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  • Pluggable Rules for Entity Framework Code First

    - by Ricardo Peres
    Suppose you want a system that lets you plug custom validation rules on your Entity Framework context. The rules would control whether an entity can be saved, updated or deleted, and would be implemented in plain .NET. Yes, I know I already talked about plugable validation in Entity Framework Code First, but this is a different approach. An example API is in order, first, a ruleset, which will hold the collection of rules: 1: public interface IRuleset : IDisposable 2: { 3: void AddRule<T>(IRule<T> rule); 4: IEnumerable<IRule<T>> GetRules<T>(); 5: } Next, a rule: 1: public interface IRule<T> 2: { 3: Boolean CanSave(T entity, DbContext ctx); 4: Boolean CanUpdate(T entity, DbContext ctx); 5: Boolean CanDelete(T entity, DbContext ctx); 6: String Name 7: { 8: get; 9: } 10: } Let’s analyze what we have, starting with the ruleset: Only has methods for adding a rule, specific to an entity type, and to list all rules of this entity type; By implementing IDisposable, we allow it to be cancelled, by disposing of it when we no longer want its rules to be applied. A rule, on the other hand: Has discrete methods for checking if a given entity can be saved, updated or deleted, which receive as parameters the entity itself and a pointer to the DbContext to which the ruleset was applied; Has a name property for helping us identifying what failed. A ruleset really doesn’t need a public implementation, all we need is its interface. The private (internal) implementation might look like this: 1: sealed class Ruleset : IRuleset 2: { 3: private readonly IDictionary<Type, HashSet<Object>> rules = new Dictionary<Type, HashSet<Object>>(); 4: private ObjectContext octx = null; 5:  6: internal Ruleset(ObjectContext octx) 7: { 8: this.octx = octx; 9: } 10:  11: public void AddRule<T>(IRule<T> rule) 12: { 13: if (this.rules.ContainsKey(typeof(T)) == false) 14: { 15: this.rules[typeof(T)] = new HashSet<Object>(); 16: } 17:  18: this.rules[typeof(T)].Add(rule); 19: } 20:  21: public IEnumerable<IRule<T>> GetRules<T>() 22: { 23: if (this.rules.ContainsKey(typeof(T)) == true) 24: { 25: foreach (IRule<T> rule in this.rules[typeof(T)]) 26: { 27: yield return (rule); 28: } 29: } 30: } 31:  32: public void Dispose() 33: { 34: this.octx.SavingChanges -= RulesExtensions.OnSaving; 35: RulesExtensions.rulesets.Remove(this.octx); 36: this.octx = null; 37:  38: this.rules.Clear(); 39: } 40: } Basically, this implementation: Stores the ObjectContext of the DbContext to which it was created for, this is so that later we can remove the association; Has a collection - a set, actually, which does not allow duplication - of rules indexed by the real Type of an entity (because of proxying, an entity may be of a type that inherits from the class that we declared); Has generic methods for adding and enumerating rules of a given type; Has a Dispose method for cancelling the enforcement of the rules. A (really dumb) rule applied to Product might look like this: 1: class ProductRule : IRule<Product> 2: { 3: #region IRule<Product> Members 4:  5: public String Name 6: { 7: get 8: { 9: return ("Rule 1"); 10: } 11: } 12:  13: public Boolean CanSave(Product entity, DbContext ctx) 14: { 15: return (entity.Price > 10000); 16: } 17:  18: public Boolean CanUpdate(Product entity, DbContext ctx) 19: { 20: return (true); 21: } 22:  23: public Boolean CanDelete(Product entity, DbContext ctx) 24: { 25: return (true); 26: } 27:  28: #endregion 29: } The DbContext is there because we may need to check something else in the database before deciding whether to allow an operation or not. And here’s how to apply this mechanism to any DbContext, without requiring the usage of a subclass, by means of an extension method: 1: public static class RulesExtensions 2: { 3: private static readonly MethodInfo getRulesMethod = typeof(IRuleset).GetMethod("GetRules"); 4: internal static readonly IDictionary<ObjectContext, Tuple<IRuleset, DbContext>> rulesets = new Dictionary<ObjectContext, Tuple<IRuleset, DbContext>>(); 5:  6: private static Type GetRealType(Object entity) 7: { 8: return (entity.GetType().Assembly.IsDynamic == true ? entity.GetType().BaseType : entity.GetType()); 9: } 10:  11: internal static void OnSaving(Object sender, EventArgs e) 12: { 13: ObjectContext octx = sender as ObjectContext; 14: IRuleset ruleset = rulesets[octx].Item1; 15: DbContext ctx = rulesets[octx].Item2; 16:  17: foreach (ObjectStateEntry entry in octx.ObjectStateManager.GetObjectStateEntries(EntityState.Added)) 18: { 19: Object entity = entry.Entity; 20: Type realType = GetRealType(entity); 21:  22: foreach (dynamic rule in (getRulesMethod.MakeGenericMethod(realType).Invoke(ruleset, null) as IEnumerable)) 23: { 24: if (rule.CanSave(entity, ctx) == false) 25: { 26: throw (new Exception(String.Format("Cannot save entity {0} due to rule {1}", entity, rule.Name))); 27: } 28: } 29: } 30:  31: foreach (ObjectStateEntry entry in octx.ObjectStateManager.GetObjectStateEntries(EntityState.Deleted)) 32: { 33: Object entity = entry.Entity; 34: Type realType = GetRealType(entity); 35:  36: foreach (dynamic rule in (getRulesMethod.MakeGenericMethod(realType).Invoke(ruleset, null) as IEnumerable)) 37: { 38: if (rule.CanDelete(entity, ctx) == false) 39: { 40: throw (new Exception(String.Format("Cannot delete entity {0} due to rule {1}", entity, rule.Name))); 41: } 42: } 43: } 44:  45: foreach (ObjectStateEntry entry in octx.ObjectStateManager.GetObjectStateEntries(EntityState.Modified)) 46: { 47: Object entity = entry.Entity; 48: Type realType = GetRealType(entity); 49:  50: foreach (dynamic rule in (getRulesMethod.MakeGenericMethod(realType).Invoke(ruleset, null) as IEnumerable)) 51: { 52: if (rule.CanUpdate(entity, ctx) == false) 53: { 54: throw (new Exception(String.Format("Cannot update entity {0} due to rule {1}", entity, rule.Name))); 55: } 56: } 57: } 58: } 59:  60: public static IRuleset CreateRuleset(this DbContext context) 61: { 62: Tuple<IRuleset, DbContext> ruleset = null; 63: ObjectContext octx = (context as IObjectContextAdapter).ObjectContext; 64:  65: if (rulesets.TryGetValue(octx, out ruleset) == false) 66: { 67: ruleset = rulesets[octx] = new Tuple<IRuleset, DbContext>(new Ruleset(octx), context); 68: 69: octx.SavingChanges += OnSaving; 70: } 71:  72: return (ruleset.Item1); 73: } 74: } It relies on the SavingChanges event of the ObjectContext to intercept the saving operations before they are actually issued. Yes, it uses a bit of dynamic magic! Very handy, by the way! So, let’s put it all together: 1: using (MyContext ctx = new MyContext()) 2: { 3: IRuleset rules = ctx.CreateRuleset(); 4: rules.AddRule(new ProductRule()); 5:  6: ctx.Products.Add(new Product() { Name = "xyz", Price = 50000 }); 7:  8: ctx.SaveChanges(); //an exception is fired here 9:  10: //when we no longer need to apply the rules 11: rules.Dispose(); 12: } Feel free to use it and extend it any way you like, and do give me your feedback! As a final note, this can be easily changed to support plain old Entity Framework (not Code First, that is), if that is what you are using.

