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• Inheritance concept java..help

  - by max

  Hi everyone. I'd be very grateful if someone could help me to understand the inheritance concept in Java. Is the following code an example of that? I mean the class WavPanel is actually a subclass of JPanel which acts as a superclass. Is that correct? If so it means that "what JPanel has, also WavPanel but it is more specific since through its methods you can do something else". Am I wrong? thank you. Max import javax.swing.JPanel; class WavPanel extends JPanel { List<Byte> audioBytes; List<Line2D.Double> lines; public WavPanel() { super(); setBackground(Color.black); resetWaveform(); } public void resetWaveform() { audioBytes = new ArrayList<Byte>(); lines = new ArrayList<Line2D.Double>(); repaint(); } }

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• Inheritance not working

  - by Pendo826

  Hey im just practicing inheritance and i encountered a problem. Im getting an error in my car class(sub-class) that the variables in Vehicle(parent) are not visible. i didnt do anything to change this and i dont even know how to make it invisible. Can anyone help me with this. public class Vehicle { private String make, model, colour; private int registrationNumber; public Vehicle() { this.make = ""; this.model = ""; this.colour = ""; this.registrationNumber = 0; } public Vehicle(String make, String model, String colour, int registrationNumber) { this.make = make; this.model = model; this.colour = colour; this.registrationNumber = registrationNumber; } public String getMake() { return make; } public void setMake(String make) { this.make = make; } public String getModel() { return model; } public void setModel(String model) { this.model = model; } public String getColour() { return colour; } public void setColour(String colour) { this.colour = colour; } public int getRegistrationNumber() { return registrationNumber; } public void setRegistrationNumber(int registrationNumber) { this.registrationNumber = registrationNumber; } public String toString() { return "Vehicle [make=" + make + ", model=" + model + ", colour=" + colour + ", registrationNumber=" + registrationNumber + "]"; } } public Car() { super(); this.doors = 0; this.shape = ""; } public Car(int doors, String shape, String make, String model, String colour, int registrationNumber) { super(); this.doors = doors; this.shape = shape; this.make = make;//Error this.model = model;//Error this.colour = colour;//Error this.registrationNumber = registrationNumber;//Error } The error message: Description Resource Path Location Type The field Vehicle.make is not visible Car.java /VehicleApp/src line 19 Java Problem The field Vehicle.model is not visible Car.java /VehicleApp/src line 20 Java Problem The field Vehicle.colour is not visible Car.java /VehicleApp/src line 21 Java Problem The field Vehicle.registrationNumber is not visible Car.java /VehicleApp/src line 22 Java Problem

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• How to delete child table records during the update of parent table using Hibernate

  - by Harsha

  I have a Parent Table A and child tables B,C with many to one relations. Lets say I have data like, for primary key 1 in parent table A I have 3 rows in child table B and 4 rows in child table C. Now if I want to delete the rows of the child table during an update of the parent table(that means Now, I want to update the table only with one row in each child tables and delete the other rows in them) then how to handle this scenario in hibernate?

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• Resolving ambiguous this pointer in C++

  - by Paul Tevis

  I'm trying to derive a new class from an old one. The base class declaration looks like this: class Driver : public Plugin, public CmdObject { protected: Driver(); public: static Driver* GetInstance(); virtual Engine& GetEngine(); public: // Plugin methods... virtual bool InitPlugin (Mgr* pMgr); virtual bool Open(); virtual bool Close(); // CmdObject virtual bool ExecObjCmd(uint16 cmdID, uint16 nbParams, CommandParam *pParams, CmdChannelError& error); Mgr *m_pMgr; protected: Services *m_pServices; Engine m_Engine; }; Its constructor looks like this: Driver::Driver() : YCmdObject("Driver", (CmdObjectType)100, true), m_Engine("MyEngine") { Services *m_pServices = NULL; Mgr *m_pMgr = NULL; } So when I created my derived class, I first tried to simply inherit from the base class: class NewDriver : public Driver and copy the constructor: NewDriver::NewDriver() : CmdObject("NewDriver", (EYCmdObjectType)100, true), m_Engine("MyNewEngine") { Services *m_pServices = NULL; Mgr *m_pMgr = NULL; } The compiler (VisualDSP++ 5.0 from Analog Devices) didn't like this: ".\NewDriver.cpp", line 10: cc0293: error: indirect nonvirtual base class is not allowed CmdObject("NewDriver", (EYCmdObjectType)100, true), That made sense, so I decided to directly inherit from Plugin and CmdObject. To avoid multiple inheritance ambiguity problems (so I thought), I used virtual inheritance: class NewDriver : public Driver, public virtual Plugin, public virtual CmdObject But then, in the implementation of a virtual method in NewDriver, I tried to call the Mgr::RegisterPlugin method that takes a Plugin*, and I got this: ".\NewDriver.cpp", line 89: cc0286: error: base class "Plugin" is ambiguous if (!m_pMgr->RegisterPlugin(this)) How is the this pointer ambiguous, and how do I resolve it? Thanks, --Paul

