The specified cast from a materialized 'System.Int32' type to the 'System.Double' type is not valid

I think the data type of the columns inside your database table is Int32 but your data model has double. You need to change the data types of your data models to int. By materialized it means the type it got when it ran the query on the database.

First make sure your model and table column data type are same.

Try to change your query to this.

var data = ctx.tblTO
           .Where(m => m.Id == Id)
           .GroupBy(m => m.EmployeeId)
           .Select(m => new
           {
               workDay = m.Select(k => k.WorkDay).DefaultIfEmpty(0).Sum(),
               onDutyDay = m.Select(k => k.OnDutyDay).DefaultIfEmpty(0).Sum(),
               holiDay = m.Select(k => k.Holiday).DefaultIfEmpty(0).Sum()
           })
           .FirstOrDefault();

If the collection is empty, it will return one element with the value of 0 and then the sum will be applied.