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  • Executing Components in an Entity Component System

    - by John
    Ok so I am just starting to grasp the whole ECS paradigm right now and I need clarification on a few things. For the record, I am trying to develop a game using C++ and OpenGL and I'm relatively new to game programming. First of all, lets say I have an Entity class which may have several components such as a MeshRenderer,Collider etc. From what I have read, I understand that each "system" carries out a specific task such as calculating physics and rendering and may use more that one component if needed. So for example, I would have a MeshRendererSystem act on all entities with a MeshRenderer component. Looking at Unity, I see that each Gameobject has, by default, got components such as a renderer, camera, collider and rigidbody etc. From what I understand, an entity should start out as an empty "container" and should be filled with components to create a certain type of game object. So what I dont understand is how the "system" works in an entity component system. http://docs.unity3d.com/ScriptReference/GameObject.html So I have a GameObject(The Entity) class like class GameObject { public: GameObject(std::string objectName); ~GameObject(void); Component AddComponent(std::string name); Component AddComponent(Component componentType); }; So if I had a GameObject to model a warship and I wanted to add a MeshRenderer component, I would do the following: warship->AddComponent(new MeshRenderer()); In the MeshRenderers constructor, should I call on the MeshRendererSystem and "subscribe" the warship object to this system? In that case, the MeshRendererSystem should probably be a Singleton("shudder"). From looking at unity's GameObject, if each object potentially has a renderer or any of the components in the default GameObject class, then Unity would iterate over all objects available. To me, this seems kind of unnecessary since some objects might not need to be rendered for example. How, in practice, should these systems be implemented?

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  • Box2D Joints in entity components system

    - by Johnmph
    I search a way to have Box2D joints in an entity component system, here is what i found : 1) Having the joints in Box2D/Body component as parameters, we have a joint array with an ID by joint and having in the other body component the same joint ID, like in this example : Entity1 - Box2D/Body component { Body => (body parameters), Joints => { Joint1 => (joint parameters), others joints... } } // Joint ID = Joint1 Entity2 - Box2D/Body component { Body => (body parameters), Joints => { Joint1 => (joint parameters), others joints... } } // Same joint ID than in Entity1 There are 3 problems with this solution : The first problem is the implementation of this solution, we must manage the joints ID to create joints and to know between which bodies they are connected. The second problem is the parameters of joint, where are they got ? on the Entity1 or Entity2 ? If they are the same parameters for the joint, there is no problem but if they are differents ? The third problem is that we can't limit number of bodies to 2 by joint (which is mandatory), a joint can only link 2 bodies, in this solution, nothing prevents to create more than 2 entities with for each a body component with the same joint ID, in this case, how we know the 2 bodies to joint and what to do with others bodies ? 2) Same solution than the first solution but by having entities ID instead of Joint ID, like in this example : Entity1 - Box2D/Body component { Body => (body parameters), Joints => { Entity2 => (joint parameters), others joints... } } Entity2 - Box2D/Body component { Body => (body parameters), Joints => { Entity1 => (joint parameters), others joints... } } With this solution, we fix the first problem of the first solution but we have always the two others problems. 3) Having a Box2D/Joint component which is inserted in the entities which contains the bodies to joint (we share the same joint component between entities with bodies to joint), like in this example : Entity1 - Box2D/Body component { Body => (body parameters) } - Box2D/Joint component { Joint => (Joint parameters) } // Shared, same as in Entity2 Entity2 - Box2D/Body component { Body => (body parameters) } - Box2D/Joint component { Joint => (joint parameters) } // Shared, same as in Entity1 There are 2 problems with this solution : The first problem is the same problem than in solution 1 and 2 : We can't limit number of bodies to 2 by joint (which is mandatory), a joint can only link 2 bodies, in this solution, nothing prevents to create more than 2 entities with for each a body component and the shared joint component, in this case, how we know the 2 bodies to joint and what to do with others bodies ? The second problem is that we can have only one joint by body because entity components system allows to have only one component of same type in an entity. So we can't put two Joint components in the same entity. 4) Having a Box2D/Joint component which is inserted in the entity which contains the first body component to joint and which has an entity ID parameter (this entity contains the second body to joint), like in this example : Entity1 - Box2D/Body component { Body => (body parameters) } - Box2D/Joint component { Entity2 => (Joint parameters) } // Entity2 is the entity ID which contains the other body to joint, the first body being in this entity Entity2 - Box2D/Body component { Body => (body parameters) } There are exactly the same problems that in the third solution, the only difference is that we can have two differents joints by entity instead of one (by putting one joint component in an entity and another joint component in another entity, each joint referencing to the other entity). 5) Having a Box2D/Joint component which take in parameter the two entities ID which contains the bodies to joint, this component can be inserted in any entity, like in this example : Entity1 - Box2D/Body component { Body => (body parameters) } Entity2 - Box2D/Body component { Body => (body parameters) } Entity3 - Box2D/Joint component { Joint => (Body1 => Entity1, Body2 => Entity2, others parameters of joint) } // Entity1 is the ID of the entity which have the first body to joint and Entity2 is the ID of the entity which have the second body to joint (This component can be in any entity, that doesn't matter) With this solution, we fix the problem of the body limitation by joint, we can only have two bodies per joint, which is correct. And we are not limited by number of joints per body, because we can create an another Box2D/Joint component, referencing to Entity1 and Entity2 and put this component in a new entity. The problem of this solution is : What happens if we change the Body1 or Body2 parameter of Joint component at runtime ? We need to add code to sync the Body1/Body2 parameters changes with the real joint object. 6) Same as solution 3 but in a better way : Having a Box2D/Joint component Box2D/Joint which is inserted in the entities which contains the bodies to joint, we share the same joint component between these entities BUT the difference is that we create a new entity to link the body component with the joint component, like in this example : Entity1 - Box2D/Body component { Body => (body parameters) } // Shared, same as in Entity3 Entity2 - Box2D/Body component { Body => (body parameters) } // Shared, same as in Entity4 Entity3 - Box2D/Body component { Body => (body parameters) } // Shared, same as in Entity1 - Box2D/Joint component { Joint => (joint parameters) } // Shared, same as in Entity4 Entity4 - Box2D/Body component { Body => (body parameters) } // Shared, same as in Entity2 - Box2D/Joint component { Joint => (joint parameters) } // Shared, same as in Entity3 With this solution, we fix the second problem of the solution 3, because we can create an Entity5 which will have the shared body component of Entity1 and an another joint component so we are no longer limited in the joint number per body. But the first problem of solution 3 remains, because we can't limit the number of entities which have the shared joint component. To resolve this problem, we can add a way to limit the number of share of a component, so for the Joint component, we limit the number of share to 2, because we can only joint 2 bodies per joint. This solution would be perfect because there is no need to add code to sync changes like in the solution 5 because we are notified by the entity components system when components / entities are added to/removed from the system. But there is a conception problem : How to know easily and quickly between which bodies the joint operates ? Because, there is no way to find easily an entity with a component instance. My question is : Which solution is the best ? Is there any other better solutions ? Sorry for the long text and my bad english.

