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  • Are trivial protected getters blatant overkill?

    - by Panzercrisis
    Something I really have not thought about before (AS3 syntax): private var m_obj:Object; protected function get obj():Object { return m_obj; } private var m_str:String; protected function get str():String { return m_str; } At least subclasses won't be able to set m_obj or m_str (though they could still modify m_obj). Is this just blatant overkill? I am not talking about doing this as opposed to making them public. I am talking about doing this instead of just making the variables themselves protected. Like this: protected var m_obj:Object; //more accessible than a private variable with a protected getter protected var m_str:String; //more accessible than a private variable with a protected getter

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  • sdl stencil buffer

    - by noddy
    I am trying to use the stencil buffer for rendering reflection and am working with SDL and OpenGL. When I give the command SDL_GL_SetAttribute(SDL_GL_STENCIL_SIZE,8),I get a return value of 0 indicating success,but when I try to get the size allocated using SDL_GL_GetAtribute( SDL_GL_STENCIL_SIZE,&i),I get a value of 0 for my stencil buffer due to which I am not getting the desired rendering. Can someone help me to correct my mistake? Is there some other initialization also required? Thanks

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  • Calgary .NET User Group &ndash; Entity Framework Code First - December 11th

    - by David Paquette
    I will be presenting at the Calgary .NET User Group on December 11th. We will start from scratch in this intro to Entity Framework Code First. We will build a simple application using ASP.NET MVC and Entity Framework and evolve the application to show how we can build scalable applications using Entity Framework Code First. Topics covered will include database initialization, code based migrations, performance profiling and performance tuning. Register at http://www.dotnetcalgary.com/

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  • Calculating the rotational force of a 2D sprite

    - by Jon
    I am wondering if someone has an elegant way of calculating the following scenario. I have an object of (n) number of squares, random shapes, but we will pretend they are all rectangles. We are dealing with no gravity, so consider the object in space, from a top down perspective. I am applying a force to the object at a specific square (as illustrated below). How do I calculate the rotational angle, based on the force being applied, at the location being applied. If applied in the center square, it would go straight. How should it behave the further I move from the center? How do I calculate the rotational velocity?

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  • How can I link to callback functions in Lua such that the callbacks will be updated when the scripts are reloaded?

    - by Raptormeat
    I'm implementing Lua scripting in my game using LuaBind, and one of the things I'm not clear on is the logistics of reloading the scripts live ingame. Currently, using the LuaBind C++ class luabind::object, I save references to Lua callbacks directly in the classes that use them. Then I can use luabind::call_function using that object in order to call the Lua code from the C++ code. I haven't tested this yet, but my assumption is that if I reload the scripts, then all the functions will be redefined, BUT the references to the OLD functions will still exist in the form of the luabind::object held by the C++ code. I would like to be able to swap out the old for the new without manually having to manage this for every script hook in the game. How best to change this so the process works? My first thought is to not save a reference to the function directly, but maybe save the function name instead, and grab the function by name every time we want to call it. I'm looking for better ideas!

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  • Exchange 2010 Deployment Notes &ndash; iPhone and Exchange ActiveSync issue

    - by BWCA
    After we moved one of our user mailboxes from Exchange 2003 to 2010, the user started getting a Cannot get mail. The connection to the server failed error message on their iPhone device. There are a lot of references on Google to check for inherited permissions to resolve the error message.  We quickly determined that we were not dealing with a permissions issue. After some additional troubleshooting and research, we were able to isolate the problem to a device partnership issue. To resolve the issue, use ADSI Edit to find the user object. When you find the user object, double-click on it and you should see a CN=ExchangeActiveSyncDevices container under the user object as shown below.  On the right-hand side, you should see one or more device partnerships.   Right-click the device partnership according to the device the user is using, and click Delete. After you remove the device partnership, please wait until Active Directory replication completes before you set up the device again.

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  • Tester/Doer pattern: Assume the caller conforms to the pattern or be defensive and repeat the check?

