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Asked: 2026-05-11T05:48:17+00:00

I am implementing a Data Access Layer (DAL), which is basically a set of

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I am implementing a Data Access Layer (DAL), which is basically a set of classes with (VB.NET) Shared functions to actually execute the database (CRUD) calls. I am trying to figure out the best place to place the calls to the DAL within the class hierarchy. Let me give an example.

Suppose I have a class Customer, with only standard ID, Name, Address1, etc. properties and maybe an overridden ToString function or so. I also have a DAL class with Shared methods, such as:

(pseudocode)  Namespace Dal  Public Class Customer  Public Shared Function Read(id As Integer) As Customer  Public Shared Function ReadList() As List(Of Customer)  Public Shared Sub Create(c As Customer)  'etc.

Now, I could call the Dal from the presentation layer like so:

Me.DataGridView1.Datasource = Dal.Customer.ReadList

However, is it not a good practice to have the presentation layer aware of the Dal at all? Should I instead put methods in the Customer object and call the Dal, like this?

Public Function ReadList() As List(Of Customer)     Return Dal.Customer.ReadList() End Sub  Public Sub Create()     Dal.Customer.Create(Me) End Sub

Would this be ‘cleaner’ OOP? Or is it acceptable practice to let the presentation call the Dal, passing the business objects like my previous example:

Me.DataGridView1.Datasource = Dal.Customer.ReadList  Dim c As New Customer c.Name = 'Alpha Corporation' c.Address1 = '123 Main Street' Dal.Customer.Create(c)

Thanks for your feedback.

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1 Answer

  1. I agree that data calls do not belong in a UI layer. Those are for presentation only.

    I think they properly belong in a service layer. The service implementation uses model objects and the persistence layer to accomplish its goals. Whether that’s an XML-based web service or local interface, the service is the object that maps to use cases and knows about units of work.

    Either put the database calls into a separate persistence layer or embed them in the model objects for extra object-oriented purity.

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