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  • [C++] Simple inheritance question

    - by xbonez
    I was going over some sample questions for an upcoming test, and this question is totally confusing me. Any help would be appreciated. Consider the following code: class GraduateStudent : public Student { ... }; If the word "public" is omitted, GraduateStudent uses private inheritance, which means which of the following? GraduateStudent objects may not use methods of Student. GraduateStudent does not have access to private objects of Student. No method of GraduateStudent may call a method of Student. Only const methods of GraduateStudent can call methods of Student.

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  • Why is execution-time method resolution faster than compile-time resolution?

    - by Felix
    At school, we about virtual functions in C++, and how they are resolved (or found, or matched, I don't know what the terminology is -- we're not studying in English) at execution time instead of compile time. The teacher also told us that compile-time resolution is much faster than execution-time (and it would make sense for it to be so). However, a quick experiment would suggest otherwise. I've built this small program: #include <iostream> #include <limits.h> using namespace std; class A { public: void f() { // do nothing } }; class B: public A { public: void f() { // do nothing } }; int main() { unsigned int i; A *a = new B; for (i=0; i < UINT_MAX; i++) a->f(); return 0; } Where I made A::f() once normal, once virtual. Here are my results: [felix@the-machine C]$ time ./normal real 0m25.834s user 0m25.742s sys 0m0.000s [felix@the-machine C]$ time ./virtual real 0m24.630s user 0m24.472s sys 0m0.003s [felix@the-machine C]$ time ./normal real 0m25.860s user 0m25.735s sys 0m0.007s [felix@the-machine C]$ time ./virtual real 0m24.514s user 0m24.475s sys 0m0.000s [felix@the-machine C]$ time ./normal real 0m26.022s user 0m25.795s sys 0m0.013s [felix@the-machine C]$ time ./virtual real 0m24.503s user 0m24.468s sys 0m0.000s There seems to be a steady ~1 second difference in favor of the virtual version. Why is this? Relevant or not: dual-core pentium @ 2.80Ghz, no extra applications running between two tests. Archlinux with gcc 4.5.0. Compiling normally, like: $ g++ test.cpp -o normal Also, -Wall doesn't spit out any warnings, either.

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  • Handling Model Inheritance in ASP.NET MVC2 & NHibernate

    - by enth
    I've gotten myself stuck on how to handle inheritance in my model when it comes to my controllers/views. Basic Model: public class Procedure : Entity { public Procedure() { } public int Id { get; set; } public DateTime ProcedureDate { get; set; } public ProcedureType Type { get; set; } } public ProcedureA : Procedure { public double VariableA { get; set; } public int VariableB { get; set; } public int Total { get; set; } } public ProcedureB : Procedure { public int Score { get; set; } } etc... many of different procedures eventually. So, I do things like list all the procedures: public class ProcedureController : Controller { public virtual ActionResult List() { IEnumerable<Procedure> procedures = _repository.GetAll(); return View(procedures); } } but now I'm kinda stuck. Basically, from the list page, I need to link to pages where the specific subclass details can be viewed/edited and I'm not sure what the best strategy is. I thought I could add an action on the ProcedureController that would conjure up the right subclass by dynamically figuring out what repository to use and loading the subclass to pass to the view. I had to store the class in the ProcedureType object. I had to create/implement a non-generic IRepository since I can't dynamically cast to a generic one. public virtual ActionResult Details(int procedureID) { Procedure procedure = _repository.GetById(procedureID, false); string className = procedure.Type.Class; Type type = Type.GetType(className, true); Type repositoryType = typeof (IRepository<>).MakeGenericType(type); var repository = (IRepository)DependencyRegistrar.Resolve(repositoryType); Entity procedure = repository.GetById(procedureID, false); return View(procedure); } I haven't even started sorting out how the view is going to determine which partial to load to display the subclass details. I'm wondering if this is a good approach? This makes determining the URL easy. It makes reusing the Procedure display code easy. Another approach is specific controllers for each subclass. It simplifies the controller code, but also means many simple controllers for the many procedure subclasses. Can work out the shared Procedure details with a partial view. How to get to construct the URL to get to the controller/action in the first place? Time to not think about it. Hopefully someone can show me the light. Thanks in advance.

