create_table :table_with_arrays do |t|
 t.integer :int_array, :array => true
 # integer[]
 t.integer :int_array, :array => true, :length => 2
 # smallint[]
 t.string :string_array, :array => true, :length => 30
 # char varying(30)[]
end

create_table :table_with_arrays do |t|
 t.integer :int_array, :array => true, :default => '{}'
 # integer[], default == []
 t.integer :int_array, :array => true, :length => 2, :default => '{1}'
 # smallint[], default == [1]
end

create_table :users do |t|
 t.string :first_name
 t.string :last_name
 t.string :nicknames, :array => true
end

class User < ActiveRecord::Base
 attr_accessible :first_name, :last_name, :nicknames
end

john = User.create(:first_name => 'John', :last_name => 'Doe')

john = User.create(:first_name => 'John', :last_name => 'Doe',
 :nicknames => ['Jack', 'Johnny'])

john = User.first
 
john.nicknames += ['Jackie boy']
# 或者
john.nicknames = john.nicknames.push('Jackie boy')
# 任何时候，属性通过"="赋值，ActiveRecord会跟踪这个更改
john.save
 
john.reload
john.nicknames
#=> ['Jack', 'Johnny', 'Jackie Boy']
 
john.nicknames.pop
john.nicknames_will_change!
# '#pop'操作会改变数组的值，所以我们需要告诉ActiveRecord它将会发生更改
john.save

[[1,2,3], [2,3,4], [4,5,nil]]
# 在PostgreSQL 可用，每个子数组元素个数一样
 
[1,2,[3,4]]
# 不可用的数组