Is there a way for a plugin to have Haml as a dependency for its view? And by that I mean, I intend for the plugin that I'm creating to have a view created by the plugin, that can be used by the application developer. for example: vendor/ plugins/ my_plugin/ lib/ app/ views/ my_plugin_demo/ index.haml.html controllers/ my_plugin_demo_controller.rb helpers/ In my plugin's init.rb, I tried: require 'my_plugin' require 'haml' #doesn't seem to make a difference :( but that didn't seem to make any difference. Has anybody had any experience with this? I can't seem to find any documentation on how to make this work. Are plugin views restricted to .erb templates?

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  • How can I use Perl to determine whether the contents of two files are identical?

    - by Zaid
    This question comes from a need to ensure that changes I've made to code doesn't affect the values it outputs to text file. Ideally, I'd roll a sub to take in two filenames and return 1or return 0 depending on whether the contents are identical or not, whitespaces and all. Given that text-processing is Perl's forté, it should be quite easy to compare two files and determine whether they are identical or not (code below untested). use strict; use warnings; sub files_match { my ( $fileA, $fileB ) = @_; open my $file1, '<', $fileA; open my $file2, '<', $fileB; while (my $lineA = <$file1>) { next if $lineA eq <$file2>; return 0 and last; } return 1; } The only way I can think of (sans CPAN modules) is to open the two files in question, and read them in line-by-line until a difference is found. If no difference is found, the files must be identical. But this approach is limited and clumsy. What if the total lines differ in the two files? Should I open and close to determine line count, then re-open to scan the texts? Yuck. I don't see anything in perlfaq5 relating to this. I want to stay away from modules unless they come with the core Perl 5.6.1 distribution.

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  • How to filter List<T> with LINQ and Reflection

    - by Ehsan Sajjad
    i am getting properties via reflection and i was doing like this to iterate on the list. private void HandleListProperty(object oldObject, object newObject, string difference, PropertyInfo prop) { var oldList = prop.GetValue(oldObject, null) as IList; var newList = prop.GetValue(newObject, null) as IList; if (prop.PropertyType == typeof(List<DataModel.ScheduleDetail>)) { List<DataModel.ScheduleDetail> ScheduleDetailsOld = oldList as List<DataModel.ScheduleDetail>; List<DataModel.ScheduleDetail> ScheduleDetailsNew = newList as List<DataModel.ScheduleDetail>; var groupOldSchedules = ScheduleDetailsOld .GroupBy(x => x.HomeHelpID) .SelectMany(s => s.DistinctBy(d => d.HomeHelpID) .Select(h => new { h.HomeHelpID, h.HomeHelpName })); } } Now i am making it generic because there will be coming different types of Lists and i don't want to put if conditions this way i want to write generic code to handle any type of list. I came up with this way: private void HandleListProperty(object oldObject, object newObject, string difference, PropertyInfo prop) { var oldList = prop.GetValue(oldObject, null) as IList; var newList = prop.GetValue(newObject, null) as IList; var ListType = prop.PropertyType; var MyListInstance = Activator.CreateInstance(ListType); MyListInstance = oldList; } i am able to get the items in MyListInstance but as the type will come at runtime i am not getting how to write linq query to filter them, any ideah how to do.

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  • Highlighting Changes in Java

    - by Buzz Lightyear
    Basically, i have done my program so that it will display differences in strings and display the whole line. I want to highlight (in a colour) the differences in the line. Example: Original at line 5 <rect x="60.01" width="855.38" id="rect_1" y="-244.35" height="641.13" style="stroke-width: 1; stroke: rgb(0, 0, 0); fill: none; "/> Edited at line 5 <rect x="298.43" width="340.00" y="131.12" height="380.00" id="rect_1" style="stroke-width: 1; stroke: rgb(0, 0, 0); fill: rgb(255, 102, 0); "/> In this example, the width is different from the 'original' from the 'edited' version. I would like to be able to highlight that difference and any other difference. My code so far: Patch patch = DiffUtils.diff(centralFile, remoteFile); StringBuffer resultsBuff = new StringBuffer(remoteFileData.length); for (Delta delta : patch.getDeltas()) { resultsBuff.append("Original at line " + delta.getOriginal().getPosition() + "\n"); for (Object line : delta.getOriginal().getLines()) { resultsBuff.append(" " + line + "\n"); } resultsBuff.append("Edited at line " + delta.getRevised().getPosition() + "\n"); for (Object line : delta.getRevised().getLines()) { resultsBuff.append(" " + line + "\n"); } resultsBuff.append("\n"); } return resultsBuff.toString(); } That will display two whole lines like the example before (the original and the edited version) I want to be able to highlight the changes that have actually been made, is there any way to do this in Java?

