Unable to cast object of type 'System.Double' to type 'System.String' linq query

Question

I'm new to Linq, the below line gives me "Unable to cast object of type 'System.Double' to type 'System.String'". How can I resolve it?

dt.AsEnumerable().Where(dataRow => !string.IsNullOrEmpty(dataRow.Field<string>(dc.ColumnName).First().ToString()) && (dataRow.Field<int>(dc.ColumnName) == 1)).Count() > 3

I'm querying a DataTable column.

Answer 1

I suspect you encountered a NullReferenceException while trying to filter for rows that are equal to 1. To avoid this, return a nullable type with Field<double?>(), eg:

dt.AsEnumerable()
  .Where(dataRow => dataRow.Field<double?>(dc.ColumnName) == 3m))
  .Count() > 3

The comparison will fail if the field is null.

If you want to retrieve the column's value while converting the NULL to eg 0, you can use the ?? operator:

.Select( dataRow => dataRow.Field<double?>(dc.ColumnName) ?? 0m)