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• Properties vs. Fields: Need help grasping the uses of Properties over Fields.

  - by pghtech

  First off, I have read through a list of postings on this topic and I don't feel I have grasped properties because of what I had come to understand about encapsulation and field modifiers (private, public..ect). One of the main aspects of C# that I have come to learn is the importance of data protection within your code by the use of encapsulation. I 'thought' I understood that to be because of the ability of the use of the modifiers (private, public, internal, protected). However, after learning about properties I am sort of torn in understanding not only properties uses, but the overall importance/ability of data protection (what I understood as encapsulation) within C#. To be more specific, everything I have read when I got to properties in C# is that you should try to use them in place of fields when you can because of: 1) they allow you to change the data type when you can't when directly accessing the field directly. 2) they add a level of protection to data access However, from what I 'thought' I had come to know about the use of field modifiers did #2, it seemed to me that properties just generated additional code unless you had some reason to change the type (#1) - because you are (more or less) creating hidden methods to access fields as opposed to directly. Then there is the whole modifiers being able to be added to Properties which further complicates my understanding for the need of properties to access data. I have read a number of chapters from different writers on "properties" and none have really explained a good understanding of properties vs. fields vs. encapsulation (and good programming methods). Can someone explain: 1) why I would want to use properties instead of fields (especially when it appears I am just adding additional code 2) any tips on recognizing the use of properties and not seeing them as simply methods (with the exception of the get;set being apparent) when tracing other peoples code? 3) Any general rules of thumb when it comes to good programming methods in relation to when to use what? Thanks and sorry for the long post - I didn't want to just ask a question that has been asked 100x without explaining why I am asking it again.

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• Application crashing on getting updated information from database using timer and storing it on loca

