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Handling close-to-impossible collisions on should-be-unique values

- by balpha

There are many systems that depend on the uniqueness of some particular value. Anything that uses GUIDs comes to mind (eg. the Windows registry or other databases), but also things that create a hash from an object to identify it and thus need this hash to be unique. A hash table usually doesn't mind if two objects have the same hash because the hashing is just used to break down the objects into categories, so that on lookup, not all objects in the table, but only those objects in the same category (bucket) have to be compared for identity to the searched object. Other implementations however (seem to) depend on the uniqueness. My example (that's what lead me to asking this) is Mercurial's revision IDs. An entry on the Mercurial mailing list correctly states The odds of the changeset hash colliding by accident in your first billion commits is basically zero. But we will notice if it happens. And you'll get to be famous as the guy who broke SHA1 by accident. But even the tiniest probability doesn't mean impossible. Now, I don't want an explanation of why it's totally okay to rely on the uniqueness (this has been discussed here for example). This is very clear to me. Rather, I'd like to know (maybe by means of examples from your own work): Are there any best practices as to covering these improbable cases anyway? Should they be ignored, because it's more likely that particularly strong solar winds lead to faulty hard disk reads? Should they at least be tested for, if only to fail with a "I give up, you have done the impossible" message to the user? Or should even these cases get handled gracefully? For me, especially the following are interesting, although they are somewhat touchy-feely: If you don't handle these cases, what do you do against gut feelings that don't listen to probabilities? If you do handle them, how do you justify this work (to yourself and others), considering there are more probable cases you don't handle, like a supernonva?

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problem finding a header with a c++ makefile

- by Max

Hi. I've started working with my first makefile. I'm writing a roguelike in C++ using the libtcod library, and have the following hello world program to test if my environment's up and running: #include "libtcod.hpp" int main() { TCODConsole::initRoot(80, 50, "PartyHack"); TCODConsole::root->printCenter(40, 25, TCOD_BKGND_NONE, "Hello World"); TCODConsole::flush(); TCODConsole::waitForKeypress(true); } My project directory structure looks like this: /CppPartyHack ----/libtcod-1.5.1 # this is the libtcod root folder --------/include ------------libtcod.hpp ----/PartyHack --------makefile --------partyhack.cpp # the above code (while we're here, how do I do proper indentation? Using those dashes is silly.) and here's my makefile: SRCDIR = . INCDIR = ../libtcod-1.5.1/include CFLAGS = $(FLAGS) -I$(INCDIR) -I$(SRCDIR) -Wall CC = gcc CPP = g++ .SUFFIXES: .o .h .c .hpp .cpp $(TEMP)/%.o : $(SRCDIR)/%.cpp $(CPP) $(CFLAGS) -o $@ -c $< $(TEMP)/%.o : $(SRCDIR)/%.c $(CC) $(CFLAGS) -o $@ -c $< CPP_OBJS = $(TEMP)partyhack.o all : partyhack partyhack : $(CPP_OBJS) $(CPP) $(CPP_OBJS) -o $@ -L../libtcod-1.5.1 -ltcod -ltcod++ -Wl,-rpath,. clean : \rm -f $(CPP_OBJS) partyhack I'm using Ubuntu, and my terminal gives me the following errors: max@max-desktop:~/Desktop/Development/CppPartyhack/PartyHack$ make g++ -c -o partyhack.o partyhack.cpp partyhack.cpp:1:23: error: libtcod.hpp: No such file or directory partyhack.cpp: In function ‘int main()’: partyhack.cpp:5: error: ‘TCODConsole’ has not been declared partyhack.cpp:6: error: ‘TCODConsole’ has not been declared partyhack.cpp:6: error: ‘TCOD_BKGND_NONE’ was not declared in this scope partyhack.cpp:7: error: ‘TCODConsole’ has not been declared partyhack.cpp:8: error: ‘TCODConsole’ has not been declared make: * [partyhack.o] Error 1 So obviously, the makefile can't find libtcod.hpp. I've double checked and I'm sure the relative path to libtcod.hpp in INCDIR is correct, but as I'm just starting out with makefiles, I'm uncertain what else could be wrong. My makefile is based off a template that the libtcod designers provided along with the library itself, and while I've looked at a few online makefile tutorials, the code in this makefile is a good bit more complicated than any of the examples the tutorials showed, so I'm assuming I screwed up something basic in the conversion. Thanks for any help.