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• Django conditional template inheritance

  - by Ed

  I have template that displays object elements with hyperlinks to other parts of my site. I have another function that displays past versions of the same object. In this display, I don't want the hyperlinks. I'm under the assumption that I can't dynamically switch off the hyperlinks, so I've included both versions in the same template. I use an if statement to either display the hyperlinked version or the plain text version. I prefer to keep them in the same template because if I need to change the format of one, it will be easy to apply it to the other right there. The template extends framework.html. Framework has a breadcrumb system and it extends base.html. Base has a simple top menu system. So here's my dilemma. When viewing the standard hyperlink data, I want to see the top menu and the breadcrumbs. But when viewing the past version plain text data, I only want the data, no menu, no breadcrumbs. I'm unsure if this is possible given my current design. I tried having framework inherit the primary template so that I could choose to call either framework (and display the breadcrumbs), or the template itself, thus skipping the breadcrumbs, but I want framework.html available for other templates as well. If framework.html extends a specific template, I lose the ability to display it in other templates. I tried writing an if statement that would display a the top_menu block and the nav_menu block from base.html and framework.html respectively. This would overwrite their blocks and allow me to turn off those elements conditional on the if. Unfortunately, it doesn't appear to be conditional; if the block elements are in the template at all, surrounded by an if or not, I lose the menus. I thought about using {% include %} to pick up the breadcrumbs and a split out top menu. In that case though, I'll have to include it all the time. No more inheritance. Is this the best option given my requirement?

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• Can simple javascript inheritance be simplified even further?

  - by Will

  John Resig (of jQuery fame) provides a concise and elegant way to allow simple JavaScript inheritance. It was so short and sweet, in fact, that it inspired me to try and simplify it even further (see code below). I've modified his original function such that it still passes all his tests and has the potential advantage of: readability (50% less code) simplicity (you don't have to be a ninja to understand it) performance (no extra wrappers around super/base method calls) consistency with C#'s base keyword Because this seems almost too good to be true, I want to make sure my logic doesn't have any fundamental flaws/holes/bugs, or if anyone has additional suggestions to improve or refute the code (perhaps even John Resig could chime in here!). Does anyone see anything wrong with my approach (below) vs. John Resig's original approach? if (!window.Class) { window.Class = function() {}; window.Class.extend = function(members) { var prototype = new this(); for (var i in members) prototype[i] = members[i]; prototype.base = this.prototype; function object() { if (object.caller == null && this.initialize) this.initialize.apply(this, arguments); } object.constructor = object; object.prototype = prototype; object.extend = arguments.callee; return object; }; } And the tests (below) are nearly identical to the original ones except for the syntax around base/super method calls (for the reason enumerated above): var Person = Class.extend( { initialize: function(isDancing) { this.dancing = isDancing; }, dance: function() { return this.dancing; } }); var Ninja = Person.extend( { initialize: function() { this.base.initialize(false); }, dance: function() { return this.base.dance(); }, swingSword: function() { return true; } }); var p = new Person(true); alert("true? " + p.dance()); // => true var n = new Ninja(); alert("false? " + n.dance()); // => false alert("true? " + n.swingSword()); // => true alert("true? " + (p instanceof Person && p instanceof Class && n instanceof Ninja && n instanceof Person && n instanceof Class));

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• Silverlight with MVVM Inheritance: ModelView and View matching the Model