    - by Daniel Hilgarth
    Assume a simple class that implements the Tester/Doer pattern: public class FooCommandHandler : ICommandHandler { public bool CanHandle(object command) { return command is FooCommand; } public void Handle(object command) { var fooCommand = (FooCommand)command; // Do something with fooCommand } } Now, if someone doesn't conform to the pattern and calls Handle without verifying the command via CanHandle, the code in Handle throws an exception. However, depending on the actual implementation of Handle this can be a whole range of different exceptions. The following implementation would check CanHandle again in Handle and throw a descriptive exception: public void Handle(object command) { if(!CanHandle(command)) throw new TesterDoerPatternUsageViolationException("Please call CanHandle first"); // actual implementation of handling the command. } This has the advantage that the exception is very descriptive. It has the disadvantage that CanHandle is called twice for "good" clients. Is there a consensus on which variation should be used?

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  • python factory function best practices

    - by Jason S
    Suppose I have a file foo.py containing a class Foo: class Foo(object): def __init__(self, data): ... Now I want to add a function that creates a Foo object in a certain way from raw source data. Should I put it as a static method in Foo or as another separate function? class Foo(object): def __init__(self, data): ... # option 1: @staticmethod def fromSourceData(sourceData): return Foo(processData(sourceData)) # option 2: def makeFoo(sourceData): return Foo(processData(sourceData)) I don't know whether it's more important to be convenient for users: foo1 = foo.makeFoo(sourceData) or whether it's more important to maintain clear coupling between the method and the class: foo1 = foo.Foo.fromSourceData(sourceData)

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  • Material tiling and offset in unity

    - by Simran kaur
    Ambiguity: What exactly is the difference between Tiling the material and Offset of material? Need to do: I need the material to be repeated n times on the object where I need to set the value of n via script.How do I do it? It seems to happen through Tiling(tried via inspector) but again what is difference between mainTextureOffset and setTextureOffset? Tried: Following is the line of code that I tried to repeat the texture n number of times on an object(repeat across the width of object), but it does nothing significant that I can see.

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  • What data-structure/algorithm will allow me to send a list of key/value dictionaries using the least amount of bits?

    - by user12365
    I have server objects that have corresponding client objects. The data to be kept in sync is inside the server object's key/value dictionary. To keep the client objects in sync with the sever objects, I want the server to send the key/value dictionary every frame for each object. What data-structure/algorithm will allow me to send a list of key/value dictionaries using the least amount of bits? Bonus constraint 1: For each type of object, the values of some keys change more often than others. Bonus constraint 2: Memory usage on the server side is relatively expensive.

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  • Tension between the dependency inversion principle and avoiding "new" in C++?

    - by Kazark
    I have seen a lot of advice that it is better to do Type object; than Type* object = new Type(); in C++ whenever possible. I understand the rational behind this and appreciate it. But according to my understanding, to practice dependency inversion requires pointers, e.g.: Type* object = new Implementation();. (Or am I wrong about that?) Is there an inherent tension between the DIP and avoiding new when using C++? If so, what patterns/principles/practices can be used to mitigate this tension?

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  • YouTube fullscreen not displaying

    - by pt2ph8
    For some reason YouTube videos in my website do not get the fullscreen button, even if I added the parameter allowFullScreen set to true both in the object and embed tag. Here's an example page: http://www.indievault.it/2011/11/09/indie-vault-alla-games-week-2011-online-la-video-gallery/ Just take a quick look at the source. The allowFullScreen param is there, but the button won't show. Here's an excerpt from the code in that page: <object width="540" height="325"><param name="movie" value="http://www.youtube.com/v/dvYQhJwwkgA"></param><param name="allowFullScreen" value="true"></param><param name="allowscriptaccess" value="always"></param><embed src="http://www.youtube.com/v/dvYQhJwwkgA" type="application/x-shockwave-flash" allowscriptaccess="always" allowfullscreen="true" width="540" height="325"></embed </object>

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  • Randomly spawning bitmaps on cnvas

    - by Toystoj
    I need some ideas in order to finish algorithm. I'm randomly placing objects (bitmaps) on canvas without overlapping. Time needed to finish it is my problem. When I need to spawn for example 80% of canvas it takes to long. So i was thinking : I should make some change when the bitmaps take off 50 % of canvas. I want to tell algorithm that it should generate new locations (x,y) where it is free space. My question is : How to render new location (x,y) in place where is free space. In summary: Things I know : object location (x,y) 4 corners (x,y) of object object width, height canvas width, height Any suggestions?

