https://gist.github.com/stream7/1069589
:limit Numeric Type Column Size Max value
1 tinyint 1 byte 127
2 smallint 2 bytes 32767
3 mediumint 3 byte 8388607
nil, 4, 11 int(11) 4 byte 2147483647
5..8 bigint 8 byte 9223372036854775807
关于sequence 字段
limit: 2 是两个字节，16 位，2 的 15 次方是 32767
class CreateTableSubjections < ActiveRecord::Migration[5.0]
def change
create_table :table_subjections do |t|
t.belongs_to :subject, index: true
t.belongs_to :video, index: true
t.string :title, limit: 40
t.string :sub_title, limit: 40
t.string :description, limit: 500
t.integer :status, limit: 1
t.integer :sequence, limit: 2 t.timestamps
end
end
end
对于多态关联的表
class CreateSubjections < ActiveRecord::Migration[5.0]
def change
create_table :subjections do |t|
t.belongs_to :subject, index: true
t.string :title, limit: 40
t.string :sub_title, limit: 40
t.string :description, limit: 500
t.string :subjectable_type, limit: 20
t.integer :subjectable_id
t.integer :status, limit: 1
t.integer :sequence, limit: 2 t.timestamps
end add_index :subjections, [:subjectable_type, :subjectable_id]
end
end
t.integer :subjectable_id 不需要设置limit，因为这个是用来做外键的，存储的是数据库的自增主键