Convert from ADO to entity framework

This is a very basic operation in EF. I highly suggest you pick up a book on EF and work through it.

We can't tell you exactly what the code is going to be because we know NOTHING about your EF database setup, like your DbContext name. We don't know what you called your reservation table name, what the Id field is, ... nothing.

But, there's a couple of different ways of doing this:

var result = myDbContext.Reservations.SingleOrDefault(r => r.Id == queryId);

or

var result = myDbContext.Reservations.Where(r => r.Id == queryId).SingleOrDefault();

or

var result = from r in myDbContext.Reservations
             where r.Id == queryId
             select r;