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  • Synchronized Property Changes (Part 4)

    - by Geertjan
    The next step is to activate the undo/redo functionality... for a Node. Something I've not seen done before. I.e., when the Node is renamed via F2 on the Node, the "Undo/Redo" buttons should start working. Here is the start of the solution, via this item in the mailing list and Timon Veenstra's BeanNode class, note especially the items in bold: public class ShipNode extends BeanNode implements PropertyChangeListener, UndoRedo.Provider { private final InstanceContent ic; private final ShipSaveCapability saveCookie; private UndoRedo.Manager manager; private String oldDisplayName; private String newDisplayName; private Ship ship; public ShipNode(Ship bean) throws IntrospectionException { this(bean, new InstanceContent()); } private ShipNode(Ship bean, InstanceContent ic) throws IntrospectionException { super(bean, Children.LEAF, new ProxyLookup(new AbstractLookup(ic), Lookups.singleton(bean))); this.ic = ic; setDisplayName(bean.getType()); setShortDescription(String.valueOf(bean.getYear())); saveCookie = new ShipSaveCapability(bean); bean.addPropertyChangeListener(WeakListeners.propertyChange(this, bean)); } @Override public Action[] getActions(boolean context) { List<? extends Action> shipActions = Utilities.actionsForPath("Actions/Ship"); return shipActions.toArray(new Action[shipActions.size()]); } protected void fire(boolean modified) { if (modified) { ic.add(saveCookie); } else { ic.remove(saveCookie); } } @Override public UndoRedo getUndoRedo() { manager = Lookup.getDefault().lookup( UndoRedo.Manager.class); return manager; } private class ShipSaveCapability implements SaveCookie { private final Ship bean; public ShipSaveCapability(Ship bean) { this.bean = bean; } @Override public void save() throws IOException { StatusDisplayer.getDefault().setStatusText("Saving..."); fire(false); } } @Override public boolean canRename() { return true; } @Override public void setName(String newDisplayName) { Ship c = getLookup().lookup(Ship.class); oldDisplayName = c.getType(); c.setType(newDisplayName); fireNameChange(oldDisplayName, newDisplayName); fire(true); fireUndoableEvent("type", ship, oldDisplayName, newDisplayName); } public void fireUndoableEvent(String property, Ship source, Object oldValue, Object newValue) { ReUndoableEdit reUndoableEdit = new ReUndoableEdit( property, source, oldValue, newValue); UndoableEditEvent undoableEditEvent = new UndoableEditEvent( this, reUndoableEdit); manager.undoableEditHappened(undoableEditEvent); } private class ReUndoableEdit extends AbstractUndoableEdit { private Object oldValue; private Object newValue; private Ship source; private String property; public ReUndoableEdit(String property, Ship source, Object oldValue, Object newValue) { super(); this.oldValue = oldValue; this.newValue = newValue; this.source = source; this.property = property; } @Override public void undo() throws CannotUndoException { setName(oldValue.toString()); } @Override public void redo() throws CannotRedoException { setName(newValue.toString()); } } @Override public String getDisplayName() { Ship c = getLookup().lookup(Ship.class); if (null != c.getType()) { return c.getType(); } return super.getDisplayName(); } @Override public String getShortDescription() { Ship c = getLookup().lookup(Ship.class); if (null != String.valueOf(c.getYear())) { return String.valueOf(c.getYear()); } return super.getShortDescription(); } @Override public void propertyChange(PropertyChangeEvent evt) { if (evt.getPropertyName().equals("type")) { String oldDisplayName = evt.getOldValue().toString(); String newDisplayName = evt.getNewValue().toString(); fireDisplayNameChange(oldDisplayName, newDisplayName); } else if (evt.getPropertyName().equals("year")) { String oldToolTip = evt.getOldValue().toString(); String newToolTip = evt.getNewValue().toString(); fireShortDescriptionChange(oldToolTip, newToolTip); } fire(true); } } Undo works when rename is done, but Redo never does, because Undo is constantly activated, since it is reactivated whenever there is a name change. And why must the UndoRedoManager be retrieved from the Lookup (it doesn't work otherwise)? Don't get that part of the code either. Help welcome!

