Question

In my Rails app, I have a class with a has_many relationship. For the sake of efficiency, I want to do some direct SQL to update many rows in the database at once, and then I want to mark the has_many relationship as no longer valid. If later code accesses the has_many relationship, I want it to reload the data. But I obviously want to skip the SQL unless it is necessary.

So for example:

class Student
  has_many courses # may have a :condition clause or some such

  def some_method
    # For some reason, we want to change all courses in here, not
    # just a single row.
    ActiveRecord::Base.connection.execute("UPDATE courses SET location = #{new_location}")
    # Not sure if we'll later do anything with self.courses, so I need to invalidate
    # that relationship.  Could do self.courses.reload right here, but I don't want to
    # do the SQL if it isn't necessary; the cache only lasts until the end of the
    # current page request.
  end
end

I may well be missing something rather obvious. Some hypothetical self.courses.invalidate method.

Answer 1

Not in their public API, but you could try the reset method on the AssociationCollection class.

Watching the log:

s = Student.first
s.courses       # Hits db
s.courses       # Hits cache 
s.courses.reset # No db
s.courses       # Hits db