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  • Handler invocation speed: Objective-C vs virtual functions

    - by Kerido
    I heard that calling a handler (delegate, etc.) in Objective-C can be even faster than calling a virtual function in C++. Is it really correct? If so, how can that be? AFAIK, virtual functions are not that slow to call. At least, this is my understanding of what happens when a virtual function is called: Compute the index of the function pointer location in vtbl. Obtain the pointer to vtbl. Dereference the pointer and obtain the beginning of the array of function pointers. Offset (in pointer scale) the beginning of the array with the index value obtained on step 1. Issue a call instruction. Unfortunately, I don't know Objective-C so it's hard for me to compare performance. But at least, the mechanism of a virtual function call doesn't look that slow, right? How can something other than static function call be faster?

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  • Fluent | Nhibernate multiple inheritance mapping?

    - by Broken Pipe
    I'm trying to map this classes: public interface IBusinessObject { Guid Id { get; set; } } public class Product { public virtual Guid Id { get; set; } public virtual int ProductTypeId { get; set; } } public class ProductWeSell : Product, IBusinessObject { } public class ProductWeDontSell : Product { } Using this Fluent mapping code: public class IBusinessObjectMap : ClassMap<IBusinessObject> { public IBusinessObjectMap() { Id(t => t.Id).GeneratedBy.Guid(); Table("BusinessObject"); } } public class ProductMap : ClassMap<Product> { public ProductMap() { Id(t => t.Id); DiscriminateSubClassesOnColumn("ProductTypeId", "null").Nullable(); } } public class ProductWeSellMap : SubclassMap<ProductWeSell> { public ProductWeSellMap() { DiscriminatorValue(1); KeyColumn("Id"); } } public class ProductWeDontSellMap : SubclassMap<ProductWeDontSell> { public ProductWeDontSellMap() { DiscriminatorValue(2); KeyColumn("Id"); } } But I get {"Duplicate class/entity mapping ProductWeSell"} error. And if we take a look at generated HBM, indeed it's duplicated, but i have no idea how to write this mapping without duplicating it if it's possible at all. Produced hbm: <hibernate-mapping xmlns="urn:nhibernate-mapping-2.2"> <class xmlns="urn:nhibernate-mapping-2.2" name="IBusinessObject" table="BusinessObject"> <joined-subclass name="ProductWeSell" table="ProductWeSell"/> </class> </hibernate-mapping> <hibernate-mapping xmlns="urn:nhibernate-mapping-2.2"> <class xmlns="urn:nhibernate-mapping-2.2" discriminator-value="null" name="Product" table="Product"> <discriminator type="String"> <column name="ProductTypeId" not-null="false" /> </discriminator> <subclass name="ProductWeDontSell" discriminator-value="2" /> <subclass name="ProductWeSell" discriminator-value="1" /> </class> </hibernate-mapping> So far I was unable to figure out how to map this using fluent Nhibernate (i haven't tried mapping this using hmb files). Any help appreciated Fluent or HBM files. The thing I'm trying to solve look identical to this topic: NHibernate inheritance mapping question

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  • Boost Python : How to only expose the constructor of a class with virtual (pure & impure) methods

    - by fallino
    Hello, I'm a newbie with Boost::Python but I tried to search on the web to do so I want to expose a 3rd party library to Python. One of the class of the library (.hpp) is composed of a public constructor with arguments a protected constructor and functions various regular functions various pure virtual functions various non pure virtual functions First, I did not succeed in building it without having errors about this protected constructor. I finally commented it. A first question would be : Is there a way to exclude these protected functions since I don't want to expose them ? (I know it's possible and easy with Py++, but I started without using it) Then I tried to expose all of my functions, beginning with the pure virtual ones (commenting them all except one), which wasn't a success too So I finally decided not to expose these virtual functions (which in fact seems logical...), but, here again, I didn't manage building it with a simple constructor with arguments (without no_init). So my second question is : Is there a way to exclude these virtual functions since I don't want to expose them ? Sorry if it seems trivial but I didn't find anything explicit on the web and I need something rather explicit :). Thanks in advance

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  • Apache/PHP: error_log per Virtual Host?

