INullable.IsNull プロパティ

定義

構造体が null かどうかを示します。Indicates whether a structure is null. このプロパティは読み取り専用です。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

プロパティ値

Boolean

このオブジェクトの値が null の場合は SqlBoolean trueSqlBoolean true if the value of this object is null. それ以外の場合は falseOtherwise, false.

次のコード例では、SqlInt32SqlString として定義された 2 つの列を含む DataTable を作成します。The following code example creates a DataTable with two columns defined as SqlInt32 and SqlString. このコードでは、既知の値の 1 行と null 値の 1 行を追加し、DataTable を反復処理します。これによって変数に値を割り当て、コンソール ウィンドウに出力を表示します。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

この例では、次の結果が表示されます。This example displays the following results:

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

注釈

任意の System.Data.SqlTypes インスタンスの既定値は null です。The default value for any System.Data.SqlTypes instance is null. Null 値をテストするには、IsNull プロパティを使用します。Use IsNull property to test for null values.

適用対象

こちらもご覧ください