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  • Different output between release and Debug

    - by AthomSfere
    I can't figure this one out. I have a c++ Application that works in Debug mode exactly as expected: #include "stdafx.h" #include <string> #include <Windows.h> #include <iostream> using namespace std; void truncateServer(std::string inString); int _tmain(int argc, char *argv[]) { char* server = argv[1]; truncateServer(server); } void truncateServer(std::string inString) { std::string server = ""; int whackCount = 0; for (unsigned int i = 0; i < inString.length(); i++) { char c = inString[i]; if (whackCount < 3) { if (c == '\\') whackCount++; else server += c; } } cout << server; } For example if I call the server I want via its UNC path \\serverName\Share\ in the debug it gives me exactly what I want: servername However, if I use the release build I get nothing: I deleted the release output folder, but the issue is exactly the same. I can only assume there is some other difference between the release and build applications that is exposing a major issue with my code? Or another difference between the outputs I need to account for. What do I need to do to get the expected output?

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  • Container of Generic Types in java

    - by Cyker
    I have a generic class Foo<T> and parameterized types Foo<String> and Foo<Integer>. Now I want to put different parameterized types into a single ArrayList. What is the correct way of doing this? Candidate 1: public class MMM { public static void main(String[] args) { Foo<String> fooString = new Foo<String>(); Foo<Integer> fooInteger = new Foo<Integer>(); ArrayList<Foo<?> > list = new ArrayList<Foo<?> >(); list.add(fooString); list.add(fooInteger); for (Foo<?> foo : list) { // Do something on foo. } } } class Foo<T> {} Candidate 2: public class MMM { public static void main(String[] args) { Foo<String> fooString = new Foo<String>(); Foo<Integer> fooInteger = new Foo<Integer>(); ArrayList<Foo> list = new ArrayList<Foo>(); list.add(fooString); list.add(fooInteger); for (Foo foo : list) { // Do something on foo. } } } class Foo<T> {} In a word, it is related to the difference between Foo<?> and the raw type Foo. Update: Grep What is the difference between the unbounded wildcard parameterized type and the raw type? on this link may be helpful.

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  • Which way of declaring a variable is fastest?

    - by ADB
    For a variable used in a function that is called very often and for implementation in J2ME on a blackberry (if that changed something, can you explain)? class X { int i; public void someFunc(int j) { i = 0; while( i < j ){ [...] i++; } } } or class X { static int i; public void someFunc(int j) { i = 0; while( i < j ){ [...] i++; } } } or class X { public void someFunc(int j) { int i = 0; while( i < j ){ [...] i++; } } } I know there is a difference how a static versus non-static class variable is accessed, but I don't know it would affect the speed. I also remember reading somewhere that in-function variables may be accessed faster, but I don't know why and where I read that. Background on the question: some painting function in games are called excessively often and even small difference in access time can affect the overall performance when a variable is used in a largish loop.

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  • C#/.NET Little Wonders: The Useful But Overlooked Sets

