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  • How to rollback in EF4?

    - by Jaxidian
    In my research about rolling back transactions in EF4, it seems everybody refers to this blog post or offers a similar explanation. In my scenario, I'm wanting to do this in a unit testing scenario where I want to rollback practically everything I do within my unit testing context to keep from updating the data in the database (yeah, we'll increment counters but that's okay). In order to do this, is it best to follow the following plan? Am I missing some concept or anything else major with this (aside from my SetupMyTest and PerformMyTest functions won't really exist that way)? using (var ts = new TransactionScope()) { // Arrange SetupMyTest(context); // Act PerformMyTest(context); var numberOfChanges = context.SaveChanges(false); // if there's an issue, chances are that an exception has been thrown by now. // Assert Assert.IsTrue(numberOfChanges > 0, "Failed to _____"); // transaction will rollback because we do not ever call Complete on it }

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  • Using EF 4 on .NET 3.5 SP1

    - by KiD0M4N
    Hi guys, I was using the latest EF 4 bits in Visual Studio 2010 RC and have fallen in love with it. However, I have to develop a small web application using .NET 3.5 SP1 (VS 2008) for work... I was wondering if it was possible to somehow utilize EF 4 in .NET 3.5 SP1/VS 2008. Regards, Karan Misra

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  • TryGetObjectByKey... empty ObjectSets

    - by Rickjaah
    When I use TryGetObjectByKey on my ObjectContext, it returns an error. An item with a duplicate value already exists. When I look at my objectContext, I see that the ObjectSets are empty. What Am I doing wrong... When I enumerate the ObjectSet by hand, by using ToArray on it, or by using the debugger, it does work. LazyLoadingEnabled = true. I reuse 2 tables from another EDMX, but they are in different namespaces and they are not the objectSets i try to approach.

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  • EF 4 - associations with keys that dont match

    - by Steve Ward
    We're using POCOs and have 2 entities: Item and ItemContact. There are 1 or more contacts per item. Item has as a primary key: ItemID LanguageCode ItemContact has: ItemID ContactID We cant add an association with a referrential constraint as they have differing keys. There isnt a strict primary / foreign key as languageCode isnt in ItemContact and ContactID isnt in Item. How can we go about mapping this with an association for contacts for an item if there isnt a direct link but I still want to see the contacts for an item? One of the entities originates in a database view so it is not possible to add foreign keys to the database Thanks Stephen Ward

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  • EF4 CTP5 - Map foreign key without object references?

    - by anon
    I feel like this should have a simple answer, but I can't find it. I have 2 POCOs: public class Category { public int Id { get; set; } public string Name { get; set; } } public class Product { public int Id { get; set; } public int CategoryId { get; set; } } Notice that there are no object references on either POCO. With Code-First, how do I make EF4 CTP5 define a relationship between the two database tables? (I know this is an unusual scenario, but I am exploring what's possible and what's not with Code-First)

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  • 'Generic' ViewModel

    - by Ian MacPherson
    Using EF 4, I have several subtypes of a 'Business' entity (customers, suppliers, haulage companies etc). They DO need to be subtypes. I am building a general viewmodel which calls into a service from which a generic repository is accessed. As I have 4 subtypes, it would be good to have a 'generic' viewmodel used for all of these. Problem is of course is that I have to call a specific type into my generic repository, for example: BusinessToRetrieve = _repository .LoadEntity<Customer>(o => o.CustomerID == customerID); It would be good to be able to call <SomethingElse>, somethingElse being one or other of the subtypes), otherwise I shall have to create 4 near identical viemodels, which seems a waste of course! The subtype entity name is available to the viewmodel but I've been unable to figure out how to make the above call convert this into a type. An issue with achieving what I want is that presumably the lambda expression being passed in wouldn't be able to resolve on a 'generic' call ?

