Creating Generic Range Class

Level: Beginner

Knowledge Required:
Generics in Visual Basic

Description:
In this article we will create a Generic Range Class, which can be further used in different types of Applications like Database Applications.

Generic Range Class:

Public Class GenericRange(Of T)
    Private _Start As T
    Private _End As T
    Private _HasStart As Boolean
    Private _HasEnd As Boolean

    Public Sub New()
        Call Me.SetStartNull()
        Call Me.SetEndNull()
    End Sub

    Public Sub New(ByVal Start As T, ByVal [End] As T)
        Me.Start = Start
        Me.End = [End]
    End Sub

    Public Property Start() As T
        Get
            If Me.HasStart Then
                Return Me._Start
            Else
                Throw New Exception("Start Value is NOT Set")
            End If
        End Get
        Set(ByVal value As T)
            If value Is Nothing Then
                Me.SetStartNull()
            Else
                Me._Start = value
                Me._HasStart = True
            End If
        End Set
    End Property

    Public Property [End]() As T
        Get
            If Me.HasEnd Then
                Return Me._End
            Else
                Throw New Exception("End Value is NOT Set")
            End If
        End Get
        Set(ByVal value As T)
            If value Is Nothing Then
                Me.SetEndNull()
            Else
                Me._End = value
                Me._HasEnd = True
            End If
        End Set
    End Property

    Public ReadOnly Property HasStart() As Boolean
        Get
            Return Me._HasStart
        End Get
    End Property

    Public ReadOnly Property HasEnd() As Boolean
        Get
            Return Me._HasEnd
        End Get
    End Property

    Public Sub SetStartNull()
        Me._HasStart = False
    End Sub

    Public Sub SetEndNull()
        Me._HasEnd = False
    End Sub
End Class

Usage:

Private Function GetOrderQueryByDate(ByRef GR As GenericRange(Of Date)) As String
    Dim sQuery As String
    Dim sWhere As String = ""

    sQuery = "SELECT * FROM Orders"

    If GR.HasStart Then
        sWhere = "OrderDate >= '" & GR.Start & "'"
    End If
    If GR.HasEnd Then
        If sWhere <> "" Then sWhere &= " AND "
        sWhere &= "OrderDate <= '" & GR.End & "'"
    End If
    If sWhere <> "" Then
        sQuery &= " WHERE " & sWhere
    End If
    Return sQuery
End Function