  - by moonground.de

  Hello Stackoverflowers! :) Today I have a special question on Silverlight (4 RC) MVVM and inheritance concepts and looking for a best practice solution... I think that i understand the basic idea and concepts behind MVVM. My Model doesn't know anything about the ViewModel as the ViewModel itself doesn't know about the View. The ViewModel knows the Model and the Views know the ViewModels. Imagine the following basic (example) scenario (I'm trying to keep anything short and simple): My Model contains a ProductBase class with a few basic properties, a SimpleProduct : ProductBase adding a few more Properties and ExtendedProduct : ProductBase adding another properties. According to this Model I have several ViewModels, most essential SimpleProductViewModel : ViewModelBase and ExtendedProductViewModel : ViewModelBase. Last but not least, according Views SimpleProductView and ExtendedProductView. In future, I might add many product types (and matching Views + VMs). 1. How do i know which ViewModel to create when receiving a Model collection? After calling my data provider method, it will finally end up having a List<ProductBase>. It containts, for example, one SimpleProduct and two ExtendedProducts. How can I transform the results to an ObservableCollection<ViewModelBase> having the proper ViewModel types (one SimpleProductViewModel and two ExtendedProductViewModels) in it? I might check for Model type and construct the ViewModel accordingly, i.e. foreach(ProductBase currentProductBase in resultList) if (currentProductBase is SimpleProduct) viewModels.Add( new SimpleProductViewModel((SimpleProduct)currentProductBase)); else if (currentProductBase is ExtendedProduct) viewModels.Add( new ExtendedProductViewModels((ExtendedProduct)currentProductBase)); ... } ...but I consider this very bad practice as this code doesn't follow the object oriented design. The other way round, providing abstract Factory methods would reduce the code to: foreach(ProductBase currentProductBase in resultList) viewModels.Add(currentProductBase.CreateViewModel()) and would be perfectly extensible but since the Model doesn't know the ViewModels, that's not possible. I might bring interfaces into game here, but I haven't seen such approach proven yet. 2. How do i know which View to display when selecting a ViewModel? This is pretty the same problem, but on a higher level. Ended up finally having the desired ObservableCollection<ViewModelBase> collection would require the main view to choose a matching View for the ViewModel. In WPF, there is a DataTemplate concept which can supply a View upon a defined DataType. Unfortunately, this doesn't work in Silverlight and the only replacement I've found was the ResourceSelector of the SLExtensions toolkit which is buggy and not satisfying. Beside that, all problems from Question 1 apply as well. Do you have some hints or even a solution for the problems I describe, which you hopefully can understand from my explanation? Thank you in advance! Thomas

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• Hierarchy inheritance

  - by reito

  I had faced the problem. In my C++ hierarchy tree I have two branches for entities of difference nature, but same behavior - same interface. I created such hierarchy trees (first in image below). And now I want to work with Item or Base classes independetly of their nature (first or second). Then I create one abstract branch for this use. My mind build (second in image below). But it not working. Working scheme seems (third in image below). It's bad logic, I think... Do anybody have some ideas about such hierarchy inheritance? How make it more logical? More simple for understanding? Image Sorry for my english - russian internet didn't help:) Update: You ask me to be more explicit, and I will be. In my project (plugins for Adobe Framemaker) I need to work with dialogs and GUI controls. In some places I working with WinAPI controls, and some other places with FDK (internal Framemaker) controls, but I want to work throw same interface. I can't use one base class and inherite others from it, because all needed controls - is a hierarchy tree (not one class). So I have one hierarchy tree for WinAPI controls, one for FDK and one abstract tree to use anyone control. For example, there is an Edit control (WinEdit and FdkEdit realization), a Button control (WinButton and FdkButton realization) and base entity - Control (WinControl and FdkControl realization). For now I can link my classes in realization trees (Win and Fdk) with inheritence between each of them (WinControl is base class for WinButton and WinEdit; FdkControl is base class for FdkButton and FdkEdit). And I can link to abstract classes (Control is base class for WinControl and FdkControl; Edit is base class for WinEdit and FdkEdit; Button is base class for WinButton and FdkButton). But I can't link my abstract tree - compiler swears. In fact I have two hierarchy trees, that I want to inherite from another one. Update: I have done this quest! :) I used the virtual inheritence and get such scheme (http://img12.imageshack.us/img12/7782/99614779.png). Abstract tree has only absolute abstract methods. All inheritence in abstract tree are virtual. Link from realization tree to abstract are virtual. On image shown only one realization tree for simplicity. Thanks for help!

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• Conceptual inheritance implementation

  - by TheSENDER

  Hi there, I'm writing a spatial data structure and I have a doubt about what's the best NODE implementation. According to my design I have an abstract node entity and three classes which inherit from it: EMPTYNODE, FULLNODE, INTERNALNODE. The first one has no particular data. The second one has 1 reference to a generic element. The third one has 2 references to other nodes. I have found several ways to implement this situation (that I have already coded) but I can't decide what's the best. The first solution that I have found is to use a single class Node that potentially performs all the operation in this way: private static class Node { private Elem elem = null; private Node left = null, right = null; public Elem getElem() { assert isFull(); return elem; } public boolean isEmpty() { return elem == null && left == null; } public boolean isFull() { return elem != null; } public boolean isInternal() { return elem == null && left != null; } } The second solution is to write an explicit division by classes where every class offers only its methods. Obviously in this way we are obliged to perform several casts to the node objects. private static abstract class Node { public abstract boolean isEmpty(); public abstract boolean isFull(); public abstract boolean isInternal(); } private static class FullNode extends Node{ private ITriangle elem; @Override public boolean isEmpty() { return false; } @Override public final boolean isFull() { return true; } @Override public final boolean isInternal() { return false; } public Elem getElem() { return elem; } } The third one solution is to use the inheritance allowing every classes to offer all the methods, but the object type should by check by "isEmpty()" and similar methods. In case of wrong call we'll throw an exception. private static abstract class Node { public abstract boolean isEmpty(); public abstract boolean isFull(); public abstract boolean isInternal(); public abstract Elem getElem(); } private static class Empty extends Node{ @Override public boolean isEmpty() { return true; } @Override public final boolean isFull() { return false; } @Override public final boolean isInternal() { return false; } @Override public Elem getElem() { throw new AssertionError(); } } What do you think about these three solutions? Which one would you use? Any other ideas? Thanks for your help. Every idea will be appreciated.