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  • EF4 and multiple abstract levels

    - by Cedric
    I need to use inheritance with EF4 and the TPH model created from DB. I created a new projet to test simples classes. There is my class model: There is my table in SQL SERVER 2008 : VEHICLE ID : int PK Owner : varchar(50) Consumption : float FirstCirculationDate : date Type : varchar(50) Discriminator : varchar(10) I added a condition in my EDMX on the Discriminator field to differentiate the Scooter, Car, Motorbike and Bike entities. MotorizedVehicle and Vehicle are Abstract. But when I compile, this error appears : Error 3032: Problem in mapping fragments starting at lines 78, 85:EntityTypes EF4InheritanceModel.Scooter, EF4InheritanceModel.Motorbike, EF4InheritanceModel.Car, EF4InheritanceModel.Bike are being mapped to the same rows in table Vehicle. Mapping conditions can be used to distinguish the rows that these types are mapped to. Edit : To Ladislav : I try it and error change to become it for all of my entities : Error 3034: Problem in mapping fragments starting at lines 72, 86:An entity is mapped to different rows within the same table. Ensure these two mapping fragments do not map two groups of entities with overlapping keys to two distinct groups of rows. To Henk (with Ladislay suggestion) : There are all of mappings details : What's wrong ? Thanks

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  • Maintaining state and data context between requests in ASP.NET + EF4

    - by Nick
    I have a EF4/ASP.NET web application that is structured to use POCOs and generic repositories, based essentially on this excellent article. The application is relatively sophisticated with one page that involves selection and linking of multiple entities to build up a complex user profile. This requires access to multiple entity types (20 or so) and associated repositories across multiple posts. When a repository is first accessed it uses the existing data context if exists, else it creates a new context. The problem is that if the lifetime of the context is only per-request (as suggested in the article) then you have to deal with multiple contexts and the complexity around detaching and attaching entities from contexts. My solution is to share the context between posts by creating a single View Model that includes all required repositories (initialised to share the same context) plus any associated data and store this model in a Session variable, retrieving from Session on subsequent page requests. Therefore maintaining the same context across all posts until the profile is saved. This works fine BUT I am concerned that I don't actually know exactly what is stored in the model session variable or more importantly the size of the Session variable. So two questions I suppose: firstly should I look for a better solution to handle the shared context across posts issue (any suggestions welcome)? And secondly what is actually stored in the Session when it includes a repository plus context? Any help appreciated!

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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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  • Generate money type fields using code first EF CTP5

    - by BBHorus
    In this blog post: EF4 Code First Control Unicode and Decimal Precision, Scale with Attributes, Dane Morgridge used attributes to control the creation of different types on your database. ...And I found this pretty unique BTW!!! How do I generate money type fields in my resulting database using code first API of EF CTP5, if is possible to do it from your model, using conventions or attributes? Sorry about my English is not my main language. Thanks in advance.

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  • EF Many-to-many dbset.Include in DAL on GenericRepository

    - by Bryant
    I can't get the QueryObjectGraph to add INCLUDE child tables if my life depended on it...what am I missing? Stuck for third day on something that should be simple :-/ DAL: public abstract class RepositoryBase<T> where T : class { private MyLPL2Context dataContext; private readonly IDbSet<T> dbset; protected RepositoryBase(IDatabaseFactory databaseFactory) { DatabaseFactory = databaseFactory; dbset = DataContext.Set<T>(); DataContext.Configuration.LazyLoadingEnabled = true; } protected IDatabaseFactory DatabaseFactory { get; private set; } protected MyLPL2Context DataContext { get { return dataContext ?? (dataContext = DatabaseFactory.Get()); } } public IQueryable<T> QueryObjectGraph(Expression<Func<T, bool>> filter, params string[] children) { foreach (var child in children) { dbset.Include(child); } return dbset.Where(filter); } ... DAL repositories public interface IBreed_TranslatedSqlRepository : ISqlRepository<Breed_Translated> { } public class Breed_TranslatedSqlRepository : RepositoryBase<Breed_Translated>, IBreed_TranslatedSqlRepository { public Breed_TranslatedSqlRepository(IDatabaseFactory databaseFactory) : base(databaseFactory) {} } BLL Repo: public IQueryable<Breed_Translated> QueryObjectGraph(Expression<Func<Breed_Translated, bool>> filter, params string[] children) { return _r.QueryObjectGraph(filter, children); } Controller: var breeds1 = _breedTranslatedRepository .QueryObjectGraph(b => b.Culture == culture, new string[] { "AnimalType_Breed" }) .ToList(); I can't get to Breed.AnimalType_Breed.AnimalTypeId ..I can drill as far as Breed.AnimalType_Breed then the intelisense expects an expression? Cues if any, DB Tables: bold is many-to-many Breed, Breed_Translated, AnimalType_Breed, AnimalType, ...