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Get Nhibernate entity and complete it from a web service.

- by Nour Sabouny

Hi every one. let's say that i have an order system. each "Order" references a "Customer" Object. when i fill the orders list in Data Access Layer, the customer object should be brought from a Customer Web Service "WCF". so i didn't map the Customer property in the Order mapping class, Id(o => o.OrderID).GeneratedBy.Identity(); //References(o => o.Customer).Not.Nullable().Column("CustomerID"); HasMany(o => o.Details).KeyColumn("OrderID").Cascade.AllDeleteOrphan(); Map(c => c.CustomerID).Not.Nullable(); and asked the nhibernate session to get me the orders list. and tried to loop on every order in the list to fill it's customer property, doe's any body have a good idea for this ???? IList<Order> lst = Session.CreateCriteria<Order>().List<Order>(); foreach (Order order in lst) order.Customer = serviceProxy.GetCustomerByID(order.CustomerID);

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How to pass data to a C++0x lambda function that will run in a different thread?

- by Dimitri C.

In our company we've written a library function to call a function asynchronously in a separate thread. It works using a combination of inheritance and template magic. The client code looks as follows: DemoThread thread; std::string stringToPassByValue = "The string to pass by value"; AsyncCall(thread, &DemoThread::SomeFunction, stringToPassByValue); Since the introduction of lambda functions I'd like to use it in combination with lambda functions. I'd like to write the following client code: DemoThread thread; std::string stringToPassByValue = "The string to pass by value"; AsyncCall(thread, [=]() { const std::string someCopy = stringToPassByValue; }); Now, with the Visual C++ 2010 this code doesn't work. What happens is that the stringToPassByValue is not copied. Instead the "capture by value" feature passes the data by reference. The result is that if the function is executed after stringToPassByValue has gone out of scope, the application crashes as its destructor is called already. So I wonder: is it possible to pass data to a lambda function as a copy? Note: One possible solution would be to modify our framework to pass the data in the lambda parameter declaration list, as follows: DemoThread thread; std::string stringToPassByValue = "The string to pass by value"; AsyncCall(thread, [=](const std::string stringPassedByValue) { const std::string someCopy = stringPassedByValue; } , stringToPassByValue); However, this solution is so verbose that our original function pointer solution is both shorter and easier to read. Update: The full implementation of AsyncCall is too big to post here. In short, what happens is that the AsyncCall template function instantiates a template class holding the lambda function. This class is derived from a base class that contains a virtual Execute() function, and upon an AsyncCall() call, the function call class is put on a call queue. A different thread then executes the queued calls by calling the virtual Execute() function, which is polymorphically dispatched to the template class which then executes the lambda function.

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jQuery find next and prev element

- by StoneHeart

I try to find a next or prev element of current element. But next() and prev() function can only work in a scope, it can not reach outside. For an example this is what I want to achieve: <ul id="ul1"> <li>1</li> <li>2</li> <li>3</li> <li> <ul id="ul2"> <li>4</li> <li> <ul id="ul3"> <li>5</li> <li>6</li> </ul> </li> <li>7</li> <li>8</li> </ul> </li> <li>9</li> </ul> If current element is ul1, next element is <li>1</li>, prev element is null. If current element is <li>1</li>, next element is <li>2</li>, prev element is ul1 If current element is <li>8</li>, next element is <li>9</li>, prev element is <li>7</li>

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NHibernate.MappingException on table insertion.