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  • How do I swap two objects in a GC language without triggering GC?

    - by TenFour04
    I have two array lists. that I want to swap each frame. My question is, does the variable 'temp' need to be a member variable to avoid triggering GC, assuming this method is called on dozens of objects each frame? I'm not creating a new object, just a new reference to an object. public void LateUpdate(){ ArrayList<int> temp = previousFrameCollisions; previousFrameCollisions = currentFrameCollisions; currentFrameCollisions = temp; currentFrameCollisions.clear(); } I've been told there's no reason to make a primitive into a member variable just to avoid GC, so my best guess is that this also applies to object references.

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  • JavaScript: scroll position (Webkit engine) [migrated]

    - by Julien
    I'm currently trying to use JavaScript to find out how far down the page the user has scrolled; for Firefox 8.0, the keyword is pageYOffset. To say things mechanically: The page has a certain height. In Firefox, the useful object is document.documentElement.scrollHeight. The browser's visible area also has a certain height. In Firefox, the object is window.innerHeight; in IE8, document.documentElement.clientHeight. I need to know where the user is in the page vertically; in other words, how many pixels down the page the user has scrolled. Does Webkit have a DOM object that refers to the current scroll position? Thank you.

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  • libgdx - collision detection with tiled map java

    - by user2875021
    currently, I am working on a 2d rpg game which is similar to final fantasy 1-4. I can load up a tiled map and the sprite can walk freely on the map. However, I will like to create a wall for it to stop walking through it. I created three tiled layer Background, Collision, Overhead and one Collision object layer with rectangles only. "How do I handle collisions with the object layer in the tiled map?" "Do I have to create every single rectangle that is in the object layer with Rectangle rectangle = new Rectangle() and rectangle.set(x, y, width, height)in the code?" Thank you very much in advance. Any help is greatly appreciated!

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  • Moving from mock to real objects?

    - by jjchiw
    I'm like doing TDD so I started everything mocking objects, creating interface, stubbing, great. The design seems to work, now I'll implement the stuff, a lot of the code used in the stubs are going to be reused in my real implementation yay! Now should I duplicate the tests to use the real object implementation (but keeping the mocks object of the sensitive stuff like Database and "services" that are out of my context (http calls, etc...)) Or just change the mocks and stubs of the actual tests to use the real objects....... So the question is that, keep two tests or replace the stubs, mocks? And after that, I should keep designing with the mocks, stubs or just go with real objects? (Just making myself clear I'll keep the mock object of the sensitive stuff like database and services that are out of my context, in both situations.)

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  • Collisions and Lists

    - by user50635
    I've run into an issue that breaks my collisions. Here's my method: Gather Input Project Rectangle Check for intersection and ispassable Update The update method is built on object_position * seconds_passed * velocity * speed. Input changes velocity and is normalized if 1. This method works well with just one object comparison, however I pass a list or a for loop to the collision detector and velocity gets changed back to a non zero when the list hits an object that passes the test and the object can pass through. Any solutions would be much appreciated. Side note is there a more proper way to simulate movement?

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  • How can I make my generic comparer (IComparer) handle nulls? [closed]

    - by Nick G
    Hi, I'm trying to write a generic object comparer for sorting, but I have noticed it does not handle the instance where one of the values it's comparing is null. When an object is null, I want it to treat it the same as the empty string. I've tried setting the null values to String.Empty but then I get an error of "Object must be of type String" when calling CompareTo() on it. public int Compare(T x, T y) { PropertyInfo propertyInfo = typeof(T).GetProperty(sortExpression); IComparable obj1 = (IComparable)propertyInfo.GetValue(x, null); IComparable obj2 = (IComparable)propertyInfo.GetValue(y, null); if (obj1 == null) obj1 = String.Empty; // This doesn't work! if (obj2 == null) obj2 = String.Empty; // This doesn't work! if (SortDirection == SortDirection.Ascending) return obj1.CompareTo(obj2); else return obj2.CompareTo(obj1); } I'm pretty stuck with this now! Any help would be appreciated.

