I have a small issue related with eager loading, I got error during eager loading.
Here are my models, CourseActivity inherit Activity, so I assume CourseActivity inherit 'belongs_to :group' relationship from Activity.
However if I add 'belongs_to :group' relationship in CourseActivity, eager loading works fine
I also enable preload_models in mongoid
I don't know that is caused by polymorphism belongs_to, since found on website "Eager loaded is supported on all relations with the exception of polymorphic belongs_to associations."