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  • Using Entity Framework Table splitting customisations in an ASP.Net application

    - by nikolaosk
    I have been teaching in the past few weeks many people on how to use Entity Framework. I have decided to provide some of the samples I am using in my classes. First let’s try to define what EF is and why it is going to help us to create easily data-centric applications.Entity Framework is an object-relational mapping (ORM) framework for the .NET Framework.EF addresses the problem of Object-relational impedance mismatch . I will not be talking about that mismatch because it is well documented in many...(read more)

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  • Entity component system -> handling components that depend on one another

    - by jtedit
    I really like the idea of an entity component system and feel it has great flexibility, but have a question. How should dependent components be handled? I'm not talking about how components should communicate with other components they depend on, I have that sorted, but rather how to ensure components are present. For example, an entity cannot have a "velocity" component if it doesn't have a "position" component, in the same way it cant have an "acceleration" component if it doesn't have a "velocity" component. My first idea was every component class overrides an "onAddedToEntity(Entity ent)" function. Then in that function it checks that prerequisite components are also added to the entity, eg: struct EntCompVelocity() : public EntityComponent{ //member variables here void onAddedToEntity(Entity ent){ if(!ent.hasComponent(EntCompPosition::Id)){ ent.addComponent(new EntCompPosition()); } } } This has the nice property that if the acceleration component adds the velocity component, the velocity component will itself add the position component to the entity so dependency "trees" will sort themselves out. However my concern is if I do this components will silently be added with default values and, in the example of adding position, many entities will appear at the origin. Another idea was to simple have the "Entity.addComponent();" function return false if the component's prerequisite components aren't already on the entity, this would force you to manually add the position component and set its value before adding the velocity component. Finally I could simply not ensure a components prerequisite components are added, the "UpdatePosition" system only deals with entities with both a position and velocity component, so therefore adding a velocity component without having a position component wont be a problem (it wont cause crashes due to null pointer/etc), but it does mean entities will carry useless unused data if you add components but not their prerequisite components. Does anyone have experience with this problem and/or any of these methods to solve it? How did you solve the problem?

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  • Entity framework entity class mapping with plain .net class

    - by Elan
    I have following in entity framework Table - Country Fields List item Country_ID Dialing_Code ISO_Alpha2 ISO_Alpha3 ISO_Full I would like to map only selected fields from this entity model to my domain class. My domain model class is public class DomainCountry { public int Country_ID { get; set; } public string Dialing_Code { get; set; } public string ISO_3166_1_Alpha_2 { get; set; } } The following will work however insert or update is not possible. In order to get insert or update we need to use ObjectSet< but it will not support in my case. IQueryable<DomainCountry> countries = context.Countries.Select( c => new DomainCountry { Country_ID = c.Country_Id, Dialing_Code = c.Dialing_Code, ISO_3166_1_Alpha_2 = c.ISO_3166_1_Alpha_2 }); It will be really fantastic could someone provide a nice solution for this. Ideally it will be kind of proxy class which will support all the futures however highly customizable i.e. only the columns we want to expose to the outer world

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  • Using Entity Framework Entity splitting customisations in an ASP.Net application

    - by nikolaosk
    I have been teaching in the past few weeks many people on how to use Entity Framework. I have decided to provide some of the samples I am using in my classes. First let’s try to define what EF is and why it is going to help us to create easily data-centric applications.Entity Framework is an object-relational mapping (ORM) framework for the .NET Framework.EF addresses the problem of Object-relational impedance mismatch . I will not be talking about that mismatch because it is well documented in many...(read more)

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  • Entity system and rendering types

    - by Papi75
    I would like to implement entity system in my game and I've got some question about entity system and rendering. Currently, my renderer got two types of elements: Current design Mesh : A default renderable with a Material, a Geometry and a Transformable Sprite : A type of mesh with some methods like "flip" and "setRect" methods and a rect member (With an imposed geometry, a quad) This objects inherit from "Spacial" class. Questions: How can I handle this two types in an entity system? I'm thinking about using "MeshComponent" and "SpriteComponent", but if I do that, an entity could have a Mesh and a Sprite at the same type, it's look stupid, right? I thought the idea to have a parent "rendering" component : "RenderableComponent" for "MeshComponent" and "SpriteComponent" but it will be difficult to handle "cast" in the game (ex: did I need to ask entity-getComponent or SpineComponent, …) Thanks a lot for reading me! My entity system work like that: --------------------------------------------------------------------------- Entity* entity = world->createEntity(); MeshComponent* mesh = entity->addComponent<MeshComponent>(material); mesh->loadFromFile("monkey.obj"); PhysicComponent* physic = entity->addComponent<PhysicComponent>(); physic->setMass(5.4f); physic->setVelocity( 0.5f, 2.f ); --------------------------------------------------------------------------- class RenderingSystem { private: Scene scene; public: void onEntityAdded( Entity* entity ) { scene.addMesh( entity->getComponent<MeshComponent>() ); } } class PhysicSystem { private: World world; public: void onEntityAdded( Entity* entity ) { world.addBody( entity->getComponent<PhysicComponent>()->getBody() ); } void process( Entity* entity ) { PhysicComponent* physic = entity->getComponent<PhysicComponent>(); } } ---------------------------------------------------------------------------

