Rails 上的 build 和 new 有什么区别? [英] What is the difference between build and new on Rails?

问题描述

谁能告诉我 Rails 上的 build 和 new 命令有什么区别?

Can anyone tell me what is the difference between build and new command on Rails?

推荐答案

new 用于特定模型的新实例:

new is for a new instance of a specific model:

foo = Foo.new

build 用于在 AR 关联中创建新实例:

build is for creating a new instance within an AR association:

bar = foo.build_bar  # (has_one or belongs_to)

或

bar = foo.bars.build # (has\_many, habtm or has_many :through)

http://api.rubyonrails.org/classes/ActiveRecord/Associations/类方法.html

更新

根据@toklands 的建议，build 和 new 是 ActiveRecord::Relation:

Per @toklands's suggestion, build and new are aliases as defined in ActiveRecord::Relation:

所以如果类 Foo 有_many Bars，下面的效果是一样的:

So if class Foo has_many Bars, the following have identical effects:

• foo.bars.new <=> foo.bars.build
• Bar.where(:foo_id=>foo.id).new <=> Bar.where(:foo_id=>foo.id).build

如果 !foo.new_record?

• foo.bars.new <=> Bar.where(:foo_id=>foo.id).new

这篇关于Rails 上的 build 和 new 有什么区别?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！