INullable.IsNull Property


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Indicates whether a structure is null. This property is read-only.

Namespace:   System.Data.SqlTypes
Assembly:  System.Data (in System.Data.dll)

ReadOnly Property IsNull As Boolean

Property Value

Type: System.Boolean

SqlBooleantrue if the value of this object is null. Otherwise, false.

The default value for any System.Data.SqlTypes instance is null. Use IsNull property to test for null values.

The following code example creates a DataTable with two columns defined as SqlInt32 and SqlString. The code adds one row of known values, one row of null values and then iterates through the DataTable, assigning the values to variables and displaying the output in the console window.

Private Sub WorkWithSqlNulls()
    Dim table As New DataTable()

    ' Specify the SqlType for each column.
    Dim idColumn As DataColumn = _
      table.Columns.Add("ID", GetType(SqlInt32))
    Dim descColumn As DataColumn = _
      table.Columns.Add("Description", GetType(SqlString))

    ' Add some data.
    Dim row As DataRow = table.NewRow()
    row("ID") = 123
    row("Description") = "Side Mirror"

    ' Add null values.
    row = table.NewRow()
    row("ID") = SqlInt32.Null
    row("Description") = SqlString.Null

    ' Initialize variables to use when
    ' extracting the data.
    Dim isColumnNull As SqlBoolean = False
    Dim idValue As SqlInt32 = SqlInt32.Zero
    Dim descriptionValue As SqlString = SqlString.Null

    ' Iterate through the DataTable and display the values.
    For Each row In table.Rows
        ' Assign values to variables. Note that you 
        ' do not have to test for null values.
        idValue = CType(row("ID"), SqlInt32)
        descriptionValue = CType(row("Description"), SqlString)

        ' Test for null value with ID column
        isColumnNull = idValue.IsNull

        ' Display variable values in console window.
        Console.Write("isColumnNull={0}, ID={1}, Description={2}", _
          isColumnNull, idValue, descriptionValue)
    Next row
End Sub

This example displays the following results:

isColumnNull=False, ID=123, Description=Side Mirror
isColumnNull=True, ID=Null, Description=Null

.NET Framework
Available since 1.1
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