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    <blockquote> <p>1.Why did Microsoft add DataContract attribute to EF-entities? Does Microsoft wanted us to use these objects everywhere in our applications? Or this is only for very simple applications and for rapid development?</p> </blockquote> <p>Generally speaking, it is a bad idea to expose your EF-Entities in the service layer because that hardly couples your service layer and model representation. so any changes done in the model ends affecting directly your services, not a good idea. also you will have to version your service layer in some moment, so avoid to expose the EF entities in your service layer.</p> <blockquote> <p>2.If I use POCO-objects, should I create auto generated EF-Entities, POCO-Entities and after that use any mapping library between them? Or I should use only POCO-objects in all components of my application?</p> </blockquote> <p>You can use POCO objects inside your service layer, to decouple it from any underlying layers (see Automapper, to cover the Entity-DTO mapping cost). but you could still use the autogenerated EF-entities among the data and business layers in your architecture. just try to not rely in EF specific features of your generated domain model in other layers different from data layer. to ease the migration to another ORM frameworks.</p> <blockquote> <p>If I already have my own business entity, which has some methods, and it should be mapped to POCO object, on which layer should I convert POCO-object to my entity (for example, I have persistence layer, business logic layer, service layer(WCF), presenter layer (client, use WCF), UI layer)? Or I shouldn't make such my own entities?</p> </blockquote> <p>Service layer <a href="http://msdn.microsoft.com/en-us/library/ms978717.aspx" rel="nofollow noreferrer">http://msdn.microsoft.com/en-us/library/ms978717.aspx</a>. you would be using your domain model transparently among the server tier (persistence, business, service and presenter layers) of your application, and the only layer that will require you a DTO mapping is the service layer, see question 1. (additionally if you are using ViewModels inside your the presenter layer -nice idea- you will require to use POCOs-mapping in the presenter layer too).</p>
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    1. POEntity Framework in Layered Architectures
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    1. COI would suggest to sent POCOs to the client, except if there is a technology that requires you to do so (RIA services apparently does it, but I need to confirm that). So you would expose a cleanest service layer
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    2. COThanks a lot. And if I'll decide to change EF to other ORM, I should modify service layer also, right?
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      1. USPavel Belousov
    3. COExactly. business and service layer. So you will not have to worry about populate and handle DTO up to the frontier of your solution, the Service Layer.
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