- by Suja

The table structure is : The controller action to insert a row to table is public bool CreateInstnParts(string data) { IDictionary myInstnParts = DeserializeData(data); try { HSInstructionPart objInstnPartBO = new HSInstructionPart(); using (ISession session = Document.OpenSession()) { using (ITransaction transaction = session.BeginTransaction()) { objInstnPartBO.DocumentId = Convert.ToInt32(myInstnParts["documentId"]); objInstnPartBO.InstructionId = Convert.ToInt32(myInstnParts["instructionId"]); objInstnPartBO.PartListId = Convert.ToInt32(myInstnParts["part"]); objInstnPartBO.PartQuantity = Convert.ToInt32(myInstnParts["quantity"]); objInstnPartBO.IncPick = Convert.ToBoolean(myInstnParts["incpick"]); objInstnPartBO.IsTracked = Convert.ToBoolean(myInstnParts["istracked"]); objInstnPartBO.UpdatedBy = User.Identity.Name; objInstnPartBO.UpdatedAt = DateTime.Now; session.Save(objInstnPartBO); transaction.Commit(); } return true; } } catch (Exception ex) { Console.Write(ex.Message); return false; } } This is throwing an exception NHibernate.MappingException was caught Message="No persister for: Hexsolve.Data.BusinessObjects.HSInstructionPart" Source="NHibernate" StackTrace: at NHibernate.Impl.SessionFactoryImpl.GetEntityPersister(String entityName) at NHibernate.Impl.SessionImpl.GetEntityPersister(String entityName, Object obj) at NHibernate.Event.Default.AbstractSaveEventListener.SaveWithGeneratedId(Object entity, String entityName, Object anything, IEventSource source, Boolean requiresImmediateIdAccess) at NHibernate.Event.Default.DefaultSaveOrUpdateEventListener.SaveWithGeneratedOrRequestedId(SaveOrUpdateEvent event) at NHibernate.Event.Default.DefaultSaveEventListener.SaveWithGeneratedOrRequestedId(SaveOrUpdateEvent event) at NHibernate.Event.Default.DefaultSaveOrUpdateEventListener.EntityIsTransient(SaveOrUpdateEvent event) at NHibernate.Event.Default.DefaultSaveEventListener.PerformSaveOrUpdate(SaveOrUpdateEvent event) at NHibernate.Event.Default.DefaultSaveOrUpdateEventListener.OnSaveOrUpdate(SaveOrUpdateEvent event) at NHibernate.Impl.SessionImpl.FireSave(SaveOrUpdateEvent event) at NHibernate.Impl.SessionImpl.Save(Object obj) at HexsolveMVC.Controllers.InstructionController.CreateInstnParts(String data) in F:\Project\HexsolveMVC\Controllers\InstructionController.cs:line 1342 InnerException: Can anyone help me solve this??

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Does Microsoft Access use the PK fields for anything?

- by chrismay

Ok this is going to sound strange, but I have inherited an app that is an Access front end with a SQL Server backend. I am in the process of writing a new front end for it, but... we need to continue using the access front end for a while even after we deploy my new front end for reasons I won't go into. So both the existing Access app and my new app will need to be able to access and work with the data. The problem is the database design is a nightmare. For example some simple parent-child table relationships have like 4 and 5 part composite primary keys. I would REALLY like to remove these PKs and replace them with unique constraints or whatever, and add a new column to each of these tables called ID that is just an identity. If I change the PK and FKs on these tables to more managable fields, will the Access app have problems? What I mean is, does access use the meta data from the tables (PK and FK info) in such a way that it would break the app to change these?

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nhibernate mapping: delete collection, insert new collection with old IDs

- by npeBeg

my issue lokks similar to this one: (link) but i have one-to-many association: <set name="Fields" cascade="all-delete-orphan" lazy="false" inverse="true"> <key column="[TEMPLATE_ID]"></key> <one-to-many class="MyNamespace.Field, MyLibrary"/> </set> (i also tried to use ) this mapping is for Template object. this one and the Field object has their ID generators set to identity. so when i call session.Update for the Template object it works fine, well, almost: if the Field object has an Id number, UPDATE sql request is called, if the Id is 0, the INSERT is performed. But if i delete a Field object from the collection it has no effect for the Database. I found that if i also call session.Delete for this Field object, everything will be ok, but due to client-server architecture i don't know what to delete. so i decided to delete all the collection elements from the DB and call session.Update with a new collection. and i've got an issue: nhibernate performs the UPDATE operation for the Field objects that has non-zero Id, but they are removed from DB! maybe i should use some other Id generator or smth.. what is the best way to make nhibernate perform "delete all"/"insert all" routine for the collection?

