僅供將來參考:
您有幾種方法來檢查db值是否爲空。
這裏的例子是完整的命名空間。
Dim reader As System.Data.SqlClient.SqlDataReader
Dim fieldIndex As Integer = 0
' reader(fieldIndex) is equivalent to reader.Item(fieldIndex)
Dim fieldValue As Object = reader.Item(fieldIndex)
Dim isFieldValueNull As Boolean
' Namespace: System.Data.SqlClient; Class: SqlDataReader
isFieldValueNull = reader.IsDBNull(fieldIndex)
' Namespace: Microsoft.VisualBasic; Module: Information
isFieldValueNull = Microsoft.VisualBasic.IsDBNull(fieldValue)
' Namespace: System; Class: Convert
isFieldValueNull = System.Convert.IsDBNull(fieldValue)
' Namespace: System; Class: DBNull
isFieldValueNull = System.DBNull.Value.Equals(fieldValue)
注:DBNull.Value
總有DBNull
一個實例,因此這是從來沒有Nothing
!
如果您想檢查數據庫值是否爲空,那麼您可以在方法調用之前放置Not
關鍵字。
Dim isFieldValueNotNull As Boolean
isFieldValueNotNull = Not reader.IsDBNull(fieldIndex)
isFieldValueNotNull = Not Microsoft.VisualBasic.IsDBNull(fieldValue)
isFieldValueNotNull = Not System.Convert.IsDBNull(fieldValue)
isFieldValueNotNull = Not System.DBNull.Value.Equals(fieldValue)
'reader'null? – Cortright