    - by Michael Stum
    On one Linux Server running Apache and PHP 5, we got multiple Virtual Hosts with separate logfiles and everything. The only thing we cannot seem to separate between virtual hosts is the php error_log. Overriding this setting in the <Location> of the httpd.conf does not seem to do anything. Did I overlook something? Is there a way to have separate php error_logs for each Virtual Host?

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  • Using interface classes and non-virtual interface idiom in C++

    - by andreas buykx
    Hi all, In C++ an interface can be implemented by a class with all its methods pure virtual: class IFoo { public: virtual void method() = 0; }; Now I want to implement this interface by a hierarchy of classes: class FooBase : public IFoo // implement interface IFoo { public: void method(); // calls methodImpl; private: virtual void methodImpl(); }; For the class hierarchy I would like to use the non-virtual interface (NVI) idiom, to deny derived classes the possibility of overriding the common behavior implemented in FooBase::method(), but it seems that all derived classes have the opportunity to override the FooBase::method() because it is declared in the interface class. Is my observation correct? And if so are there other options to both use interface classes and the NVI idiom?

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  • fcgio.cpp: In destructor 'virtual fcgi_streambuf::~fcgi_streambuf()':

    - by skyeagle
    I am attempting to build fastcgi on a Linux Ubuntu 10.x machine. I run the following commands: ./configure make and I get the following error: fcgio.cpp: In destructor 'virtual fcgi_streambuf::~fcgi_streambuf()': fcgio.cpp:50: error: 'EOF' was not declared in this scope fcgio.cpp: In member function 'virtual int fcgi_streambuf::overflow(int)': fcgio.cpp:70: error: 'EOF' was not declared in this scope fcgio.cpp:75: error: 'EOF' was not declared in this scope fcgio.cpp: In member function 'virtual int fcgi_streambuf::sync()': fcgio.cpp:86: error: 'EOF' was not declared in this scope fcgio.cpp:87: error: 'EOF' was not declared in this scope fcgio.cpp: In member function 'virtual int fcgi_streambuf::underflow()': fcgio.cpp:107: error: 'EOF' was not declared in this scope make[2]: *** [fcgio.lo] Error 1 make[2]: Leaving directory `/somepath/fcgi-2.4.0/libfcgi' make[1]: *** [all-recursive] Error 1 make[1]: Leaving directory `/somepath/fcgi-2.4.0' make: *** [all] Error 2 I notice that others have had the same problem and have asked this question in various fora etc - however, I have not as yet, seen an answer to this question/problem. Has anyone ever managed to build fastcgi on Linux? How do I fix this problem?

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  • Creating an HTTP-Redirected Virtual Directopry in IIS 6.0 without specifying physical path & WMI/ADS

    - by Steve Johnson
    My question is : Is it possible to create a working IIS 6.0 Virtual Directory with providing Physical Path of the Virtual Directory.? I know that manually, it is not possible via IIS but programmatically such a virtual directory can be created. If an HTTPRedirect is set on that virtual directory but the site physical path is not specified, then will it work? Simply stated, how to create an HTTp-redirected Virtual Directory , directly without specifying any physical path to a folder or network share. Here is my code. Try If Directory.Exists(HomeDirectory) = False And Path.StartsWith("http://") = False Then Directory.CreateDirectory(HomeDirectory) End If Dim website As DirectoryEntry website = New DirectoryEntry("IIS://" & IISServer & "/W3SVC/" & WebsiteId & "/Root") Dim NewVDir As DirectoryEntry = website.Children.Add(VDirName, "IIsWebVirtualDir") If Path.StartsWith("http://") = False Then NewVDir.Properties("Path")(0) = Path NewVDir.Properties("HttpRedirect").Clear() Else NewVDir.Properties("HttpRedirect")(0) = Path End If If ((Perm And Permission.Read) = Permission.Read) Then NewVDir.Properties("AccessRead")(0) = True End If If ((Perm And Permission.Write) = Permission.Write) Then NewVDir.Properties("AccessWrite")(0) = True End If If ((Perm And Permission.DirBrowse) = Permission.DirBrowse) Then NewVDir.Properties("EnableDirBrowsing")(0) = True End If If ((Perm And Permission.CreatetApplication) = Permission.CreatetApplication) Then NewVDir.Invoke("AppCreate", True) End If If ((Perm And Permission.ScriptOnly) = Permission.ScriptOnly) Then NewVDir.Properties("AccessScript")(0) = True End If If ((Perm And Permission.ScriptNExecute) = Permission.ScriptNExecute) Then NewVDir.Properties("AccessExecute")(0) = True End If NewVDir.Properties("AuthAnonymous")(0) = True NewVDir.Properties("AuthNTLM")(0) = True NewVDir.Properties("AnonymousUserName")(0) = AnonUserName NewVDir.Properties("AnonymousUserPass")(0) = AnonPassword NewVDir.Properties("AppFriendlyName")(0) = AppFriendlyName NewVDir.CommitChanges() website.CommitChanges() NewVDir.Close() website.Close() Success = True Catch Err As Exception Throw New Exception("My Custom Exception Here: " & Err.Message) End Try

