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  • Method 'SingleOrDefault' not supported by Linq to Entities

    - by user300992
    I read other posts on similar problem on using SingleOfDefault on Linq-To-Entity, some suggested using "First()" and some others suggested using "Extension" method to implement the Single(). This code throws exception: Movie movie = (from a in movies where a.MovieID == '12345' select a).SingleOrDefault(); If I convert the object query to a List using .ToList(), "SingleOrDefault()" actually works perfectly without throwing any error. My question is: Is it not good to convert to List? Is it going to be performance issue for more complicated queries? What does it get translated in SQL? Movie movie = (from a in movies.ToList() where a.MovieID == '12345' select a).SingleOrDefault();

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  • .DBML file and LINQ to SQL

    - by Rishabh Ohri
    In my DBML file I have mapped some tables and stored procedures, and the stored procedures return type is ISingleResult . T is some mapped table. But I want to take the data into my own created entities rather than LINQ to SQL created entites. The entites created by me are also the same as the mapped table entities and their use lies when we send data across the a web service. So , how can I proceed by creating a wrapper around the DBML file so that I always get data in my own created entites.

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  • Use Any() and Count() in Dynamic Linq

    - by ArpanDesai
    I am trying to write dynamic Linq Library query to fetch record on condition, Customers who has order count is greater than 3 and ShipVia field equal 2. Below is my syntax what i have tried. object[] objArr = new object[10]; objArr[0] = 1; IQueryable<Customer> test = db.Customers.Where("Orders.Count(ShipVia=2)", objArr); and IQueryable<Customer> test = db.Customers.Where("Orders.Any(ShipVia=2).Count()", objArr); But both are not working. In second query Any returns true so it won't work with Count. Suggest me a way to implement this.

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  • return from a linq where statement

    - by Vaccano
    I have the following link function MyLinqToSQLTable.Where(x => x.objectID == paramObjectID).ToList(); I most of the time you can change a linq call to be several lines by adding curly brackets around the method body. Like this: MyLinqToSQLTable.Where(x => { x.objectID == paramObjectID; }).ToList(); Problem is the implied return that was there when I just did a Boolean compare is now not done. Return (x.objectID == paramObjectID); is not accepted either. How do do this? can I do this? NOTE: I know that I can add another where clause if needed. But I would still like to know the answer to this.

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  • Instantiating a context in LINQ to Entities

    - by Jagd
    I've seen two different manners that programmers approach when creating an entity context in their code. The first is like such, and you can find it all over the MSDN code examples: public void DoSomething() { using TaxableEducationEntities context = new TaxableEducationEntities()) { // business logic and whatever else } } The second is to create the context as a private attribute in some class that encapsulates your business logic. So you would have something like: public class Education_LINQ { private TaxableEducationEntities context = new TaxableEducationEntities(); public void DoSomething() { var result = from a in context.luAction select a; // business logic and whatever else } } Which way is more efficient? Assume that you have two methods, one called DoSomething1() and another called DoSomething2(), and both methods incorporate the using statement to open the context and do whatever with it. Were you to call one method after the other, would there be any superfluous overhead going on, since essentially both methods create the context and then clean it up when they're done? As opposed to having just one private attribute that is created when a class object is instantiated, and then in turn cleaned up when the object goes out of scope?

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  • Compile error when calling ToList() when accessing many to many with Linq To Entities

    - by KallDrexx
    I can't figure out what I am doing wrong. I have the following method: public IList<WObject> GetRelationshipMembers(int relId) { var members = from r in _container.ObjectRelationships where r.Id == relId select r.WObjects; return members.ToList<WObject>(); } This returns the following error: Instance argument: cannot convert from 'System.Linq.IQueryable<System.Data.Objects.DataClasses.EntityCollection<Project.DomainModel.Entities.WObject>>' to 'System.Collections.Generic.IEnumerable<Project.DomainModel.Entities.WObject>' How can I convert the EntityCollection to a list without lazy loading?