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  • How to include a child object's child object in Entity Framework 5

    - by Brendan Vogt
    I am using Entity Framework 5 code first and ASP.NET MVC 3. I am struggling to get a child object's child object to populate. Below are my classes.. Application class; public class Application { // Partial list of properties public virtual ICollection<Child> Children { get; set; } } Child class: public class Child { // Partial list of properties public int ChildRelationshipTypeId { get; set; } public virtual ChildRelationshipType ChildRelationshipType { get; set; } } ChildRelationshipType class: public class ChildRelationshipType { public int Id { get; set; } public string Name { get; set; } } Part of GetAll method in the repository to return all the applications: return DatabaseContext.Applications .Include("Children"); The Child class contains a reference to the ChildRelationshipType class. To work with an application's children I would have something like this: foreach (Child child in application.Children) { string childName = child.ChildRelationshipType.Name; } I get an error here that the object context is already closed. How do I specify that each child object must include the ChildRelationshipType object like what I did above?

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  • Entity Type specific updates in entity component system

    - by Nathan
    I am currently familiarizing myself with the entity component paradigm. For an example, take a collision system, that detects if entities collide and if they do let them explode. So the collision system has to test collision based on the position component and then set the state of those entities to exploding. But what if the "effect" (setting the state to exploding) is different for different entities? For example, a ship fades out while for an asteroid a particle system must be created. Since entities and components are only data, this must happen in some system. The collision system could do it, but then it must switch over the entity type, which in my opinion is a cumbersome and difficult to extend solution. So how do I trigger "entity type dependend" updates on an entity?

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  • Differences Between NHibernate and Entity Framework