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  • Virtual destructor - How does it work?

    - by Prabhu
    Hello All, Few hours back I was fiddling with a Memory Leak issue and it turned out that I really got some basic stuff about virtual destructor wrong!! Let me put explain my class design. class Base { virtual push_elements()<br>{}<br> }; class Derived:public Base { vector<int> x; public: void push_elements(){ for(int i=0;i <5;i++) x.push_back(i); } }; void main() { Base* b = new Derived(); b->push_elements(); delete b; } The bounds checker tool reported a memory leak in the derived class vector. And I figured out that the destructor is not virtual and the derived class destructor is not called.And it surprisingly got fixed when I made the destructor virtual. But my question is "isn't the vector deallocated automatically even if the derived class destructor is not called"? Is that a quirk in BoundsChecker tool or is my understanding of virtual destructor is wrong:)

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  • How do virtual destructors work?

    - by Prabhu
    Few hours back I was fiddling with a Memory Leak issue and it turned out that I really got some basic stuff about virtual destructors wrong! Let me put explain my class design. class Base { virtual push_elements() {} }; class Derived:public Base { vector<int> x; public: void push_elements(){ for(int i=0;i <5;i++) x.push_back(i); } }; void main() { Base* b = new Derived(); b->push_elements(); delete b; } The bounds checker tool reported a memory leak in the derived class vector. And I figured out that the destructor is not virtual and the derived class destructor is not called. And it surprisingly got fixed when I made the destructor virtual. Isn't the vector deallocated automatically even if the derived class destructor is not called? Is that a quirk in BoundsChecker tool or is my understanding of virtual destructor wrong?

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  • NHibernate requires events to be virtual?

    - by Jimit
    I'm attempting to map an entity hierarchy using NHibernate almost all of which have events. When attempting to build a session factory however, I get error messages similar to the following: Core.Domain.Entities.Delivery: method remove_Scheduled should be virtual Delivery is an entity in my domain model with an event called Scheduled. Since events cannot be declared virtual I'm at a loss as to how to proceed here. Why would NHibernate need events to be virtual?

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  • Debug website on host from virtual machine

    - by Luchaguate
    I have a Windows 7 machine hosting a Windows 7 virtual machine. I am developing a web application using visual studio 2010 on my host machine. I want to run the application in debug mode and access my localhost server from a browser on the virtual machine. (The purpose of this is to be able to debug an application that uses Windows Authentication using different users without having to log off and on for different users on my host machine...) I am using a bridged connection for the virtual machine. I googled how to solve this problem and most of the threads that I found said that if I was using a bridged connection, I could access the server on the host machine by just entering the IP address of my host machine into the url in the browser of the virtual machine. I have tried some different urls using the IP but none of them have worked. As an example, suppose I run my web application in visual studio on my host machine and its url is http://localhost:62789/MyPage.aspx Assume also that I ran ipconfig in CommandPrompt on my host machine and found out that the IP address for my host machine is xxx.xxx.xxx.x. What url should I enter on the virtual machine to access my web application? Thanks in advance.

