值得参考的NULL替换值
Imports System
Imports System.Reflection
Namespace DotNetNuke
'*********************************************************************
'
' Null Class
'
' Class for dealing with the translation of database null values
'
'*********************************************************************
Public Class Null
' define application encoded null values
Public Shared ReadOnly Property NullInteger() As Integer
Get
Return -1
End Get
End Property
Public Shared ReadOnly Property NullDecimal() As Decimal
Get
Return Decimal.MinValue
End Get
End Property
Public Shared ReadOnly Property NullDate() As Date
Get
Return Date.MinValue
End Get
End Property
Public Shared ReadOnly Property NullString() As String
Get
Return ""
End Get
End Property
Public Shared ReadOnly Property NullBoolean() As Boolean
Get
Return False
End Get
End Property
Public Shared ReadOnly Property NullGuid() As Guid
Get
Return Guid.Empty
End Get
End Property
' sets a field to an application encoded null value ( used in Presentation layer )
Public Shared Function SetNull(ByVal objField As Object) As Object
If Not objField Is Nothing Then
If TypeOf objField Is Integer Then
SetNull = NullInteger
ElseIf TypeOf objField Is Single Then
SetNull = NullInteger
ElseIf TypeOf objField Is Double Then
SetNull = NullInteger
ElseIf TypeOf objField Is Decimal Then
SetNull = NullDecimal
ElseIf TypeOf objField Is Date Then
SetNull = NullDate
ElseIf TypeOf objField Is String Then
SetNull = NullString
ElseIf TypeOf objField Is Boolean Then
SetNull = NullBoolean
ElseIf TypeOf objField Is Guid Then
SetNull = NullGuid
Else
Throw New NullReferenceException
End If
Else ' assume string
SetNull = NullString
End If
End Function
' sets a field to an application encoded null value ( used in BLL layer )
Public Shared Function SetNull(ByVal objPropertyInfo As PropertyInfo) As Object
Select Case objPropertyInfo.PropertyType.ToString
Case "System.Int16", "System.Int32", "System.Int64", "System.Single", "System.Double"
SetNull = NullInteger
Case "System.Decimal"
SetNull = NullDecimal
Case "System.DateTime"
SetNull = NullDate
Case "System.String", "System.Char"
SetNull = NullString
Case "System.Boolean"
SetNull = NullBoolean
Case "System.Guid"
SetNull = NullGuid
Case Else
' Enumerations default to the first entry
Dim pType As Type = objPropertyInfo.PropertyType
If pType.BaseType.Equals(GetType(System.Enum)) Then
Dim objEnumValues As System.Array = System.Enum.GetValues(pType)
Array.Sort(objEnumValues)
SetNull = System.Enum.ToObject(pType, objEnumValues.GetValue(0))
Else
Throw New NullReferenceException
End If
End Select
End Function
' convert an application encoded null value to a database null value ( used in DAL )
Public Shared Function GetNull(ByVal objField As Object, ByVal objDBNull As Object) As Object
GetNull = objField
If objField Is Nothing Then
GetNull = objDBNull
ElseIf TypeOf objField Is Integer Then
If Convert.ToInt32(objField) = NullInteger Then
GetNull = objDBNull
End If
ElseIf TypeOf objField Is Single Then
If Convert.ToSingle(objField) = NullInteger Then
GetNull = objDBNull
End If
ElseIf TypeOf objField Is Double Then
If Convert.ToDouble(objField) = NullInteger Then
GetNull = objDBNull
End If
ElseIf TypeOf objField Is Decimal Then
If Convert.ToDecimal(objField) = NullDecimal Then
GetNull = objDBNull
End If
ElseIf TypeOf objField Is Date Then
If Convert.ToDateTime(objField) = NullDate Then
GetNull = objDBNull
End If
ElseIf TypeOf objField Is String Then
If objField Is Nothing Then
GetNull = objDBNull
Else
If objField.ToString = NullString Then
GetNull = objDBNull
End If
End If
ElseIf TypeOf objField Is Boolean Then
If Convert.ToBoolean(objField) = NullBoolean Then
GetNull = objDBNull
End If
ElseIf TypeOf objField Is Guid Then
If CType(objField, System.Guid).Equals(NullGuid) Then
GetNull = objDBNull
End If
Else
Throw New NullReferenceException
End If
End Function
' checks if a field contains an application encoded null value
Public Shared Function IsNull(ByVal objField As Object) As Boolean
If Not objField Is Nothing Then
If TypeOf objField Is Integer Then
IsNull = objField.Equals(NullInteger)
ElseIf TypeOf objField Is Decimal Then
IsNull = objField.Equals(NullDecimal)
ElseIf TypeOf objField Is Date Then
Dim objDate As DateTime = CType(objField, DateTime)
IsNull = objDate.Date.Equals(NullDate.Date)
ElseIf TypeOf objField Is String Then
IsNull = objField.Equals(NullString)
ElseIf TypeOf objField Is Boolean Then
IsNull = objField.Equals(NullBoolean)
ElseIf TypeOf objField Is Guid Then
IsNull = objField.Equals(NullGuid)
Else ' complex object
IsNull = False
End If
Else
IsNull = True
End If
End Function
End Class
End Namespace