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Does everything after my try statement have to be encompassed in that try statement to access variab

- by Mithrax

I'm learning java and one thing I've found that I don't like, is generally when I have code like this: import java.util.*; import java.io.*; public class GraphProblem { public static void main(String[] args) { if (args.length < 2) { System.out.println("Error: Please specify a graph file!"); return; } FileReader in = new FileReader(args[1]); Scanner input = new Scanner(in); int size = input.nextInt(); WeightedGraph graph = new WeightedGraph(size); for(int i = 0; i < size; i++) { graph.setLabel(i,Character.toString((char)('A' + i))); } for(int i = 0; i < size; i++) { for(int j = 0; j < size; j++) { graph.addEdge(i, j, input.nextInt()); } } // .. lots more code } } I have an uncaught exception around my FileReader. So, I have to wrap it in a try-catch to catch that specific exception. My question is does that try { } have to encompass everything after that in my method that wants to use either my FileReader (in) or my Scanner (input)? If I don't wrap the whole remainder of the program in that try statement, then anything outside of it can't access the in/input because it may of not been initialized or has been initialized outside of its scope. So I can't isolate the try-catch to just say the portion that intializes the FileReader and close the try statement immediately after that. So, is it the "best practice" to have the try statement wrapping all portions of the code that are going to access variables initialized in it? Thanks!

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Best Practice: Protecting Personally Identifiable Data in a ASP.NET / SQL Server 2008 Environment

- by William

Thanks to a SQL injection vulnerability found last week, some of my recommendations are being investigated at work. We recently re-did an application which stores personally identifiable information whose disclosure could lead to identity theft. While we read some of the data on a regular basis, the restricted data we only need a couple of times a year and then only two employees need it. I've read up on SQL Server 2008's encryption function, but I'm not convinced that's the route I want to go. My problem ultimately boils down to the fact that we're either using symmetric keys or assymetric keys encrypted by a symmetric key. Thus it seems like a SQL injection attack could lead to a data leak. I realize permissions should prevent that, permissions should also prevent the leaking in the first place. It seems to me the better method would be to asymmetrically encrypt the data in the web application. Then store the private key offline and have a fat client that they can run the few times a year they need to access the restricted data so the data could be decrypted on the client. This way, if the server get compromised, we don't leak old data although depending on what they do we may leak future data. I think the big disadvantage is this would require re-writing the web application and creating a new fat application (to pull the restricted data). Due to the recent problem, I can probably get the time allocated, so now would be the proper time to make the recommendation. Do you have a better suggestion? Which method would you recommend? More importantly why?

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Actionscript Enterframe Movement

- by David

I am trying to make accelerated movement, but I am running into a problem that, for the life of me, I cannot understand. My class definition: public class Player extends MovieClip { private var stageRef:Stage; private var key:KeyObject; private var acceleration:int = .5; private var curSpeed:int = 0; public function Player(stageRef:Stage) { this.stageRef = stageRef; addEventListener(Event.ENTER_FRAME, enterFrame); key = new KeyObject(stageRef); } public function enterFrame(e:Event) : void { if(key.isDown(key.RIGHT)) { x += 5; } } } This works to move my position in the x direction at a constant rate. However, if I change enterFrame to public function enterFrame(e:Event) : void { if(key.isDown(key.RIGHT)) { x += acceleration; } } No movement occurs. Is there something going on in the event I do not understand? Why is it that I can have x increased by a constant value but not a constant value as defined in a variable in the class? Is it a scope issue?

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WHY JSLint complains: "someFunction() was used before it was defined"?

- by 7hi4g0

Searching for the JSLint error "was used before it was defined" i've found these: JSLint: Using a function before it's defined error Function was used before it was defined - JSLint JSLint: was used before it was defined jsLint error: “somefunction() was used before it was defined” jslint - Should we tolerate misordered definitions? Problem None of those answers WHY the error is shown. Elaboration According to the ECMA-262 Specification functions are evaluated before execution starts, hence all functions declared using the function keyword are available to all the code idenpendent of the place they were declared (assuming they are acessible on that scope). This is otherwise known as hoisting. Douglas Crockford seems to think it is better to declare every function before the code that uses it regardless of the hoisting effect. According to StackOverflowNewbie in his question, this raises some code organization problems. Not to mention some people, like me, prefer to declare their functions underneath the main/init code. On those questions there are some ways to avoid or fix the error, such as using function expressions vs function declarations. But none of them showed me the reason of the error. Not even Crockford's site. Question(s) Why is it an error to call a function before the declaration, even if it was declared using the function keyword? Is it better to use function expressions instead of function declaration in the JSLint context? If one is preferred, why? Note Not looking for answers like: Crockford is a tyrant Is just Crockford's opinion Thank you :*

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How to copy a variable in JavaScript?

