ActiveRecord Associations: Any gotchas if has_many WITHOUT corresponding belongs_to?

Question

A phone has many messages.

An email address has many messages.

A message either belongs to a phone, email, or neither. The belongs_to association is optional.

The following associations seem to work fine for these relationships:

• Phone model has_many :messages
• Email model has_many :messages
• Message model does NOT have belongs_to :phones, :email

Is this okay or is there some proper way to specify a "can_belong_to" relationship?

Answer 1

It is completely correct unidirectional relation. Using both is sometimes called "curcular dependency" by some purists and may cause problems when using validates_associated.

From the other side using only has_many :messages may be not enough when you want retrieve phone information from one message. Generally it is matter of convenience.