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  • How do I swap two objects in C# (specifically Mono) without triggering GC?

    - by TenFour04
    I have two array lists. that I want to swap each frame. My question is, does the variable 'temp' need to be a member variable to avoid triggering GC, assuming this method is called on dozens of objects each frame? I'm not creating a new object, just a new reference to an object. public void LateUpdate(){ ArrayList<int> temp = previousFrameCollisions; previousFrameCollisions = currentFrameCollisions; currentFrameCollisions = temp; currentFrameCollisions.clear(); } I've been told there's no reason to make a primitive into a member variable just to avoid GC, so my best guess is that this also applies to object references.

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  • change texture at runtime

    - by user1509674
    How can I change the texture at runtime. I have done changing the label(text) at runtime. The following code is used using UnityEngine; using System.Collections; public class switchtime : MonoBehaviour { // Use this for initialization private bool showLabel = false; private bool showLabe2 = false; private bool showLabe3 = false; private bool showLabe4 = false; public void Start() { Invoke("ToggleLabel", 1); Invoke("ToggleLabel2", 3); Invoke("ToggleLabel3",6 ); Invoke("ToggleLabel4", 9); } public void ToggleLabel() { showLabel = !showLabel; } public void ToggleLabel2() { showLabe2 = !showLabe2; } public void ToggleLabel3() { showLabe3 = !showLabe3; } public void ToggleLabel4() { showLabe4 = !showLabe4; } public void OnGUI() { if (showLabel) { GUI.Label(new Rect(300, 200, 100, 20), "Copying window file.."); } if (showLabe2) { GUI.Label(new Rect(40, 40, 100, 20), "Epanding windows file.."); } if (showLabe3) { GUI.Label(new Rect(80, 80, 100, 20), "Installing Feature.."); } if (showLabe4) { GUI.Label(new Rect(100, 100, 100, 20), "Installing Updates"); } } } Now I need to change the GUITexture at runtime. How can do this? Can anybody help me in coding? Here is some changes I made. I worked on changing the gameObject when mouse is placed on it. This is the code I applied and its working for me using UnityEngine; using System.Collections; public class change : MonoBehaviour { // Use this for initialization public GameObject newSprite; private Vector3 currentSpritePosition; void update() { } void Start() { newSprite.renderer.enabled = false; currentSpritePosition = transform.position; //then make it invisible renderer.enabled = false; //give the new sprite the position of the latter newSprite.transform.position = currentSpritePosition; //then make it visible newSprite.renderer.enabled = true; } void OnMouseExit(){ //just the reverse process renderer.enabled = true; newSprite.renderer.enabled = false; } } Now the problem is that, in same code I need to set a time so that the text get loaded without the mouse click. I mean a particular time to load each text one after the another. Here is my screen shot Here I have placed the image one below the another,when the mouse is hovered on it it will change the text from bold to normal text.Changes process stated in (image 2,3).That code I posted is working for me.

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  • SQL Server Requery() sometimes hangs

    - by PSU
    I have an issue with Visual C++ and Microsoft SQL Server 2008R2. The following code will occasionally hang: Object->Update(); if(Object->CanRestart()) { //Why does this not return?? m_pDBRoRBaseObject->Requery(); } Object is derived from CRecordset. It looks to me as though a call to ::SQLExecute(m_hstmt) in the Requery() method is hanging, but I can't (with my current skill set anyway) figure out a way around this. Has anyone had a similar problem, or an insight of any sort?

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  • How can I find the closest vector to another in a specific direction?

