在Ruby on Rails的构建方法 [英] build method on ruby on rails

问题描述

新建轨道，我跟随在敏捷Web开发使用Rails 3.1中发现的油库项目。一切都很好，直到我在本书中使用的建的方法迷路了。

New to rails and I'm following the Depot project found in the Agile web development with rails 3.1. Everything was fine until I got lost when the book used the "build" method.

@cart = current_cart
product = Product.find(params[:product_id])
@line_item = @cart.line_items.build(product: product)

我的谷歌搜索使我明白，.build方法仅仅是一个创建于表中的行（与表之间的关联），更清洁的方式。但在上述code，我期待code看起来就像是这样的：

My google searches led me to understand that the .build method is just a cleaner way to create a row in the table (with association between tables). But on the code above, I was expecting the code would look like something like this:

@line_item = @cart.line_items.build(product_id => params[:product_id])

我不明白为什么笔者不得不存储产品的整排（产品= Product.find（PARAMS [：PRODUCT_ID]）），而不是刚开的product_id ...

I don't understand why the author had to store the whole row of products( product = Product.find(params[:product_id])) instead of just getting the product_id...

有没有更多的它比我能理解？

Is there more to it than what I can understand?

推荐答案

您误解了建立。这只是新，没有什么特别的别名。 <一href=\"https://github.com/rails/rails/blob/959fb8ea651fa6638aaa7caced20d921ca2ea5c1/activerecord/lib/active_record/relation.rb#L84\">https://github.com/rails/rails/blob/959fb8ea651fa6638aaa7caced20d921ca2ea5c1/activerecord/lib/active_record/relation.rb#L84

You misunderstood build. It's just an alias of new, nothing special. https://github.com/rails/rails/blob/959fb8ea651fa6638aaa7caced20d921ca2ea5c1/activerecord/lib/active_record/relation.rb#L84

建立不会创造的数据库，只是在内存中创建一个新对象的记录，这样的观点可以利用这个对象并显示的东西，尤其是对形式。

build won't "create" a record in database, just create a new object in memory so that the view can take this object and display something, especially for a form.

有关你的第二个问题，是的，你通过撰写ID方式将正常工作。但更好的方法是不信任参数。相反，通过先找到在DB验证。

For your second question, yes, your way of composing by id will work as well. But a better approach is not to trust param. Instead, verify it by finding in db at first.

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