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  • Using unordered_multimap as entity and component storage

    - by natebot13
    The Setup I've made a few games (more like animations) using the Object Oriented method with base classes for objects that extend them, and objects that extend those, and found I couldn't wrap my head around expanding that system to larger game ideas. So I did some research and discovered the Entity-Component system of designing games. I really like the idea, and thoroughly understood the usefulness of it after reading Byte54's perfect answer here: Role of systems in entity systems architecture. With that said, I have decided to create my current game idea using the described Entity-Component system. Having basic knowledge of C++, and SFML, I would like to implement the backbone of this entity component system using an unordered_multimap without classes for the entities themselves. Here's the idea: An unordered_mulitmap stores entity IDs as the lookup term, while the value is an inherited Component object. Examlpe: ____________________________ |ID |Component | ---------------------------- |0 |Movable | |0 |Accelable | |0 |Renderable | |1 |Movable | |1 |Renderable | |2 |Renderable | ---------------------------- So, according to this map of objects, the entity with ID 0 has three components: Movable, Accelable, and Renderable. These component objects store the entity specific data, such as the location, the acceleration, and render flags. The entity is simply and ID, with the components attached to that ID describing its attributes. Problem I want to store the component objects within the map, allowing the map have full ownership of the components. The problem I'm having, is I don't quite understand enough about pointers, shared pointers, and references in order to get that set up. How can I go about initializing these components, with their various member variables, within the unordered_multimap? Can the base component class take on the member variables of its child classes, when defining the map as unordered_multimap<int, component>? Requirements I need a system to be able to grab an entity, with all of its' attached components, and access members from the components in order to do the necessary calculations and reassignments for position, velocity, etc. Need a clarification? Post a comment with your concerns and I will gladly edit or comment back! Thanks in advance! natebot13

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  • Linq to Entities and POCO foreign key relations mapping (1 to 0..1) problem

    - by brainnovative
    For my ASP.NET MVC 2 application I use Entity Framework 1.0 as my data access layer (repository). But I decided I want to return POCO. For the first time I have encountered a problem when I wanted to get a list of Brands with their optional logos. Here's what I did: public IQueryable<Model.Products.Brand> GetAll() { IQueryable<Model.Products.Brand> brands = from b in EntitiesCtx.Brands.Include("Logo") select new Model.Products.Brand() { BrandId = b.BrandId, Name = b.Name, Description = b.Description, IsActive = b.IsActive, Logo = /*b.Logo != null ? */new Model.Cms.Image() { ImageId = b.Logo.ImageId, Alt = b.Logo.Alt, Url = b.Logo.Url }/* : null*/ }; return brands; } You can see in the comments what I would like to achieve. It worked fine whenever a Brand had a Logo otherwise it through an exception that you can assign null to the non-nullable type int (for Id). My workaround was to use nullable in the POCO class but that's not natural - then I have to check not only if Logo is null in my Service layer or Controllers and Views but mostly for Logo.ImageId.HasValue. It's not justified to have a non null Logo property if the id is null. Can anyone think of a better solution?

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  • Linq to Entities custom ordering via position mapping table

    - by Bigfellahull
    Hi, I have a news table and I would like to implement custom ordering. I have done this before via a positional mapping table which has newsIds and a position. I then LEFT OUTER JOIN the position table ON news.newsId = position.itemId with a select case statement CASE WHEN [position] IS NULL THEN 9999 ELSE [position] END and order by position asc, articleDate desc. Now I am trying to do the same with Linq to Entities. I have set up my tables with a PK, FK relationship so that my News object has an Entity Collection of positions. Now comes the bit I can't work out. How to implement the LEFT OUTER JOIN. I have so far: var query = SelectMany (n => n.Positions, (n, s) => new { n, s }) .OrderBy(x => x.s.position) .ThenByDescending(x => x.n.articleDate) .Select(x => x.n); This kinda works. However this uses a INNER JOIN so not what I am after. I had another idea: ret = ret.OrderBy(n => n.ShufflePositions.Select(s => s.position)); However I get the error DbSortClause expressions must have a type that is order comparable. I also tried ret = ret.GroupJoin(tse.ShufflePositions, n => n.id, s => s.itemId, (n, s) => new { n, s }) .OrderBy(x => x.s.Select(z => z.position)) .ThenByDescending(x => x.n.articleDate) .Select(x => x.n); but I get the same error! If anyone can help me out, it would be much appreciated!