  - by Amit Battan

  In our multi - user application we are continuously interacting with database. We have a common class through which we are sending POST queries to database and obtaining xml files in return. We are using delegates of NSXMLParser to parse the obtained file. The problem with us is we are facing many crashes in it generally when application is idle and changed data in database is being fetched in background through timer which is invoked after every few seconds. We have also dealt with error handling through try and catch but it proves to be of no use in this case and mostly application crashes with following error : Exception Type: EXC_BAD_ACCESS (SIGBUS) Exception Codes: KERN_PROTECTION_FAILURE at 0x0000000000000020 Strange thing is that many times the fetching of updated data at background works very fine, same methods being successfully executed under similar conditions but suddenly it crashes on one of them. The codes we are using is as follows: // we are using timer in this way: chkOnlineUser=[NSTimer scheduledTimerWithTimeInterval:15 target:mmObject selector:@selector(threadOnlineUser) userInfo:NULL repeats:YES]; // this method being called in timer -(void)threadOnlineUser{//HeartBeat in Thread [NSThread detachNewThreadSelector:@selector(onlineUserRefresh) toTarget:self withObject:nil]; } // this performs actual updation -(void)onlineUserRefresh{ NSAutoreleasePool *pool =[[NSAutoreleasePool alloc]init]; @try{ if(chkTimer==1){ return; } chkTimer=1; if([allUserArray count]==0){ [user parseXMLFileUser:@"all" andFlag:3]; [allUserArray removeAllObjects]; [allUserArray addObjectsFromArray:[user users]]; } [objHeartBeat parseXMLFile:[loginID intValue] timeOut:10]; NSMutableDictionary *tDictOL=[[NSMutableDictionary alloc] init]; tDictOL=[objHeartBeat onLineList]; NSArray *tArray=[[NSArray alloc] init]; tArray=[[tDictOL objectForKey:@"onlineuser"] componentsSeparatedByString:@","]; [loginUserArray removeAllObjects]; for(int l=0;l less than [tArray count] ;l++){ int t;//=[[tArray objectAtIndex:l] intValue]; if([[allUserArray valueForKey:@"Id"] containsObject:[tArray objectAtIndex:l]]){ t = [[allUserArray valueForKey:@"Id"] indexOfObject:[tArray objectAtIndex:l]]; [loginUserArray addObject:[allUserArray objectAtIndex:t]]; } } [onlineTable reloadData]; [logInUserPopUp removeAllItems]; if([loginUserArray count]==1){ [labelLoginUser setStringValue:@"Only you are online"]; [logInUserPopUp setEnabled:YES]; }else{ [labelLoginUser setStringValue:[NSString stringWithFormat:@" %d users online",[loginUserArray count]]]; [logInUserPopUp setEnabled:YES]; } NSMenu *menu = [[NSMenu alloc] initWithTitle:@"menu"]; NSMenuItem *itemOne = [[NSMenuItem alloc] initWithTitle:@"" action:NULL keyEquivalent:@""]; [menu addItem:itemOne]; for(int l=0;l less than [loginUserArray count];l++){ NSString *tempStr= [NSString stringWithFormat:@"%@ %@",[[[loginUserArray objectAtIndex:l] objectForKey:@"user_fname"] stringByTrimmingCharactersInSet:[NSCharacterSet whitespaceAndNewlineCharacterSet]],[[[loginUserArray objectAtIndex:l] objectForKey:@"user_lname"] stringByTrimmingCharactersInSet:[NSCharacterSet whitespaceAndNewlineCharacterSet]]]; if(![tempStr isEqualToString:@""]){ NSMenuItem *itemOne = [[NSMenuItem alloc] initWithTitle:tempStr action:NULL keyEquivalent:@""]; [menu addItem:itemOne]; }else if(l==0){ NSMenuItem *itemOne = [[NSMenuItem alloc] initWithTitle:tempStr action:NULL keyEquivalent:@""]; [menu addItem:itemOne]; } } [logInUserPopUp setMenu:menu]; if([lastUpdateTime isEqualToString:@""]){ }else { [self fetchUpdatedInfo:lastUpdateTime]; [self fetchUpdatedGroup:lastUpdateTime];// function same as fetchUpdatedInfo [avObject fetchUpdatedInfo:lastUpdateTime];// function same as fetchUpdatedInfo [esTVObject fetchUpdatedInfo:lastUpdateTime];// function same as fetchUpdatedInfo } lastUpdateTime=[[tDictOL objectForKey:@"lastServerTime"] copy]; } @catch (NSException * e) { [queryByPost insertException:@"MainModule" inFun:@"onlineUserRefresh" excp:[e description] userId:[loginID intValue]]; NSRunAlertPanel(@"Error Panel", @"Main Module- onlineUserRefresh....%@", @"OK", nil, nil,e); } @finally { NSLog(@"Internal Update Before Bye"); chkTimer=0; NSLog(@"Internal Update Bye");// Some time application crashes after this log // Some time application crahses after "Internal Update Bye" log } } // The method which we are using to obtain updated data is of following form: -(void)fetchUpdatedInfo:(NSString *)UpdTime{ @try { if(initAfterLoginComplete==0){ return; } [user parseXMLFileUser:UpdTime andFlag:[loginID intValue]]; [tempUserUpdatedArray removeAllObjects]; [tempUserUpdatedArray addObjectsFromArray:[user users]]; if([tempUserUpdatedArray count]0){ if([contactsView isHidden]){ [topContactImg setImage:[NSImage imageNamed:@"btn_contacts_off_red.png"]]; }else { [topContactImg setImage:[NSImage imageNamed:@"btn_contacts_red.png"]]; } }else { return; } int chkprof=0; for(int l=0;l less than [tempUserUpdatedArray count];l++){ NSArray *tempArr1 = [allUserArray valueForKey:@"Id"]; int s; if([[[tempUserUpdatedArray objectAtIndex:l] objectForKey:@"Id"] intValue]==profile_Id){ chkprof=1; } if([tempArr1 containsObject:[[tempUserUpdatedArray objectAtIndex:l] objectForKey:@"Id"]]){ s = [tempArr1 indexOfObject:[[tempUserUpdatedArray objectAtIndex:l] objectForKey:@"Id"]]; [allUserArray replaceObjectAtIndex:s withObject:[tempUserUpdatedArray objectAtIndex:l]]; }else { [allUserArray addObject:[tempUserUpdatedArray objectAtIndex:l]]; } NSArray *tempArr2 = [tempUser valueForKey:@"Id"]; if([tempArr2 containsObject:[[tempUserUpdatedArray objectAtIndex:l] objectForKey:@"Id"]]){ s = [tempArr2 indexOfObject:[[tempUserUpdatedArray objectAtIndex:l] objectForKey:@"Id"]]; [tempUser replaceObjectAtIndex:s withObject:[tempUserUpdatedArray objectAtIndex:l]]; }else { [tempUser addObject:[tempUserUpdatedArray objectAtIndex:l]]; } } NSSortDescriptor *sortDescriptor = [[NSSortDescriptor alloc] initWithKey:@"user_fname" ascending:YES]; [tempUser sortUsingDescriptors:[NSMutableArray arrayWithObject:sortDescriptor]]; [userListTableView reloadData]; [groupsArray removeAllObjects]; for(int z=0;z less than [tempGroups count];z++){ NSMutableArray *tempMArr=[[NSMutableArray alloc] init]; for(int l=0;l less than [allUserArray count];l++){ if([[[allUserArray objectAtIndex:l] objectForKey:@"GroupId"] intValue]==[[[tempGroups objectAtIndex:z] objectForKey:@"group_id"] intValue]){ [tempMArr addObject:[allUserArray objectAtIndex:l]]; } } [groupsArray insertObject:tempMArr atIndex:z]; [tempMArr release]; tempMArr= nil; } for(int n=0;n less than [tempGroups count];n++){ [[groupsArray objectAtIndex:n] addObject:[tempGroups