n tier design Service accesses data layer?

Question

Hi,

In an n-tier architecture should the Service Layer access the Data Layer directly? or should it go throw the BusinessLayer ?

Shouldn't the layer be able to access only the below layer?

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Me http://www.zapacila.com

Answer 1

Hi,
Service layer should not access Data Acess layer unless it's a Data service layer which provide a data service for business logic layer.

Shouldn't the layer be able to access only the below layer?

Yes, and this the resoan we called it a layer.

The best practice is don't make service layer access the business logic directly inserted access the business facade which access the business logic, so now you have a service facade layer and business facade layer and all business logic encapsulate inside the business logic layer.

For more infomation see the following patterns & practice link:
http://apparch.codeplex.com/Wiki/View.aspx?title=Application%20Patterns&referringTitle=Home

Thanks

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Answer 2

How will the Data Layer return data? using DTO`s?

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Me http://www.zapacila.com

Answer 3

Dear Jap,

We had similar question on Architect Role on 11th July and the title is "service layer management" , for your reference.

Service layer exposes the Interfaces that handles the business logic, which could be authentication, authorization, etc. So it always sits on top of the Business layer.

And it is not preferred to access the data layer directly from the service layer.

Cheers,
Vishal Mohan

Answer 4

Still if the direction is from top to bottom and  Service-> Business -> Data Layer how will datalayer return data? if what format?

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Me http://www.zapacila.com

Answer 5

Still if the direction is from top to bottom and  Service-> Business -> Data Layer how will datalayer return data? if what format?

Hi,
There is more than one option, you can return DTO which is a business logic class without operations (Methods) there is a very good article for Rudy Lacovara on DTO here
http://rlacovara.blogspot.com/2009/02/high-performance-data-access-layer.html

Another option you can return data set or reader etc, there is a good thread on ASP.NET forum which discuss similar question
http://forums.asp.net/p/1120895/1753031.aspx

Thanks

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Answer 6

Now lets take a scenario of an employee management, for the employee management we have the Business layer which comprises of CRUD Methods, and others methods required.

A Service layer can be built on top of this business layer and can expose a set of related Methods for example:-

//the service layer method

[DataObjectMethod(DataObjectMethodType.Select)]
public IList<Employee> SearchEmployee(string EmployeeName)
        {      
              // add the CAS    

            return employeeBusinessObject.Search(EmployeeName);
        }


// business layer

public IList<Employee> Search(string EmployeeName)

 {

  //add businesslogic;
   

            return employeeDataLayerObject.Search(EmployeeName);

 }

hope this makes some sense.

Answer 7

And if the Business Layer and the Data layer are on the same tier? won't dto be somehow of an overhead?

Thanks. guys!! Really apreciate it!

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Me http://www.zapacila.com

Answer 8

Do you think it`s ok to make a shared DTO ? to use for all layers? business <-> data  service <-> business  presentation <-> service??

\\or should i define DTO for data layer and business layer  another type of DTO for service with presentation

\\or use inheritance ?

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Me http://www.zapacila.com