    - by Ricardo Peres
    Introduction NHibernate and Entity Framework are two of the most popular O/RM frameworks on the .NET world. Although they share some functionality, there are some aspects on which they are quite different. This post will describe this differences and will hopefully help you get started with the one you know less. Mind you, this is a personal selection of features to compare, it is by no way an exhaustive list. History First, a bit of history. NHibernate is an open-source project that was first ported from Java’s venerable Hibernate framework, one of the first O/RM frameworks, but nowadays it is not tied to it, for example, it has .NET specific features, and has evolved in different ways from those of its Java counterpart. Current version is 3.3, with 3.4 on the horizon. It currently targets .NET 3.5, but can be used as well in .NET 4, it only makes no use of any of its specific functionality. You can find its home page at NHForge. Entity Framework 1 came out with .NET 3.5 and is now on its second major version, despite being version 4. Code First sits on top of it and but came separately and will also continue to be released out of line with major .NET distributions. It is currently on version 4.3.1 and version 5 will be released together with .NET Framework 4.5. All versions will target the current version of .NET, at the time of their release. Its home location is located at MSDN. Architecture In NHibernate, there is a separation between the Unit of Work and the configuration and model instances. You start off by creating a Configuration object, where you specify all global NHibernate settings such as the database and dialect to use, the batch sizes, the mappings, etc, then you build an ISessionFactory from it. The ISessionFactory holds model and metadata that is tied to a particular database and to the settings that came from the Configuration object, and, there will typically be only one instance of each in a process. Finally, you create instances of ISession from the ISessionFactory, which is the NHibernate representation of the Unit of Work and Identity Map. This is a lightweight object, it basically opens and closes a database connection as required and keeps track of the entities associated with it. ISession objects are cheap to create and dispose, because all of the model complexity is stored in the ISessionFactory and Configuration objects. As for Entity Framework, the ObjectContext/DbContext holds the configuration, model and acts as the Unit of Work, holding references to all of the known entity instances. This class is therefore not lightweight as its NHibernate counterpart and it is not uncommon to see examples where an instance is cached on a field. Mappings Both NHibernate and Entity Framework (Code First) support the use of POCOs to represent entities, no base classes are required (or even possible, in the case of NHibernate). As for mapping to and from the database, NHibernate supports three types of mappings: XML-based, which have the advantage of not tying the entity classes to a particular O/RM; the XML files can be deployed as files on the file system or as embedded resources in an assembly; Attribute-based, for keeping both the entities and database details on the same place at the expense of polluting the entity classes with NHibernate-specific attributes; Strongly-typed code-based, which allows dynamic creation of the model and strongly typing it, so that if, for example, a property name changes, the mapping will also be updated. Entity Framework can use: Attribute-based (although attributes cannot express all of the available possibilities – for example, cascading); Strongly-typed code mappings. Database Support With NHibernate you can use mostly any database you want, including: SQL Server; SQL Server Compact; SQL Server Azure; Oracle; DB2; PostgreSQL; MySQL; Sybase Adaptive Server/SQL Anywhere; Firebird; SQLLite; Informix; Any through OLE DB; Any through ODBC. Out of the box, Entity Framework only supports SQL Server, but a number of providers exist, both free and commercial, for some of the most used databases, such as Oracle and MySQL. See a list here. Inheritance Strategies Both NHibernate and Entity Framework support the three canonical inheritance strategies: Table Per Type Hierarchy (Single Table Inheritance), Table Per Type (Class Table Inheritance) and Table Per Concrete Type (Concrete Table Inheritance). Associations Regarding associations, both support one to one, one to many and many to many. However, NHibernate offers far more collection types: Bags of entities or values: unordered, possibly with duplicates; Lists of entities or values: ordered, indexed by a number column; Maps of entities or values: indexed by either an entity or any value; Sets of entities or values: unordered, no duplicates; Arrays of entities or values: indexed, immutable. Querying NHibernate exposes several querying APIs: LINQ is probably the most used nowadays, and really does not need to be introduced; Hibernate Query Language (HQL) is a database-agnostic, object-oriented SQL-alike language that exists since NHibernate’s creation and still offers the most advanced querying possibilities; well suited for dynamic queries, even if using string concatenation; Criteria API is an implementation of the Query Object pattern where you create a semi-abstract conceptual representation of the query you wish to execute by means of a class model; also a good choice for dynamic querying; Query Over offers a similar API to Criteria, but using strongly-typed LINQ expressions instead of strings; for this, although more refactor-friendlier that Criteria, it is also less suited for dynamic queries; SQL, including stored procedures, can also be used; Integration with Lucene.NET indexer is available. As for Entity Framework: LINQ to Entities is fully supported, and its implementation is considered very complete; it is the API of choice for most developers; Entity-SQL, HQL’s counterpart, is also an object-oriented, database-independent querying language that can be used for dynamic queries; SQL, of course, is also supported. Caching Both NHibernate and Entity Framework, of course, feature first-level cache. NHibernate also supports a second-level cache, that can be used among multiple ISessionFactorys, even in different processes/machines: Hashtable (in-memory); SysCache (uses ASP.NET as the cache provider); SysCache2 (same as above but with support for SQL Server SQL Dependencies); Prevalence; SharedCache; Memcached; Redis; NCache; Appfabric Caching. Out of the box, Entity Framework does not have any second-level cache mechanism, however, there are some public samples that show how we can add this. ID Generators NHibernate supports different ID generation strategies, coming from the database and otherwise: Identity (for SQL Server, MySQL, and databases who support identity columns); Sequence (for Oracle, PostgreSQL, and others who support sequences); Trigger-based; HiLo; Sequence HiLo (for databases that support sequences); Several GUID flavors, both in GUID as well as in string format; Increment (for single-user uses); Assigned (must know what you’re doing); Sequence-style (either uses an actual sequence or a single-column table); Table of ids; Pooled (similar to HiLo but stores high values in a table); Native (uses whatever mechanism the current database supports, identity or sequence). Entity Framework only supports: Identity generation; GUIDs; Assigned values. Properties NHibernate supports properties of entity types (one to one or many to one), collections (one to many or many to many) as well as scalars and enumerations. It offers a mechanism for having complex property types generated from the database, which even include support for querying. It also supports properties originated from SQL formulas. Entity Framework only supports scalars, entity types and collections. Enumerations support will come in the next version. Events and Interception NHibernate has a very rich event model, that exposes more than 20 events, either for synchronous pre-execution or asynchronous post-execution, including: Pre/Post-Load; Pre/Post-Delete; Pre/Post-Insert; Pre/Post-Update; Pre/Post-Flush. It also features interception of class instancing and SQL generation. As for Entity Framework, only two events exist: ObjectMaterialized (after loading an entity from the database); SavingChanges (before saving changes, which include deleting, inserting and updating). Tracking Changes For NHibernate as well as Entity Framework, all changes are tracked by their respective Unit of Work implementation. Entities can be attached and detached to it, Entity Framework does, however, also support self-tracking entities. Optimistic Concurrency Control NHibernate supports all of the imaginable scenarios: SQL Server’s ROWVERSION; Oracle’s ORA_ROWSCN; A column containing date and time; A column containing a version number; All/dirty columns comparison. Entity Framework is more focused on Entity Framework, so it only supports: SQL Server’s ROWVERSION; Comparing all/some columns. Batching NHibernate has full support for insertion batching, but only if the ID generator in use is not database-based (for example, it cannot be used with Identity), whereas Entity Framework has no batching at all. Cascading Both support cascading for collections and associations: when an entity is deleted, their conceptual children are also deleted. NHibernate also offers the possibility to set the foreign key column on children to NULL instead of removing them. Flushing Changes NHibernate’s ISession has a FlushMode property that can have the following values: Auto: changes are sent to the database when necessary, for example, if there are dirty instances of an entity type, and a query is performed against this entity type, or if the ISession is being disposed; Commit: changes are sent when committing the current transaction; Never: changes are only sent when explicitly calling Flush(). As for Entity Framework, changes have to be explicitly sent through a call to AcceptAllChanges()/SaveChanges(). Lazy Loading NHibernate supports lazy loading for Associated entities (one to one, many to one); Collections (one to many, many to many); Scalar properties (thing of BLOBs or CLOBs). Entity Framework only supports lazy loading for: Associated entities; Collections. Generating and Updating the Database Both NHibernate and Entity Framework Code First (with the Migrations API) allow creating the database model from the mapping and updating it if the mapping changes. Extensibility As you can guess, NHibernate is far more extensible than Entity Framework. Basically, everything can be extended, from ID generation, to LINQ to SQL transformation, HQL native SQL support, custom column types, custom association collections, SQL generation, supported databases, etc. With Entity Framework your options are more limited, at least, because practically no information exists as to what can be extended/changed. It features a provider model that can be extended to support any database. Integration With Other Microsoft APIs and Tools When it comes to integration with Microsoft technologies, it will come as no surprise that Entity Framework offers the best support. For example, the following technologies are fully supported: ASP.NET (through the EntityDataSource); ASP.NET Dynamic Data; WCF Data Services; WCF RIA Services; Visual Studio (through the integrated designer). Documentation This is another point where Entity Framework is superior: NHibernate lacks, for starters, an up to date API reference synchronized with its current version. It does have a community mailing list, blogs and wikis, although not much used. Entity Framework has a number of resources on MSDN and, of course, several forums and discussion groups exist. Conclusion Like I said, this is a personal list. I may come as a surprise to some that Entity Framework is so behind NHibernate in so many aspects, but it is true that NHibernate is much older and, due to its open-source nature, is not tied to product-specific timeframes and can thus evolve much more rapidly. I do like both, and I chose whichever is best for the job I have at hands. I am looking forward to the changes in EF5 which will add significant value to an already interesting product. So, what do you think? Did I forget anything important or is there anything else worth talking about? Looking forward for your comments!