    - by James Michael Hare
    Once again we consider some of the lesser known classes and keywords of C#.  Today we will be looking at two set implementations in the System.Collections.Generic namespace: HashSet<T> and SortedSet<T>.  Even though most people think of sets as mathematical constructs, they are actually very useful classes that can be used to help make your application more performant if used appropriately. A Background From Math In mathematical terms, a set is an unordered collection of unique items.  In other words, the set {2,3,5} is identical to the set {3,5,2}.  In addition, the set {2, 2, 4, 1} would be invalid because it would have a duplicate item (2).  In addition, you can perform set arithmetic on sets such as: Intersections: The intersection of two sets is the collection of elements common to both.  Example: The intersection of {1,2,5} and {2,4,9} is the set {2}. Unions: The union of two sets is the collection of unique items present in either or both set.  Example: The union of {1,2,5} and {2,4,9} is {1,2,4,5,9}. Differences: The difference of two sets is the removal of all items from the first set that are common between the sets.  Example: The difference of {1,2,5} and {2,4,9} is {1,5}. Supersets: One set is a superset of a second set if it contains all elements that are in the second set. Example: The set {1,2,5} is a superset of {1,5}. Subsets: One set is a subset of a second set if all the elements of that set are contained in the first set. Example: The set {1,5} is a subset of {1,2,5}. If We’re Not Doing Math, Why Do We Care? Now, you may be thinking: why bother with the set classes in C# if you have no need for mathematical set manipulation?  The answer is simple: they are extremely efficient ways to determine ownership in a collection. For example, let’s say you are designing an order system that tracks the price of a particular equity, and once it reaches a certain point will trigger an order.  Now, since there’s tens of thousands of equities on the markets, you don’t want to track market data for every ticker as that would be a waste of time and processing power for symbols you don’t have orders for.  Thus, we just want to subscribe to the stock symbol for an equity order only if it is a symbol we are not already subscribed to. Every time a new order comes in, we will check the list of subscriptions to see if the new order’s stock symbol is in that list.  If it is, great, we already have that market data feed!  If not, then and only then should we subscribe to the feed for that symbol. So far so good, we have a collection of symbols and we want to see if a symbol is present in that collection and if not, add it.  This really is the essence of set processing, but for the sake of comparison, let’s say you do a list instead: 1: // class that handles are order processing service 2: public sealed class OrderProcessor 3: { 4: // contains list of all symbols we are currently subscribed to 5: private readonly List<string> _subscriptions = new List<string>(); 6:  7: ... 8: } Now whenever you are adding a new order, it would look something like: 1: public PlaceOrderResponse PlaceOrder(Order newOrder) 2: { 3: // do some validation, of course... 4:  5: // check to see if already subscribed, if not add a subscription 6: if (!_subscriptions.Contains(newOrder.Symbol)) 7: { 8: // add the symbol to the list 9: _subscriptions.Add(newOrder.Symbol); 10: 11: // do whatever magic is needed to start a subscription for the symbol 12: } 13:  14: // place the order logic! 15: } What’s wrong with this?  In short: performance!  Finding an item inside a List<T> is a linear - O(n) – operation, which is not a very performant way to find if an item exists in a collection. (I used to teach algorithms and data structures in my spare time at a local university, and when you began talking about big-O notation you could immediately begin to see eyes glossing over as if it was pure, useless theory that would not apply in the real world, but I did and still do believe it is something worth understanding well to make the best choices in computer science). Let’s think about this: a linear operation means that as the number of items increases, the time that it takes to perform the operation tends to increase in a linear fashion.  Put crudely, this means if you double the collection size, you might expect the operation to take something like the order of twice as long.  Linear operations tend to be bad for performance because they mean that to perform some operation on a collection, you must potentially “visit” every item in the collection.  Consider finding an item in a List<T>: if you want to see if the list has an item, you must potentially check every item in the list before you find it or determine it’s not found. Now, we could of course sort our list and then perform a binary search on it, but sorting is typically a linear-logarithmic complexity – O(n * log n) - and could involve temporary storage.  So performing a sort after each add would probably add more time.  As an alternative, we could use a SortedList<TKey, TValue> which sorts the list on every Add(), but this has a similar level of complexity to move the items and also requires a key and value, and in our case the key is the value. This is why sets tend to be the best choice for this type of processing: they don’t rely on separate keys and values for ordering – so they save space – and they typically don’t care about ordering – so they tend to be extremely performant.  The .NET BCL (Base Class Library) has had the HashSet<T> since .NET 3.5, but at that time it did not implement the ISet<T> interface.  As of .NET 4.0, HashSet<T> implements ISet<T> and a new set, the SortedSet<T> was added that gives you a set with ordering. HashSet<T> – For Unordered Storage of Sets When used right, HashSet<T> is a beautiful collection, you can think of it as a simplified Dictionary<T,T>.  That is, a Dictionary where the TKey and TValue refer to the same object.  This is really an oversimplification, but logically it makes sense.  I’ve actually seen people code a Dictionary<T,T> where they store the same thing in the key and the value, and that’s just inefficient because of the extra storage to hold both the key and the value. As it’s name implies, the HashSet<T> uses a hashing algorithm to find the items in the set, which means it does take up some additional space, but it has lightning fast lookups!  Compare the times below between HashSet<T> and List<T>: Operation HashSet<T> List<T> Add() O(1) O(1) at end O(n) in middle Remove() O(1) O(n) Contains() O(1) O(n)   Now, these times are amortized and represent the typical case.  