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POServices and Repositories in DDD (C#)
 

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    <p>How do <code>Services</code> and <code>Repositories</code> relate to each other in DDD? I mean, I've been reading up on DDD for the past 2 days and everywhere I go, there's always a <code>Service</code> layer and there's always a <code>Repository</code> layer. How do these differentiate or compliment each other?</p> <p>From what I've read, isn't the <code>Repository</code> the layer responsible for delegating interactions between the application and the data?</p> <p>So, what's the need for the <code>Service</code> layer if it has to implement the <code>Repository</code> to interact with the data anyway even though the <code>Repository</code> probably already implements the methods needed to do so?</p> <p>I'd appreciate some enlightenment on the subject.</p> <p>P.S. Don't know if this will help any, but I'm working with an ASP.NET MVC 2 application in which I'm trying to implement the Repository pattern. I just finished implementing the Dependency Injection pattern (for the first time ever)...</p> <p><strong>UPDATE</strong></p> <p>Okay, with so many answers, I think I understand what the difference is. So, to review (correct me if I'm wrong):</p> <ul> <li><p>A <code>Repository</code> layer interacts only with a single object out of the database or the ORM, <code>IEmployeeRepository</code> -> <code>Employee</code>.</p></li> <li><p>A <code>Service</code> layer encapsulates more complex functionality on objects returned from <code>Repositories</code>, either one or multiple.</p></li> </ul> <p>So, then I have a sub question. Is it considered bad practice to create abstract objects to be sent to my views? For example an <code>AEmployee</code> (<code>A</code> for <code>abstract</code> because to me <code>I</code> means <code>interface</code>) which contains properties from <code>Employee</code> and <code>X</code> or <code>X</code>?</p> <p>Actually, one more subquestion. If a <code>Service</code> layer can be considered "tuned" for an application does it need to be implemented with an interface?</p>
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    1. COI believe services can aggregate multiple repositories.
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    2. COThere's quite a discrepancy between the common/popular usage of Repository's and Service's (the usage found in many examples & tutorials) and how Domain Driven Design defines these. I believe it is important to understand the differences.
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    3. CO@Sergey is right - there should be one repository per aggregate root, but a service can (and will) work across multiple reposities, made possible by the unit of work pattern. and by the way - how many times can a question like this be asked? there are plenty of questions regarding this on stack overflow.
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