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  • EF 4.0 Code only assocation from abstract to derived

    - by Jeroen
    Using EF 4.0 Code only i want to make an assocation between an abstract and normal class. I have class 'Item', 'ContentBase' and 'Test'. 'ContentBase' is abstract and 'Test' derives from it. 'ContentBase' has a property 'Item' that links to an instance of 'Item'. So that 'Test.Item' or any class that derives from 'ContentBase' has an 'Item' navigation property. In my DB every record for Test has a matching record for Item. public class Item { public int Id { get; set;} } public abstract class ContentBase { public int ContentId { get; set;} public int Id { get; set;} public Item Item { get; set;} } public class Test : ContentBase { public string Name { get; set;} } now some init code public void SomeInitFunction() { var itemConfig = new EntityConfiguration<Item>(); itemConfig.HasKey(p => p.Id); itemConfig.Property(p => p.Id).IsIdentity(); this.ContextBuilder.Configurations.Add(itemConfig); var testConfig = new EntityConfiguration<Test>(); testConfig.HasKey(p => p.ContentId); testConfig.Property(p => p.ContentId).IsIdentity(); // the problem testConfig.Relationship(p => p.Item).HasConstraint((p, q) => p.Id == q.Id); this.ContextBuilder.Configurations.Add(testConfig); } This gives an error: A key is registered for the derived type 'Test'. Keys must be registered for the root type 'ContentBase'. anyway i try i get an error. What am i a doing wrong?

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  • Table-per-type inheritance insert problem

    - by gzak
    I followed this article on making a table-per-type inheritance model for my entities, but I get the following error when I try to add an instance of a subclass to the database. Here is how I create the subtype: var cust = db.Users.CreateObject<Customer>(); // Customer inherits User db.Users.AddObject(cust); db.SaveChanges(); I get the following error when I make that last call: "A value shared across entities or associations is generated in more than one location. Check that mapping does not split an EntityKey to multiple store-generated columns." With the following inner exception: "An item with the same key has already been added." Any ideas on what I could be missing?

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  • WCF data services (OData), query with inheritance limitation?

    - by Mathieu Hétu
    Project: WCF Data service using internally EF4 CTP5 Code-First approach. I configured entities with inheritance (TPH). See previous question on this topic: Previous question about multiple entities- same table The mapping works well, and unit test over EF4 confirms that queries runs smoothly. My entities looks like this: ContactBase (abstract) Customer (inherits from ContactBase), this entity has also several Navigation properties toward other entities Resource (inherits from ContactBase) I have configured a discriminator, so both Customer and Resource map to the same table. Again, everythings works fine on the Ef4 point of view (unit tests all greens!) However, when exposing this DBContext over WCF Data services, I get: - CustomerBases sets exposed (Customers and Resources sets seems hidden, is it by design?) - When I query over Odata on Customers, I get this error: Navigation Properties are not supported on derived entity types. Entity Set 'ContactBases' has a instance of type 'CodeFirstNamespace.Customer', which is an derived entity type and has navigation properties. Please remove all the navigation properties from type 'CodeFirstNamespace.Customer'. Stacktrace: at System.Data.Services.Serializers.SyndicationSerializer.WriteObjectProperties(IExpandedResult expanded, Object customObject, ResourceType resourceType, Uri absoluteUri, String relativeUri, SyndicationItem item, DictionaryContent content, EpmSourcePathSegment currentSourceRoot) at System.Data.Services.Serializers.SyndicationSerializer.WriteEntryElement(IExpandedResult expanded, Object element, ResourceType expectedType, Uri absoluteUri, String relativeUri, SyndicationItem target) at System.Data.Services.Serializers.SyndicationSerializer.<DeferredFeedItems>d__b.MoveNext() at System.ServiceModel.Syndication.Atom10FeedFormatter.WriteItems(XmlWriter writer, IEnumerable`1 items, Uri feedBaseUri) at System.ServiceModel.Syndication.Atom10FeedFormatter.WriteFeedTo(XmlWriter writer, SyndicationFeed feed, Boolean isSourceFeed) at System.ServiceModel.Syndication.Atom10FeedFormatter.WriteFeed(XmlWriter writer) at System.ServiceModel.Syndication.Atom10FeedFormatter.WriteTo(XmlWriter writer) at System.Data.Services.Serializers.SyndicationSerializer.WriteTopLevelElements(IExpandedResult expanded, IEnumerator elements, Boolean hasMoved) at System.Data.Services.Serializers.Serializer.WriteRequest(IEnumerator queryResults, Boolean hasMoved) at System.Data.Services.ResponseBodyWriter.Write(Stream stream) Seems like a limitation of WCF Data services... is it? Not much documentation can be found on the web about WCF Data services (OData) and inheritance specifications. How can I overpass this exception? I need these navigation properties on derived entities, and inheritance seems the only way to provide mapping of 2 entites on the same table with Ef4 CTP5... Any thoughts?