In the very worst case, the operations could be linear if they involve a resizing of the collection – but this is true for both the List and HashSet so that’s a less of an issue when comparing the two. The key thing to note is that in the general case, HashSet is constant time for adds, removes, and contains!  This means that no matter how large the collection is, it takes roughly the exact same amount of time to find an item or determine if it’s not in the collection.  Compare this to the List where almost any add or remove must rearrange potentially all the elements!  And to find an item in the list (if unsorted) you must search every item in the List. So as you can see, if you want to create an unordered collection and have very fast lookup and manipulation, the HashSet is a great collection. And since HashSet<T> implements ICollection<T> and IEnumerable<T>, it supports nearly all the same basic operations as the List<T> and can use the System.Linq extension methods as well. All we have to do to switch from a List<T> to a HashSet<T>  is change our declaration.  Since List and HashSet support many of the same members, chances are we won’t need to change much else. 1: public sealed class OrderProcessor 2: { 3: private readonly HashSet<string> _subscriptions = new HashSet<string>(); 4:  5: // ... 6:  7: public PlaceOrderResponse PlaceOrder(Order newOrder) 8: { 9: // do some validation, of course... 10: 11: // check to see if already subscribed, if not add a subscription 12: if (!_subscriptions.Contains(newOrder.Symbol)) 13: { 14: // add the symbol to the list 15: _subscriptions.Add(newOrder.Symbol); 16: 17: // do whatever magic is needed to start a subscription for the symbol 18: } 19: 20: // place the order logic! 21: } 22:  23: // ... 24: } 25: Notice, we didn’t change any code other than the declaration for _subscriptions to be a HashSet<T>.  Thus, we can pick up the performance improvements in this case with minimal code changes. SortedSet<T> – Ordered Storage of Sets Just like HashSet<T> is logically similar to Dictionary<T,T>, the SortedSet<T> is logically similar to the SortedDictionary<T,T>. The SortedSet can be used when you want to do set operations on a collection, but you want to maintain that collection in sorted order.  Now, this is not necessarily mathematically relevant, but if your collection needs do include order, this is the set to use. So the SortedSet seems to be implemented as a binary tree (possibly a red-black tree) internally.  Since binary trees are dynamic structures and non-contiguous (unlike List and SortedList) this means that inserts and deletes do not involve rearranging elements, or changing the linking of the nodes.  There is some overhead in keeping the nodes in order, but it is much smaller than a contiguous storage collection like a List<T>.  Let’s compare the three: Operation HashSet<T> SortedSet<T> List<T> Add() O(1) O(log n) O(1) at end O(n) in middle Remove() O(1) O(log n) O(n) Contains() O(1) O(log n) O(n)   The MSDN documentation seems to indicate that operations on SortedSet are O(1), but this seems to be inconsistent with its implementation and seems to be a documentation error.  There’s actually a separate MSDN document (here) on SortedSet that indicates that it is, in fact, logarithmic in complexity.  Let’s put it in layman’s terms: logarithmic means you can double the collection size and typically you only add a single extra “visit” to an item in the collection.  Take that in contrast to List<T>’s linear operation where if you double the size of the collection you double the “visits” to items in the collection.  This is very good performance!  It’s still not as performant as HashSet<T> where it always just visits one item (amortized), but for the addition of sorting this is a good thing. Consider the following table, now this is just illustrative data of the relative complexities, but it’s enough to get the point: Collection Size O(1) Visits O(log n) Visits O(n) Visits 1 1 1 1 10 1 4 10 100 1 7 100 1000 1 10 1000   Notice that the logarithmic – O(log n) – visit count goes up very slowly compare to the linear – O(n) – visit count.  This is because since the list is sorted, it can do one check in the middle of the list, determine which half of the collection the data is in, and discard the other half (binary search).  So, if you need your set to be sorted, you can use the SortedSet<T> just like the HashSet<T> and gain sorting for a small performance hit, but it’s still faster than a List<T>. Unique Set Operations Now, if you do want to perform more set-like operations, both implementations of ISet<T> support the following, which play back towards the mathematical set operations described before: IntersectWith() – Performs the set intersection of two sets.  Modifies the current set so that it only contains elements also in the second set. UnionWith() – Performs a set union of two sets.  Modifies the current set so it contains all elements present both in the current set and the second set. ExceptWith() – Performs a set difference of two sets.  Modifies the current set so that it removes all elements present in the second set. IsSupersetOf() – Checks if the current set is a superset of the second set. IsSubsetOf() – Checks if the current set is a subset of the second set. For more information on the set operations themselves, see the MSDN description of ISet<T> (here). What Sets Don’t Do Don’t get me wrong, sets are not silver bullets.  You don’t really want to use a set when you want separate key to value lookups, that’s what the IDictionary implementations are best for. Also sets don’t store temporal add-order.  That is, if you are adding items to the end of a list all the time, your list is ordered in terms of when items were added to it.  This is something the sets don’t do naturally (though you could use a SortedSet with an IComparer with a DateTime but that’s overkill) but List<T> can. Also, List<T> allows indexing which is a blazingly fast way to iterate through items in the collection.  Iterating over all the items in a List<T> is generally much, much faster than iterating over a set. Summary Sets are an excellent tool for maintaining a lookup table where the item is both the key and the value.  In addition, if you have need for the mathematical set operations, the C# sets support those as well.  The HashSet<T> is the set of choice if you want the fastest possible lookups but don’t care about order.  In contrast the SortedSet<T> will give you a sorted collection at a slight reduction in performance.   Technorati Tags: C#,.Net,Little Wonders,BlackRabbitCoder,ISet,HashSet,SortedSet