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  • Allocating Entities within an Entity System

    - by miguel.martin
    I'm quite unsure how I should allocate/resemble my entities within my entity system. I have various options, but most of them seem to have cons associated with them. In all cases entities are resembled by an ID (integer), and possibly has a wrapper class associated with it. This wrapper class has methods to add/remove components to/from the entity. Before I mention the options, here is the basic structure of my entity system: Entity An object that describes an object within the game Component Used to store data for the entity System Contains entities with specific components Used to update entities with specific components World Contains entities and systems for the entity system Can create/destroy entites and have systems added/removed from/to it Here are my options, that I have thought of: Option 1: Do not store the Entity wrapper classes, and just store the next ID/deleted IDs. In other words, entities will be returned by value, like so: Entity entity = world.createEntity(); This is much like entityx, except I see some flaws in this design. Cons There can be duplicate entity wrapper classes (as the copy-ctor has to be implemented, and systems need to contain entities) If an Entity is destroyed, the duplicate entity wrapper classes will not have an updated value Option 2: Store the entity wrapper classes within an object pool. i.e. Entities will be return by pointer/reference, like so: Entity& e = world.createEntity(); Cons If there is duplicate entities, then when an entity is destroyed, the same entity object may be re-used to allocate another entity. Option 3: Use raw IDs, and forget about the wrapper entity classes. The downfall to this, I think, is the syntax that will be required for it. I'm thinking about doing thisas it seems the most simple & easy to implement it. I'm quite unsure about it, because of the syntax. i.e. To add a component with this design, it would look like: Entity e = world.createEntity(); world.addComponent<Position>(e, 0, 3); As apposed to this: Entity e = world.createEntity(); e.addComponent<Position>(0, 3); Cons Syntax Duplicate IDs

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  • In an Entity/Component system, can component data be implemented as a simple array of key-value pairs? [on hold]

    - by 010110110101
    I'm trying to wrap my head around how to organize components in an Entity Component Systems once everything in the current scene/level is loaded in memory. (I'm a hobbyist BTW) Some people seem to implement the Entity as an object that contains a list of of "Component" objects. Components contain data organized as an array of key-value pairs. Where the value is serialized "somehow". (pseudocode is loosely in C# for brevity) class Entity { Guid _id; List<Component> _components; } class Component { List<ComponentAttributeValue> _attributes; } class ComponentAttributeValue { string AttributeName; object AttributeValue; } Others describe Components as an in-memory "table". An entity acquires the component by having its key placed in a table. The attributes of the component-entity instance are like the columns in a table class Renderable_Component { List<RenderableComponentAttributeValue> _entities; } class RenderableComponentAttributeValue { Guid entityId; matrix4 transformation; // other stuff for rendering // everything is strongly typed } Others describe this actually as a table. (and such tables sound like an EAV database schema BTW) (and the value is serialized "somehow") Render_Component_Table ---------------- Entity Id Attribute Name Attribute Value and when brought into running code: class Entity { Guid _id; Dictionary<string, object> _attributes; } My specific question is: Given various components, (Renderable, Positionable, Explodeable, Hideable, etc) and given that each component has an attribute with a particular name, (TRANSLATION_MATRIX, PARTICLE_EMISSION_VELOCITY, CAN_HIDE, FAVORITE_COLOR, etc) should: an entity contain a list of components where each component, in turn, has their own array of named attributes with values serialized somehow or should components exist as in-memory tables of entity references and associated with each "row" there are "columns" representing the attribute with values that are specific to each entity instance and are strongly typed or all attributes be stored in an entity as a singular array of named attributes with values serialized somehow (could have name collisions) or something else???

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  • Performance due to entity update

    - by Rizzo
    I always think about 2 ways to code the global Step() function, both with pros and cons. Please note that AIStep is just to provide another more step for whoever who wants it. // Approach 1 step foreach( entity in entities ) { entity.DeltaStep( delta_time ); if( time_for_fixed_step ) entity.FixedStep(); if( time_for_AI_step ) entity.AIStep(); ... // all kind of updates you want } PRO: you just have to iterate once over all entities. CON: fidelity could be lower at some scenarios, since the entity.FixedStep() isn't going all at a time. // Approach 2 step foreach( entity in entities ) entity.DeltaStep( delta_time ); if( time_for_fixed_step ) foreach( entity in entities ) entity.FixedStep(); if( time_for_AI_step ) foreach( entity in entities ) entity.FixedStep(); // all kind of updates you want SEPARATED PRO: fidelity on FixedStep is higher, shouldn't be much time between all entities update, rather than Approach 1 where you may have to wait other updates until FixedStep() comes. CON: you iterate once for each kind of update. Also, a third approach could be a hybrid between both of them, something in the way of foreach( entity in entities ) { entity.DeltaStep( delta_time ); if( time_for_AI_step ) entity.AIStep(); // all kind of updates you want BUT FixedStep() } if( time_for_fixed_step ) { foreach( entity in entities ) { entity.FixedStep(); } } Just two loops, don't caring about time fidelity in nothing other than at FixedStep(). Any thoughts on this matter? Should it really matters to make all steps at once or am I thinking on problems that don't exist?

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  • Update Related Entity Of Detached Entity

    - by Hemslingo
    I'm having an issue updating an entity with multiple related entities. I've got a very simple model which consists of an article entity and a list of categories the article can be related to. You can choose from a check box list which of these categories are associated to it...which works fine. The problem crops up when I actually come to update an existing entity using the dbContext. As I am updating this entity, I have already detached it from the context ready to re-attach it later so the update can execute properly. I can see that after I posting the model, the category(s) are being added to the article entity just fine and it looks like it updates in the repository with no errors occurring. When I look in the database the article has updated as normal but the category(s) have not. Here is my (simplified) update code... public virtual bool Attach(T entity) { _dbContext.Entry(entity).State = EntityState.Modified; _dbSet.Attach(entity); return this.Commit(); } Any help will be much appreciated.

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  • Pre-filtering and shaping OData feeds using WCF Data Services and the Entity Framework - Part 2

