原来ActiveRecord默认约定的join表名字是两个表哪个名字短哪个就排在前面啊 以前一直不知道的说

join_table_name.rb

# Generates a join table name from two provided table names.
# The names in the join table names end up in lexicographic order.
#
#   join_table_name("members", "clubs")         # => "clubs_members"
#   join_table_name("members", "special_clubs") # => "members_special_clubs"
def join_table_name(first_table_name, second_table_name)
  if first_table_name < second_table_name
    join_table = "#{first_table_name}_#{second_table_name}"
  else
    join_table = "#{second_table_name}_#{first_table_name}"
  end

  model.table_name_prefix + join_table + model.table_name_suffix
end