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  • How can I resolve Hibernate 3's ConstraintViolationException when updating a Persistent Entity's Col

    - by Tim Visher
    I'm trying to discover why two nearly identical class sets are behaving different from Hibernate 3's perspective. I'm fairly new to Hibernate in general and I'm hoping I'm missing something fairly obvious about the mappings or timing issues or something along those lines but I spent the whole day yesterday staring at the two sets and any differences that would lead to one being able to be persisted and the other not completely escaped me. I appologize in advance for the length of this question but it all hinges around some pretty specific implementation details. I have the following class mapped with Annotations and managed by Hibernate 3.? (if the specific specific version turns out to be pertinent, I'll figure out what it is). Java version is 1.6. ... @Embeddable public class JobStateChange implements Comparable<JobStateChange> { @Temporal(TemporalType.TIMESTAMP) @Column(nullable = false) private Date date; @Enumerated(EnumType.STRING) @Column(nullable = false, length = JobState.FIELD_LENGTH) private JobState state; @ManyToOne(fetch = FetchType.LAZY) @JoinColumn(name = "acting_user_id", nullable = false) private User actingUser; public JobStateChange() { } @Override public int compareTo(final JobStateChange o) { return this.date.compareTo(o.date); } @Override public boolean equals(final Object obj) { if (this == obj) { return true; } else if (!(obj instanceof JobStateChange)) { return false; } JobStateChange candidate = (JobStateChange) obj; return this.state == candidate.state && this.actingUser.equals(candidate.getUser()) && this.date.equals(candidate.getDate()); } @Override public int hashCode() { return this.state.hashCode() + this.actingUser.hashCode() + this.date.hashCode(); } } It is mapped as a Hibernate CollectionOfElements in the class Job as follows: ... @Entity @Table( name = "job", uniqueConstraints = { @UniqueConstraint( columnNames = { "agency", //Job Name "payment_type", //Job Name "payment_file", //Job Name "date_of_payment", "payment_control_number", "truck_number" }) }) public class Job implements Serializable { private static final long serialVersionUID = -1131729422634638834L; ... @org.hibernate.annotations.CollectionOfElements @JoinTable(name = "job_state", joinColumns = @JoinColumn(name = "job_id")) @Sort(type = SortType.NATURAL) private final SortedSet<JobStateChange> stateChanges = new TreeSet<JobStateChange>(); ... public void advanceState( final User actor, final Date date) { JobState nextState; LOGGER.debug("Current state of {} is {}.", this, this.getCurrentState()); if (null == this.currentState) { nextState = JobState.BEGINNING; } else { if (!this.isAdvanceable()) { throw new IllegalAdvancementException(this.currentState.illegalAdvancementStateMessage); } if (this.currentState.isDivergent()) { nextState = this.currentState.getNextState(this); } else { nextState = this.currentState.getNextState(); } } JobStateChange stateChange = new JobStateChange(nextState, actor, date); this.setCurrentState(stateChange.getState()); this.stateChanges.add(stateChange); LOGGER.debug("Advanced {} to {}", this, this.getCurrentState()); } private void setCurrentState(final JobState jobState) { this.currentState = jobState; } boolean isAdvanceable() { return this.getCurrentState().isAdvanceable(this); } ... @Override public boolean equals(final Object obj) { if (obj == this) { return true; } else if (!