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• Does this inheritance design belong in the database?

  - by Berryl

  === CLARIFICATION ==== The 'answers' older than March are not answers to the question in this post! Hello In my domain I need to track allocations of time spent on Activities by resources. There are two general types of Activities of interest - ones base on a Project and ones based on an Account. The notion of Project and Account have other features totally unrelated to both each other and capturing allocations of time, and each is modeled as a table in the database. For a given Allocation of time however, it makes sense to not care whether the allocation was made to either a Project or an Account, so an ActivityBase class abstracts away the difference. An ActivityBase is either a ProjectActivity or an AccountingActivity (object model is below). Back to the database though, there is no direct value in having tables for ProjectActivity and AccountingActivity. BUT the Allocation table needs to store something in the column for it's ActivityBase. Should that something be the Id of the Project / Account or a reference to tables for ProjectActivity / Accounting? How would the mapping look? === Current Db Mapping (Fluent) ==== Below is how the mapping currently looks: public class ActivityBaseMap : IAutoMappingOverride<ActivityBase> { public void Override(AutoMapping<ActivityBase> mapping) { //mapping.IgnoreProperty(x => x.BusinessId); //mapping.IgnoreProperty(x => x.Description); //mapping.IgnoreProperty(x => x.TotalTime); mapping.IgnoreProperty(x => x.UniqueId); } } public class AccountingActivityMap : SubclassMap<AccountingActivity> { public void Override(AutoMapping<AccountingActivity> mapping) { mapping.References(x => x.Account); } } public class ProjectActivityMap : SubclassMap<ProjectActivity> { public void Override(AutoMapping<ProjectActivity> mapping) { mapping.References(x => x.Project); } } There are two odd smells here. Firstly, the inheritance chain adds nothing in the way of properties - it simply adapts Projects and Accounts into a common interface so that either can be used in an Allocation. Secondly, the properties in the ActivityBase interface are redundant to keep in the db, since that information is available in Projects and Accounts. Cheers, Berryl ==== Domain ===== public class Allocation : Entity { ... public virtual ActivityBase Activity { get; private set; } ... } public abstract class ActivityBase : Entity { public virtual string BusinessId { get; protected set; } public virtual string Description { get; protected set; } public virtual ICollection<Allocation> Allocations { get { return _allocations.Values; } } public virtual TimeQuantity TotalTime { get { return TimeQuantity.Hours(Allocations.Sum(x => x.TimeSpent.Amount)); } } } public class ProjectActivity : ActivityBase { public virtual Project Project { get; private set; } public ProjectActivity(Project project) { BusinessId = project.Code.ToString(); Description = project.Description; Project = project; } }

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• Rails single table inheritance/subclass find condition in parent

  - by slythic

  Hi all, I have a table called Users (class User < ActiveRecord::Base) and a subclass/STI of it for Clients (class Client < User). Client "filtering" works as expected, in other words Client.find(:all) works to find all the clients. However, for users I need to filter the result to only find users that are NOT clients (where type is null or blank). I've tried the following in my index controller but no matter what I put for the type it returns all users regardless of type. User.find(:all, :conditions => { :type => nil }, :order => 'name') Any clue on how to get this condition to work? Thanks!

