RowFilter of DataView for DBNull values of object type

Question

How would the filter string looks like for DBNull values in DataTable.

"IsNull("Column1", 'Null Column')='Null Column'"
"IsNull("Column1", 'Null Column')<>'Null Column'"

This string to filter Null values in the Column1. It works fine if it is a String column and throws exception for other types.

Any idea on this?

And also i want to know whether Null and DBNull for object type of column is same?

        dt.Columns.Add(new DataColumn("Title", typeof (string)));
        dt.Columns.Add(new DataColumn("TitleID", typeof(Int32)) {AllowDBNull = true});
        dt.Columns.Add(new DataColumn("Date", typeof(object)) );
        dt.Columns.Add(new DataColumn("Desc", typeof(string)));

        for(int i =0; i<10; i++)
        {
            var input = i%2 == 0 ? (object) i : DBNull.Value;
            var result = input.Equals(DBNull.Value);

            DataRow row = dt.NewRow();
            row["Title"] = "C#" + i;
            row["TitleID"] = i % 2 == 0 ? (object) i : DBNull.Value;
            row["Date"] = i == 2 ? (object) DateTime.Now : DBNull.Value;
            row["Desc"] = i % 2 == 0 ? null : ""; 
            dt.Rows.Add(row);
        }

        DataView defView = dt.DefaultView;

        defView.RowFilter = "IsNull(Date, 'Null Column')='Null Column'";

        var filtered = defView;

Answer 1

I am filtering the DataTable based on NULL Email ID :

  var results = from DataRow myRow in dtCustomer.Rows
                          where (object)myRow["EmailID"] == DBNull.Value
                          select myRow;
            DataTable dt = results.CopyToDataTable();

And there is a good explanation about NULL and DBNULL here.

As per the msdn remarks:

   // DataTable dtCst = dtCustomer.Select("Isnull(EmailID,'Null Column') =
                                           'Null Column'").CopyToDataTable();
  //or
        DataView dataView = dtCustomer.DefaultView;
        dataView.RowFilter = "Isnull(EmailID,'Null Column') = 'Null Column'";

I have also tested with JoinDate which is NULL in DB and datatype is datetime and also tested with date type.

   dataView.RowFilter = "Isnull(JoinDate,'Null Column') = 'Null Column'";

Updated

Update your code :

 dt.Columns.Add(new DataColumn("Date", typeof(DateTime)) { AllowDBNull = true });

in your for loop :

if (i == 2)
   {
      row["Date"] = DateTime.Now;
   }

then filter. it will work.

Answer 2

Try

 dataView.RowFilter = "JoinDate IS null";