objectAtIndex:n]]; } [groupsListOV reloadData]; if(chkprof==1){ [self profileShow:profile_Id]; }else { } [self selectUserInTable:0]; }@catch (NSException * e) { NSRunAlertPanel(@"Error Panel", @"%@", @"OK", nil, nil,e); } } // The method which we are using to frame select query and parse obtained data is: -(void)parseXMLForUser:(int)UId stringVar:(NSString*)stringVar{ @try{ if(queryByPost) [queryByPost release]; queryByPost=[QueryByPost new]; // common class used to invoke method to send request via POST method //obtaining data for xml parsing NSString *query=[NSString stringWithFormat:@"Select * from userinfo update_time = '%@' AND NOT owner_id ='%d' ",stringVar,UId]; NSData *obtainedData=[queryByPost executeQuery:query WithAction:@"query"]; // method invoked to perform post query if(obtainedData==nil){ // data not obtained so return return; } // initializing dictionary to be obtained after parsing if(obtainedDictionary) [obtainedDictionary release]; obtainedDictionary=[NSMutableDictionary new]; // xml parsing if (updatedDataParser) // airportsListParser is an NSXMLParser instance variable [updatedDataParser release]; updatedDataParser = [[NSXMLParser alloc] initWithData:obtainedData]; [updatedDataParser setDelegate:self]; [updatedDataParser setShouldResolveExternalEntities:YES]; BOOL success = [updatedDataParser parse]; } @catch (NSException *e) { NSLog(@"wtihin parseXMLForUser- parseXMLForUser:stringVar: - %@",[e description]); } } //The method which will attempt to interact 4 times with server if interaction with it is found to be unsuccessful , is of following form: -(NSData*)executeQuery:(NSString*)query WithAction:(NSString*)doAction{ NSLog(@"within ExecuteQuery:WithAction: Query is: %@ and Action is: %@",query,doAction); NSString *returnResult; @try { NSString *returnResult; NSMutableURLRequest *postRequest; NSError *error; NSData *searchData; NSHTTPURLResponse *response; postRequest=[self directMySQLQuery:query WithAction:doAction]; // this method sends actual POST request NSLog(@"after directMYSQL in QueryByPost- performQuery... ErrorLogMsg"); searchData = [NSURLConnection sendSynchronousRequest:postRequest returningResponse:&response error:&error]; returnResult = [[NSString alloc] initWithData:searchData encoding:NSASCIIStringEncoding]; NSString *resultToBeCompared=[returnResult stringByTrimmingCharactersInSet:[NSCharacterSet whitespaceAndNewlineCharacterSet]]; NSLog(@"result obtained - %@/ resultToBeCompared - %@",returnResult,resultToBeCompared); if(![resultToBeCompared isEqualToString:@""]){ }else { sleep(10); postRequest=[self directMySQLQuery:query WithAction:doAction]; searchData = [NSURLConnection sendSynchronousRequest:postRequest returningResponse:&response error:&error]; if(![resultToBeCompared isEqualToString:@""]){ }else { sleep(10); postRequest=[self directMySQLQuery:query WithAction:doAction]; searchData = [NSURLConnection sendSynchronousRequest:postRequest returningResponse:&response error:&error]; if(![resultToBeCompared isEqualToString:@""]){ }else { sleep(10); postRequest=[self directMySQLQuery:query WithAction:doAction]; searchData = [NSURLConnection sendSynchronousRequest:postRequest returningResponse:&response error:&error]; if(![resultToBeCompared isEqualToString:@""]){ }else { sleep(10); postRequest=[self directMySQLQuery:query WithAction:doAction]; searchData = [NSURLConnection sendSynchronousRequest:postRequest returningResponse:&response error:&error]; if(![resultToBeCompared isEqualToString:@""]){ }else { return nil; } } } } } returnResult = [[NSString alloc] initWithData:searchData encoding:NSASCIIStringEncoding]; return searchData; } @catch (NSException * e) { NSLog(@"within QueryByPost , execurteQuery:WithAction - %@",[e description]); return nil; } } // The method which sends POST request to server , is of following form: -(NSMutableURLRequest *)directMySQLQuery:(NSString*)query WithAction:(NSString*)doAction{ @try{ NSLog(@"Query is: %@ and Action is: %@",query,doAction); // some pre initialization NSString *stringBoundary,*contentType; NSURL *cgiUrl ; NSMutableURLRequest *postRequest; NSMutableData *postBody; NSString *ans=@"434"; cgiUrl = [NSURL URLWithString:@"http://keysoftwareservices.com/API.php"]; postRequest = [NSMutableURLRequest requestWithURL:cgiUrl]; [postRequest setHTTPMethod:@"POST"]; stringBoundary = [NSString stringWithString:@"0000ABCQueryxxxxxx"]; contentType = [NSString stringWithFormat:@"multipart/form-data; boundary=%@", stringBoundary]; [postRequest addValue:contentType forHTTPHeaderField: @"Content-Type"]; //setting up the body: postBody = [NSMutableData data]; [postBody appendData:[[NSString stringWithFormat:@"\r\n\r\n--%@\r\n",stringBoundary] dataUsingEncoding:NSUTF8StringEncoding]]; [postBody appendData:[[NSString stringWithString:@"Content-Disposition: form-data; name=\"code\"\r\n\r\n"] dataUsingEncoding:NSUTF8StringEncoding]]; [postBody appendData:[[NSString stringWithString:ans] dataUsingEncoding:NSUTF8StringEncoding]]; [postBody appendData:[[NSString stringWithFormat:@"\r\n--%@\r\n",stringBoundary] dataUsingEncoding:NSUTF8StringEncoding]]; [postBody appendData:[[NSString stringWithString:@"Content-Disposition: form-data; name=\"action\"\r\n\r\n"] dataUsingEncoding:NSUTF8StringEncoding]]; [postBody appendData:[[NSString stringWithString:doAction] dataUsingEncoding:NSUTF8StringEncoding]]; [postBody appendData:[[NSString stringWithFormat:@"\r\n--%@\r\n",stringBoundary] dataUsingEncoding:NSUTF8StringEncoding]]; [postBody appendData:[[NSString stringWithString:@"Content-Disposition: form-data; name=\"devmode\"\r\n\r\n"] dataUsingEncoding:NSUTF8StringEncoding]]; [postBody appendData:[[NSString stringWithString:[[[NSBundle mainBundle] infoDictionary] objectForKey:@"devmode"]] dataUsingEncoding:NSUTF8StringEncoding]]; [postBody appendData:[[NSString stringWithFormat:@"\r\n--%@\r\n",stringBoundary] dataUsingEncoding:NSUTF8StringEncoding]]; [postBody appendData:[[NSString stringWithString:@"Content-Disposition: form-data; name=\"q\"\r\n\r\n"] dataUsingEncoding:NSUTF8StringEncoding]]; [postBody appendData:[[NSString stringWithString:query] dataUsingEncoding:NSUTF8StringEncoding]]; [postBody appendData:[[NSString stringWithFormat:@"\r\n--%@--\r\n",stringBoundary] dataUsingEncoding:NSUTF8StringEncoding]]; [postRequest setHTTPBody:postBody]; NSLog(@"Direct My SQL ok");// Some time application crashes afte this log //Some time application crashes after "Direct My SQL ok" log return [postRequest mutableCopy]; }@catch (NSException * e) { NSLog(@"NSException %@",e); NSRunAlertPanel(@"Error Panel", @"Within QueryByPost- directMySQLQuery...%@", @"OK", nil, nil,e); return nil; } }

