foo_1.rb

class Foo
  
  # Do some stuff...
  
  # We want to update a field from another model with a value from this model
  after_commit :update_bar_field
  
  # Do more stuff...
  private
  
  def update_bar_field
    # We want to update Bar#bar_field_2 with the value of Foo#foo_field_2
    # Bar and foo are related by bar_field_1 and foo_field_1
    # (yes, we might use associations instead, but this is an example ;-) )
    Bar.where(bar_field_1: foo_field_1).update(bar_field_2: foo_field_2)
  end
end

foo_2.rb

class Foo
  
  # Do some stuff...
  
  # We want to update a field from another model with a value from this model
  after_commit :update_bar_field
  
  # Do more stuff...
  private
  
  def update_bar_field
    # We want to update Bar#bar_field_2 with the value of Foo#foo_field_2
    # Bar and foo are related by bar_field_1 and foo_field_1
    # (yes, we might use associations instead, but this is an example ;-) )
    Bar.by_bar_field_1(foo_field_1).update(bar_field_2: foo_field_2)
  end
end

foo_bar_wisper.rb

class Foo
  include Wisper::Publisher

  # Do some stuff...
  
  # We want to update a field from another model with a value from this model
  after_commit -> (foo) { foo.broadcast(:foo_saved, foo.foo_field) }  
end

class Bar
  
end