To be singular or to be plural

ActiveRecord's relationship is sensitive to the plurality of the database table name.

Let's say, blogs contains many posts, then blogs should be on singular side and posts on plural side.

class Blog < ActiveRecord::BASE
  has_many :posts    #a plural declare
end

 
class Post < ActiveRecord::BASE
  belongs_to :blog   #a singular declare
end

For has_one and belongs_to relationship, it should be singular. Suppose each user has only one avatar:

class Avator < ActiveRecord::BASE
  belongs_to :user  #a singular declare
end

 
class User < ActiveRecord::BASE
  has_one :avatar   #a singular declare
end

If you don't follow the convention, it won't work.