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• spring 3 uploadify giving 404 Error

  - by Rajkumar

  I am using Spring 3 and implementing Uploadify. The problem is, the files are updating properly but it is giving HTTP Error 404, on completion of file upload. I tried every possible solution, but none of them works. The files are uploaded. Values are storing in DB properly, only that i am getting HTTP Error 404. Any help is appreciated and Thanks in advance. The JSP Page $(function() { $('#file_upload').uploadify({ 'swf' : 'scripts/uploadify.swf', 'fileObjName' : 'the_file', 'fileTypeExts' : '*.gif; *.jpg; *.jpeg; *.png', 'multi' : true, 'uploader' : '/photo/savePhoto', 'fileSizeLimit' : '10MB', 'uploadLimit' : 50, 'onUploadStart' : function(file) { $('#file_upload').uploadify('settings', 'formData', {'trip_id' :'1', 'trip_name' :'Sample Trip', 'destination_trip' :'Mumbai','user_id' :'1','email' :'[email protected]','city_id' :'12'}); }, 'onQueueComplete' : function(queueData) { console.log('queueData : '+queueData); window.location.href = "trip/details/1"; } }); }); The Controller @RequestMapping(value="photo/{action}", method=RequestMethod.POST) public String postHandler(@PathVariable("action") String action, HttpServletRequest request) { if(action.equals("savePhoto")) { try{ MultipartHttpServletRequest multipartRequest = (MultipartHttpServletRequest)request; MultipartFile file = multipartRequest.getFile("the_file"); String trip_id = request.getParameter("trip_id"); String trip_name = request.getParameter("trip_name"); String destination_trip = request.getParameter("destination_trip"); String user_id = request.getParameter("user_id"); String email = request.getParameter("email"); String city_id = request.getParameter("city_id"); photo.savePhoto(file,trip_id,trip_name,destination_trip,user_id,email,city_id); photo.updatetrip(photo_id,trip_id); }catch(Exception e ){e.printStackTrace();} } return ""; } spring config <bean class="org.springframework.web.multipart.commons.CommonsMultipartResolver" id="multipartResolver"> <property name="maxUploadSize" value="10000000"/> </bean>

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• NHibernate Oracle stored procedure problem

  - by Mr. Flint

  ------Using VS2008, ASP.Net with C#, Oracle, NHibernate---- I have tested my stored procedure. It's working but not with NHibernate. Here are the codes: Procedure : create or replace procedure ThanaDelete (id number) as begin delete from thana_tbl where thana_code = id; end Mapping File: <?xml version="1.0" encoding="utf-8" ?> <hibernate-mapping xmlns="urn:nhibernate-mapping-2.2" assembly="DataTransfer" namespace="DataTransfer"> <class name="DataTransfer.Models.Thana, DataTransfer" table="THANA_TBL"> <id name="THANA_CODE" column="THANA_CODE" type="Int32" unsaved-value="0"> <generator class="native"> <param name="sequence"> SEQ_TEST </param> </generator> </id> <property name="THANA_NAME" column="THANA_NAME" type="string" not-null="false"/> <property name="DISTRICT_CODE" column="DISTRICT_CODE" type="Int32" not-null="false"/> <property name="USER_ID" column="USER_ID" type="string" not-null="false"/> <property name="TRANSACTION_DATE" column="TRANSACTION_DATE" type="Date" not-null="false"/> <property name="TRANSACTION_TIME" column="TRANSACTION_TIME" type="string" not-null="false"/> <sql-delete>exec THANADELETE ? </sql-delete> </class> </hibernate-mapping> error: Message: could not delete: [DataTransfer.Models.Thana#10][SQL: exec THANADELETE ?] Source: NHibernate Inner Exception System.Data.OracleClient.OracleException Message: ORA-00900: invalid SQL statement

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• The worker processcalls OpenSubKey but returns null by accessing Remote Registry service.

  - by Cary

  My web server is deployed in IIS 6. The web server starts the Remote Registry service in the remote machine successfully by creating a process to run some remote operation commands. This first line runs successfully. But the second line returns null. #1 RegistryKey remoteRegKey = RegistryKey.OpenRemoteBaseKey(RegistryHive.LocalMachine, "139.24.185.27"); #2 RegistryKey targetKey = remoteRegKey.OpenSubKey(@"SOFTWARE\Wow6432Node\XXXX\XXXX\Config\Modality", true); I tried to find the reason from MSDN. It tells only one case it would return null. The case is when the subkey does not exist. If it has not enough permission, it will throw exception. But the subkey really exists. I change another machine to debug my code with Visual Studio 2008. It can run two lines successfully. If it has enough permission, it should not only can open the LocalMachine, but also can open any of its subkeys. I am quite confusing about this.

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• Deploying a Java application. How?

  - by danpalmer

  I am new to Java (and Eclipse) but I have used .NET (and Visual Studio) a fair amount. I also know about compiling C/C++ code and things like that. I know that at the end I get either an EXE or a nice binary file that can be run from the command line. I have been making a Java utility that uses some external libraries. I need to compile this into an executable that I can run from the command line on a unix machine, but I cannot find any way to do this. I can build and run/debug in Eclipse, but that is no use to me as this code will be run on a webserver. I just need all the dependancies compiled in to one file but after hours of searching on Google, the best thing I could find was the Fat-JAR plugin for Eclipse and after using that I just get the following error when I try to run the file: Exception in thread "main" java.lang.NoClassDefFoundError: Network/jar This is really confusing me and as it is such an essential thing to be able to do I am sure I must be missing something blindingly obvious, but as I said, after hours of searching I have gotten nowhere. I really appreciate any help you can give me. Thanks.

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• Editing a .class file directly, playing around with opcodes

  - by echox

  Hi, today I just tried to play a little bit around with the opcodes in compiled java class file. After inserting iinc 1,1 the java virtual machine responds with: Exception in thread "main" java.lang.ClassFormatError: Truncated class file at java.lang.ClassLoader.defineClass1(Native Method) at java.lang.ClassLoader.defineClassCond(ClassLoader.java:632) at java.lang.ClassLoader.defineClass(ClassLoader.java:616) at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:141) at java.net.URLClassLoader.defineClass(URLClassLoader.java:283) at java.net.URLClassLoader.access$000(URLClassLoader.java:58) at java.net.URLClassLoader$1.run(URLClassLoader.java:197) at java.security.AccessController.doPrivileged(Native Method) at java.net.URLClassLoader.findClass(URLClassLoader.java:190) at java.lang.ClassLoader.loadClass(ClassLoader.java:307) at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:301) at java.lang.ClassLoader.loadClass(ClassLoader.java:248) Could not find the main class: Test. Program will exit. This is my example source code: public class Test { public static void main(String[] args) { int i = 5; i++; i++; i++; System.out.println("Number: " + i + "\n"); } } The opcode for an increment is 0x84 + 2 bytes for operands. There's only one section in the resulting class file, which contains 0x84: [..] 8401 0184 0101 8401 01[..] So I would translate this as: iinc 1,1 iinc 1,1 iinc 1,1 corresponding to my i++; i++; i++; I then tried to append just 840101 to increment the variable once more, but that didn't work and resulted in the ClassFormatError. Is there anything like a checksum for the class file? I looked up the format of a classfile in http://java.sun.com/docs/books/jvms/second_edition/html/ClassFile.doc.html but could not find anything which points out to some kind of bytes_of_classfile or something. I also don't understand why the error is "Truncated Class File", because I did append something :-) I know its not a good idea to edit class files directly, but I'm just interested on the VM internals here.

