What is the difference between build and new on Rails?

Question

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

Answer 1

I observed a difference between .build and .new when using them to create a 'dummy' object for a view form, using a using nested resource.

.build creates a parent_id .new does not

Nested Resource example: @list.items (where Item is nested under List)

@list.items.build ...produces an object with all nil values EXCEPT for list_id.

Item.new creates a new item object, with all nil values.

It showed up in my 'show' page when iterating over @list.items Not an issue until I needed @list.items further down same 'show' page in another form, where iteration on @list.items exposed the item (the one produced by .build) that had an associated list_id, but nothing else.

Some sample outputs below...

@list.items.build => #

---

2.2.3 :002 > Item.all.build => #

---

2.2.3 :003 > Item.new => # 2.2.3 :004 >