gistfile1.rb

# collection association e.g. has_many

owners = People.all
association_name = :photos

owners.each do |owner|
  records = Array(whatever_you_want)
  
  association = owner.association(association_name)
  association.loaded!
  association.target.concat(records)
  records.each { |record| association.set_inverse_instance(record) }
end

# singular association e.g. has_one

owners = People.all
association_name = :photos

owners.each do |owner|
  record = whatever_you_want
  
  association = owner.association(association_name)
  association.target = record
  association.set_inverse_instance(record)
end