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  • Why won't EF4 generate a method to support my Function Import?

    - by Deane
    I have a stored proc in my database which returns an integer. I added a Function Import to my model. This appears in the EDMX file: <Function Name="GetTotalEntityCount" Aggregate="false" BuiltIn="false" NiladicFunction="false" IsComposable="false" ParameterTypeSemantics="AllowImplicitConversion" Schema="dbo" /> However, no method actually gets generated for this. It should be top level, right? using (MyContext context = new MyContext()) { context.MyMethodShouldBeRightHere(); } Nothing appears in Intellisense, I've gone through the designer.cs file and there's nothing in there, and reflected the DLL...nothing. The code generator is just not generating any code to support this stored proc. I added another table to my database and updated the model, and that came in, so the model will update, it's just specifically ignoring this stored proc. I've tried everything I can think of, and consulted every resource I can find, and as near as I can tell, I'm doing everything right. I'm using EF4, database-first. (I'm pretty sure on the version, anyway. This shows up in the generated file: Runtime Version:4.0.30319.1 )

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  • EntityFramwork System.OutOfMemoryException on 100MB upload

    - by Win
    Upload works fine for 62MB file. However, it throws exception if it is 100MB. I found few questions in stackoverflow, but none is very specific about datatype. Appreciate your help! ASP.Net 4, IIS7, EntityFramework 4.1, Visual Studio 2010 SP1, SQL 2008 DataType is varbinary(max) applicationHost.config <section name="requestFiltering" overrideModeDefault="Allow" /> web.config <httpRuntime maxRequestLength="1148576" executionTimeout="3600"/> <security > <requestFiltering> <requestLimits maxAllowedContentLength="112400000" /> </requestFiltering> </security>

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  • Help decoding MSDN Dynamic Data Article

    - by davemackey
    I'm trying to run through this msdn article: http://msdn.microsoft.com/en-us/library/dd723645.aspx One of the steps is: In the class file for the page, change the base class from UserControl to EntityTemplateUserControl. Nowhere is it made clear what page is being referenced. Can someone help me? I don't see any relevant class in the pages I have, so I assumed maybe they were talking about the ascx and didn't really mean page, but I'm not seeing an option there either.