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• Java InputReader. Detect if file being read is binary?

  - by Trizicus

  I had posted a question in regards to this code. I found that JTextArea does not support the binary type data that is loaded. So my new question is how can I go about detecting the 'bad' file and canceling the file I/O and telling the user that they need to select a new file? class Open extends SwingWorker<Void, String> { File file; JTextArea jta; Open(File file, JTextArea jta) { this.file = file; this.jta = jta; } @Override protected Void doInBackground() throws Exception { BufferedReader br = null; try { br = new BufferedReader(new FileReader(file)); String line = br.readLine(); while(line != null) { publish(line); line = br.readLine(); } } finally { try { br.close(); } catch (IOException e) { } } return null; } @Override protected void process(List<String> chunks) { for(String s : chunks) jta.append(s + "\n"); } }

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• Can I serialize an object if I didn't write the class used to instantiate that object?

  - by Richard77

  Hello, I've a simple class [Serializable] public class MyClass { public String FirstName { get; set: } public String LastName { get; set: } //Bellow is what I would like to do //But, it's not working //I get an exception ContactDataContext db = new ContactDataContext(); public void Save() { Contact contact = new Contact(); contact.FirstName = FirstName; contact.LastName = LastName; db.Contacts.InsertOnSubmit(contact); db.SubmitChanges(); } } I wanted to attach a Save method to the class so that I could call it on each object. When I introduced the above statement which contains ContactDataContext, I got the following error "In assembly ... PublicKeyToken=null' is not marked as serializable" It's clear that the DataContext class is generated by the framework (). I checked and did not see where that class was marked serialize. What can I do to overcome that? What's the rule when I'm not the author of a class? Just go ahead and mark the DataContext class as serializable, and pretend that everything will work? Thanks for helping

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• How should I avoid memoization causing bugs in Ruby?

  - by Andrew Grimm

  Is there a consensus on how to avoid memoization causing bugs due to mutable state? In this example, a cached result had its state mutated, and therefore gave the wrong result the second time it was called. class Greeter def initialize @greeting_cache = {} end def expensive_greeting_calculation(formality) case formality when :casual then "Hi" when :formal then "Hello" end end def greeting(formality) unless @greeting_cache.has_key?(formality) @greeting_cache[formality] = expensive_greeting_calculation(formality) end @greeting_cache[formality] end end def memoization_mutator greeter = Greeter.new first_person = "Bob" # Mildly contrived in this case, # but you could encounter this in more complex scenarios puts(greeter.greeting(:casual) << " " << first_person) # => Hi Bob second_person = "Sue" puts(greeter.greeting(:casual) << " " << second_person) # => Hi Bob Sue end memoization_mutator Approaches I can see to avoid this are: greeting could return a dup or clone of @greeting_cache[formality] greeting could freeze the result of @greeting_cache[formality]. That'd cause an exception to be raised when memoization_mutator appends strings to it. Check all code that uses the result of greeting to ensure none of it does any mutating of the string. Is there a consensus on the best approach? Is the only disadvantage of doing (1) or (2) decreased performance? (I also suspect freezing an object may not work fully if it has references to other objects) Side note: this problem doesn't affect the main application of memoization: as Fixnums are immutable, calculating Fibonacci sequences doesn't have problems with mutable state. :)

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• Streaming Media Player Tutorial Stops Unexpectedly. How Should I Debug (And Other Questions From A

  - by Danny

  Hello! I'm a fledgling in the Android and Eclipse ways. I was reading and downloaded the source code for a Streaming Media Player tutorial from Pocket Journey, here. However, when I try to run it through the "Run As..." or "Debug As..." features in Eclipse, the emulator reports: "Sorry! The application Android Tutorials (process com.pocketjourney.tutorials) has stopped unexpectedly. Please try again." Now, from stepping through the Tutorial 1 activity (for those of you that may be familiar with it), it seems something funky happens here: button.setOnClickListener(new View.OnClickListener() { public void onClick(View view) { Toast.makeText(Tutorial1.this, "Button Clicked",Toast.LENGTH_SHORT).show(); }}); My questions are: What's up with that line? Apparently, other comments haven't had this problem; am I missing some library that I should be downloading from someplace? How should I go about debugging this other than/in addition to stepping through code? I'm used to Visual Studio, which has a nice box with exception details for me to sift through and copy/paste to google with. Eclipse debugging showed a "No Source Code" page, or a list of exceptions. I've heard of something called LogCat; is that relevant here? Thanks in advance!