- by Michael Stum

I have this JavaScript code: for (var idx in data) { var row = $("<tr></tr>"); row.click(function() { alert(idx); }); table.append(row); } So I'm looking through an array, dynamically creating rows (the part where I create the cells is omitted as it's not important). Important is that I create a new function which encloses the idx variable. However, idx is only a reference, so at the end of the loop, all rows have the same function and all alert the same value. One way I solve this at the moment is by doing this: function GetRowClickFunction(idx){ return function() { alert(idx); } } and in the calling code I call row.click(GetRowClickFunction(idx)); This works, but is somewhat ugly. I wonder if there is a better way to just copy the current value of idx inside the loop? While the problem itself is not jQuery specific (it's related to JavaScript closures/scope), I use jQuery and hence a jQuery-only solution is okay if it works.

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PHP Session variable isset(..)=1 after session_start()

- by Nicsoft

Hello! I guess I am not understanding the scope of session variables, or the session itself, in PHP, hence this question: This is my code if(!session_id()==""){ echo "Getting rid of session"."</br>"; session_destroy(); } echo "Before session_start(): ".isset($_SESSION["first_date_of_week"])."</br>"; session_start(); echo "After session_start(): ".isset($_SESSION["first_date_of_week"])." ".$_SESSION["first_date_of_week"]->format("Y-m-d")."</br>"; The output is: Before session_start(): After session_start(): 1 2011-01-09 How come that when doing the isset(..) on the session variable it is set directly after starting the session, even though I haven't even used it or set it yet? It does, however, still have the same value as before. Also, session_id()="" since the if-clause is never triggered. I never kill the session, how come it is set to ""? I.e. I refresh the page and expects the session to still be alive. Using the isset(..) function is then pretty useless testing if it has been set already... Thanks in advance! /Niklas

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When should EntityManagerFactory instance be created/opened ?

- by masato-san

Ok, I read bunch of articles/examples how to write Entity Manager Factory in singleton. One of them easiest for me to understand a bit: http://javanotepad.blogspot.com/2007/05/jpa-entitymanagerfactory-in-web.html I learned that EntityManagerFactory (EMF) should only be created once preferably in application scope. And also make sure to close the EMF once it's used (?) So I wrote EMF helper class for business methods to use: public class EmProvider { private static final String DB_PU = "KogaAlphaPU"; public static final boolean DEBUG = true; private static final EmProvider singleton = new EmProvider(); private EntityManagerFactory emf; private EmProvider() {} public static EmProvider getInstance() { return singleton; } public EntityManagerFactory getEntityManagerFactory() { if(emf == null) { emf = Persistence.createEntityManagerFactory(DB_PU); } if(DEBUG) { System.out.println("factory created on: " + new Date()); } return emf; } public void closeEmf() { if(emf.isOpen() || emf != null) { emf.close(); } emf = null; if(DEBUG) { System.out.println("EMF closed at: " + new Date()); } } }//end class And my method using EmProvider: public String foo() { EntityManager em = null; List<Object[]> out = null; try { em = EmProvider.getInstance().getEntityManagerFactory().createEntityManager(); Query query = em.createNativeQuery(JPQL_JOIN); //just some random query out = query.getResultList(); } catch(Exception e) { //handle error.... } finally { if(em != null) { em.close(); //make sure to close EntityManager } } I made sure to close EntityManager (em) within method level as suggested. But when should EntityManagerFactory be closed then? And why EMF has to be singleton so bad??? I read about concurrency issues but as I am not experienced multi-thread-grammer, I can't really be clear on this idea.

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Recursive powerof-function, see if you can solve it

- by Jonas B

First of all, this is not schoolwork - just my curiousity as I for some reason can't get my head around it and solve it. I come up with these stupid things all the time and it annoys the hell out of me when I cant solve them. Code example is in C# but solution doesn't have to be in any particular programming-language. long powerofnum(short num, long powerof) { return powerofnum2(num, powerof, powerof); } long powerofnum2(short num, long powerof, long holder) { if (num == 1) return powerof; else { return powerof = powerofnum2(num - 1, holder * powerof, holder); } } As you can see I have two methods. I call for powerofnum(value, powerofvalue) which then calls the next method with the powerofvalue also in a third parameter as a placeholder so it remembers the original powerof value through the recursion. What I want to accomplish is to do this with only one method. I know I could just declare a variable in the first method with the powerof value to remember it and then iterate from 0 to value of num. But as this is a theoretical question I want it done recursively. I could also in the first method just take a third parameter called whatever to store the value just like I do in the second method that is called by the first, but that looks really stupid. Why should you have to write what seems like the same parameter twice? Rules explained in short: no iteration scope-specific variables only only one method Anyhow, I'd appreciate a clean solution. Good luck :)