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  • Entity Date Modelset Generates Errors in Visual Web Developer

    - by davemackey
    I attempted to add a ADO.NET Entity Data Model to my Visual Web Developer 2010 Express project and it generates but returns a whole slew of errors. Why is this generating errors? Here are the main errors: 'Public Property ID As Integer' has multiple definitions with identical signatures. Method 'Onaddress_IDChanging' cannot be declared 'Partial' because only one method 'Onaddress_IDChanging' can be marked 'Partial'. '_line1' is already declared as 'Private _line1 As String' in this class.

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  • Entity Framework won't SaveChanges on new entity with two-level relationship

    - by Tim Rourke
    I'm building an ASP.NET MVC site using the ADO.NET Entity Framework. I have an entity model that includes these entities, associated by foreign keys: Report(ID, Date, Heading, Report_Type_ID, etc.) SubReport(ID, ReportText, etc.) - one-to-one relationship with Report. ReportSource(ID, Name, Description) - one-to-many relationship with Sub_Report. ReportSourceType(ID, Name, Description) - one-to-many relationship with ReportSource. Contact (ID, Name, Address, etc.) - one-to-one relationship with Report_Source. There is a Create.aspx page for each type of SubReport. The post event method returns a new Sub_Report entity. Before, in my post method, I followed this process: Set the properties for a new Report entity from the page's fields. Set the SubReport entity's specific properties from the page's fields. Set the SubReport entity's Report to the new Report entity created in 1. Given an ID provided by the page, look up the ReportSource and set the Sub_Report entity's ReportSource to the found entity. SaveChanges. This workflow succeeded just fine for a couple of weeks. Then last week something changed and it doesn't work any more. Now instead of the save operation, I get this Exception: UpdateException: "Entities in 'DIR2_5Entities.ReportSourceSet' participate in the 'FK_ReportSources_ReportSourceTypes' relationship. 0 related 'ReportSourceTypes' were found. 1 'Report_Source_Types' is expected." The debug visualizer shows the following: The SubReport's ReportSource is set and loaded, and all of its properties are correct. The Report_Source has a valid ReportSourceType entity attached. In SQL Profiler the prepared SQL statement looks OK. Can anybody point me to what obvious thing I'm missing? TIA Notes: The Report and SubReport are always new entities in this case. The Report entity contains properties common to many types of reports and is used for generic queries. SubReports are specific reports with extra parameters varying by type. There is actually a different entity set for each type of SubReport, but this question applies to all of them, so I use SubReport as a simplified example.

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  • Parse XML tree with no id using LINQ to XML

    - by Danny
    Requirement I want to read a XML tree, fill my objects with encountered attributes and after every run a method (insert it into my db). The amount of parents is not specified, also the order is not specified, it could be, address-death-death-address-address for example Input file Overview: <Root> <Element> <Element2> <Parent> <Child> <Grandchild> <Grandchild> </Child> </Parent> </Element2> </Element1> </Root> Full example: <?xml version="1.0" encoding="utf-8" ?> <Root> <Element1> <Element2> <Parent> <Child> <Grandchild> <number>01</number> <name>Person</name> <Rows> <Row> <number>0110</number> <name>ID</name> <value>123456789</value> </Row> </Rows> </Grandchild> <Grandchild> <number>08</number> <name>Address</name> <Rows> <Row> <number>1110</number> <name>street</name> <value>first aveneu</value> </Row> <Row> <number>1120</number> <name>streetnumber</name> <value>345</value> </Row> <Row> <number>1130</number> <name>zip</name> <value>2938PS</value> </Row> <Row> <number>1160</number> <name>country</name> <value>Germany</value> </Row> </Rows> </Grandchild> </Child> </Parent> <Parent> <Child> <Grandchild> <number>01</number> <name>Person</name> <Rows> <Row> <number>0110</number> <name>ID</name> <value>987654321</value> </Row> </Rows> </Grandchild> <Grandchild> <number>06</number> <name>Death</name> <Rows> <Row> <number>0810</number> <name>date</name> <value>2012-01-03</value> </Row> <Row> <number>0820</number> <name>placeOfDeath</name> <value>attic</value> </Row> <Row> <number>0830</number> <name>funeral</name> <value>burrial</value> </Row> </Rows> </Grandchild> </Child> </Parent> </Element2> </Element1> </Root> Desired result After encounter of parent determine type of grandchild (number 6 is death number 8 is address) Every parent has ALWAYS grandchild number 1 'Person', the second grandchild is either death or address. reading first parent Person person = new Person(); person.ID = value; <--- filled with 123456789 person.street = value; <--- filled with first aveneu person.streetnumber = value; <--- filled with 345 person.zip = value; <--- filled with 2938PS person.country = value; <--- filled with germany person.DoMethod(); // inserts the value in db Continue reading next parent. Person person = new Person(); person.ID = value; <--- filled with 987654321 person.date = value; <--- filled with 2012-01-03 person.placeOfDeath = value; <--- filled with attic person.funeral = value; <--- filled with burrial person.DoMethod(); // insert the values in db Continue reading till no parents found EDIT: how do I target the name element of the second grandchild for every child? Like address or death Code/Credit I got no further then this, with help of Daniel Hilgarth: Linq to XML (C#) parse XML tree with no attributes/id to object The XML tree has changed, and I am really stuck.. in the meantime I try to post new working code...