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• Subclassing UIButton but can't access my properties

  - by Ross Ellerington

  Hi, I've created a sub class of UIButton: // // DetailButton.h #import <Foundation/Foundation.h> #import <MapKit/MapKit.h> @interface MyDetailButton : UIButton { NSObject *annotation; } @property (nonatomic, retain) NSObject *annotation; @end // // DetailButton.m // #import "MyDetailButton.h" @implementation MyDetailButton @synthesize annotation; @end I figured that I can then create this object and set the annotation object by doing the following: MyDetailButton* rightButton = [MyDetailButton buttonWithType:UIButtonTypeDetailDisclosure]; rightButton.annotation = localAnnotation; localAnnotation is an NSObject but it is really an MKAnnotation. I can't see why this doesn't work but at runtime I get this error: 2010-05-27 10:37:29.214 DonorMapProto1[5241:207] *** -[UIButton annotation]: unrecognized selector sent to instance 0x445a190 2010-05-27 10:37:29.215 DonorMapProto1[5241:207] *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '*** -[UIButton annotation]: unrecognized selector sent to instance 0x445a190' ' I can't see why it's even looking at UIButton because I've subclassed that so it should be looking at the MyDetailButton class to set that annotation property. Have I missed something really obvious. It feels like it :) Thanks in advance for any help you can provide Ross

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• Java performance issue

  - by Colby77

  Hi, I've got a question related to java performance and method execution. In my app there are a lot of place where I have to validate some parameter, so I've written a Validator class and put all the validation methods into it. Here is an example: public class NumberValidator { public static short shortValidator(String s) throws ValidationException{ try{ short sh = Short.parseShort(s); if(sh < 1){ throw new ValidationException(); } return sh; }catch (Exception e) { throw new ValidationException("The parameter is wrong!"); } } ... But I'm thinking about that. Is this OK? It's OO and modularized, but - considering performance - is it a good idea? What if I had awful lot of invocation at the same time? The snippet above is short and fast, but there are some methods that take more time. What happens when there are a lot of calling to a static method or an instance method in the same class and the method is not synchronized? All the calling methods have to fall in line and the JVM executes them sequentially? Is it a good idea to have some class that are identical to the above-mentioned and randomly call their identical methods? I think it is not, because "Don't repeat yourself " and "Duplication is Evil" etc. But what about performance? Thanks is advance.

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• SIGABRT on any UIView touch

  - by bitcruncher

  Hi. I'm afraid no amount of Googling has been able to save my hyde on this. I seem to be getting SIGABRT error anytime I touch the screen of the phone, on any UIView. The debugger console posts this error before the SIGABRT: .... [310:207] *** -[UIView _exclusiveTouchView]: unrecognized selector sent to instance 0x14c0c0 .... [310:207] *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '*** -[UIView _exclusiveTouchView]: unrecognized selector sent to instance 0x14c0c0' (this is not my specific call to _exclusiveTouchView, of course.) I would gladly post some code, but the truth is I cannot find (or guess) where this problem may be coming from. This is not happening on any ONE UIView but on all the UIViews in my stack. I can summarize the display logic, though, perhaps that will shed some light. So the application is created and a UIWindow is alloc'd. A single viewcontroller is then alloc'd, which makes and adds its own blank self.view, to which the other UIViews, representing the different game states, are attached. Interestingly enough, this error is does NOT happen on the Simulator, but happens consistently on the device. And I should also mention that the application has yet to override/use any of the touchesBegan:/Ended:/Moved: etc... In other words, this error happens without these methods in the code. I'm really not understanding where this error is coming from... Any suggestions?

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• Java Polynomial Multiplication with ArrayList

  - by user1506919

  I am having a problem with one of my methods in my program. The method is designed to take 2 arraylists and the perform multiplication between the two like a polynomial. For example, if I was to say list1={3,2,1} and list2={5,6,7}; I am trying to get a return value of 15,28,38,20,7. However, all I can get is an error message that says: Exception in thread "main" java.lang.IndexOutOfBoundsException: Index: 0, Size: 0. I have provided the method below: private static ArrayList<Integer> multiply(ArrayList<Integer> list1,ArrayList<Integer> list2) { ArrayList<Integer> array =new ArrayList<Integer>(list1.size()+list2.size()); for (int i=0;i<array.size();i++) array.add(i, 0); for (int i = 0; i < list1.size(); i++) for (int j = 0; j < list2.size(); j++) array.set(i+j, ((list1.get(i) * list2.get(j))+array.get(i+j))); return array; } Any help with solving this problem is greatly appreciated.

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• File Locked by Services (after service code reading the text file)

  - by rvpals

  I have a windows services written in C# .NET. The service is running on a internal timer, every time the interval hits, it will go and try to read this log file into a String. My issue is every time the log file is read, the service seem to lock the log file. The lock on that log file will continue until I stop the windows service. At the same time the service is checking the log file, the same log file needs to be continuously updated by another program. If the file lock is on, the other program could not update the log file. Here is the code I use to read the text log file. private string ReadtextFile(string filename) { string res = ""; try { System.IO.FileStream fs = new System.IO.FileStream(filename, System.IO.FileMode.Open, System.IO.FileAccess.Read); System.IO.StreamReader sr = new System.IO.StreamReader(fs); res = sr.ReadToEnd(); sr.Close(); fs.Close(); } catch (System.Exception ex) { HandleEx(ex); } return res; } Thank you.

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• Python socket error on UDP data receive. (10054)

  - by Charles

  I currently have a problem using UDP and Python socket module. We have a server and clients. The problem occurs when we send data to a user. It's possible that user may have closed their connection to the server through a client crash, disconnect by ISP, or some other improper method. As such, it is possible to send data to a closed socket. Of course with UDP you can't tell if the data really reached or if it's closed, as it doesn't care (atleast, it doesn't bring up an exception). However, if you send data and it is closed off, you get data back somehow (???), which ends up giving you a socket error on sock.recvfrom. [Errno 10054] An existing connection was forcibly closed by the remote host. Almost seems like an automatic response from the connection. Although this is fine, and can be handled by a try: except: block (even if it lowers performance of the server a little bit). The problem is, I can't tell who this is coming from or what socket is closed. Is there anyway to find out 'who' (ip, socket #) sent this? It would be great as I could instantly just disconnect them and remove them from the data. Any suggestions? Thanks.

