EF query readonly Iqueryable

Question

I have tens of different views and on some, the data that comes from database, must be manipulated before shown to user.

for example:

var students = _repository.Students.Select(c => { c.StartDate = FixDateToCurrentYear(c.StartDate ); c.EndDate = FixDateToCurrentYear(c.EndDate); return c; }).ToList();

So basically I now have a variable, where Students StartDate and EndDate have been fixed by some logic, which is not relevant at the moment.

The problem here is that, whenever somewhere a SaveChanges() function is called, then the changed dates for students are also persisted to database.

I only want to use the changed dates for the logic in specific view. How could I handle this?

I have heard about .AsNoTracking(); but this must be put directly to DbSet item, but I want to handle it on controller side, is it possible?

Answer 1

Pull the students from the db first and the do a select to an anonymous type. EF won't know how to track changes on that.

var students = 
    _repository.Students.ToList()
               .Select(s => 
                   new { StartDate = FixDateToCurrentYear(c.StartDate),
                         EndDate = FixDateToCurrentYear(c.EndDate),
                         Student = s });

Answer 2

The quickest thing I can think of is to perform your fix at the point you display it to the user, e.g. in Razor:

@FixDateToCurrentYear(student.StartDate)

In this way, you're not actually changing the value, you're just changing how it's displayed.

If you need to do more than display, you will need to create a partial buddy class, add a new property and modify its get method:

public partial class Student
{
    DateTime StartDateComputed {
        get
        {
            return  FixDateToCurrentYear(StartDate);
        }
        set;
    }
}

Now, use StartDateComputed instead of StartDate and the same for EndDate.