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  • virtual serial port on Arch linux

    - by Milan
    Hello, I am using Arch linux and I need to create virtual serial port on it. I tried everything but it seems doesnt work. All I want is to connect that virtual port to another virtual port over TCP and after that to use it in my python application to communicate with python application to other side. Is that posible? Please help me. Thanx

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  • Handling Model Inheritance in ASP.NET MVC2

    - by enth
    I've gotten myself stuck on how to handle inheritance in my model when it comes to my controllers/views. Basic Model: public class Procedure : Entity { public Procedure() { } public int Id { get; set; } public DateTime ProcedureDate { get; set; } public ProcedureType Type { get; set; } } public ProcedureA : Procedure { public double VariableA { get; set; } public int VariableB { get; set; } public int Total { get; set; } } public ProcedureB : Procedure { public int Score { get; set; } } etc... many of different procedures eventually. So, I do things like list all the procedures: public class ProcedureController : Controller { public virtual ActionResult List() { IEnumerable<Procedure> procedures = _repository.GetAll(); return View(procedures); } } but now I'm kinda stuck. Basically, from the list page, I need to link to pages where the specific subclass details can be viewed/edited and I'm not sure what the best strategy is. I thought I could add an action on the ProcedureController that would conjure up the right subclass by dynamically figuring out what repository to use and loading the subclass to pass to the view. I had to store the class in the ProcedureType object. I had to create/implement a non-generic IRepository since I can't dynamically cast to a generic one. public virtual ActionResult Details(int procedureID) { Procedure procedure = _repository.GetById(procedureID, false); string className = procedure.Type.Class; Type type = Type.GetType(className, true); Type repositoryType = typeof (IRepository<>).MakeGenericType(type); var repository = (IRepository)DependencyRegistrar.Resolve(repositoryType); Entity procedure = repository.GetById(procedureID, false); return View(procedure); } I haven't even started sorting out how the view is going to determine which partial to load to display the subclass details. I'm wondering if this is a good approach? This makes determining the URL easy. It makes reusing the Procedure display code easy. Another approach is specific controllers for each subclass. It simplifies the controller code, but also means many simple controllers for the many procedure subclasses. Can work out the shared Procedure details with a partial view. How to get to construct the URL to get to the controller/action in the first place? Time to not think about it. Hopefully someone can show me the light. Thanks in advance.

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  • C++ - Error: expected unqualified-id before ‘using’

    - by Francisco P.
    Hello, everyone. I am having some trouble on a project I'm working on. Here's the header file for the calor class: #ifndef _CALOR_ #define _CALOR_ #include "gradiente.h" using namespace std; class Calor : public Gradiente { public: Calor(); Calor(int a); ~Calor(); int getTemp(); int getMinTemp(); void setTemp(int a); void setMinTemp(int a); void mostraSensor(); }; #endif When I try to compile it: calor.h|6|error: expected unqualified-id before ‘using’| Why does this happen? I've been searching online and learned this error occurs mostly due to corrupted included files. Makes no sense to me, though. This class inherits from gradiente: #ifndef _GRADIENTE_ #define _GRADIENTE_ #include "sensor.h" using namespace std; class Gradiente : public Sensor { protected: int vActual, vMin; public: Gradiente(); ~Gradiente(); } #endif Which in turn inherits from sensor #ifndef _SENSOR_ #define _SENSOR_ #include <iostream> #include <fstream> #include <string> #include "definicoes.h" using namespace std; class Sensor { protected: int tipo; int IDsensor; bool estadoAlerta; bool estadoActivo; static int numSensores; public: Sensor(/*PARAMETROS*/); Sensor(ifstream &); ~Sensor(); int getIDsensor(); bool getEstadoAlerta(); bool getEstadoActivo(); void setEstadoAlerta(int a); void setEstadoActivo(int a); virtual void guardaSensor(ofstream &); virtual void mostraSensor(); // FUNÇÃO COMUM /* virtual int funcaoComum() = 0; virtual int funcaoComum(){return 0;};*/ }; #endif For completeness' sake, here's definicoes.h #ifndef _DEFINICOES_ #define _DEFINICOES_ const unsigned int SENSOR_MOVIMENTO = 0; const unsigned int SENSOR_SOM = 1; const unsigned int SENSOR_PRESSAO = 2; const unsigned int SENSOR_CALOR = 3; const unsigned int SENSOR_CONTACTO = 4; const unsigned int MIN_MOVIMENTO = 10; const unsigned int MIN_SOM = 10; const unsigned int MIN_PRESSAO = 10; const unsigned int MIN_CALOR = 35; #endif Any help'd be much appreciated. Thank you for your time. Thanks for your time!

