Has many represents the second counter part of belongs to relation. It assumes the current model is referenced by an object (or no objects) of another model.
Usually, it's used when another model optionally extend the current model by composition. A common example is the usage of
UserInfois setup after registration and filling of form from the user. An User can then exists without
UserInfo– this handle all the connection lifecycle – while
UserInfowill handle all the optional informations about the user.
has_one user_info : UserInfo
belongs_to user : User