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• C#: Inheritance, Overriding, and Hiding

  - by Rosarch

  I'm having difficulty with an architectural decision for my C# XNA game. The basic entity in the world, such as a tree, zombie, or the player, is represented as a GameObject. Each GameObject is composed of at least a GameObjectController, GameObjectModel, and GameObjectView. These three are enough for simple entities, like inanimate trees or rocks. However, as I try to keep the functionality as factored out as possible, the inheritance begins to feel unwieldy. Syntactically, I'm not even sure how best to accomplish my goals. Here is the GameObjectController: public class GameObjectController { protected GameObjectModel model; protected GameObjectView view; public GameObjectController(GameObjectManager gameObjectManager) { this.gameObjectManager = gameObjectManager; model = new GameObjectModel(this); view = new GameObjectView(this); } public GameObjectManager GameObjectManager { get { return gameObjectManager; } } public virtual GameObjectView View { get { return view; } } public virtual GameObjectModel Model { get { return model; } } public virtual void Update(long tick) { } } I want to specify that each subclass of GameObjectController will have accessible at least a GameObjectView and GameObjectModel. If subclasses are fine using those classes, but perhaps are overriding for a more sophisticated Update() method, I don't want them to have to duplicate the code to produce those dependencies. So, the GameObjectController constructor sets those objects up. However, some objects do want to override the model and view. This is where the trouble comes in. Some objects need to fight, so they are CombatantGameObjects: public class CombatantGameObject : GameObjectController { protected new readonly CombatantGameModel model; public new virtual CombatantGameModel Model { get { return model; } } protected readonly CombatEngine combatEngine; public CombatantGameObject(GameObjectManager gameObjectManager, CombatEngine combatEngine) : base(gameObjectManager) { model = new CombatantGameModel(this); this.combatEngine = combatEngine; } public override void Update(long tick) { if (model.Health <= 0) { gameObjectManager.RemoveFromWorld(this); } base.Update(tick); } } Still pretty simple. Is my use of new to hide instance variables correct? Note that I'm assigning CombatantObjectController.model here, even though GameObjectController.Model was already set. And, combatants don't need any special view functionality, so they leave GameObjectController.View alone. Then I get down to the PlayerController, at which a bug is found. public class PlayerController : CombatantGameObject { private readonly IInputReader inputReader; private new readonly PlayerModel model; public new PlayerModel Model { get { return model; } } private float lastInventoryIndexAt; private float lastThrowAt; public PlayerController(GameObjectManager gameObjectManager, IInputReader inputReader, CombatEngine combatEngine) : base(gameObjectManager, combatEngine) { this.inputReader = inputReader; model = new PlayerModel(this); Model.Health = Constants.PLAYER_HEALTH; } public override void Update(long tick) { if (Model.Health <= 0) { gameObjectManager.RemoveFromWorld(this); for (int i = 0; i < 10; i++) { Debug.WriteLine("YOU DEAD SON!!!"); } return; } UpdateFromInput(tick); // .... } } The first time that this line is executed, I get a null reference exception: model.Body.ApplyImpulse(movementImpulse, model.Position); model.Position looks at model.Body, which is null. This is a function that initializes GameObjects before they are deployed into the world: public void Initialize(GameObjectController controller, IDictionary<string, string> data, WorldState worldState) { controller.View.read(data); controller.View.createSpriteAnimations(data, _assets); controller.Model.read(data); SetUpPhysics(controller, worldState, controller.Model.BoundingCircleRadius, Single.Parse(data["x"]), Single.Parse(data["y"]), bool.Parse(data["isBullet"])); } Every object is passed as a GameObjectController. Does that mean that if the object is really a PlayerController, controller.Model will refer to the base's GameObjectModel and not the PlayerController's overriden PlayerObjectModel? In response to rh: This means that now for a PlayerModel p, p.Model is not equivalent to ((CombatantGameObject)p).Model, and also not equivalent to ((GameObjectController)p).Model. That is exactly what I do not want. I want: PlayerController p; p.Model == ((CombatantGameObject)p).Model p.Model == ((GameObjectController)p).Model How can I do this? override?

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• Type casting in TPC inheritance

  - by Mohsen Esmailpour

  I have several products like HotelProduct, FlightProduct ... which derived from BaseProduct class. The table of these products will be generated in TPC manner in database. There is OrderLine class which has a BaseProduct. My problem is when i select an OrderLine with related product i don't know how cast BaseProduct to derived product. for example i have this query: var order = (from odr in _context.Orders join orderLine in _context.OrderLines on odr.Id equals orderLine.OrderId join hotel in _context.Products.OfType<HotelProduct>() on orderLine.ProductId equals hotel.Id where odr.UserId == userId && odr.Id == orderId orderby odr.OrderDate descending select odr).SingleOrDefault(); In OrderLine i have BaseProduct properties not properties of HotelProduct. Is there any way to cast BaseProduct to derived class in OrderLine or any other solutions ?

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• Simultaneous private and public inheritance in C++

  - by gspr

  Suppose a class Y publicly inherits a class X. Is it possible for a class Z to privately inherit Y while publicly inheriting X? To make this clearer, suppose X defines public methods x1 and x2. Y inherits X, overrides x1 and provides a method y. Does C++ allow for a third class Z to subclass Y in such a way that Y's implementation of x1 and y are privately available to it, while the outside world only sees it inheriting X publicly, i.e. having only a single public method x2?

