How to check if a column value is null in a datatable in C#?

Question

So what i'm trying to do, is to loop through the datatable's column to get the value out of it.

For example, this is my datatable

emp_id      f_name         email            remarks
1            Jim          Jim@yahoo.com
2            Apple        apple@gmail.com  
3            Peter
4            Amy          amy@gmail.com

In this datatable, you can see that Peter's email is missing. I want to retrieve this record set a values in remarks "No email".

How can I do this?

Answer 1

Try this query, so you don't have to retrieve and modify the DataTable:

select  emp_id,
        f_name,
        email,
        ISNULL(email,'No Email') AS 'remark'
from [tablename]

if you want to retrieve only the null email add where in the query like this

 select  emp_id,
            f_name,
            email,
            ISNULL(email,'No Email') AS 'remark'
    from [tablename] where email is null

if you are using MySQL, replace ISNULL to IFNULL

Answer 2

You can easily achieve this in LINQ:

var noemaillist = (from m in databaseContext.TableName
                  where m.email == String.Empty
                  select m).ToList();
if(noemaillist != null)
{
   foreach(var item in noemaillist)
   {
      item.remarks = "No email";
   }
}
databaseContext.SubmitChanges();

This will return the list with empty email id's and set the remarks column to "No email" for the corresponding empty email fields.

Answer 3

foreach(DataRow dr in dt.Select("email is NULL or email=''"))
{
   dr["Remarks"]="No Email";
}
dt.AcceptChanges();

The above will set value of column "Remarks" as required.

Answer 4

在ADO.NET中，具有IsDBNull(<column>)属性，在LINQ中，您可以通过email != NULL检查它email != NULL

Answer 5

  foreach (DataColumn col in dataTable.Columns)
            {
                foreach (DataRow row in dataTable.Rows)
                {
                  var x=row[col.ColumnName].ToString();
                  if (string.IsNullOrEmpty(x))
                  {
                      var colName = col.ColumnName.ToString();
                      row["remarks"] = string.Format("{0} is required", colName);
                  }

                }
            }