    - by Sniper
    Perhaps I am not phrasing it incorrectly in my searches, but I can not find anything on this. I have a vector3 with a specific direction that it is facing, I want to get the closest object to that position in that specific direction. Basically I want to get the object that is being aimed at. I have thought about finding all objects within a box and then finding the closest object to my vector from them results, but I am sure that there is a more efficient way. The Z axis is optional, the objects are most likely within a few meters of the search vector. http://i.stack.imgur.com/FafAu.jpg

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  • Inheritance Mapping Strategies with Entity Framework Code First CTP5: Part 3 – Table per Concrete Type (TPC) and Choosing Strategy Guidelines

    - by mortezam
    This is the third (and last) post in a series that explains different approaches to map an inheritance hierarchy with EF Code First. I've described these strategies in previous posts: Part 1 – Table per Hierarchy (TPH) Part 2 – Table per Type (TPT)In today’s blog post I am going to discuss Table per Concrete Type (TPC) which completes the inheritance mapping strategies supported by EF Code First. At the end of this post I will provide some guidelines to choose an inheritance strategy mainly based on what we've learned in this series. TPC and Entity Framework in the Past Table per Concrete type is somehow the simplest approach suggested, yet using TPC with EF is one of those concepts that has not been covered very well so far and I've seen in some resources that it was even discouraged. The reason for that is just because Entity Data Model Designer in VS2010 doesn't support TPC (even though the EF runtime does). That basically means if you are following EF's Database-First or Model-First approaches then configuring TPC requires manually writing XML in the EDMX file which is not considered to be a fun practice. Well, no more. You'll see that with Code First, creating TPC is perfectly possible with fluent API just like other strategies and you don't need to avoid TPC due to the lack of designer support as you would probably do in other EF approaches. Table per Concrete Type (TPC)In Table per Concrete type (aka Table per Concrete class) we use exactly one table for each (nonabstract) class. All properties of a class, including inherited properties, can be mapped to columns of this table, as shown in the following figure: As you can see, the SQL schema is not aware of the inheritance; effectively, we’ve mapped two unrelated tables to a more expressive class structure. If the base class was concrete, then an additional table would be needed to hold instances of that class. I have to emphasize that there is no relationship between the database tables, except for the fact that they share some similar columns. TPC Implementation in Code First Just like the TPT implementation, we need to specify a separate table for each of the subclasses. We also need to tell Code First that we want all of the inherited properties to be mapped as part of this table. In CTP5, there is a new helper method on EntityMappingConfiguration class called MapInheritedProperties that exactly does this for us. Here is the complete object model as well as the fluent API to create a TPC mapping: public abstract class BillingDetail {     public int BillingDetailId { get; set; }     public string Owner { get; set; }     public string Number { get; set; } }          public class BankAccount : BillingDetail {     public string BankName { get; set; }     public string Swift { get; set; } }          public class CreditCard : BillingDetail {     public int CardType { get; set; }     public string ExpiryMonth { get; set; }     public string ExpiryYear { get; set; } }      public class InheritanceMappingContext : DbContext {     public DbSet<BillingDetail> BillingDetails { get; set; }              protected override void OnModelCreating(ModelBuilder modelBuilder)     {         modelBuilder.Entity<BankAccount>().Map(m =>         {             m.MapInheritedProperties();             m.ToTable("BankAccounts");         });         modelBuilder.Entity<CreditCard>().Map(m =>         {             m.MapInheritedProperties();             m.ToTable("CreditCards");         });                 } } The Importance of EntityMappingConfiguration ClassAs a side note, it worth mentioning that EntityMappingConfiguration class turns out to be a key type for inheritance mapping in Code First. Here is an snapshot of this class: namespace System.Data.Entity.ModelConfiguration.Configuration.Mapping {     public class EntityMappingConfiguration<TEntityType> where TEntityType : class     {         public ValueConditionConfiguration Requires(string discriminator);         public void ToTable(string tableName);         public void MapInheritedProperties();     } } As you have seen so far, we used its Requires method to customize TPH. We also used its ToTable method to create a TPT and now we are using its MapInheritedProperties along with ToTable method to create our TPC mapping. TPC Configuration is Not Done Yet!We are not quite done with our TPC configuration and there is more into this