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• INSERT 0..n records into table 'A' based on content of table 'B' in MySql 5

  - by Robert Gowland

  Using MySql 5, I have a task where I need to update one table based on the contents of another table. For example, I need to add 'A1' to table 'A' if table 'B' contains 'B1'. I need to add 'A2a' and 'A2b' to table 'A' if table 'B' contains 'B2', etc.. In our case, the value in table 'B' we're interested is an enum. Right now I have a stored procedure containing a series of statements like: INSERT INTO A SELECT 'A1' FROM B WHERE B.Value = 'B1'; --Repeat for 'B2' -> 'A2a'; 'B2' -> 'A2b'; 'B3' -> 'A3', etc... Is there a nicer more DRY way of accomplishing this? Edit: There may be values in table 'B' that have no equivalent value for table 'A'.

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• Templates, interfaces (multiple inheritance) and static functions (named constructors)

  - by fledgling Cxx user

  Setup I have a graph library where I am trying to decompose things as much as possible, and the cleanest way to describe it that I found is the following: there is a vanilla type node implementing only a list of edges: class node { public: int* edges; int edge_count; }; Then, I would like to be able to add interfaces to this whole mix, like so: template <class T> class node_weight { public: T weight; }; template <class T> class node_position { public: T x; T y; }; and so on. Then, the actual graph class comes in, which is templated on the actual type of node: template <class node_T> class graph { protected: node_T* nodes; public: static graph cartesian(int n, int m) { graph r; r.nodes = new node_T[n * m]; return r; } }; The twist is that it has named constructors which construct some special graphs, like a Cartesian lattice. In this case, I would like to be able to add some extra information into the graph, depending on what interfaces are implemented by node_T. What would be the best way to accomplish this? Possible solution I thought of the following humble solution, through dynamic_cast<>: template <class node_T, class weight_T, class position_T> class graph { protected: node_T* nodes; public: static graph cartesian(int n, int m) { graph r; r.nodes = new node_T[n * m]; if (dynamic_cast<node_weight<weight_T>>(r.nodes[0]) != nullptr) { // do stuff knowing you can add weights } if (dynamic_cast<node_position<positionT>>(r.nodes[0]) != nullptr) { // do stuff knowing you can set position } return r; } }; which would operate on node_T being the following: template <class weight_T, class position_T> class node_weight_position : public node, public node_weight<weight_T>, public node_position<position_T> { // ... }; Questions Is this -- philosophically -- the right way to go? I know people don't look nicely at multiple inheritance, though with "interfaces" like these it should all be fine. There are unfortunately problems with this. From what I know at least, dynamic_cast<> involves quite a bit of run-time overhead. Hence, I run into a problem with what I had solved earlier: writing graph algorithms that require weights independently of whether the actual node_T class has weights or not. The solution with this 'interface' approach would be to write a function: template <class node_T, class weight_T> inline weight_T get_weight(node_T const & n) { if (dynamic_cast<node_weight<weight_T>>(n) != nullptr) { return dynamic_cast<node_weight<weight_T>>(n).weight; } return T(1); } but the issue with it is that it works using run-time information (dynamic_cast), yet in principle I would like to decide it at compile-time and thus make the code more efficient. If there is a different solution that would solve both problems, especially a cleaner and better one than what I have, I would love to hear about it!

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• mysql master slave "table already exists" but table not exists

  - by Korjavin Ivan

  I have 1 master mysql process, and 2 slave. Today on both slaves i see : Error 'Table 'bgbilling.contract_status_balance_dump' already exists' on query. Default database: 'bgbilling'. Query: 'CREATE TABLE contract_status_balance_dump( UNIQUE(cid) ) SELECT cid, MAX(yy*12+(mm-1))%12 + 1 AS mm,FLOOR(MAX(yy*12+(mm-1)) / 12) AS yy FROM contract_balance GROUP BY cid' "show tables" does not show this table. I tryed stop slave , and do "drop table contract_status_balance_dump" but: ERROR 1051 (42S02): Unknown table 'contract_status_balance_dump' How its possible? And how fix that?

