CODEWITHSUNDEEP
vb.netdesign-patterns
w0051977
w0051977

Reputation: 15797

One DTO per database table?

Say I have a Data Transfer object like the one below:

Public Class Person
Private _Name As String
Private _Age As Integer

Public Property Name() As String
    Get
        Return _Name
    End Get
    Set(ByVal value As String)
        _Name = value
    End Set
End Property

Public Property Age() As Integer
    Get
        Return _Age
    End Get
    Set(ByVal value As Integer)
        _Age = value
    End Set
End Property

End Class

This is an object representation of the following table:

CREATE TABLE Person (PersonID int identity primary key, Name varchar(30), age int)

Say I wanted to create an order table in the database as follows:

CREATE TABLE Order (OrderID int identity primary key, PersonID FOREIGN KEY references Person(ID), OrderDate datetime)

I believe I could simply add two more instance variables and properties to the Data Transfer Object (assuming that there is always a maximum of one order per person). Is this advisable or should you always have one DTO per database table?

Upvotes: 0

Views: 1401

Answers (1)

Joe Enos
Joe Enos

Reputation: 40393

Your assumption of one order per person doesn't really seem right. It may be true now, but the fact that you've got them separated out into two tables with a one-to-many means that you've designed it so that you can have multiple orders per person.

I'd stick with separate classes, but if you want to get everything at once, have complex DTOs, like:

class PersonDTO
  String Name
  Integer Age
  OrderDTO() Orders

' or

class OrderDTO
  Integer OrderID
  PersonDTO Person
  DateTime OrderDate

You'd have to build your SQL accordingly, either using JOINs or an ORM to get the complex object back in a single query, or just make multiple queries, but this way a single DTO would get you everything you need, while still allowing you to keep them separate.

I'd probably avoid having both classes be complex - you'd have a circular reference, which is tricky when you're serializing this stuff, so I'd just determine which one would be more valuable.

Upvotes: 1

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