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  • Where is the best place to call the .tolist(); inside my controller classes or inside my model repository classes

    - by john G
    I have the following action method, inside my asp.net mvc web application:- public JsonResult LoadZoneByDataCenter(string id) { var zonelist = repository.getrealtedzone(Convert.ToInt32(id)).ToList(); //code goes here Which calls the following model repository method:- public IQueryable<Zone> getrealtedzone(int? dcid) { return tms.Zones.Where(a=> a.DataCenterID == dcid || dcid == null); } Currently I am calling the .tolist() which will interpret the Database from my action method, but my question is where is the best place to call the .tolist() inside the controller or inside the model classes and why ? thanks

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  • ZendFramework Headscript Helper - Make scripts unique

    - by tokam
    How can I ensure that the headScript and headStyle helper include css files only once when added? The reason I am asking is that I would like to display some contents in a lightbox and all Flashmassages.E.g. notifications like profile successfully edited. To display flashmessages in the lightbox i would like to check at the top of my layout script if they are set, in case they are i would like to attach the required javascript library using the headScript helper. The problem is that I have no control about the scripts which were already added at this point. Maybe at a page where the library is needed for an other use case, it has already been added with addScript. How can I ensure all scripts are added only once to my helper? I already checked that these helpers extend Zend_View_Helper_Placeholder_Container_Standalone which uses an ArrayObject internally to hold the data and provides getters & setter to the array object. Maybe a solution here would be to check each time when adding a script file if it already exists using the ArrayObject?

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  • EF 4 Query - Issue with Multiple Parameters

    - by Brian
    Hello, A trick to avoiding filtering by nullable parameters in SQL was something like the following: select * from customers where (@CustomerName is null or CustomerName = @CustomerName) This worked well for me in LINQ to SQL: string customerName = "XYZ"; var results = (from c in ctx.Customers where (customerName == null || (customerName != null && c.CustomerName == customerName)) select c); But that above query, when in ADO.NET EF, doesn't work for me; it should filter by customer name because it exists, but it doesn't. Instead, it's querying all the customer records. Now, this is a simplified example, because I have many fields that I'm utilizing this kind of logic with. But it never actually filters, queries all the records, and causes a timeout exception. But the wierd thing is another query does something similarly, with no issues. Any ideas why? Seems like a bug to me, or is there a workaround for this? I've since switched to extension methods which works. Thanks.

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  • A generic Find method to search by Guid type for class implementing IDbSet interface

    - by imak
    I am implementing a FakeDataSet class by implementing IDbSet interface. As part of implementing this interface, I have to implement Find method. All my entity classes has an Guid type Id column. I am trying to implement Find method for this FakeDbSet class but having hard time to write it in a generic way. Below is my attempts for writing this method but since it does not know about Id been Guid type, I am getting compilation error on m.Id call. Any ideas on how this could be accomplished? public class FakeDataSet<T> : IDbSet<T> where T: class, new() { // Other methods for implementing IDbSet interface public T Find(params object[] keyValues) { var keyValue = (Guid)keyValues.FirstOrDefault(); return this.SingleOrDefault(m => m.Id == keyValue); // How can I write this } }

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  • Getting a mirrored mesh from my data structure