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• Vaadin table hide columns and container customization

  - by Alex

  Hello I am testing a project, using Vaadin and Hibernate. I am trying to use the HbnContainer class to show data into table. The problem is that I do not want to show all the properties of the two classes in the table. For example: @Entity @Table(name="users") class User { @Id @GeneratedValue(strategy=GenerationType.AUTO) private Long id; private String name; @ManyToOne(cascade=CascadeType.PERSIST) private UserRole role; //getters and setters } and a second class: @Entity @Table(name="user_roles") class UserRole { @Id @GeneratedValue(strategy=GenerationType.AUTO) private Long id; private String name; //getters and setters } Next, I retrieve my data using the HbnContainer, and connect it to the table: HbnContainer container = new HbnContainer(User.class, app); table.setContainerDataSource(container); The Table will only display the columns from User, and for the "role" it will put the role id instead. How can I hide that column, and replace it with the UserRole.name ? I managed to use a ColumnGenerator() to get the string value in the table, for the UserRole - but I couldn't remove the previous column, with the numerical value. What am I missing? Or, what is the best way to "customize" your data, before displaying a table (if i want to show data in a table from more than one object type.. what do I do?) If I can't find a simple solution soon, I think I will just build the tables "by hand".. So, any advice on this matter? Thank you, Alex

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• Dojo Table not Rendering in IE6

  - by Mike Carey

  I'm trying to use Dojo (1.3) checkBoxes to make columns appear/hide in a Dojo Grid that's displayed below the checkBoxes. I got that functionality to work fine, but I wanted to organize my checkBoxes a little better. So I tried putting them in a table. My dojo.addOnLoad function looks like this: dojo.addOnLoad(function(){ var checkBoxes = []; var container = dojo.byId('checkBoxContainer'); var table = dojo.doc.createElement("table"); var row1= dojo.doc.createElement("tr"); var row2= dojo.doc.createElement("tr"); var row3= dojo.doc.createElement("tr"); dojo.forEach(grid.layout.cells, function(cell, index){ //Add a new "td" element to one of the three rows }); dojo.place(addRow, table); dojo.place(removeRow, table); dojo.place(findReplaceRow, table); dojo.place(table, container); }); What's frustrating is: 1) Using the Dojo debugger I can see that the HTML is being properly generated for the table. 2) I can take that HTML and put just the table in an empty HTML file and it renders the checkBoxes in the table just fine. 3) The page renders correctly in Firefox, just not IE6. The HTML that is being generated looks like so: <div id="checkBoxContainer"> <table> <tr> <td> <div class="dijitReset dijitInline dijitCheckBox" role="presentation" widgetid="dijit_form_CheckBox_0" wairole="presentation"> <input class="dijitReset dijitCheckBoxInput" id="dijit_form_CheckBox_0" tabindex="0" type="checkbox" name="" dojoattachevent= "onmouseover:_onMouse,onmouseout:_onMouse,onclick:_onClick" dojoattachpoint="focusNode" unselectable="on" aria-pressed="false"/> </div> <label for="dijit_form_CheckBox_0"> Column 1 </label> </td> <td> <div class="dijitReset dijitInline dijitCheckBox" role="presentation" widgetid="dijit_form_CheckBox_1" wairole="presentation"> <input class="dijitReset dijitCheckBoxInput" id="dijit_form_CheckBox_1" tabindex="0" type="checkbox" name="" dojoattachevent= "onmouseover:_onMouse,onmouseout:_onMouse,onclick:_onClick" dojoattachpoint="focusNode" unselectable="on" aria-pressed="false"/> </div> </td> </tr> <tr> ... </tr> </table> </div> I would have posted to the official DOJO forums, but it says they're deprecated and they're using a mailing list now. They said if a mailing list doesn't work for you, use stackoverflos.com. So, here I am! Thanks for any insight you can provide.

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• Communication with a single-threaded apartment

  - by hmm

  How do I communicate with a method in a single threaded apartment process in .NET? I have something like a coordinator worker pattern need with the single threaded apartment process acting like the worker. I cannot use named pipes read/writes for my scenario due to certain reasons. Is there any other way to delegate work to the single threaded apartment process?

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• How to resize table via javascript in IE?

  - by MartyIX

  I've got this table: <table id="correctness" style="overflow: hidden;"> <tr><td style="overflow: hidden;"> <div id="correctness-message"></div> <span class="hide"> <button type="button" class="hide" onclick="new DisplayEffect('correctness').Hide(500);">Hide</button> </span> </td> </tr> </table> and a function for resizing the table: function resize(element, size) { element.style.height = size + "px";}; which is called for a certain amount of time (e.g. 1 second) with the ID of table (i.e. "correctness") in order to resize the table from zero height to its full height. This code works in Firefox and Chrome but it doesn't work in IE8. What it does is that it displays right away whole table even thought the height set in "resize" method is much lower. It seems that the cell sets the height of parent table and not the other way around. Is it possible to change the behaviour? I like changing the height of the table better because I can set visibility of the table easily. Thanks for any help!

