[Rails] 判斷內容是空或有

tags: ruby, rails, empty, blank, present, nil

Rails 方法

.blank?

• Rails Method
• 任何型態都可使用不會噴錯
• 空白的字串也算空

nil.blank?     #true
[].blank?      #true
{}.blank?      #true
"".blank?      #true
" ".blank?     #true
"abc".blank?   #false
123.blank?     #false

.present?

• Rails Method
• 任何型態都可使用不會噴錯
• 空白的字串也算空

nil.present?   #false
[].present?    #false
{}.present?    #false
"".present?    #false
" ".present?   #false
"abc".present? #true
123.present?   #true

.persisted? & new_record

判斷 Object 是否已經存在資料庫的 method：

• new_record: 尚未存入資料庫
• persisted: 已存入資料庫

a = User.new   #還沒存入資料庫以前
a.persisted?   #false
a.new_record?  #true

a.save         #存入資料庫
a.persisted?   #true
a.new_record?  #false

Ruby 內建方法

.empty?

• Ruby Method
• 可以判斷 [], {} 和字串
• 無法判斷 nil 和數值（會噴錯）
• 字串內有空白就不算 empty

nil.empty?     #NoMethodError: undefined method `empty?' for nil:NilClass
[].empty?      #true
{}.empty?      #true
"".empty?      #true
" ".empty?     #false
"abc".empty?   #false
123.empty?     #NoMethodError: undefined method `empty?' for 123:Fixnum

.any?

• Ruby Method
• 只能判斷 [] 和 {}

nil.any?       #NoMethodError: undefined method `any?' for nil:NilClass
[].any?        #false
{}.any?        #false
"".any?        #NoMethodError: undefined method `any?' for "":String
" ".any?       #NoMethodError: undefined method `any?' for "":String
"abc".any?     #NoMethodError: undefined method `any?' for "":String
123.any?       #NoMethodError: undefined method `any?' for 123:Fixnum

.nil?

• Ruby Method
• 只能判斷該物件是否為 nil

nil.nil?       #true
[].nil?        #false
{}.nil?        #false
"".nil?        #false
" ".nil?       #false
"abc".nil?     #false
123.nil?       #false

.exist?

User.where(name: 'Aaron').exist?		# []

參考

• .nil? .empty? .blank? .present? 傻傻分不清楚？