Create default values in a datatable

Instead iterating for each row setting a default value like this

foreach(DataRow dr in dt.Rows)
{
dr["column"] = defaultValue
}

Just set the .DefaultValue property in the column. This will save some seconds.

dt.Columns["column"].DefaultValue = defaultValue;

You can also set expressions for calculated fields, per example if you want to concatenate the values of two columns.

dt.Columns["column"].Expression = "Column1+Column2";