CODEWITHSUNDEEP
vb.netdesign-patterns
w0051977
w0051977

Reputation: 15807

Application layer references data layer directly

In my experience the application layer should reference the business layer and the business layer should reference the data layer. I want to make a change to an app so that the application layer references the data layer directly as shown below:

    Imports System.Data.SqlClient

Public Class ApplicationLayerClass

    Public Function ProcessAllPersons()
        Dim data As New DataLayerClass
        Dim list As List(Of Person) = data.getAllPersons()
        For Each person In list
            'Call this function from the application client.  Do some complex work on the person here.
        Next
    End Function
End Class

Public Class DataLayerClass
    Public Function getAllPersons() As List(Of Person)
        Dim list As List(Of Person) = New List(Of Person)
        Dim p As New Person
        Dim objCommand As New SqlCommand
        Dim strConString As String = "Data Source=IANSCOMPUTER;Initial Catalog=Test;Integrated Security=True"
        Dim objCon As New SqlConnection
        objCon.ConnectionString = strConString
        objCon.Open()
        objCommand.Connection = objCon
        objCommand.CommandText = "select * from person "
        Dim objDR As SqlDataReader = objCommand.ExecuteReader
        If objDR.HasRows Then
            Using objCon
                Do While objDR.Read
                    p.Name = objDR("Name")
                    p.age = objDR("Age")
                    list.Add(p)
                Loop
            End Using
        End If
        Return list
    End Function
End Class

Public Class Person
    Public Name As String
    Public age As String
End Class

Alternatively I could create a class in the business layer that uses the adaptor pattern (http://en.wikipedia.org/wiki/Adapter_pattern) i.e. a function called BusinessLayerClass.ProcessAllPersons, which is called by ApplicationLayerClass.ProcessAllPersons and calls DataLayerClass.getAllPersons. Which option is more appropriate? I suppose it depends to some extent on the problem domain.

Upvotes: 1

Views: 516

Answers (3)

David Osborne
David Osborne

Reputation: 6791

If you have no intention of changing your database provider and you have the ADO.net skills that a business layer would protect developers from, then you don't need a business layer.

However, where are you going to put your business logic?

Upvotes: 0

guillaume31
guillaume31

Reputation: 14064

the business layer should reference the data layer

This is one approach but arguably not the best if you're aiming at maximum decoupling between your modules and being able to change your data access layer easily without touching your business layer (this is called Persistence Ignorance).

Have a look at Onion Architecture and/or Hexagonal Architecture. These architectural styles emphasize on your business layer being at the core of the system and independent from any other layer.

Concretely, how it works is you define abstractions for data access objects in your business core, which will be implemented in peripheral modules and used by the application layer.

http://jeffreypalermo.com/blog/the-onion-architecture-part-1/

http://alistair.cockburn.us/Hexagonal+architecture

http://blog.kamil.dworakowski.name/2010/08/from-layers-to-hexagon-architecture.html

Upvotes: 0

Big Daddy
Big Daddy

Reputation: 5224

If you have a valid reason for calling the data layer directly, then do it. If you add a pass-through function in the business layer, then all you've done is added more code for no apparent benefit.

Now, if your business layer is exposed via an interface, IBusinessLayer for example, then adding a ProcessAllPersons() function to it and having it pass the call directly to the data layer makes more sense and consistency. This is what I would recommend.

Upvotes: 1

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