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  • Can YAML have inheritance?

    - by Jason
    This question involves a lot of symfony but it should be easy enough for someone to follow who only knows YAML and not symfony. My symfony models come from a three-step process: First, I create the tables in MySQL. Second, I run a symfony command (symfony doctrine:build-schema) to convert my table structure into a YAML file. Third, I run another symfony command (symfony doctrine:build-model) to convert the YAML file into PHP code. Here's the problem: there are some tables in the database that I don't want to end up in my symfony code. For example, let's say I have two tables: one called my_table and another called wordpress. The YAML file I end up with might look like this: MyTable: connection: doctrine tableName: my_table Wordpress: connection: doctrine tableName: wordpress That's great except the wordpress table has nothing to do with my symfony models. The result is that every single time I make a change to my database and generate this YAML file, I have to manually remove wordpress. It's annoying! I'd like to be able to create a file called baseConfig.php or something that looks like this: $config = array( 'MyTable' => array( 'connection' => 'doctrine', 'tableName' => 'my_table', ), 'Wordpress' => array( 'connection' => 'doctrine', 'tableName' => 'wordpress', ), ); And then I could have a separate file called config.php or something where I could make modifications to the base config: unset($config['Wordpress']); So my question is: is there any way to convert YAML into executable PHP code (as opposed to load YAML INTO PHP code like what sfYaml::load() does) to achieve this sort of thing? Or is there maybe some other way to achieve YAML inheritance? Thanks, Jason

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  • Inheritance using prototype / "new"

    - by mikkol
    Hi I'm new in Javascript OO and want to know more about about inheritance. Hope you can provide some advice! I see this great post: How to "properly" create a custom object in JavaScript? which talks about how a class is inherited as I see in other websites, ex.: function man(x) { this.x = x; this.y = 2; } man.prototype.name = "man"; man.prototype.two = function() { this.y = "two"; } function shawn() { man.apply(this, arguments); }; shawn.prototype = new man; The above post claims that in order not to call "man"'s constructor while inheriting, one can use a helper like this instead: function subclassOf(base) { _subclassOf.prototype= base.prototype; return new _subclassOf(); } function _subclassOf() {}; shawn.prototype = subclassOf(man); While I understand its intention, I don't see why we can't call shawn.prototype = man.prototype; I see it works exactly the same. Or is there something I'm missing? Thanks in advance!

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  • System.AccessViolationException when using TPT inheritance in Entity Framework CTP5