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• Hibernate JDBCConnectionException: Communications link failure and java.io.EOFException: Can not read response from server

  - by Marc

  I get a quite well-known using MySql jdbc driver : JDBCConnectionException: Communications link failure, java.io.EOFException: Can not read response from server. This is caused by the wait_timeout parameter in my.cnf. So I decided to use c3p0 pool connection along with Hibernate. Here is what I added to hibernate.cfg.xml : <property name="hibernate.connection.provider_class">org.hibernate.connection.C3P0ConnectionProvider</property> <property name="c3p0.min_size">10</property> <property name="c3p0.max_size">100</property> <property name="c3p0.timeout">1000</property> <property name="c3p0.preferredTestQuery">SELECT 1</property> <property name="c3p0.acquire_increment">1</property> <property name="c3p0.idle_test_period">2</property> <property name="c3p0.max_statements">50</property> idle_test_period is volontarily low for test purposes. Looking at the mysql logs I can see the "SELECT 1" request which is regularly sent to the mysql server so it works. Unfortunately I still get this EOF exception within my app if I wait longer than 'wait_timout' seconds (set to 10 for test purposes). I'm using Hibernate 4.1.1 and mysql-jdbc-connector 5.1.18. So what am I doing wrong? Thanks, Marc.

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• curios about CCSpriteBatchNode's addchild method

  - by lzyy

  when diving into "learn cocos2d game development with ios5", in ch08 in EnemyCache.m -(id) init { if ((self = [super init])) { // get any image from the Texture Atlas we're using CCSpriteFrame* frame = [[CCSpriteFrameCache sharedSpriteFrameCache] spriteFrameByName:@"monster-a.png"]; batch = [CCSpriteBatchNode batchNodeWithTexture:frame.texture]; [self addChild:batch]; [self initEnemies]; [self scheduleUpdate]; } return self; } so batch is with texture "monster-a.png" in EnemyEntity.m's initWithType method switch (type) { case EnemyTypeUFO: enemyFrameName = @"monster-a.png"; bulletFrameName = @"shot-a.png"; break; case EnemyTypeCruiser: enemyFrameName = @"monster-b.png"; bulletFrameName = @"shot-b.png"; shootFrequency = 1.0f; initialHitPoints = 3; break; case EnemyTypeBoss: enemyFrameName = @"monster-c.png"; bulletFrameName = @"shot-c.png"; shootFrequency = 2.0f; initialHitPoints = 15; break; default: [NSException exceptionWithName:@"EnemyEntity Exception" reason:@"unhandled enemy type" userInfo:nil]; } if ((self = [super initWithSpriteFrameName:enemyFrameName])) { //... } so the returned object may be in 3 different frame. since Only the CCSprites that are contained in that texture can be added to the CCSpriteBatchNode, obviously, 'monster-b.png' is not contained in 'monster-a.png', why the different enemy can still be added to the batch?

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• Dynamic checkboxlist

  - by Steve

  Hi, I am currently building a dynamic url tab system that user can say what urls they want to be displayed on a tabpage control. In the database i have the following columns. userID, int URLName var Enabled bit I am pulling the data back ok but what i am trying do is populate a checkbox list with the urlname and its status on a user options page so they can say what tabs they want displayed. I have wrote the following methods to get the urls and create the checkboxes however i keep getting the following error. ex = {"InvalidArgument=Value of '1' is not valid for 'index'.\r\nParameter name: index"} It reads the first row ok but when it hits the 2nd row that is being returned i get that error. Has anyone got any ideas? Thanks private void GetUserURLS() { db.initiateCommand("[Settings].[LoadAllUserURLS]", CommandType.StoredProcedure); sqlp = db.addParameter("@UserID", _UserID, SqlDbType.Int, ParameterDirection.Input); sqlp = db.addParameter("@spErrorID", DBNull.Value, SqlDbType.Int, ParameterDirection.InputOutput); db.executeCommand(); CreateCheckBoxes(db.getTable(0).Rows); db.releaseCommand(); } private void CreateCheckBoxes(DataRowCollection rows) { try { int i = 0; foreach (DataRow row in rows) { //Gets the url name and path when the status is enabled. The status of Enabled / Disabled is setup in the users option page string URLName = row["URLName"].ToString(); bool enabled = Convert.ToBoolean(row["Enabled"]); CheckedListBox CB = new CheckedListBox(); CB.Items.Insert(i, URLName); CB.Tag = "CB" + i.ToString(); checkedListBox1.Items.Add(CB); i++; } } catch (Exception ex) { //Log error Functionality func = new Functionality(); func.LogError(ex); //Error message the user will see string FriendlyError = "There has been populating checkboxes with the urls - A notification has been sent to development"; Classes.ShowMessageBox.MsgBox(FriendlyError, "There has been an Error", MessageBoxButtons.OK, MessageBoxIcon.Error); } }

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• linux new/delete, malloc/free large memory blocks

  - by brian_mk

  Hi folks, We have a linux system (kubuntu 7.10) that runs a number of CORBA Server processes. The server software uses glibc libraries for memory allocation. The linux PC has 4G physical memory. Swap is disabled for speed reasons. Upon receiving a request to process data, one of the server processes allocates a large data buffer (using the standard C++ operator 'new'). The buffer size varies depening upon a number of parameters but is typically around 1.2G Bytes. It can be up to about 1.9G Bytes. When the request has completed, the buffer is released using 'delete'. This works fine for several consecutive requests that allocate buffers of the same size or if the request allocates a smaller size than the previous. The memory appears to be free'd ok - otherwise buffer allocation attempts would eventually fail after just a couple of requests. In any case, we can see the buffer memory being allocated and freed for each request using tools such as KSysGuard etc. The problem arises when a request requires a buffer larger than the previous. In this case, operator 'new' throws an exception. It's as if the memory that has been free'd from the first allocation cannot be re-allocated even though there is sufficient free physical memory available. If I kill and restart the server process after the first operation, then the second request for a larger buffer size succeeds. i.e. killing the process appears to fully release the freed memory back to the system. Can anyone offer an explanation as to what might be going on here? Could it be some kind of fragmentation or mapping table size issue? I am thinking of replacing new/delete with malloc/free and use mallopt to tune the way the memory is being released to the system. BTW - I'm not sure if it's relevant to our problem, but the server uses Pthreads that get created and destroyed on each processing request. Cheers, Brian.

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• 3 matchers expected, 4 recorded.