(obj instanceof Job)) { return false; } Job otherJob = (Job) obj; return this.getName().equals(otherJob.getName()) && this.getDateOfPayment().equals(otherJob.getDateOfPayment()) && this.getPaymentControlNumber().equals(otherJob.getPaymentControlNumber()) && this.getTruckNumber().equals(otherJob.getTruckNumber()); } @Override public int hashCode() { return this.getName().hashCode() + this.getDateOfPayment().hashCode() + this.getPaymentControlNumber().hashCode() + this.getTruckNumber().hashCode(); } ... } The purpose of JobStateChange is to record when the Job moves through a series of State Changes that are outline in JobState as enums which know about advancement and decrement rules. The interface used to advance Jobs through a series of states is to call Job.advanceState() with a Date and a User. If the Job is advanceable according to rules coded in the enum, then a new StateChange is added to the SortedSet and everyone's happy. If not, an IllegalAdvancementException is thrown. The DDL this generates is as follows: ... drop table job; drop table job_state; ... create table job ( id bigint generated by default as identity, current_state varchar(25), date_of_payment date not null, beginningCheckNumber varchar(8) not null, item_count integer, agency varchar(10) not null, payment_file varchar(25) not null, payment_type varchar(25) not null, endingCheckNumber varchar(8) not null, payment_control_number varchar(4) not null, truck_number varchar(255) not null, wrapping_system_type varchar(15) not null, printer_id bigint, primary key (id), unique (agency, payment_type, payment_file, date_of_payment, payment_control_number, truck_number) ); create table job_state ( job_id bigint not null, acting_user_id bigint not null, date timestamp not null, state varchar(25) not null, primary key (job_id, acting_user_id, date, state) ); ... alter table job add constraint FK19BBD12FB9D70 foreign key (printer_id) references printer; alter table job_state add constraint FK57C2418FED1F0D21 foreign key (acting_user_id) references app_user; alter table job_state add constraint FK57C2418FABE090B3 foreign key (job_id) references job; ... The database is seeded with the following data prior to running tests ... insert into job (id, agency, payment_type, payment_file, payment_control_number, date_of_payment, beginningCheckNumber, endingCheckNumber, item_count, current_state, printer_id, wrapping_system_type, truck_number) values (-3, 'RRB', 'Monthly', 'Monthly','4501','1998-12-01 08:31:16' , '00000001','00040000', 40000, 'UNASSIGNED', null, 'KERN', '02'); insert into job_state (job_id, acting_user_id, date, state) values (-3, -1, '1998-11-30 08:31:17', 'UNASSIGNED'); ... After the database schema is automatically generated and rebuilt by the Hibernate tool. The following test runs fine up until the call to Session.flush() ... @ContextConfiguration(locations = { "/applicationContext-data.xml", "/applicationContext-service.xml" }) public class JobDaoIntegrationTest extends AbstractTransactionalJUnit4SpringContextTests { @Autowired private JobDao jobDao; @Autowired private SessionFactory sessionFactory; @Autowired private UserService userService; @Autowired private PrinterService printerService; ... @Test public void saveJob_JobAdvancedToAssigned_AllExpectedStateChanges() { //Get an unassigned Job Job job = this.jobDao.getJob(-3L); assertEquals(JobState.UNASSIGNED, job.getCurrentState()); Date advancedToUnassigned = new GregorianCalendar(1998, 10, 30, 8, 31, 17).getTime(); assertEquals(advancedToUnassigned, job.getStateChange(JobState.UNASSIGNED).getDate()); //Satisfy advancement constraints and advance job.setPrinter(this.printerService.getPrinter(-1L)); Date advancedToAssigned = new Date(); job.advanceState( this.userService.getUserByUsername("admin"), advancedToAssigned); assertEquals(JobState.ASSIGNED, job.getCurrentState()); assertEquals(advancedToUnassigned, job.getStateChange(JobState.UNASSIGNED).getDate()); assertEquals(advancedToAssigned, job.getStateChange(JobState.ASSIGNED).getDate()); //Persist to DB this.sessionFactory.getCurrentSession().flush(); ... } ... } The error thrown is SQLCODE=-803, SQLSTATE=23505: could not insert collection rows: [jaci.model.job.Job.stateChanges#-3] org.hibernate.exception.ConstraintViolationException: could not insert collection rows: [jaci.model.job.Job.stateChanges#-3] at org.hibernate.exception.SQLStateConverter.convert(SQLStateConverter.java:94) at org.hibernate.exception.JDBCExceptionHelper.convert(JDBCExceptionHelper.java:66) at org.hibernate.persister.collection.AbstractCollectionPersister.insertRows(AbstractCollectionPersister.java:1416) at org.hibernate.action.CollectionUpdateAction.execute(CollectionUpdateAction.java:86) at