# What is the difference between new and build?

**URL:** <https://www.ruby-forum.com/t/what-is-the-difference-between-new-and-build/197196>\
**Category:** Rails\
**Created:** [April 23, 2010, 9:38am UTC](https://www.ruby-forum.com/t/what-is-the-difference-between-new-and-build/197196 "2010-04-23T09:38:02Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![manoj](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/d9b06d/32.png) [@manoj](https://www.ruby-forum.com/u/manoj)\
**Post date:** [April 23, 2010, 9:38am UTC](https://www.ruby-forum.com/t/what-is-the-difference-between-new-and-build/197196/1 "2010-04-23T09:38:02Z")

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What is the difference between

parent.children \<\< child.new

and

parent.children.build(params[:child])

---

<div class="post-metadata">

**Author:** ![manoj](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/d9b06d/32.png) [@manoj](https://www.ruby-forum.com/u/manoj)\
**Post date:** [April 23, 2010, 10:41am UTC](https://www.ruby-forum.com/t/what-is-the-difference-between-new-and-build/197196/2 "2010-04-23T10:41:32Z")

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In the first one, the child is saved right away.  
In the second, the child is not saved until the parent is saved

You may find this usefull:  
[http://blog.mrbrdo.net/2009/10/27/ruby-on-rails-new-vs-create-vs-build/](http://blog.mrbrdo.net/2009/10/27/ruby-on-rails-new-vs-create-vs-build/)

---

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**Author:** ![manoj](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/d9b06d/32.png) [@manoj](https://www.ruby-forum.com/u/manoj)\
**Post date:** [April 26, 2010, 6:18am UTC](https://www.ruby-forum.com/t/what-is-the-difference-between-new-and-build/197196/3 "2010-04-26T06:18:04Z")

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Sharagoz wrote:

> In the first one, the child is saved right away.  
> In the second, the child is not saved until the parent is saved
> 
> You may find this usefull:  
> [http://blog.mrbrdo.net/2009/10/27/ruby-on-rails-new-vs-create-vs-build/](http://blog.mrbrdo.net/2009/10/27/ruby-on-rails-new-vs-create-vs-build/)

Thanks Sharagoz. I got some idea about this.