建立和新的on Rails的之间的区别是什么？ [英] What is the difference between build and new on Rails?

问题描述

谁能告诉我什么是on Rails的构建和新的命令之间的区别是什么？

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

推荐答案

新是一个特定的模式的一个新实例：

new is for a new instance of a specific model:

foo = Foo.new

构建是内AR协会创建一个新的实例：

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)

<一个href="http://api.rubyonrails.org/classes/ActiveRecord/Associations/ClassMethods.html">http://api.rubyonrails.org/classes/ActiveRecord/Associations/ClassMethods.html

每@ toklands的建议，建立和新的作为<一个定义的别名href="https://github.com/rails/rails/blob/959fb8ea651fa6638aaa7caced20d921ca2ea5c1/activerecord/lib/active_record/relation.rb#L84">ActiveRecord::Relation:

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

因此​​，如果类Foo的has_many酒吧，下面有同样的效果：

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

• foo.bars.new ＆LT; => foo.bars.build
• Bar.where（：foo_id =＆GT; foo.id）。新＆LT; => Bar.where（：foo_id =＆GT; foo.id）.build

• 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 ＆LT; => Bar.where（：foo_id =＆GT; foo.id）。新

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

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