Object-Oriented database design with the DatabaseObjects library

Option Strict Off
Option Explicit On

Imports DatabaseObjects
Imports System.Collections

Public Class Categories
    Implements IDatabaseObjects
    Implements IEnumerable

    Default Public ReadOnly Property Item(ByVal intIndex As Integer) As Category
        Get

            Return NorthwindDB.Database.ObjectByOrdinal(Me, intIndex)

        End Get
    End Property

    Default Public ReadOnly Property Item(ByVal strCategoryName As String) As Category
        Get

            Return NorthwindDB.Database.ObjectByKey(Me, strCategoryName)

        End Get
    End Property

    Public ReadOnly Property Count() As Integer
        Get

            Return NorthwindDB.Database.ObjectsCount(Me)

        End Get
    End Property

    Private Function DistinctFieldAutoIncrements() As Boolean Implements IDatabaseObjects.DistinctFieldAutoIncrements

        Return True

    End Function

    Private Function DistinctFieldName() As String Implements IDatabaseObjects.DistinctFieldName

        Return "CategoryID"

    End Function

    Private Function ItemInstance() As IDatabaseObject Implements IDatabaseObjects.ItemInstance

        Return New Category(Me)

    End Function

    Private Function KeyFieldName() As String Implements IDatabaseObjects.KeyFieldName

        Return "CategoryName"

    End Function

    Private Function OrderBy() As SQL.SQLSelectOrderByFields Implements IDatabaseObjects.OrderBy

        Dim objOrderByFields As SQL.SQLSelectOrderByFields = New SQL.SQLSelectOrderByFields

        objOrderByFields.Add("CategoryName", SQL.OrderBy.Ascending)

        Return objOrderByFields

    End Function

    Private Function Subset() As SQL.SQLConditions Implements IDatabaseObjects.Subset

    End Function

    Private Function TableName() As String Implements IDatabaseObjects.TableName

        Return "Categories"

    End Function

    Private Function GetEnumerator() As System.Collections.IEnumerator Implements System.Collections.IEnumerable.GetEnumerator

        Return NorthwindDB.Database.ObjectsList(Me).GetEnumerator

    End Function

    Private Function TableJoins(ByVal objPrimaryTable As DatabaseObjects.SQL.SQLSelectTable, ByVal objTables As DatabaseObjects.SQL.SQLSelectTables) As DatabaseObjects.SQL.SQLSelectTableJoins Implements DatabaseObjects.IDatabaseObjects.TableJoins

    End Function

End Class


Public Class Category
    Implements IDatabaseObject

    Private pobjParent As IDatabaseObjects
    Private pintID As Integer
    Private pstrName As String

    Friend Sub New(ByVal objParent As IDatabaseObjects)

        pobjParent = objParent

    End Sub

    Friend ReadOnly Property ID() As Integer
        Get

            Return pintID

        End Get
    End Property

    Public ReadOnly Property Name() As String
        Get

            Return pstrName

        End Get
    End Property

    Public ReadOnly Property Products() As Products
        Get

            Products = New Products(NorthwindDB.Database)
            Products.Category = Me

        End Get
    End Property

    Private Property DistinctValue() As Object Implements IDatabaseObject.DistinctValue
        Get

            Return pintID

        End Get

        Set(ByVal Value As Object)

            pintID = Value

        End Set
    End Property

    Private Property IsSaved() As Boolean Implements IDatabaseObject.IsSaved
        Get
            'This function can be implemented using a boolean variable to hold
            'whether this object has been saved or not. However, if the object is
            'using an Identity field the following shortcut can be used as it is
            'logically equivalent. The Property Let IsSaved does
            'not need to be implemented

            Return pintID <> 0

        End Get

        Set(ByVal Value As Boolean)

        End Set
    End Property

    Public Sub Save()

        NorthwindDB.Database.ObjectSave(pobjParent, Me)

    End Sub

    Private Sub Load(ByVal objFields As SQL.SQLFieldValues) Implements IDatabaseObject.LoadFields

        pstrName = objFields("CategoryName").Value

    End Sub

    Private Function SaveFields() As SQL.SQLFieldValues Implements IDatabaseObject.SaveFields

        Dim objFields As SQL.SQLFieldValues
        objFields = New SQL.SQLFieldValues

        objFields.Add("CategoryName", pstrName)

        Return objFields

    End Function

End Class