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Different approaches for finding users within Active Directory

- by EvilDr

I'm a newbie to AD programming, but after a couple of weeks of research have found the following three ways to search for users in Active Directory using the account name as the search parameter: Option 1 - FindByIdentity Dim ctx As New PrincipalContext(ContextType.Domain, Environment.MachineName) Dim u As UserPrincipal = UserPrincipal.FindByIdentity(ctx, IdentityType.SamAccountName, "MYDOMAIN\Administrator") If u Is Nothing Then Trace.Warn("No user found.") Else Trace.Warn("Name=" & u.Name) Trace.Warn("DisplayName=" & u.DisplayName) Trace.Warn("DistinguishedName=" & u.DistinguishedName) Trace.Warn("EmployeeId=" & u.EmployeeId) Trace.Warn("EmailAddress=" & u.EmailAddress) End If Option 2 - DirectorySearcher Dim connPath As String = "LDAP://" & Environment.MachineName Dim de As New DirectoryEntry(connPath) Dim ds As New DirectorySearcher(de) ds.Filter = String.Format("(&(objectClass=user)(anr={0}))", Split(User.Identity.Name, "\")(1)) ds.PropertiesToLoad.Add("name") ds.PropertiesToLoad.Add("displayName") ds.PropertiesToLoad.Add("distinguishedName") ds.PropertiesToLoad.Add("employeeId") ds.PropertiesToLoad.Add("mail") Dim src As SearchResult = ds.FindOne() If src Is Nothing Then Trace.Warn("No user found.") Else For Each propertyKey As String In src.Properties.PropertyNames Dim valueCollection As ResultPropertyValueCollection = src.Properties(propertyKey) For Each propertyValue As Object In valueCollection Trace.Warn(propertyKey & "=" & propertyValue.ToString) Next Next End If Option 3 - PrincipalSearcher Dim ctx2 As New PrincipalContext(ContextType.Domain, Environment.MachineName) Dim sp As New UserPrincipal(ctx2) sp.SamAccountName = "MYDOMAIN\Administrator" Dim s As New PrincipalSearcher s.QueryFilter = sp Dim p2 As UserPrincipal = s.FindOne() If p2 Is Nothing Then Trace.Warn("No user found.") Else Trace.Warn(p2.Name) Trace.Warn(p2.DisplayName) Trace.Warn(p2.DistinguishedName) Trace.Warn(p2.EmployeeId) Trace.Warn(p2.EmailAddress) End If All three of these methods return the same results, but I was wondering if any particular method is better or worse than the others? Option 1 or 3 seem to be the best as they provide strongly-typed property names, but I might be wrong? My overall objective is to find a single user within AD based on the user principal value passed via the web browser when using Windows Authentication on a site (e.g. "MYDOMAIN\MyUserAccountName")

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GUID or int entity key with SQL Compact/EF4?

- by David Veeneman

This is a follow-up to an earlier question I posted on EF4 entity keys with SQL Compact. SQL Compact doesn't allow server-generated identity keys, so I am left with creating my own keys as objects are added to the ObjectContext. My first choice would be an integer key, and the previous answer linked to a blog post that shows an extension method that uses the Max operator with a selector expression to find the next available key: public static TResult NextId<TSource, TResult>(this ObjectSet<TSource> table, Expression<Func<TSource, TResult>> selector) where TSource : class { TResult lastId = table.Any() ? table.Max(selector) : default(TResult); if (lastId is int) { lastId = (TResult)(object)(((int)(object)lastId) + 1); } return lastId; } Here's my take on the extension method: It will work fine if the ObjectContext that I am working with has an unfiltered entity set. In that case, the ObjectContext will contain all rows from the data table, and I will get an accurate result. But if the entity set is the result of a query filter, the method will return the last entity key in the filtered entity set, which will not necessarily be the last key in the data table. So I think the extension method won't really work. At this point, the obvious solution seems to be to simply use a GUID as the entity key. That way, I only need to call Guid.NewGuid() method to set the ID property before I add a new entity to my ObjectContext. Here is my question: Is there a simple way of getting the last primary key in the data store from EF4 (without having to create a second ObjectContext for that purpose)? Any other reason not to take the easy way out and simply use a GUID? Thanks for your help.

