How to implement Interfaces in the Data access layer?

petre ricardo

IDE : VS 2008,

Platform : .NET 3.5,

Hi,

I typically dont create interfaces unless i have to, however in my current application i have to create interfaces in the Data access layer. I'm a in a minor confusion that hwo do i create those interfaces more how to implement them:

the following code might make things clear:

I have the following class and interface in the data access namespace

 

using ConsoleApplication8.BusinessLayer;
using 
ConsoleApplication8.DataAccessLayer ;
using System.Data ;
using System 
;

Namespace DataAccessLayer 

{

    Public Class CountryGateway : 
ICountryGateway 
     {      
        public 
void InitCountry() 

         {

             //write 
code 

         }

                
        public 
Int32 saveCountry(ByRef obj As Country) 

      {

            //write 
code 

      }


        // 
        //implementation 
for other methods SearchByIndex() SearchByName and 
UpdateCountry() 
        //
        //

   }

    Interface 
ICountryGateway {
        void 
InitCountry() ;
        Int32 
saveCountry(ref obj As 
Country) ;
        DataSet 
SearchByIndex(countryNo As 
String)
        DataSet 
SearchByName(countryName As 
String);
        Int32 
updateCountry(ref country As 
Country);
    }




}

Namespace 
BusinessLayer {

    Public Class Country 
{

    }


}

1. Is this way implement the interface in the data access layer? (in this case the class CountryGateway access the database.) i.e: That we should create interfaces to access DB in the DAL and then we should also write the implementation for those interfaces in the DAL?

2. I have been told that we should create interfaces than abstract classes espcially in the data access layer, is there a particular reason for this?

3 Replies

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Dushan Stankovic17y ago
Thanks Master Billa for reference us that article, that guy did a good job.
But in this post Petre asked us about interfaces, I must sad interface classes, and it's usage. You are so right about complexity of interfaces like public stuffs in DAL, and guy in CodeProject do simplify that.
That is in .NET 2.0, and in 3.5 or grater we have LINQ and auto generated classes for more easier DAL developing. Thanks for that :), but always is good to know to implement our own mechanism.
Master Billa17y ago
Hi

yes your way correct, but there issues, see interface are would come as common. it's should base on your every object base.

See here great sample code implemented common way interface and implemeted

http://www.codeproject.com/KB/database/Lightweight_DAL_in_NET_2.aspx

thank you
Dushan Stankovic17y ago
Hi!
If you creating some service project, like WCF, you must use interfaces because they are Service Contract for endpoints.

In Console app, or WinForm app, I use interface if entitys in my database have a same behavior i.e. Car and Truck (Car is vehicle, is Steerable, may start and stop, .... like Truck) and with interface I define public stuff for all same class but implement that stuffs in particular classes.
Because you can use interface like this:

IDrivable myD = new MyCar() as IDrivable;

it is easy to use one instance for different classes.

This is basic for the interface usage, if you need more continue this post.

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