C# 检查列是否返回空值的最佳方法（从数据库到 .net 应用程序）
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Best way to check if column returns a null value (from database to .net application)
提问by soldieraman
I have a table with a DateTime column the column can have NULL values
我有一个带有 DateTime 列的表，该列可以有 NULL 值
Now I connect to the database using an ODBC connection and get the value into a DataTable in .net / c#.
现在我使用 ODBC 连接连接到数据库，并将值放入 .net/c# 中的 DataTable。
I am able to check it for NULL by going
我可以通过去检查它是否为 NULL
if(String.IsNullOrEmpty(table.rows[0][0].ToString())
{
//Whatever I want to do
}
Is String.IsNullOrEmpty the correct way to check for null values.
String.IsNullOrEmpty 是否是检查空值的正确方法。
采纳答案by jball
Use DBNull.Value.Equalson the object without converting it to a string.
在对象上使用DBNull.Value.Equals而不将其转换为字符串。
Here's an example:
下面是一个例子：
if (! DBNull.Value.Equals(row[fieldName]))
{
//not null
}
else
{
//null
}
回答by jspcal
row.IsNull("column")
row.IsNull("列")
回答by Rabbi
Just check for
只需检查
if(table.rows[0][0] == null)
{
//Whatever I want to do
}
or you could
或者你可以
if(t.Rows[0].IsNull(0))
{
//Whatever I want to do
}
回答by Marcin Seredynski
System.Convert.IsDbNull][1](table.rows[0][0]);
IIRC, the (table.rows[0][0] == null)won't work, as DbNull.Value != null;
IIRC，这(table.rows[0][0] == null)行不通，因为DbNull.Value != null;
回答by Mariano Desanze
Just use DataRow.IsNull. It has overrides accepting a column index, a column name, or a DataColumn objectas parameters.
只需使用DataRow.IsNull。它具有接受列索引、列名或DataColumn 对象作为参数的覆盖。
Example using the column index:
使用列索引的示例：
if (table.rows[0].IsNull(0))
{
//Whatever I want to do
}
And although the function is called IsNullit really compares with DbNull(which is exactly what you need).
尽管调用IsNull了该函数，但它确实与DbNull（这正是您需要的）进行了比较。
What if I want to check for DbNull but I don't have a DataRow? Use Convert.IsDBNull.
如果我想检查 DbNull 但我没有 DataRow 怎么办？使用Convert.IsDBNull。
回答by priyanka
If we are using EF and reading the database element in while loop then,
如果我们使用 EF 并在 while 循环中读取数据库元素，则
using( var idr = connection, SP.......)
{
while(idr.read())
{
if(String.IsNullOrEmpty(idr["ColumnNameFromDB"].ToString())
//do something
}
}
