c# - Linq Select causes InvalidCastException -

var courses = db.courses.select(course => new model.course() {     dates = db.dates         .where(date => date.courseid == course.id)         .select(date => date._date.tostring())         .tolist() });  return courses.tolist(); 

the return call causes system.invalidcastexception. if remove dates, there no error.

here's course class:

public class course {     public list<string> dates { get; set; } } 

screenshot vs:

the .tostring() on _date column causing invalidcastexception. linq sql trying convert _date string using tostring() not exist in sql. need grab date sql , convert string in memory.

try this:

// grab db list of courses , dates.  // put dates in list of datetime, can use datetime2. // note courses iqueryable. var courses = db.courses.select(course => new list<datetime> {     dates = db.dates         .where(date => date.courseid == course.id)         .select(date => date._date).tolist() });  // extract data sql calling our iqueryable's tolist() of method. puts data list in memory. // using list.select() method, convert dates strings. return ienumerable. // convert resulting ienumerable list. return courses           .tolist()           .select(course => new model.course           {              // here, using .net framework's datetime.tostring()              // can use formatting options available that.              dates = course.dates.select(date => date.tostring()).tolist()           })           .tolist();