Best way to check if column returns a null value (

问题:

I have a table with a DateTime column the column can have NULL values

Now I connect to the database using an ODBC connection and get the value into a DataTable in .net / c#.

I am able to check it for NULL by going

if(String.IsNullOrEmpty(table.rows[0][0].ToString())
{
     //Whatever I want to do
}

Is String.IsNullOrEmpty the correct way to check for null values.

回答1:

Use DBNull.Value.Equals on the object without converting it to a string.

Here's an example:

   if (! DBNull.Value.Equals(row[fieldName])) 
   {
      //not null
   }
   else
   {
      //null
   }

回答2:

Just use DataRow.IsNull. It has overrides accepting a column index, a column name, or a DataColumn object as parameters.

Example using the column index:

if (table.rows[0].IsNull(0))
{
    //Whatever I want to do
}

And although the function is called IsNull it really compares with DbNull (which is exactly what you need).

---

What if I want to check for DbNull but I don't have a DataRow? Use Convert.IsDBNull.

回答3:

System.Convert.IsDbNull][1](table.rows[0][0]);

IIRC, the (table.rows[0][0] == null) won't work, as DbNull.Value != null;

回答4:

row.IsNull("column")

回答5:

If we are using EF and reading the database element in while loop then,

   using( var idr = connection, SP.......)
{
    while(idr.read())
{
if(Sting.ISNullOrEmpty(idr["ColumnNameFromDB"].ToString())
  //do something
}
}
}

回答6:

Just check for

if(table.rows[0][0] == null)
{
     //Whatever I want to do
}

or you could

if(t.Rows[0].IsNull(0))
{
     //Whatever I want to do
}