Adding children via small subform


I’ve read AWDR and especially the part concerning adding child
line_items to an order. Unfortunately I want to do my process in
reverse and in doing what I thought would work I get a null object error
when trying to append the children to the parent.

This is a major stumbling block in my Rails use as almost every one of
my projects has needed this so its a pretty vital problem I need to

My two tables:
Reviews -< Pictures
(Parent) -< (Child)

I have a form where you first add a Review and after clicking an Ajax
link it produces a sub-form ready for inputting the child pictures.
However, no matter whether I want just one child or a group of children
on the form I can’t seem to get the Child objects to ‘<<’ (append) to
the parent object.

In the book you collect your cart of ‘children’ (line_items) then append
these after creating an order.

My code is (in this instance I try it with just a single child):
@picture =[:picture])
@review =[:review]) <<

I’m totally at a loss and I’m on hands and knees. Please please help
me. I want to go far with Rails and this is killing me.

Thank you for reading.


If I understand your problem correctly (and I’m not sure that I do, so
please excuse me if that’s the case), you shouldn’t need to be
appending your ‘children’ to the parent in that fashion.

Try instead doing something like
@review =[:review])
@picture =[:picture])
@picture.review_id =

That will give you a new ‘review’ record, plus a new ‘picture’ record
with the review_id field in the ‘picture’ record pointing to the
‘review’ record.

There may be a more elegant way of achieving the same thing, but
hopefully this is clear enough and addresses the issue you’re seeing.


Dave M.