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Call HashMap from jsp EL ?

- by Parhs

Here is my Entity Class public enum UnitType { HOSPITAL, HEALTHCENTER } public static LinkedHashMap<UnitType, String> unitType = new LinkedHashMap<UnitType, String>() { { put(UnitType.HEALTHCENTER, "???t?? ??e?a?"); put(UnitType.HOSPITAL, "??s???µe??"); } }; @Id @GeneratedValue(strategy = GenerationType.IDENTITY) private Long id; private String name; private String address; @Column(columnDefinition = "TEXT") private String info; @Enumerated(EnumType.STRING) private UnitType type; At my jsp <c:forEach var="unit" items="${requestScope.units}"> <tr> <td>${unit.id}</td> <td>${unit.name}</td> <td>${unit.address}</td> <td>??!?</td> <td><a href="#">?e??ss?te?a</a></td> </tr> </c:forEach> How can i place the text value of the enum at ??!? .. Any idea? Tried some ways but nothing worked..

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How can I stop the iPhone from displaying a transform change until after the screen is redrawn

- by Ed Marty

I have found the UIScrollView's zooming mechanism to be clunk and essentially unusable. So instead, I'm rolling my own. I have a UIView that resizes itself with the pinch-zoom, and that's working fine. When the zoom is complete, the view needs to reset its transform and redraw the images. The zoom works essentially in the same way the UIScrollView does. It sets the transform property of the UIView until complete. Then, when the zoom finishes, I want to reset the transform to CGAffineTransformIdentity, resize the frame to be the size it was before, and tell the view to redraw itself at the new size. It all works pretty well, except when I change the transform to identity then redraw the image, there is a slight flicker before the image completely redraws. This is due to the fact that I'm using a subclass of CATiledLayer, since the view can be of arbitrary size. I've overridden the fadeDuration to be zero, but there is still a flicker while the transform is reset before the redraw is finished. Is there any simple way to overcome this without creating another view to draw with then replacing it?

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Javascript memory leak/ performance issue?

- by Tom

I just cannot for the life of me figure out this memory leak in Internet Explorer. insertTags simple takes string str and places each word within start and end tags for HTML (usually anchor tags). transliterate is for arabic numbers, and replaces normal numbers 0-9 with a &#..n; XML identity for their arabic counterparts. fragment = document.createDocumentFragment(); for (i = 0, e = response.verses.length; i < e; i++) { fragment.appendChild((function(){ p = document.createElement('p'); p.setAttribute('lang', (response.unicode) ? 'ar' : 'en'); p.innerHTML = ((response.unicode) ? (response.surah + ':' + (i+1)).transliterate() : response.surah + ':' + (i+1)) + ' ' + insertTags(response.verses[i], '<a href="#" onclick="window.popup(this);return false;" class="match">', '</a>'); try { return p } finally { p = null; } })()); } params[0].appendChild( fragment ); fragment = null; I would love some links other than MSDN and about.com, because neither of them have sufficiently explained to me why my script leaks memory. I am sure this is the problem, because without it everything runs fast (but nothing displays). I've read that doing a lot of DOM manipulations can be dangerous, but the for loops a max of 286 times (# of verses in surah 2, the longest surah in the Qur'an).

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How hide some nodes in Richfaces Tree (do not render nodes by condition)?