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• mysql alter to table

  - by user485783

  Hi, I drop the mysql alter code below to database via phpmyadmin one by one, it it work fine, is there anyone could help me how to drop it all together at once? or do you know the the samples of php code that may execute it? just let me know please. thanks in advace ALTER TABLE user ADD title varchar(16) COLLATE utf8_bin NOT NULL DEFAULT '' AFTER user_id ALTER TABLE customer ADD title varchar(16) COLLATE utf8_bin NOT NULL DEFAULT '' AFTER customer_id ALTER TABLE customer ADD date_birtdate datetime NOT NULL DEFAULT '0000-00-00 00:00:00' AFTER lastname ALTER TABLE customer ADD security_question varchar(96) COLLATE utf8_bin NOT NULL DEFAULT '' AFTER fax ALTER TABLE customer ADD security_answer varchar(96) COLLATE utf8_bin NOT NULL DEFAULT '' AFTER fax ALTER TABLE customer ADD pin_number text COLLATE utf8_bin AFTER password ALTER TABLE customer ADD notes text COLLATE utf8_bin AFTER bank_number ALTER TABLE customer ADD last_active datetime NOT NULL DEFAULT '0000-00-00 00:00:00' AFTER date_added

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• Prototypal inheritance should save memory, right?

  - by Techpriester

  Hi Folks, I've been wondering: Using prototypes in JavaScript should be more memory efficient than attaching every member of an object directly to it for the following reasons: The prototype is just one single object. The instances hold only references to their prototype. Versus: Every instance holds a copy of all the members and methods that are defined by the constructor. I started a little experiment with this: var TestObjectFat = function() { this.number = 42; this.text = randomString(1000); } var TestObjectThin = function() { this.number = 42; } TestObjectThin.prototype.text = randomString(1000); randomString(x) just produces a, well, random String of length x. I then instantiated the objects in large quantities like this: var arr = new Array(); for (var i = 0; i < 1000; i++) { arr.push(new TestObjectFat()); // or new TestObjectThin() } ... and checked the memory usage of the browser process (Google Chrome). I know, that's not very exact... However, in both cases the memory usage went up significantly as expected (about 30MB for TestObjectFat), but the prototype variant used not much less memory (about 26MB for TestObjectThin). I also checked: The TestObjectThin instances contain the same string in their "text" property, so they are really using the property of the prototype. Now, I'm not so sure what to think about this. The prototyping doesn't seem to be the big memory saver at all. I know that prototyping is a great idea for many other reasons, but I'm specifically concerned with memory usage here. Any explanations why the prototype variant uses almost the same amount of memory? Am I missing something?

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• When to use SQL Table Alias

  - by Rossini

  I curious to know how people are using table alias. The other developers where I work always use table alias, and always use the alias of a, b, c, ect. Here's an example SELECT a.TripNum, b.SegmentNum, b.StopNum, b.ArrivalTime FROM Trip a, Segment b WHERE a.TripNum = b.TripNum I disagree with them, and think table alias should be use more sparingly. I think it should be used when including the same table twice in a query, or when the table name is very long and using a shorter name in the query will make the query easier to read. I also think the alias should be a good name instead of a letter. In the above example if I felt I needed to use 1 letter table alias I would use t for the Trip table and s for the segment table.

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• C++ Storing variables and inheritance

  - by Kaa

  Hello Everyone, Here is my situation: I have an event driven system, where all my handlers are derived from IHandler class, and implement an onEvent(const Event &event) method. Now, Event is a base class for all events and contains only the enumerated event type. All actual events are derived from it, including the EventKey event, which has 2 fields: (uchar) keyCode and (bool)isDown. Here's the interesting part: I generate an EventKey event using the following syntax: Event evt = EventKey(15, true); and I ship it to the handlers: EventDispatch::sendEvent(evt); // void EventDispatch::sendEvent(const Event &event); (EventDispatch contains a linked list of IHandlers and calls their onEvent(const Event &event) method with the parameter containing the sent event. Now the actual question: Say I want my handlers to poll the events in a queue of type Event, how do I do that? x Dynamic pointers with reference counting sound like too big of a solution. x Making copies is more difficult than it sounds, since I'm only receiving a reference to a base type, therefore each time I would need to check the type of event, upcast to EventKey and then make a copy to store in a queue. Sounds like the only solution - but is unpleasant since I would need to know every single type of event and would have to check that for every event received - sounds like a bad plan. x I could allocate the events dynamically and then send around pointers to those events, enqueue them in the array if wanted - but other than having reference counting - how would I be able to keep track of that memory? Do you know any way to implement a very light reference counter that wouldn't interfere with the user? What do you think would be a good solution to this design? I thank everyone in advance for your time. Sincerely, Kaa

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