Object-Oriented database design with the DatabaseObjects library

' ___________________________________________________
'
'  � Hi-Integrity Systems 2007. All rights reserved.
'  www.hisystems.com.au - Toby Wicks
' ___________________________________________________
'

''' --------------------------------------------------------------------------------
''' <summary>
''' This class extends DatabaseObjects by storing all objects associated with this
''' DatabaseObjects collection in memory. Any objects added via VolatileObjectAdd 
''' or VolatileObjectDelete only affect the memory list until VolatileObjectsSave() is 
''' called. VolatileObjectsSave will actually delete all objects in the database
''' and then save all objects in the memory list to the database.
''' </summary>
''' --------------------------------------------------------------------------------
'''
Public MustInherit Class DatabaseObjectsVolatile
    Inherits DatabaseObjects
    Implements IEnumerable

    Private pobjParent As Object
    Private pobjItems As IList
    Private pobjItemsDeleted As IList = New ArrayList

    ''' --------------------------------------------------------------------------------
    ''' <summary>
    ''' Initializes a new DatabaseObjects with it's associated database.
    ''' </summary>
    ''' 
    ''' <param name="objDatabase">
    ''' The database that this collection is associated with.
    ''' </param>
    ''' --------------------------------------------------------------------------------
    Protected Sub New(ByVal objDatabase As Database)

        MyBase.New(objDatabase)

        pobjItems = MyBase.ObjectsList

    End Sub

    ''' --------------------------------------------------------------------------------
    ''' <summary>
    ''' Initializes a new DatabaseObjects with it's associated database.
    ''' </summary>
    ''' 
    ''' <param name="objDatabase">
    ''' The database that this collection is associated with.
    ''' </param>
    '''
    ''' <param name="objParent">
    ''' The parent collection that this collection is associated with. This is often
    ''' useful so that the SubSet property can use the Parent to filter 
    ''' by a particular value pertinent to the parent object. Using the object
    ''' is optional. 
    ''' </param>
    ''' --------------------------------------------------------------------------------
    Protected Sub New(ByVal objDatabase As Database, ByVal objParent As Object)

        MyBase.New(objDatabase)

        pobjParent = objParent
        pobjItems = MyBase.ObjectsList

    End Sub

    ''' --------------------------------------------------------------------------------
    ''' <summary>
    ''' Returns the parent object that this collection is associated with.
    ''' </summary>
    ''' --------------------------------------------------------------------------------
    Protected ReadOnly Property Parent() As Object
        Get

            Return pobjParent

        End Get
    End Property

    ''' --------------------------------------------------------------------------------
    ''' <summary>
    ''' Adds an item to the in-memory list, and flags the item to be saved to the database 
    ''' when VolatileObjectsSave() is called. 
    ''' </summary>
    ''' --------------------------------------------------------------------------------
    ''' 
    Protected Sub VolatileObjectAdd(ByVal objItem As IDatabaseObject)

        pobjItems.Add(objItem)

    End Sub

    ''' --------------------------------------------------------------------------------
    ''' <summary>
    ''' Returns an item at the specific index in the in-memory list.
    ''' </summary>
    ''' --------------------------------------------------------------------------------
    ''' 
    Protected ReadOnly Property VolatileObjectByOrdinal(ByVal intIndex As Integer) As IDatabaseObject
        Get

            Return DirectCast(pobjItems(intIndex), IDatabaseObject)

        End Get
    End Property

    ''' --------------------------------------------------------------------------------
    ''' <summary>
    ''' Removes the item from the in-memory list, and flags the item to be deleted when
    ''' VolatileObjectsSave() is called.
    ''' </summary>
    ''' --------------------------------------------------------------------------------
    ''' 
    Protected Sub VolatileObjectDelete(ByVal objItem As IDatabaseObject)

        pobjItemsDeleted.Add(objItem)
        pobjItems.Remove(objItem)

    End Sub

    ''' --------------------------------------------------------------------------------
    ''' <summary>
    ''' Firstly, all items flagged for deletion (via VolatileObjectDelete) are deleted 
    ''' in the database. 
    ''' Secondly, all items that have been added to the in-memory list (via VolatileObjectAdd)
    ''' are added/saved to the database.
    ''' </summary>
    ''' 
    ''' <example> 
    ''' <code>
    ''' Friend Sub SaveAll()
    ''' 
    '''     Mybase.VolatileObjectsSave()
    ''' 
    ''' End Sub
    ''' </code>
    ''' </example>    
    ''' --------------------------------------------------------------------------------
    ''' 
    Protected Overridable Sub VolatileObjectsSave()

        For Each objItem As IDatabaseObject In pobjItemsDeleted
            Database.ObjectDelete(Me, objItem)
        Next

        For Each objItem As IDatabaseObject In pobjItems
            Database.ObjectSave(Me, objItem)
        Next

    End Sub

    ''' --------------------------------------------------------------------------------
    ''' <summary>
    ''' Returns the number of items in the in-memory list.
    ''' </summary>
    ''' --------------------------------------------------------------------------------
    ''' 
    Protected ReadOnly Property VolatileObjectsCount() As Integer
        Get

            Return pobjItems.Count

        End Get
    End Property

    ''' --------------------------------------------------------------------------------
    ''' <summary>
    ''' Returns the enumerator for all objects currently in the in-memory list.
    ''' </summary>
    ''' --------------------------------------------------------------------------------
    ''' 
    Protected Function VolatileObjectsEnumerator() As System.Collections.IEnumerator Implements System.Collections.IEnumerable.GetEnumerator

        Return pobjItems.GetEnumerator

    End Function

End Class