    - by rajbk
    In the previous post, you saw how to create an OData feed and pre-filter the data. In this post, we will see how to shape the data. A sample project is attached at the bottom of this post. Pre-filtering and shaping OData feeds using WCF Data Services and the Entity Framework - Part 1 Shaping the feed The Product feed we created earlier returns too much information about our products. Let’s change this so that only the following properties are returned – ProductID, ProductName, QuantityPerUnit, UnitPrice, UnitsInStock. We also want to return only Products that are not discontinued.  Splitting the Entity To shape our data according to the requirements above, we are going to split our Product Entity into two and expose one through the feed. The exposed entity will contain only the properties listed above. We will use the other Entity in our Query Interceptor to pre-filter the data so that discontinued products are not returned. Go to the design surface for the Entity Model and make a copy of the Product entity. A “Product1” Entity gets created.   Rename Product1 to ProductDetail. Right click on the Product entity and select “Add Association” Make a one to one association between Product and ProductDetails.   Keep only the properties we wish to expose on the Product entity and delete all other properties on it (see diagram below). You delete a property on an Entity by right clicking on the property and selecting “delete”. Keep the ProductID on the ProductDetail. Delete any other property on the ProductDetail entity that is already present in the Product entity. Your design surface should look like below:    Mapping Entity to Database Tables Right click on “ProductDetail” and go to “Table Mapping”   Add a mapping to the “Products” table in the Mapping Details.   After mapping ProductDetail, you should see the following.   Add a referential constraint. Lets add a referential constraint which is similar to a referential integrity constraint in SQL. Double click on the Association between the Entities and add the constraint with “Principal” set to “Product”. Let us review what we did so far. We made a copy of the Product entity and called it ProductDetail We created a one to one association between these entities Excluding the ProductID, we made sure properties were not duplicated between these entities  We added a ProductDetail entity to Products table mapping (Entity to Database). We added a referential constraint between the entities. Lets build our project. We get the following error: ”'NortwindODataFeed.Product' does not contain a definition for 'Discontinued' and no extension method 'Discontinued' accepting a first argument of type 'NortwindODataFeed.Product' could be found …" The reason for this error is because our Product Entity no longer has a “Discontinued” property. We “moved” it to the ProductDetail entity since we want our Product Entity to contain only properties that will be exposed by our feed. Since we have a one to one association between the entities, we can easily rewrite our Query Interceptor like so: [QueryInterceptor("Products")] public Expression<Func<Product, bool>> OnReadProducts() { return o => o.ProductDetail.Discontinued == false; } Similarly, all “hidden” properties of the Product table are available to us internally (through the ProductDetail Entity) for any additional logic we wish to implement. Compile the project and view the feed. We see that the feed returns only the properties that were part of the requirement.   To see the data in JSON format, you have to create a request with the following request header Accept: application/json, text/javascript, */* (easy to do in jQuery) The result should look like this: { "d" : { "results": [ { "__metadata": { "uri": "http://localhost.:2576/DataService.svc/Products(1)", "type": "NorthwindModel.Product" }, "ProductID": 1, "ProductName": "Chai", "QuantityPerUnit": "10 boxes x 20 bags", "UnitPrice": "18.0000", "UnitsInStock": 39 }, { "__metadata": { "uri": "http://localhost.:2576/DataService.svc/Products(2)", "type": "NorthwindModel.Product" }, "ProductID": 2, "ProductName": "Chang", "QuantityPerUnit": "24 - 12 oz bottles", "UnitPrice": "19.0000", "UnitsInStock": 17 }, { ... ... If anyone has the $format operation working, please post a comment. It was not working for me at the time of writing this.  We have successfully pre-filtered our data to expose only products that have not been discontinued and shaped our data so that only certain properties of the Entity are exposed. Note that there are several other ways you could implement this like creating a QueryView, Stored Procedure or DefiningQuery. You have seen how easy it is to create an OData feed, shape the data and pre-filter it by hardly writing any code of your own. For more details on OData, Google it with your favorite search engine :-) Also check out the one of the most passionate persons I have ever met, Pablo Castro – the Architect of Aristoria WCF Data Services. Watch his MIX 2010 presentation titled “OData: There's a Feed for That” here. Download Sample Project for VS 2010 RTM NortwindODataFeed.zip

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  • insert,update, delete derived entity in entity framework 4.0

    - by user282807
    Hi! How do i insert an entity that is derived from another entity. here is my code but it's not working:(applicationreplacement derived from application Blockquote ObjectContect _ctx public void AddReplacementApp(Application entity,ApplicationReplacement rentity) { _ctx.CreateObjectSet<Application>(rentity); _ctx.SaveChanges(); } Blockquote

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  • Question on the implementation of my Entity System

    - by miguel.martin
    I am currently creating an Entity System, in C++, it is almost completed (I have all the code there, I just have to add a few things and test it). The only thing is, I can't figure out how to implement some features. This Entity System is based off a bit from the Artemis framework, however it is different. I'm not sure if I'll be able to type this out the way my head processing it. I'm going to basically ask whether I should do something over something else. Okay, now I'll give a little detail on my Entity System itself. Here are the basic classes that my Entity System uses to actually work: Entity - An Id (and some methods to add/remove/get/etc Components) Component - An empty abstract class ComponentManager - Manages ALL components for ALL entities within a Scene EntitySystem - Processes entities with specific components Aspect - The class that is used to help determine what Components an Entity must contain so a specific EntitySystem can process it EntitySystemManager - Manages all EntitySystems within a Scene EntityManager - Manages entities (i.e. holds all Entities, used to determine whether an Entity has been changed, enables/disables them, etc.) EntityFactory - Creates (and destroys) entities and assigns an ID to them Scene - Contains an EntityManager, EntityFactory, EntitySystemManager and ComponentManager. Has functions to update and initialise the scene. Now in order for an EntitySystem to efficiently know when to check if an Entity is valid for processing (so I can add it to a specific EntitySystem), it must recieve a message from the EntityManager (after a call of activate(Entity& e)). Similarly the EntityManager must know when an Entity is destroyed from the EntityFactory in the Scene, and also the ComponentManager must know when an Entity is created AND destroyed. I do have a Listener/Observer pattern implemented at the moment, but with this pattern I may remove a Listener (which is this case is dependent on the method being called). I mainly have this implemented for specific things related to a game, i.e. Teams, Tagging of entities, etc. So... I was thinking maybe I should call a private method (using friend classes) to send out when an Entity has been activated, deleted, etc. i.e. taken from my EntityFactory void EntityFactory::killEntity(Entity& e) { // if the entity doesn't exsist in the entity manager within the scene if(!getScene()->getEntityManager().doesExsist(e)) { return; // go back to the caller! (should throw an exception or something..) } // tell the ComponentManager and the EntityManager that we killed an Entity getScene()->getComponentManager().doOnEntityWillDie(e); getScene()->getEntityManager().doOnEntityWillDie(e); // notify the listners for(Mouth::iterator i = getMouth().begin(); i != getMouth().end(); ++i) { (*i)->onEntityWillDie(*this, e); } _idPool.addId(e.getId()); // add the ID to the pool delete &e; // delete the entity } As you can see on the lines where I am telling the ComponentManager and the EntityManager that an Entity will die, I am calling a method to make sure it handles it appropriately. Now I realise I could do this without calling it explicitly, with the help of that for loop notifying all listener objects connected to the EntityFactory's Mouth (an object used to tell listeners that there's an event), however is this a good idea (good design, or what)? I've gone over the PROS and CONS, I just can't decide what I want to do. Calling Explicitly: PROS Faster? Since these functions are explicitly called, they can't be "removed" CONS Not flexible Bad design? (friend functions) Calling through Listener objects (i.e. ComponentManager/EntityManager inherits from a EntityFactoryListener) PROS More Flexible? Better Design? CONS Slower? (virtual functions) Listeners can be removed, i.e. may be removed and not get called again during the program, which could cause in a crash. P.S. If you wish to view my current source code, I am hosting it on BitBucket.

