Rails Console

禁用 IRB 多行编辑以提升粘贴性能

bundle exec rails console -- --nomultiline

参考来源：GitHub: rails issues#39909 Can 'rails console' pass '--nomultiline' to IRB?

关闭或开启 SQL 日志输出

• 关闭 SQL 日志

  ActiveRecord::Base.logger = nil

• 开启 SQL 日志

  ActiveRecord::Base.logger = Logger.new(STDOUT)

参考来源：GitHub: rails issues#5149 Logging ActiveRecord queries from Rails console?

设置时间展示格式

• Rails 5.2 默认格式 Mon, 08 Dec 2025 17:55:30 CST +08:00
  Rails 6.1/7.2 默认格式 Mon, 08 Dec 2025 17:55:30.967256462 CST +08:00
  Rails 8.1 默认格式 2025-12-08 17:55:30.967256462 CST +08:00
  设置为更易读的格式 2025-12-08 17:55:30 +08:00

  class ActiveSupport::TimeWithZone
    def inspect
      "#{time.strftime('%F %T')} #{formatted_offset}"
    end
  end

• Rails 5.2/6.1/7.2/8.1 默认格式 Mon, 08 Dec 2025
  设置为更易读的格式 2025-12-08

  class Date
    def inspect
      strftime('%F')
    end
  end

参考来源：

• Stack Overflow: Configure Rails console's default date time format
• Rails API documentation: ActiveSupport::TimeWithZone#inspect
• Rails API documentation: Date#inspect

名词复数化

'book'.pluralize    # books
'box'.pluralize     # boxes
'person'.pluralize  # people
'man'.pluralize     # men
'sheep'.pluralize   # sheep
'data'.pluralize    # data

参考来源：Rails API documentation: String#pluralize

多行字符串 (heredoc)

# 保留行首空白，结尾的 EOF 必须单独行且在行首
# "  first line\n  second line\n"
str = <<EOF
  first line
  second line
EOF

# 保留行首空白，结尾的 EOF 必须单独行，可以不在行首
# "  first line\n  second line\n"
str = <<-EOF
  first line
  second line
  EOF

# 忽略行首空白，结尾的 EOF 必须单独行，可以不在行首
# "first line\nsecond line\n"
str = <<~EOF
  first line
  second line
  EOF

参考来源：Ruby-Doc 3.4.1: Literals

变量判空方法

	nil?	if()	empty?	blank?	present?
nil	true	false	NoMethodError	true	false
false	false	false	NoMethodError	true	false
true	false	true	NoMethodError	false	true
0	false	true	NoMethodError	false	true
1	false	true	NoMethodError	false	true
""	false	true	true	true	false
" "	false	true	false	true	false
[]	false	true	true	true	false
[nil]	false	true	false	false	true
{}	false	true	true	true	false

提示

其中 blank? 和 present? 是 Rails 扩展的方法，且 present? = !blank?

参考来源：

• Stack Overflow: How to understand nil vs. empty vs. blank in Ruby
• Rails API documentation: Object#present?

非预期的 delete_all 行为

通常调用 delete_all 方法时，期望是直接删除数据库中的记录，即对应到 SQL 语句的 DELETE 操作，例如：

Post.where(user_id: 123).delete_all
# 期望执行的 SQL 语句: DELETE FROM posts WHERE user_id = 123;

但在某些情况下，delete_all 方法会表现出非预期的行为，对应的 SQL 语句是 UPDATE 而不是 DELETE，例如：

User.find(123).posts.delete_all
# 期望执行的 SQL 语句: DELETE FROM posts WHERE user_id = 123;
# 实际执行的 SQL 语句: UPDATE posts SET user_id = NULL WHERE user_id = 123;

原因是两个例子中调用的 delete_all 方法是不同的：

• Post.where(user_id: 123).class 返回 User::ActiveRecord_Relation，调用的是 ActiveRecord::Relation 上的 delete_all 方法，官方文档中明确说明对应到单条 SQL DELETE 语句
• User.find(123).posts.class 返回 Post::ActiveRecord_Associations_CollectionProxy，调用的是 ActiveRecord::Associations::CollectionProxy 上的 delete_all 方法，官方文档中表示会根据关联的 :dependent 选项来决定删除策略

原始描述如下：

• ActiveRecord::Relation#delete_all

  This is a single SQL DELETE statement that goes straight to the database, much more efficient than destroy_all.

• ActiveRecord::Associations::CollectionProxy#delete_all

  Deletes all the records from the collection according to the strategy specified by the :dependent option. If no :dependent option is given, then it will follow the default strategy.
  For has_many associations, the default deletion strategy is :nullify. This sets the foreign keys to NULL.

参考来源：

• Stack Overflow: ActiveRecord delete_all method updating instead of deleting
• Rails API documentation: ActiveRecord::Relation#delete_all
• Rails API documentation: ActiveRecord::Associations::CollectionProxy#delete_all

Rails 延迟加载 (lazy loading)

Rails 中的数据库查询通常是延迟加载 (lazy loading) 的，不会在定义时立即执行，而是在实际需要数据时才执行，例如：

ActiveRecord::Base.logger = Logger.new(STDOUT)

puts '========== breakpoint 1 =========='
users = User.where(active: true)
puts '========== breakpoint 2 =========='
names = users.pluck(:name)
puts '========== breakpoint 3 =========='

将以上代码保存为 lazy.rb，执行 bundle exec rails runner lazy.rb 运行该文件，输出结果如下：

========== breakpoint 1 ==========
========== breakpoint 2 ==========
D, [2025-12-16T00:25:20.297256 #17260] DEBUG -- :   User Pluck (0.1ms)  SELECT "users"."name" FROM "users" WHERE "users"."active" = TRUE /*application='Demo'*/
========== breakpoint 3 ==========

但在 Rails Console 中，默认会调用 inspect 方法来展示每一次输入的返回值，这会触发查询的执行，按行输入的效果为：

demo(dev):001> puts '========== breakpoint 1 =========='
# ========== breakpoint 1 ==========
# => nil

demo(dev):002> users = User.where(active: true)
#   User Load (0.1ms)  SELECT "users".* FROM "users" WHERE "users"."active" = TRUE /* loading for pp */ LIMIT 11 /*application='Demo'*/
# => 
# [#<User:0x00007fd39142d1e8
# ...

demo(dev):003> puts '========== breakpoint 2 =========='
# ========== breakpoint 2 ==========
# => nil

demo(dev):004> names = users.pluck(:name)
#   User Pluck (0.1ms)  SELECT "users"."name" FROM "users" WHERE "users"."active" = TRUE /*application='Demo'*/
# => ["admin1", "admin2", "admin3"]

demo(dev):005> puts '========== breakpoint 3 =========='
# ========== breakpoint 3 ==========
# => nil

为了避免在 Rails Console 中触发不必要的查询，可以通过一次粘贴多行，或者在单行结尾强制返回值为 nil 的方式，例如：

users = User.where(active: true); nil
names = users.pluck(:name)
#   User Pluck (0.1ms)  SELECT "users"."name" FROM "users" WHERE "users"."active" = TRUE /*application='Demo'*/
# => ["admin", "admin2", "admin3"]

同理，在 Rails Console 中调用 each、map 等迭代方法时，也会隐式调用 inspect 来展示结果，可以通过以下方式避免刷屏：

User.where(active: true).each do |u|
  puts u.name
end; nil # 在迭代结束后将返回值强制设为 nil，避免结果刷屏

参考来源：Rails Tutorials: Lazy loading in rails