story even though the fluent API we saw perfectly created a TPC mapping for us in the database. To see why, let's start working with our object model. For example, the following code creates two new objects of BankAccount and CreditCard types and tries to add them to the database: using (var context = new InheritanceMappingContext()) {     BankAccount bankAccount = new BankAccount();     CreditCard creditCard = new CreditCard() { CardType = 1 };                      context.BillingDetails.Add(bankAccount);     context.BillingDetails.Add(creditCard);     context.SaveChanges(); } Running this code throws an InvalidOperationException with this message: The changes to the database were committed successfully, but an error occurred while updating the object context. The ObjectContext might be in an inconsistent state. Inner exception message: AcceptChanges cannot continue because the object's key values conflict with another object in the ObjectStateManager. Make sure that the key values are unique before calling AcceptChanges. The reason we got this exception is because DbContext.SaveChanges() internally invokes SaveChanges method of its internal ObjectContext. ObjectContext's SaveChanges method on its turn by default calls AcceptAllChanges after it has performed the database modifications. AcceptAllChanges method merely iterates over all entries in ObjectStateManager and invokes AcceptChanges on each of them. Since the entities are in Added state, AcceptChanges method replaces their temporary EntityKey with a regular EntityKey based on the primary key values (i.e. BillingDetailId) that come back from the database and that's where the problem occurs since both the entities have been assigned the same value for their primary key by the database (i.e. on both BillingDetailId = 1) and the problem is that ObjectStateManager cannot track objects of the same type (i.e. BillingDetail) with the same EntityKey value hence it throws. If you take a closer look at the TPC's SQL schema above, you'll see why the database generated the same values for the primary keys: the BillingDetailId column in both BankAccounts and CreditCards table has been marked as identity. How to Solve The Identity Problem in TPC As you saw, using SQL Server’s int identity columns doesn't work very well together with TPC since there will be duplicate entity keys when inserting in subclasses tables with all having the same identity seed. Therefore, to solve this, either a spread seed (where each table has its own initial seed value) will be needed, or a mechanism other than SQL Server’s int identity should be used. Some other RDBMSes have other mechanisms allowing a sequence (identity) to be shared by multiple tables, and something similar can be achieved with GUID keys in SQL Server. While using GUID keys, or int identity keys with different starting seeds will solve the problem but yet another solution would be to completely switch off identity on the primary key property. As a result, we need to take the responsibility of providing unique keys when inserting records to the database. We will go with this solution since it works regardless of which database engine is used. Switching Off Identity in Code First We can switch off identity simply by placing DatabaseGenerated attribute on the primary key property and pass DatabaseGenerationOption.None to its constructor. DatabaseGenerated attribute is a new data annotation which has been added to System.ComponentModel.DataAnnotations namespace in CTP5: public abstract class BillingDetail {     [DatabaseGenerated(DatabaseGenerationOption.None)]     public int BillingDetailId { get; set; }     public string Owner { get; set; }     public string Number { get; set; } } As always, we can achieve the same result by using fluent API, if you prefer that: modelBuilder.Entity<BillingDetail>()             .Property(p => p.BillingDetailId)             .HasDatabaseGenerationOption(DatabaseGenerationOption.None); Working With The Object Model Our TPC mapping is ready and we can try adding new records to the database. But, like I said, now we need to take care of providing unique keys when creating new objects: using (var context = new InheritanceMappingContext()) {     BankAccount bankAccount = new BankAccount()      {          BillingDetailId = 1                          };     CreditCard creditCard = new CreditCard()      {          BillingDetailId = 2,         CardType = 1     };                      context.BillingDetails.Add(bankAccount);     context.BillingDetails.Add(creditCard);     context.SaveChanges(); } Polymorphic Associations with TPC is Problematic The main problem with this approach is that it doesn’t support Polymorphic Associations very well. After all, in the database, associations are represented as foreign key relationships and in TPC, the subclasses are all mapped to different tables so a polymorphic association to their base class (abstract BillingDetail in our example) cannot be represented as a simple foreign key relationship. For example, consider the the domain model we introduced here where User has a polymorphic association with BillingDetail. This would be problematic in our TPC Schema, because if User has a many-to-one