Ruby on rails学习：Rails 的 active_record 数据表的常见类型

Active Record supports the following database column types:

:string - is for small data types such as a title. (Should you choose string or text?)
:text - is for longer pieces of textual data, such as a paragraph of information
:binary - is for storing data such as images, audio, or movies.
:boolean - is for storing true or false values.
:date - store only the date
:datetime - store the date and time into a column.
:time - is for time only
:timestamp - for storing date and time into a column.(What's the difference between datetime and timestamp?)
:decimal - is for decimals (example of how to use decimals).
:float - is for decimals. (What's the difference between decimal and float?)
:integer - is for whole numbers.
:primary_key - unique key that can uniquely identify each row in a table

There's also references used to create associations. But, I'm not sure this is an actual data type.

New Rails 4 datatypes available in PostgreSQL:

:hstore - storing key/value pairs within a single value (learn more about this new data type)
:array - an arrangement of numbers or strings in a particular row (learn more about it and see examples)
:cidr_address - used for IPv4 or IPv6 host addresses
:inet_address - used for IPv4 or IPv6 host addresses, same as cidr_address but it also accepts values with nonzero bits to the right of the netmask
:mac_address - used for MAC host addresses

Learn more about the address datatypes here and here.

I'm taking a guess that you're referring to t.references :associated_model in a migration?

Suppose two models, Post and Author.

class Post < ActiveRecord::Base
  belongs_to :author
end

class Author < ActiveRecord::Base
  has_many :posts
end

create_table :posts do |t|
  t.references :author
end