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  • Entity Framework 4 mapping fragment error when adding new entity scalar

    - by Jason Morse
    I have an Entity Framework 4 model-first design. I create a first draft of my model in the designer and all was well. I compiled, generated database, etc. Later on I tried to add a string scalar (Nullable = true) to one of my existing entities and I keep getting this type of error when I compile: Error 3004: Problem in mapping fragments starting at line 569: No mapping specified for properties MyEntity.MyValue in Set MyEntities. An Entity with Key (PK) will not round-trip when: Entity is type [MyEntities.MyEntity] I keep having to manually open the EDMX file and correct the XML whenever I add scalars. Ideas on what's going on?

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  • Add Or Condition to Entity in Entity Framework

    - by Blakewell
    Can you add an "Or" condition to an entity in the entity framework? For example something like: Property1 == (1 or 2 or 3) The message I get when putting the value of "1 || 2 || 3" or "1,2,3" or "1 or 2 or 3" returns this message: condition is not compatible with the type of the member

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  • What .Net Namespace contains Entity for use in a generic repository?

    - by Sara
    I have a question that I'm ashamed to ask, but I'm going to have a go at it anyway. I am creating a generic repository in asp.net mvc. I came across an example on this website which I find to be exactly what I was looking for, but there is one problem. It references an object - Entity - and I don't know what namespace it is in. I typically create my repositories and use Entity Framework but I decided to use a generic repository because I am using the same code in multiple projects over and over again. Here is the code: public interface IRepository { void Save(ENTITY entity) where ENTITY : Entity; void Delete<ENTITY>(ENTITY entity) where ENTITY : Entity; ENTITY Load<ENTITY>(int id) where ENTITY : Entity; IQueryable<ENTITY> Query<ENTITY>() where ENTITY : Entity; IList<ENTITY> GetAll<ENTITY>() where ENTITY : Entity; IQueryable<ENTITY> Query<ENTITY>(IDomainQuery<ENTITY> whereQuery) where ENTITY : Entity; ENTITY Get<ENTITY>(int id) where ENTITY : Entity; IList<ENTITY> GetObjectsForIds<ENTITY>(string ids) where ENTITY : Entity; void Flush(); } Can someone please tell me what namespace Entity is in? As you can tell, a constraint is placed on the code so that it must be an Entity type. I know that there is an Entity in System.Data.Entity, but that isn't what I need. I have had instances before where I was looking for some namespace that took me forever to find, but I have searched and I'm unable to find the appropriate namespace to cast my generic items correctly. I could cast it as a class and be done with it, but it is bugging me that I can't find Entity anywhere. Can someone help me....please..... :-) Here is a link to the original post. http://stackoverflow.com/questions/1472719/asp-net-mvc-how-many-repositories

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  • Entity Framework + AutoMapper ( Entity to DTO and DTO to Entity )

    - by vbobruisk
    Hello. i got some problems using EF with AutoMapper. =/ for example : i got 2 related entities ( Customers and Orders ) and theyr DTO classes : class CustomerDTO { public string CustomerID {get;set;} public string CustomerName {get;set;} public IList< OrderDTO Orders {get;set;} } class OrderDTO { public string OrderID {get;set;} public string OrderDetails {get;set;} public CustomerDTO Customers {get;set;} } //when mapping Entity to DTO the code works Customers cust = getCustomer(id); Mapper.CreateMap< Customers, CustomerDTO (); Mapper.CreateMap< Orders, OrderDTO (); CustomerDTO custDTO = Mapper.Map(cust); //but when i try to map back from DTO to Entity it fails with AutoMapperMappingException. Mapper.Reset(); Mapper.CreateMap< CustomerDTO , Customers (); Mapper.CreateMap< OrderDTO , Orders (); Customers customerModel = Mapper.Map< CustomerDTO ,Customers (custDTO); // exception is thrown here Am i doeing something wrong ? Thanks in Advance !

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  • Databinding to an Entity Framework in WPF

    - by King Chan
    Is it good to use databinding to Entity Framework's Entity in WPF? I created a singleton entity framework context: To have only one connection and it won't open and close all the time. So I can pass the Entity around to any class, and can modify the Entity and make changes to the database. All ViewModels getting the entity out from the same Context and databinding to the View saves me time from mapping new object, but now I imagine there is problem in not using the newest Context: A ViewModel databinding to a Entity, then someone else updated the data. The ViewModel will still display the old data, because the Context is never being dispose to refresh. I always create new Context and then dispose of it. If I want to pass the Entity around, then there will be conflicts between Context and Entity. What is the suggested way of doing this ?

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  • What is an Entity? Why is it called Entity?

    - by rkrauter
    What is the deal with Entities (when talking about the Entity Framework)? From what I understand, it is pretty much an in memory representation of a data store like sql tables. Entities are smart enough to track changes and apply those changes to the data store. Is there anything more to it? Thanks in advance.

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  • Entity Framework self referencing entity deletion.

    - by Viktor
    Hello. I have a structure of folders like this: Folder1 Folder1.1 Folder1.2 Folder2 Folder2.1 Folder2.1.1 and so on.. The question is how to cascade delete them(i.e. when remove folder2 all children are also deleted). I can't set an ON DELETE action because MSSQL does not allow it. Can you give some suggesions? UPDATE: I wrote this stored proc, can I just leave it or it needs some modifications? SET ANSI_NULLS ON GO SET QUOTED_IDENTIFIER ON GO CREATE PROCEDURE sp_DeleteFoldersRecursive @parent_folder_id int AS BEGIN SET NOCOUNT ON; IF @parent_folder_id = 0 RETURN; CREATE TABLE #temp(fid INT ); DECLARE @Count INT; INSERT INTO #temp(fid) SELECT FolderId FROM Folders WHERE FolderId = @parent_folder_id; SET @Count = @@ROWCOUNT; WHILE @Count > 0 BEGIN INSERT INTO #temp(fid) SELECT FolderId FROM Folders WHERE EXISTS (SELECT FolderId FROM #temp WHERE Folders.ParentId = #temp.fid) AND NOT EXISTS (SELECT FolderId FROM #temp WHERE Folders.FolderId = #temp.fid); SET @Count = @@ROWCOUNT; END DELETE Folders FROM Folders INNER JOIN #temp ON Folders.FolderId = #temp.fid; DROP TABLE #temp; END GO

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