  - by user564159

  I get this exception during the mock recording time. Searched for a solution in this forum. Made sure that i did not mess up any another parameter. The below mock expection is giving the error. EasyMock.expect(slotManager.addSlotPageletBinding(EasyMock.isA(String.class), EasyMock.isA(String.class), EasyMock.isA(helloWorld.class))).andReturn(true); before this statement i have another mock expection on the same method with TWO parameter(overloaded method).Below is that mock. EasyMock.expect(slotManager.addSlotPageletBinding(EasyMock.isA(String.class),EasyMock.isA(String.class))).andReturn(true).anyTimes(); Could any one guide me on this. Thanks. java.lang.IllegalStateException: 3 matchers expected, 4 recorded. at org.easymock.internal.ExpectedInvocation.createMissingMatchers(ExpectedInvocation.java:56) at org.easymock.internal.ExpectedInvocation.(ExpectedInvocation.java:48) at org.easymock.internal.ExpectedInvocation.(ExpectedInvocation.java:40) at org.easymock.internal.RecordState.invoke(RecordState.java:76) at org.easymock.internal.MockInvocationHandler.invoke(MockInvocationHandler.java:38) at org.easymock.internal.ObjectMethodsFilter.invoke(ObjectMethodsFilter.java:72) at org.easymock.classextension.internal.ClassProxyFactory$1.intercept(ClassProxyFactory.java:79) at com.amazon.inca.application.SlotManager$$EnhancerByCGLIB$$3bf5ac02.addSlotPageletBinding() at com.amazon.iris3.apps.Iris3YourAccountApplicationTest.testBuildIncaViewConfiguration(Iris3YourAccountApplicationTest.java:107) at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25) at java.lang.reflect.Method.invoke(Method.java:597) at junit.framework.TestCase.runTest(TestCase.java:168) at junit.framework.TestCase.runBare(TestCase.java:134) at junit.framework.TestResult$1.protect(TestResult.java:110) at junit.framework.TestResult.runProtected(TestResult.java:128) at junit.framework.TestResult.run(TestResult.java:113) at junit.framework.TestCase.run(TestCase.java:124) at junit.framework.TestSuite.runTest(TestSuite.java:232) at junit.framework.TestSuite.run(TestSuite.java:227) at org.junit.internal.runners.JUnit38ClassRunner.run(JUnit38ClassRunner.java:83) at org.eclipse.jdt.internal.junit4.runner.JUnit4TestReference.run(JUnit4TestReference.java:46) at org.eclipse.jdt.internal.junit.runner.TestExecution.run(TestExecution.java:38) at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:467) at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:683) at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run(RemoteTestRunner.java:390) at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.main(RemoteTestRunner.java:197)

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• How do I use HttpWebRequest GET method w/ ContentType="application/json"

  - by Stephen Patten

  Hello, This one is real simple, run this Silverlight4 example with the ContentType property commented out and you'll get back a response from from my service in xml. Now uncomment the property and run it and you'll get an ProtocolViolationException, what should happen is the service returns JSON formatted data. HttpWebRequest wreq = (HttpWebRequest)WebRequestCreator.ClientHttp.Create(new Uri("http://stephenpattenconsulting.com/Services/GetFoodDescriptionsLookup(2100)")); //wreq.ContentType = "application/json"; wreq.BeginGetResponse((cb) => { HttpWebRequest rq = cb.AsyncState as HttpWebRequest; HttpWebResponse resp = rq.EndGetResponse(cb) as HttpWebResponse; // Exception StreamReader rdr = new StreamReader(resp.GetResponseStream()); string result = rdr.ReadToEnd(); rdr.Close(); }, wreq); EDIT: While perusing SO, I noticed similar posts, like this one Why am I getting ProtocolViolationException when trying to use HttpWebRequest? and this one How do I use HttpWebRequest with GET method EDIT: The WCF 4 end point is 'adapted' from this link http://geekswithblogs.net/michelotti/archive/2010/08/21/restful-wcf-services-with-no-svc-file-and-no-config.aspx. I can use Fiddler's request builder to to construct the proper requests and changing the content type does yield the correct results.

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• Struts ActionError

  - by user287663

  Hi all. Anyone knows why the code below doesn't compile? The reason is that it could not find symbol for ActionError. Thanks in advance. package com.hbs; import javax.servlet.RequestDispatcher; import javax.servlet.ServletException; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpSession; import javax.servlet.http.HttpServletResponse; import org.apache.struts.action.Action; import org.apache.struts.action.ActionError; import org.apache.struts.action.ActionErrors; import org.apache.struts.action.ActionForm; import org.apache.struts.action.ActionMapping; import org.apache.struts.action.ActionForward; import org.apache.struts.util.MessageResources; import org.apache.commons.beanutils.PropertyUtils; public class FeedbackAction extends org.apache.struts.action.Action { private final static String SUCCESS = "success"; public ActionForward execute(ActionMapping mapping, ActionForm form, HttpServletRequest request, HttpServletResponse response) throws Exception { ActionErrors errors = new ActionErrors(); String fullName = (String)PropertyUtils.getSimpleProperty(form, "fullName"); String fullName1 = ""; if(fullName.equals(fullName1)) { errors.add("fullName", new ActionError("error.fullName", fullName)); saveErrors(request,errors); return (new ActionForward(mapping.getInput())); } return mapping.findForward(SUCCESS); } }

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• EF Forced Concurrency Checks

  - by Imran

  Hi, I have an issue with EF 4.0 that I hope someone can help with. I currently have an entity that I want to update in a last in wins fashion (i.e. ignore concurrency checks and just overwrite whats in the db with what is submitted). It seems Entity Framework not only includes the primary key of the entity in the where clause of the generated sql, but also any foreign key fields. This is annoying as it means that I don't get true last in wins semantics and need to know what value the fk field had before the update or I get a concurrency exception. I am aware that this can be short circuited by including a foreign key field as well as the navigation property on the entity. I would like to avoid this if possible as it's not a very clean solution. I was just wondering if there was any other way to override this behaviour? It seems like more of a bug than a feature. I have no problem with ef doing concurrency checks if I instruct it to do so but not being able to bypass concurrency completely is a bit of a hindrance as there are many valid scenarios where this is not needed

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