    - by Steve
    Here's the background: I'm in the beginning stages of an RTS game in Unity. I have a procedurally generated terrain with a perlin-noise height map, as well as a function to generate a river. The problem is that the graphical creation of the map is taking the data structure of the map and rotating it by 180 degrees. I noticed this problem when I was creating my rivers. I would set the River's height to flat, and noticed that the actual tiles that were flat in the graphical representation were flipped and mirrored. Here's 3 screenshots of the map from different angles: http://imgur.com/a/VLHHq As you can see, if you flipped (graphically) the river by 180 degrees on the z axis, it would fit where the terrain is flattened. I have a suspicion it is being caused by a misunderstanding on my part of how vertices work. Alas, here is a snippet of the code that is used: This code here creates a new array of Tile objects, which hold the information for each tile, including its type, coordinate, height, and it's 4 vertices public DTileMap (int size_x, int size_y) { this.size_x = size_x; this.size_y = size_y; //Initialize Map_Data Array of Tile Objects map_data = new Tile[size_x, size_y]; for (int j = 0; j < size_y; j++) { for (int i = 0; i < size_x; i++) { map_data [i, j] = new Tile (); map_data[i,j].coordinate.x = (int)i; map_data[i,j].coordinate.y = (int)j; map_data[i,j].vertices[0] = new Vector3 (i * GTileMap.TileMap.tileSize, map_data[i,j].Height, -j * GTileMap.TileMap.tileSize); map_data[i,j].vertices[1] = new Vector3 ((i+1) * GTileMap.TileMap.tileSize, map_data[i,j].Height, -(j) * GTileMap.TileMap.tileSize); map_data[i,j].vertices[2] = new Vector3 (i * GTileMap.TileMap.tileSize, map_data[i,j].Height, -(j-1) * GTileMap.TileMap.tileSize); map_data[i,j].vertices[3] = new Vector3 ((i+1) * GTileMap.TileMap.tileSize, map_data[i,j].Height, -(j-1) * GTileMap.TileMap.tileSize); } } This code sets the river tiles to height 0 foreach (Tile t in map_data) { if (t.realType == "Water") { t.vertices[0].y = 0f; t.vertices[1].y = 0f; t.vertices[2].y = 0f; t.vertices[3].y = 0f; } } And below is the code to generate the actual graphics from the data: public void BuildMesh () { DTileMap.DTileMap map = new DTileMap.DTileMap (size_x, size_z); int numTiles = size_x * size_z; int numTris = numTiles * 2; int vsize_x = size_x + 1; int vsize_z = size_z + 1; int numVerts = vsize_x * vsize_z; // Generate the mesh data Vector3[] vertices = new Vector3[ numVerts ]; Vector3[] normals = new Vector3[numVerts]; Vector2[] uv = new Vector2[numVerts]; int[] triangles = new int[ numTris * 3 ]; int x, z; for (z=0; z < vsize_z; z++) { for (x=0; x < vsize_x; x++) { normals [z * vsize_x + x] = Vector3.up; uv [z * vsize_x + x] = new Vector2 ((float)x / size_x, 1f - (float)z / size_z); } } for (z=0; z < vsize_z; z+=1) { for (x=0; x < vsize_x; x+=1) { if (x == vsize_x - 1 && z == vsize_z - 1) { vertices [z * vsize_x + x] = DTileMap.DTileMap.map_data [x - 1, z - 1].vertices [3]; } else if (z == vsize_z - 1) { vertices [z * vsize_x + x] = DTileMap.DTileMap.map_data [x, z - 1].vertices [2]; } else if (x == vsize_x - 1) { vertices [z * vsize_x + x] = DTileMap.DTileMap.map_data [x - 1, z].vertices [1]; } else { vertices [z * vsize_x + x] = DTileMap.DTileMap.map_data [x, z].vertices [0]; vertices [z * vsize_x + x+1] = DTileMap.DTileMap.map_data [x, z].vertices [1]; vertices [(z+1) * vsize_x + x] = DTileMap.DTileMap.map_data [x, z].vertices [2]; vertices [(z+1) * vsize_x + x+1] = DTileMap.DTileMap.map_data [x, z].vertices [3]; } } } } for (z=0; z < size_z; z++) { for (x=0; x < size_x; x++) { int squareIndex = z * size_x + x; int triOffset = squareIndex * 6; triangles [triOffset + 0] = z * vsize_x + x + 0; triangles [triOffset + 2] = z * vsize_x + x + vsize_x + 0; triangles [triOffset + 1] = z * vsize_x + x + vsize_x + 1; triangles [triOffset + 3] = z * vsize_x + x + 0; triangles [triOffset + 5] = z * vsize_x + x + vsize_x + 1; triangles [triOffset + 4] = z * vsize_x + x + 1; } } // Create a new Mesh and populate with the data Mesh mesh = new Mesh (); mesh.vertices = vertices; mesh.triangles = triangles; mesh.normals = normals; mesh.uv = uv; // Assign our mesh to our filter/renderer/collider MeshFilter mesh_filter = GetComponent<MeshFilter> (); MeshCollider mesh_collider = GetComponent<MeshCollider> (); mesh_filter.mesh = mesh; mesh_collider.sharedMesh = mesh; calculateMeshTangents (mesh); BuildTexture (map); } If this looks familiar to you, its because i got most of it from Quill18. I've been slowly adapting it for my uses. And please include any suggestions you have for my code. I'm still in the very early prototyping stage.