    - by Ben
    Hi, I'm using TPT inheritance in EF CTP5 with SQL CE 4. I have an abstract base class "Widget" with common properties like "Title". I can successfully save concrete Widget implementations e.g. "TwitterWidget". However, I have a problem retrieving all widgets (or rather ALL widget implementations). My repository exposes the following: public IQueryable<Widget> GetAll(); This effectively returns the IDbSet from the DbContext. The following queries work fine: repo.GetAll().ToList(); repo.GetAll().Where(w => w.Title == "Test").ToList(); repo.GetAll().SingleOrDefault(w => w.Title == "Test"); repo.GetAll().Where(w => w.Title == "Test").OrderBy(x => x.Title).ToList(); However, if I write the following query: repo.GetAll().OrderBy(w => w.Title); I get the following error: Test 'PlanetCloud.Portfolio.Tests.Data.PersistenceTestFixture.Can_get_widgets' failed: System.AccessViolationException : Attempted to read or write protected memory. This is often an indication that other memory is corrupt. at System.Data.SqlServerCe.NativeMethodsHelper.GetValues(IntPtr pSeCursor, Int32 seGetColumn, IntPtr prgBinding, Int32 cDbBinding, IntPtr pData, IntPtr pError) at System.Data.SqlServerCe.NativeMethods.GetValues(IntPtr pSeCursor, Int32 seGetColumn, IntPtr prgBinding, Int32 cDbBinding, IntPtr pData, IntPtr pError) at System.Data.SqlServerCe.SqlCeDataReader.FetchValue(Int32 index) at System.Data.SqlServerCe.SqlCeDataReader.IsDBNull(Int32 ordinal) at lambda_method(Closure , Shaper ) at System.Data.Common.Internal.Materialization.Shaper.HandleEntityAppendOnly[TEntity](Func`2 constructEntityDelegate, EntityKey entityKey, EntitySet entitySet) at lambda_method(Closure , Shaper ) at System.Data.Common.Internal.Materialization.Coordinator`1.ReadNextElement(Shaper shaper) at System.Data.Common.Internal.Materialization.Shaper`1.SimpleEnumerator.MoveNext() at System.Collections.Generic.List`1..ctor(IEnumerable`1 collection) at System.Linq.Enumerable.ToList[TSource](IEnumerable`1 source) However, I can execute the following query without problems: var widgets = repo.GetAll().OfType<Widget>().OrderBy(w => w.Title).ToList(); So if I specify the type as the base class prior to my orderby clause it works. The question is why?

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  • Duplicate column name by JPA with @ElementCollection and @Inheritance

    - by gerry
    I've created the following scenario: @javax.persistence.Entity @Inheritance(strategy = InheritanceType.TABLE_PER_CLASS) public class MyEntity implements Serializable{ @Id @GeneratedValue protected Long id; ... @ElementCollection @CollectionTable(name="ENTITY_PARAMS") @MapKeyColumn (name = "ENTITY_KEY") @Column(name = "ENTITY_VALUE") protected Map<String, String> parameters; ... } As well as: @javax.persistence.Entity public class Sensor extends MyEntity{ @Id @GeneratedValue protected Long id; ... // so here "protected Map<String, String> parameters;" is inherited !!!! ... } So running this example, no tables are created and i get the following message: WARNUNG: Got SQLException executing statement "CREATE TABLE ENTITY_PARAMS (Entity_ID BIGINT NOT NULL, ENTITY_VALUE VARCHAR(255), ENTITY_KEY VARCHAR(255), Sensor_ID BIGINT NOT NULL, ENTITY_VALUE VARCHAR(255))": com.mysql.jdbc.exceptions.jdbc4.MySQLSyntaxErrorException: Duplicate column name 'ENTITY_VALUE' I also tried overriding the attributes on the Sensor class... @AttributeOverrides({ @AttributeOverride(name = "ENTITY_KEY", column = @Column(name = "SENSOR_KEY")), @AttributeOverride(name = "ENTITY_VALUE", column = @Column(name = "SENSOR_VALUE")) }) ... but the same error. Can anybody help me?

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  • C++ struct, public data members and inheritance

    - by Marius
    Is it ok to have public data members in a C++ class/struct in certain particular situations? How would that go along with inheritance? I've read opinions on the matter, some stated already here http://stackoverflow.com/questions/952907/practices-on-when-to-implement-accessors-on-private-member-variables-rather-than http://stackoverflow.com/questions/670958/accessors-vs-public-members or in books/articles (Stroustrup, Meyers) but I'm still a little bit in the shade. I have some configuration blocks that I read from a file (integers, bools, floats) and I need to place them into a structure for later use. I don't want to expose these externally just use them inside another class (I actually do want to pass these config parameters to another class but don't want to expose them through a public API). The fact is that I have many such config parameters (15 or so) and writing getters and setters seems an unnecessary overhead. Also I have more than one configuration block and these are sharing some of the parameters. Making a struct with all the data members public and then subclassing does not feel right. What's the best way to tackle that situation? Does making a big struct to cover all parameters provide an acceptable compromise (I would have to leave some of these set to their default values for blocks that do not use them)?

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