- by VestniK

I have a tree of categories and courses in my SEAM application. Courses may be active and inactive. I want to be able to show only active or all courses in my tree. I've decided to always build complete tree in my PAGE scope component since building this tree is quite expensive operation. I have boolean flag courseActive in the data wrapped by TreeNode<T>. Now I can't find the way to show courses node only if this flag is true. The best result I've achieved with the following code: <h:outputLabel for="showInactiveCheckbox" value="show all courses: "/> <h:selectBooleanCheckbox id="showInactiveCheckbox" value="#{categoryTreeEditorModel.showAllCoursesInTree}"> <a4j:support event="onchange" reRender="categoryTree"/> </h:selectBooleanCheckbox> <rich:tree id="categoryTree" value="#{categoryTree}" var="item" switchType="ajax" ajaxSubmitSelection="true" reRender="categoryTree,controls" adviseNodeOpened="#{categoryTreeActions.adviseRootOpened}" nodeSelectListener="#{categoryTreeActions.processSelection}" nodeFace="#{item.typeName}"> <rich:treeNode type="Category" icon="..." iconLeaf="..."> <h:outputText value="#{item.title}"/> </rich:treeNode> <rich:treeNode type="Course" icon="..." iconLeaf="..." rendered="#{item.courseActive or categoryTreeEditorModel.showAllCoursesInTree}"> <h:outputText rendered="#{item.courseActive}" value="#{item.title}"/> <h:outputText rendered="#{not item.courseActive}" value="#{item.title}" style="color:#{a4jSkin.inactiveTextColor}"/> </rich:treeNode> </rich:tree> the only problem is if some node is not listed in any rich:treeNode it just still shown with title obtained by Object.toString() method insted of being hidden. Does anybody know how to not show some nodes in the Richfases tree according to some condition?

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What are possible/good ways to prototype iPhone applications?

- by Ted Johnson

This is intentionally left broad. If you wanted to show users what iPhone/mobile applications could to for them. The more interactive the better, but it must be quick to build as you can't code up every idea. Let us assume real-time games are out of scope. Throw out ideas or state which approach would be best. Here are some of my ideas, what are yours? Hack a app that loads mostly web or image content, but has hyperlinks to get around in. This would mean static data. Build screens which look great but can only be navigated in a story board type fashion. Load the web version or equivalent on the iPhone and say: now image the buttons and navigation is better. A paper based prototype. Flash or video walk through running on the phone. String existing iPhone apps and web pages together with minimal glue just to convey the idea. Can anyone share prototyping methods for other mobile devices? Ex: The palm prototype was just a block of wood and note pad that was carried around.

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How to get acts on taggable working

- by Schipperius

I am new to ruby on rails (and programming) and this is probably a really stupid question. I am using Rails 3.2 and trying to use acts_as_taggable_on to generate tags on articles and to have those tags show on article index and show pages as a clickable links. I have tags clickable on both the article show and index pages, but the links just go back to the index page and don't sort according to the tag name. I have scoured the Internet and pieced together the code below from various sources, but I am clearly missing something. Any help is greatly appreciated, as I have exhausted my seemingly limited knowledge! Thanks. Here is what I have: class ArticlesController < ApplicationController def tagged @articles = Article.all(:order => 'created_at DESC') @tags = Article.tag_counts_on(:tags) @tagged_articles = Article.tagged_with(params[:tags]) respond_to do |format| format.html # index.html.erb format.json { render :json => @articles } end end def index @article = Article.new @articles = Article.paginate :page => params[:page], :per_page => 3 @tags = Article.tag_counts_on(:tags) respond_to do |format| format.html # index.html.erb format.json { render json: @articles } end end module ArticlesHelper include ActsAsTaggableOn::TagsHelper end class Article < ActiveRecord::Base acts_as_ordered_taggable acts_as_ordered_taggable_on :tags, :location, :about attr_accessible :tag_list scope :by_join_date, order("created_at DESC") end article/index.html.erb <% tag_cloud(@tags, %w(tag1 tag2 tag3 tag4)) do |tag| %> <%= link_to tag.name, articles_path(:id => tag.name) %> <% end %> article/show.html.erb <%= raw @article.tags.map { |tag| link_to tag.name, articles_path(:tag_id => tag) }.join(" | ") %>

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Is there any function in Matlab for changing the form of matrix?

- by niko

Hi, I have to get the unknown matrix by changing the form of known matrix considering the following rules: H = [-P'|I] G = [I|P] where H is known matrix G is unknown matrix which has to be calculated I is identity matrix So for example if we had a matrix H = [1 1 1 1 0 0; 0 0 1 1 0 1; 1 0 0 1 1 0] its form has to be changed to H = [1 1 1 1 0 0; 0 1 1 0 1 0; 1 1 0 0 0 1] so -P' = [1 1 1; 0 1 0; 1 1 0] and in case of binary matrices -P = P therefore G = [1 0 0 1 1 1; 0 1 0 0 1 0; 0 0 1 1 1 0] I know how to solve it on the paper by performing basic row operations but don't know how if there is any function already written in Matlab to calculate G from H or H from G by considering the above rules. I would be very thankful if anyone of you could suggest any method for solving the given problem. Thank you.

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