SqlDataReader.IsDBNull(Int32) 方法
定义
重要
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获取一个值，该值指示列中是否包含不存在的或缺少的值。
public:
override bool IsDBNull(int i);public:
virtual bool IsDBNull(int i);public override bool IsDBNull (int i);public bool IsDBNull (int i);override this.IsDBNull : int -> boolabstract member IsDBNull : int -> bool
override this.IsDBNull : int -> boolPublic Overrides Function IsDBNull (i As Integer) As BooleanPublic Function IsDBNull (i As Integer) As Boolean参数
- i
- Int32
从零开始的列序号。
返回
如果指定的列值等效于 DBNull，则为 true；否则为 false。
实现
注解
调用此方法以检查 null 列值，然后调用类型化 get 方法 (例如、 GetByteGetChar等) 以避免引发错误。
using System;
using System.Data;
using System.Data.SqlClient;
class Program {
static void Main(string[] args) {
using (var connection = new SqlConnection(@"Data Source=(local);Initial Catalog=AdventureWorks2012;Integrated Security=SSPI")) {
var command = new SqlCommand("SELECT p.FirstName, p.MiddleName, p.LastName FROM HumanResources.Employee AS e" +
" JOIN Person.Person AS p ON e.BusinessEntityID = p.BusinessEntityID;", connection);
connection.Open();
var reader = command.ExecuteReader();
while (reader.Read()) {
Console.Write(reader.GetString(reader.GetOrdinal("FirstName")));
// display middle name only of not null
if (!reader.IsDBNull(reader.GetOrdinal("MiddleName")))
Console.Write(" {0}", reader.GetString(reader.GetOrdinal("MiddleName")));
Console.WriteLine(" {0}", reader.GetString(reader.GetOrdinal("LastName")));
}
connection.Close();
}
}
}
Imports System.Data
Imports System.Data.SqlClient
Module Module1
Sub Main()
Using connection As New SqlConnection("Data Source=(local);Initial Catalog=AdventureWorks2012;Integrated Security=SSPI")
Dim command As New SqlCommand("SELECT p.FirstName, p.MiddleName, p.LastName FROM HumanResources.Employee AS e" & _
" JOIN Person.Person AS p ON e.BusinessEntityID = p.BusinessEntityID;", connection)
connection.Open()
Dim reader As SqlDataReader = command.ExecuteReader()
While reader.Read()
Console.Write(reader.GetString(reader.GetOrdinal("FirstName")))
' display middle name only of not null
If Not reader.IsDBNull(reader.GetOrdinal("MiddleName")) Then
Console.Write(" {0}", reader.GetString(reader.GetOrdinal("MiddleName")))
End If
Console.WriteLine(" {0}", reader.GetString(reader.GetOrdinal("LastName")))
End While
connection.Close()
End Using
End Sub
End Module