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  • Why I am getting Null from this statement. Query Syntax in C#

    - by Shantanu Gupta
    This is not working. Returns Null to dept_list. var dept_list = ((from map in DtMapGuestDepartment.AsEnumerable() where map.Field<Nullable<long>>("Guest_Id") == 174 select map.Field<Nullable<long>>("Department_id")).Distinct())as IEnumerable<DataRow>; DataTable dt = dept_list.CopyToDataTable(); //dept_list comes null here This works as desired. var dept_list = from map in DtMapGuestDepartment.AsEnumerable() where map.Field<Nullable<long>>("Guest_Id") == 174 select map; DataTable dt = dept_list.CopyToDataTable(); //when used like this runs correct. What mistake is being done by me here. ?

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  • State / Screen management in Entity Component Systems

    - by David Lively
    My entity/component system is happily humming along and, despite some performance concerns I initially had, everything is working fine. However, I've realized that I missed a crucial point when starting this thing: how do you handle different screens? At the moment, I have a GameManager class which owns a component manager and entity manager. When I create an entity, the entity manager assigns it an ID and makes sure it's tracked. When I modify the components that are assigned to an entity. an UpdateEntity method is called, which alerts each of the systems that they may need to add or remove the entity from their respective entity lists. A problem with this is that the collection of entities operated on by each system is determined solely by the individual Systems, typically based on a "required component" filter. (An entity has to have a Renderable component to be rendered, for instance.) In this situation, I can't just keep collections of entities per screen and only Update/Draw those collections. They'd have to either be added and removed depending on their applicability to the current screen, which would cause their associated components to be removed, or enable/disable entities in a group per screen to hide what's not supposed to be visible. These approaches seem like really, really crappy kludges. What's a good way to handle this? A pretty straightforward way that comes to mind is to create a separate GameManager (which in my implementation owns all of the systems, entities, etc.) per screen, which means that everything outside of the device context would be duplicated. That's bothersome because some things are always visible, or I might want to continue to display the game under a translucent menu window. Another option would be to add a "layer" key to the GameManager class, which could be checked against a displayable layer stack held by the game manager. *System.Draw() would be called for each active layer, in the required order as determined by the stack. When the systems request an iterator for their respective entity collections, it would be pre-filtered to a (cached) set of those entities that participate in the active layer. Those collections could be updated from the same UpdateEntity event that's already used to maintain each system's entity collections. Still, kinda feels like a hack. If I've coded myself into a corner, feel free to throw tomatoes as long as they're labeled with a helpful suggestion. Hooray for learning curves.

