INullable.IsNull Property
Definition
Important
Some information relates to prerelease product that may be substantially modified before it’s released. Microsoft makes no warranties, express or implied, with respect to the information provided here.
Indicates whether a structure is null. This property is read-only.
public:
property bool IsNull { bool get(); };
public bool IsNull { get; }
member this.IsNull : bool
Public ReadOnly Property IsNull As Boolean
Property Value
true
if the value of this object is null. Otherwise, false
.
Examples
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.
static private void WorkWithSqlNulls()
{
DataTable table = new DataTable();
// Specify the SqlType for each column.
DataColumn idColumn =
table.Columns.Add("ID", typeof(SqlInt32));
DataColumn descColumn =
table.Columns.Add("Description", typeof(SqlString));
// Add some data.
DataRow nRow = table.NewRow();
nRow["ID"] = 123;
nRow["Description"] = "Side Mirror";
table.Rows.Add(nRow);
// Add null values.
nRow = table.NewRow();
nRow["ID"] = SqlInt32.Null;
nRow["Description"] = SqlString.Null;
table.Rows.Add(nRow);
// Initialize variables to use when
// extracting the data.
SqlBoolean isColumnNull = false;
SqlInt32 idValue = SqlInt32.Zero;
SqlString descriptionValue = SqlString.Null;
// Iterate through the DataTable and display the values.
foreach (DataRow row in table.Rows)
{
// Assign values to variables. Note that you
// do not have to test for null values.
idValue = (SqlInt32)row["ID"];
descriptionValue = (SqlString)row["Description"];
// Test for null value in ID column.
isColumnNull = idValue.IsNull;
// Display variable values in console window.
Console.Write("isColumnNull={0}, ID={1}, Description={2}",
isColumnNull, idValue, descriptionValue);
Console.WriteLine();
}
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"
table.Rows.Add(row)
' Add null values.
row = table.NewRow()
row("ID") = SqlInt32.Null
row("Description") = SqlString.Null
table.Rows.Add(row)
' 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)
Console.WriteLine()
Next row
End Sub
This example displays the following results:
isColumnNull=False, ID=123, Description=Side Mirror
isColumnNull=True, ID=Null, Description=Null
Remarks
The default value for any System.Data.SqlTypes instance is null. Use IsNull property to test for null values.
Applies to
See also
Обратна връзка
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