relationship with BillingDetail, the Users table would need a single foreign key column, which would have to refer both concrete subclass tables. This isn’t possible with regular foreign key constraints. Schema Evolution with TPC is Complex A further conceptual problem with this mapping strategy is that several different columns, of different tables, share exactly the same semantics. This makes schema evolution more complex. For example, a change to a base class property results in changes to multiple columns. It also makes it much more difficult to implement database integrity constraints that apply to all subclasses. Generated SQLLet's examine SQL output for polymorphic queries in TPC mapping. For example, consider this polymorphic query for all BillingDetails and the resulting SQL statements that being executed in the database: var query = from b in context.BillingDetails select b; Just like the SQL query generated by TPT mapping, the CASE statements that you see in the beginning of the query is merely to ensure columns that are irrelevant for a particular row have NULL values in the returning flattened table. (e.g. BankName for a row that represents a CreditCard type). TPC's SQL Queries are Union Based As you can see in the above screenshot, the first SELECT uses a FROM-clause subquery (which is selected with a red rectangle) to retrieve all instances of BillingDetails from all concrete class tables. The tables are combined with a UNION operator, and a literal (in this case, 0 and 1) is inserted into the intermediate result; (look at the lines highlighted in yellow.) EF reads this to instantiate the correct class given the data from a particular row. A union requires that the queries that are combined, project over the same columns; hence, EF has to pad and fill up nonexistent columns with NULL. This query will really perform well since here we can let the database optimizer find the best execution plan to combine rows from several tables. There is also no Joins involved so it has a better performance than the SQL queries generated by TPT where a Join is required between the base and subclasses tables. Choosing Strategy GuidelinesBefore we get into this discussion, I want to emphasize that there is no one single "best strategy fits all scenarios" exists. As you saw, each of the approaches have their own advantages and drawbacks. Here are some rules of thumb to identify the best strategy in a particular scenario: If you don’t require polymorphic associations or queries, lean toward TPC—in other words, if you never or rarely query for BillingDetails and you have no class that has an association to BillingDetail base class. I recommend TPC (only) for the top level of your class hierarchy, where polymorphism isn’t usually required, and when modification of the base class in the future is unlikely. If you do require polymorphic associations or queries, and subclasses declare relatively few properties (particularly if the main difference between subclasses is in their behavior), lean toward TPH. Your goal is to minimize the number of nullable columns and to convince yourself (and your DBA) that a denormalized schema won’t create problems in the long run. If you do require polymorphic associations or queries, and subclasses declare many properties (subclasses differ mainly by the data they hold), lean toward TPT. Or, depending on the width and depth of your inheritance hierarchy and the possible cost of joins versus unions, use TPC. By default, choose TPH only for simple problems. For more complex cases (or when you’re overruled by a data modeler insisting on the importance of nullability constraints and normalization), you should consider the TPT strategy. But at that point, ask yourself whether it may not be better to remodel inheritance as delegation in the object model (delegation is a way of making composition as powerful for reuse as inheritance). Complex inheritance is often best avoided for all sorts of reasons unrelated to persistence or ORM. EF acts as a buffer between the domain and relational models, but that doesn’t mean you can ignore persistence concerns when designing your classes. SummaryIn this series, we focused on one of the main structural aspect of the object/relational paradigm mismatch which is inheritance and discussed how EF solve this problem as an ORM solution. We learned about the three well-known inheritance mapping strategies and their implementations in EF Code First. Hopefully it gives you a better insight about the mapping of inheritance hierarchies as well as choosing the best strategy for your particular scenario. Happy New Year and Happy Code-Firsting! References ADO.NET team blog Java Persistence with Hibernate book a { color: #5A99FF; } a:visited { color: #5A99FF; } .title { padding-bottom: 5px; font-family: Segoe UI; font-size: 11pt; font-weight: bold; padding-top: 15px; } .code, .typeName { font-family: consolas; } .typeName { color: #2b91af; } .padTop5 { padding-top: 5px; } .padTop10 { padding-top: 10px; } .exception { background-color: #f0f0f0; font-style: italic; padding-bottom: 5px; padding-left: 5px; padding-top: 5px; padding-right: 5px; }

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