org.hibernate.engine.ActionQueue.execute(ActionQueue.java:279) at org.hibernate.engine.ActionQueue.executeActions(ActionQueue.java:263) at org.hibernate.engine.ActionQueue.executeActions(ActionQueue.java:170) at org.hibernate.event.def.AbstractFlushingEventListener.performExecutions(AbstractFlushingEventListener.java:321) at org.hibernate.event.def.DefaultFlushEventListener.onFlush(DefaultFlushEventListener.java:50) at org.hibernate.impl.SessionImpl.flush(SessionImpl.java:1027) at jaci.dao.JobDaoIntegrationTest.saveJob_JobAdvancedToAssigned_AllExpectedStateChanges(JobDaoIntegrationTest.java:98) at org.springframework.test.context.junit4.SpringTestMethod.invoke(SpringTestMethod.java:160) at org.springframework.test.context.junit4.SpringMethodRoadie.runTestMethod(SpringMethodRoadie.java:233) at org.springframework.test.context.junit4.SpringMethodRoadie$RunBeforesThenTestThenAfters.run(SpringMethodRoadie.java:333) at org.springframework.test.context.junit4.SpringMethodRoadie.runWithRepetitions(SpringMethodRoadie.java:217) at org.springframework.test.context.junit4.SpringMethodRoadie.runTest(SpringMethodRoadie.java:197) at org.springframework.test.context.junit4.SpringMethodRoadie.run(SpringMethodRoadie.java:143) at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.invokeTestMethod(SpringJUnit4ClassRunner.java:160) at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.run(SpringJUnit4ClassRunner.java:97) Caused by: com.ibm.db2.jcc.b.lm: DB2 SQL Error: SQLCODE=-803, SQLSTATE=23505, SQLERRMC=1;ACI_APP.JOB_STATE, DRIVER=3.50.152 at com.ibm.db2.jcc.b.wc.a(wc.java:575) at com.ibm.db2.jcc.b.wc.a(wc.java:57) at com.ibm.db2.jcc.b.wc.a(wc.java:126) at com.ibm.db2.jcc.b.tk.b(tk.java:1593) at com.ibm.db2.jcc.b.tk.c(tk.java:1576) at com.ibm.db2.jcc.t4.db.k(db.java:353) at com.ibm.db2.jcc.t4.db.a(db.java:59) at com.ibm.db2.jcc.t4.t.a(t.java:50) at com.ibm.db2.jcc.t4.tb.b(tb.java:200) at com.ibm.db2.jcc.b.uk.Gb(uk.java:2355) at com.ibm.db2.jcc.b.uk.e(uk.java:3129) at com.ibm.db2.jcc.b.uk.zb(uk.java:568) at com.ibm.db2.jcc.b.uk.executeUpdate(uk.java:551) at org.hibernate.jdbc.NonBatchingBatcher.addToBatch(NonBatchingBatcher.java:46) at org.hibernate.persister.collection.AbstractCollectionPersister.insertRows(AbstractCollectionPersister.java:1389) Therein lies my problem… A nearly identical Class set (in fact, so identical that I've been chomping at the bit to make it a single class that serves both business entities) runs absolutely fine. It is identical except for name. Instead of Job it's Web. Instead of JobStateChange it's WebStateChange. Instead of JobState it's WebState. Both Job and Web's SortedSet of StateChanges are mapped as a Hibernate CollectionOfElements. Both are @Embeddable. Both are SortType.Natural. Both are backed by an Enumeration with some advancement rules in it. And yet when a nearly identical test is run for Web, no issue is discovered and the data flushes fine. For the sake of brevity I won't include all of the Web classes here, but I will include the test and if anyone wants to see the actual sources, I'll include them (just leave a comment). The data seed: insert into web (id, stock_type, pallet, pallet_id, date_received, first_icn, last_icn, shipment_id, current_state) values (-1, 'PF', '0011', 'A', '2008-12-31 08:30:02', '000000001', '000080000', -1, 'UNSTAGED'); insert into web_state (web_id, date, state, acting_user_id) values (-1, '2008-12-31 08:30:03', 'UNSTAGED', -1); The test: ... @ContextConfiguration(locations = { "/applicationContext-data.xml", "/applicationContext-service.xml" }) public class WebDaoIntegrationTest extends AbstractTransactionalJUnit4SpringContextTests { @Autowired private WebDao webDao; @Autowired private UserService userService; @Autowired private SessionFactory sessionFactory; ... @Test public void saveWeb_WebAdvancedToNewState_AllExpectedStateChanges() { Web web = this.webDao.getWeb(-1L); Date advancedToUnstaged = new GregorianCalendar(2008, 11, 31, 8, 30, 3).getTime(); assertEquals(WebState.UNSTAGED, web.getCurrentState()); assertEquals(advancedToUnstaged, web.getState(WebState.UNSTAGED).getDate()); Date advancedToStaged = new