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  • Entity Framework 4.1 Release Candidate Released

    - by shiju
    Microsoft ADO.NET team has announced the Release Candidate version of Entity Framework 4.1. You can download the  Entity Framework 4.1 Release Candidate from here . You can also use NuGet to get Entity Framework 4.1 Release Candidate. The Code First approach is available with Entity Framework 4.1.I have upgraded my ASP.NET MVC 3/EF Code First demo web app (http://efmvc.codeplex.com) to Entity Framework 4.1  version

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  • Entity Framework 4.0: My Favorite Books

    - by nannette
    I'm in the process of reading several Entity Framework 4.0 books. I'm going to recommend two such books: 1) Programming Entity Framework: Building Data Centric Apps with the ADO.NET Entity Framework by Julia Lerman 2) Entity Framework 4.0 Recipes: A Problem-Solution Approach by Larry Tenny and Zeeshan Hirani Visit these Entity Framework 4.0 Quick Start videos by Julia Lerman. The book links include numerous detailed reviews. If you can only afford one of the books, I'd recommend Julia's book as the...(read more)

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  • Many sources of movement in an entity system

    - by Sticky
    I'm fairly new to the idea of entity systems, having read a bunch of stuff (most usefully, this great blog and this answer). Though I'm having a little trouble understanding how something as simple as being able to manipualate the position of an object by an undefined number of sources. That is, I have my entity, which has a position component. I then have some event in the game which tells this entity to move a given distance, in a given time. These events can happen at any time, and will have different values for position and time. The result is that they'd be compounded together. In a traditional OO solution, I'd have some sort of MoveBy class, that contains the distance/time, and an array of those inside my game object class. Each frame, I'd iterate through all the MoveBy, and apply it to the position. If a MoveBy has reached its finish time, remove it from the array. With the entity system, I'm a little confused as how I should replicate this sort of behavior. If there were just one of these at a time, instead of being able to compound them together, it'd be fairly straightforward (I believe) and look something like this: PositionComponent containing x, y MoveByComponent containing x, y, time Entity which has both a PositionComponent and a MoveByComponent MoveBySystem that looks for an entity with both these components, and adds the value of MoveByComponent to the PositionComponent. When the time is reached, it removes the component from that entity. I'm a bit confused as to how I'd do the same thing with many move by's. My initial thoughts are that I would have: PositionComponent, MoveByComponent the same as above MoveByCollectionComponent which contains an array of MoveByComponents MoveByCollectionSystem that looks for an entity with a PositionComponent and a MoveByCollectionComponent, iterating through the MoveByComponents inside it, applying/removing as necessary. I guess this is a more general problem, of having many of the same component, and wanting a corresponding system to act on each one. My entities contain their components inside a hash of component type - component, so strictly have only 1 component of a particular type per entity. Is this the right way to be looking at this? Should an entity only ever have one component of a given type at all times?

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  • What does Symfony Framework offer that Zend Framework does not?

    - by Fatmuemoo
    I have professionally working with Zend Framework for about a year. No major complaints. With some modifications, it has done a good job. I'm beginning to work on a side project where I want to heavily rely on MongoDb and Doctrine. I thought it might be a good idea to broaden my horizons and learn another enterprise level framework. There seems to be a lot a buzz about Symfony. After quickly looking over the site and documentation, I must say I came away pretty underwhelmed. I'm woundering what, if anything, Symfony has to offer that Zend doesn't? What would the advantage be in choosing Symfony?

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  • How to differentiate between to similer fields in Linq Join tables

    - by Azhar
    How to differentiate between to select new fields e.g. Description c.Description and lt.Description DataTable lDt = new DataTable(); try { lDt.Columns.Add(new DataColumn("AreaTypeID", typeof(Int32))); lDt.Columns.Add(new DataColumn("CategoryRef", typeof(Int32))); lDt.Columns.Add(new DataColumn("Description", typeof(String))); lDt.Columns.Add(new DataColumn("CatDescription", typeof(String))); EzEagleDBDataContext lDc = new EzEagleDBDataContext(); var lAreaType = (from lt in lDc.tbl_AreaTypes join c in lDc.tbl_AreaCategories on lt.CategoryRef equals c.CategoryID where lt.AreaTypeID== pTypeId select new { lt.AreaTypeID, lt.Description, lt.CategoryRef, c.Description }).ToArray(); for (int j = 0; j< lAreaType.Count; j++) { DataRow dr = lDt.NewRow(); dr["AreaTypeID"] = lAreaType[j].LandmarkTypeID; dr["CategoryRef"] = lAreaType[j].CategoryRef; dr["Description"] = lAreaType[j].Description; dr["CatDescription"] = lAreaType[j].; lDt.Rows.Add(dr); } } catch (Exception ex) { }