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  • Programação paralela no .NET Framework 4 – Parte I

    - by anobre
    Introdução O avanço de tecnologia nos últimos anos forneceu, a baixo custo, acesso  a workstations com inúmeros CPUs. Facilmente encontramos hoje máquinas clientes com 2, 4 e até 8 núcleos, sem considerar os “super-servidores” com até 36 processadores :) Da wikipedia: A Unidade central de processamento (CPU, de acordo com as iniciais em inglês) ou o processador é a parte de um sistema de computador que executa as instruções de um programa de computador, e é o elemento primordial na execução das funções de um computador. Este termo tem sido usado na indústria de computadores pelo menos desde o início dos anos 1960[1]. A forma, desenho e implementação de CPUs têm mudado dramaticamente desde os primeiros exemplos, mas o seu funcionamento fundamental permanece o mesmo. Fazendo uma analogia, seria muito interessante delegarmos tarefas no mundo real que podem ser executadas independentemente a pessoas diferentes, atingindo desta forma uma  maior performance / produtividade na sua execução. A computação paralela se baseia na idéia que um problema maior pode ser dividido em problemas menores, sendo resolvidos de forma paralela. Este pensamento é utilizado há algum tempo por HPC (High-performance computing), e através das facilidades dos últimos anos, assim como a preocupação com consumo de energia, tornaram esta idéia mais atrativa e de fácil acesso a qualquer ambiente. No .NET Framework A plataforma .NET apresenta um runtime, bibliotecas e ferramentas para fornecer uma base de acesso fácil e rápido à programação paralela, sem trabalhar diretamente com threads e thread pool. Esta série de posts irá apresentar todos os recursos disponíveis, iniciando os estudos pela TPL, ou Task Parallel Library. Task Parallel Library A TPL é um conjunto de tipos localizados no namespace System.Threading e System.Threading.Tasks, a partir da versão 4 do framework. A partir da versão 4 do framework, o TPL é a maneira recomendada para escrever código paralelo e multithreaded. http://msdn.microsoft.com/en-us/library/dd460717(v=VS.100).aspx Task Parallelism O termo “task parallelism”, ou em uma tradução live paralelismo de tarefas, se refere a uma ou mais tarefas sendo executadas de forma simultanea. Considere uma tarefa como um método. A maneira mais fácil de executar tarefas de forma paralela é o código abaixo: Parallel.Invoke(() => TrabalhoInicial(), () => TrabalhoSeguinte()); O que acontece de verdade? Por trás nos panos, esta instrução instancia de forma implícita objetos do tipo Task, responsável por representar uma operação assíncrona, não exatamente paralela: public class Task : IAsyncResult, IDisposable É possível instanciar Tasks de forma explícita, sendo uma alternativa mais complexa ao Parallel.Invoke. var task = new Task(() => TrabalhoInicial()); task.Start(); Outra opção de instanciar uma Task e já executar sua tarefa é: var t = Task<int>.Factory.StartNew(() => TrabalhoInicialComValor());var t2 = Task<int>.Factory.StartNew(() => TrabalhoSeguinteComValor()); A diferença básica entre as duas abordagens é que a primeira tem início conhecido, mais utilizado quando não queremos que a instanciação e o agendamento da execução ocorra em uma só operação, como na segunda abordagem. Data Parallelism Ainda parte da TPL, o Data Parallelism se refere a cenários onde a mesma operação deva ser executada paralelamente em elementos de uma coleção ou array, através de instruções paralelas For e ForEach. A idéia básica é pegar cada elemento da coleção (ou array) e trabalhar com diversas threads concomitantemente. A classe-chave para este cenário é a System.Threading.Tasks.Parallel // Sequential version foreach (var item in sourceCollection) { Process(item); } // Parallel equivalent Parallel.ForEach(sourceCollection, item => Process(item)); Complicado né? :) Demonstração Acesse aqui um vídeo com exemplos (screencast). Cuidado! Apesar da imensa vontade de sair codificando, tome cuidado com alguns problemas básicos de paralelismo. Neste link é possível conhecer algumas situações. Abraços.

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