Date(); web.advanceState( this.userService.getUserByUsername("admin"), advancedToStaged); this.sessionFactory.getCurrentSession().flush(); web = this.webDao.getWeb(web.getId()); assertEquals( "Web should have moved to STAGED State.", WebState.STAGED, web.getCurrentState()); assertEquals(advancedToUnstaged, web.getState(WebState.UNSTAGED).getDate()); assertEquals(advancedToStaged, web.getState(WebState.STAGED).getDate()); assertNotNull(web.getState(WebState.UNSTAGED)); assertNotNull(web.getState(WebState.STAGED)); } ... } As you can see, I assert that the Web was reconstituted the way I expect, I advance it, flush it to the DB, and then re-get it and verify that the states are as I expect. Everything works perfectly. Not so with Job. A possibly pertinent detail: the reconstitution code works fine if I cease to map JobStateChange.data as a TIMESTAMP and instead as a DATE, and ensure that all of the StateChanges always occur on different Dates. The problem is that this particular business entity can go through many state changes in a single day and so it needs to be sorted by time stamp rather than by date. If I don't do this then I can't sort the StateChanges correctly. That being said, WebStateChange.date is also mapped as a TIMESTAMP and so I again remain absolutely befuddled as to where this error is arising from. I tried to do a fairly thorough job of giving all of the technical details of the implementation but as this particular question is very implementation specific, if I missed anything just let me know in the comments and I'll include it. Thanks so much for your help! UPDATE: Since it turns out to be important to the solution of my problem, I have to include the pertinent bits of the WebStateChange class as well. ... @Embeddable public class WebStateChange implements Comparable<WebStateChange> { @Temporal(TemporalType.TIMESTAMP) @Column(nullable = false) private Date date; @Enumerated(EnumType.STRING) @Column(nullable = false, length = WebState.FIELD_LENGTH) private WebState state; @ManyToOne(fetch = FetchType.LAZY) @JoinColumn(name = "acting_user_id", nullable = false) private User actingUser; ... WebStateChange( final WebState state, final User actingUser, final Date date) { ExceptionUtils.illegalNullArgs(state, actingUser, date); this.state = state; this.actingUser = actingUser; this.date = new Date(date.getTime()); } @Override public int compareTo(final WebStateChange otherStateChange) { return this.date.compareTo(otherStateChange.date); } @Override public boolean equals(final Object candidate) { if (this == candidate) { return true; } else if (!(candidate instanceof WebStateChange)) { return false; } WebStateChange candidateWebState = (WebStateChange) candidate; return this.getState() == candidateWebState.getState() && this.getUser().equals(candidateWebState.getUser()) && this.getDate().equals(candidateWebState.getDate()); } @Override public int hashCode() { return this.getState().hashCode() + this.getUser().hashCode() + this.getDate().hashCode(); } ... }

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  • cisco 2911 router vs 2811 router

    - by NickToyota
    Just wondering if anyone has experience with the cisco 2911 or 2900 series routers. I understand it is newer and similar to the 2811 but more robust. The price difference is not that much more. I am trying to determine if I should go with the 29xx or 28xx series for a small-medium sized company. ISP bandwidth load balancing and fail over is required. T1 and ADSL lines already in place.

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  • Differences between KVR16N11H/8 and KVR16N11/8 memory except for height?

    - by rzetterberg
    I accidentally ordered KVR16N11/8 instead of KVR16N11H/8 and I'm wondering if I'm going to have compability issues with my Intel DP67DE motherboard. When searching for compatible RAM on Kingstons site for that motherboard the KVR16N11H/8 RAM was one of the compatible ones. The KVR16N11/8 did not show up as compatible for that motherboard. The only difference I can see is that they have different physical height, or am I missing something?

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