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  • How to differentiate between two similar fields in Linq Join tables

    - by Azhar
    How to differentiate between two select new fields e.g. Description c.Description and lt.Description DataTable lDt = new DataTable(); try { lDt.Columns.Add(new DataColumn("AreaTypeID", typeof(Int32))); lDt.Columns.Add(new DataColumn("CategoryRef", typeof(Int32))); lDt.Columns.Add(new DataColumn("Description", typeof(String))); lDt.Columns.Add(new DataColumn("CatDescription", typeof(String))); EzEagleDBDataContext lDc = new EzEagleDBDataContext(); var lAreaType = (from lt in lDc.tbl_AreaTypes join c in lDc.tbl_AreaCategories on lt.CategoryRef equals c.CategoryID where lt.AreaTypeID== pTypeId select new { lt.AreaTypeID, lt.Description, lt.CategoryRef, c.Description }).ToArray(); for (int j = 0; j< lAreaType.Count; j++) { DataRow dr = lDt.NewRow(); dr["AreaTypeID"] = lAreaType[j].LandmarkTypeID; dr["CategoryRef"] = lAreaType[j].CategoryRef; dr["Description"] = lAreaType[j].Description; dr["CatDescription"] = lAreaType[j].; lDt.Rows.Add(dr); } } catch (Exception ex) { }

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  • Dump Linq-To-Sql now that Entity Framework 4.0 has been released?

    - by DanM
    The relative simplicity of Linq-To-Sql as well as all the criticism leveled at version 1 of Entity Framework (especially, the vote of no confidence) convinced me to go with Linq-To-Sql "for the time being". Now that EF 4.0 is out, I wonder if it's time to start migrating over to it. Questions: What are the pros and cons of EF 4.0 relative to Linq-To-Sql? Is EF 4.0 finally ready for prime time? Is now the time to switch over?

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  • Organizing an entity system with external component managers?

    - by Gustav
    I'm designing a game engine for a top-down multiplayer 2D shooter game, which I want to be reasonably reuseable for other top-down shooter games. At the moment I'm thinking about how something like an entity system in it should be designed. First I thought about this: I have a class called EntityManager. It should implement a method called Update and another one called Draw. The reason for me separating Logic and Rendering is because then I can omit the Draw method if running a standalone server. EntityManager owns a list of objects of type BaseEntity. Each entity owns a list of components such as EntityModel (the drawable representation of an entity), EntityNetworkInterface, and EntityPhysicalBody. EntityManager also owns a list of component managers like EntityRenderManager, EntityNetworkManager and EntityPhysicsManager. Each component manager keeps references to the entity components. There are various reasons for moving this code out of the entity's own class and do it collectively instead. For example, I'm using an external physics library, Box2D, for the game. In Box2D, you first add the bodies and shapes to a world (owned by the EntityPhysicsManager in this case) and add collision callbacks (which would be dispatched to the entity object itself in my system). Then you run a function which simulates everything in the system. I find it hard to find a better solution to do this than doing it in an external component manager like this. Entity creation is done like this: EntityManager implements the method RegisterEntity(entityClass, factory) which registers how to create an entity if that class. It also implements the method CreateEntity(entityClass) which would return an object of type BaseEntity. Well now comes my problem: How would the reference to a component be registered to the component managers? I have no idea how I would reference the component managers from a factory/closure.

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  • sync Framework for Compact Framework

    - by CF_Maintainer
    Has anyone got sync framework to work on a mobile device as a sync mechanism in place of RDA or Merge replication? If yes, could you point me to any resources available. If one was to start a green field compact framework based application, what would one use as the sync mechanism (sync framework/RDA/Merge replication/any other...)? Thanks

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