Rails: How do I get only the saved models with .collection?

Question

I have a model Post that has_many of model Comment.

On a Posts show action, there is a list of Comments found with @comments = @post.comments.

I also have a form for creating new Comments. The form has its object created with @comment = @post.comments.build.

This all works for listing and successfully creating comments.

The problem occurs when there is an error when the comment is submitted. The errors are shown in the same form (so, on Post#show) via render "posts/show". In this case, I have to set @comments = @post.comments again, but this time the list of comments includes the not-yet-saved comment that the user is trying to create.

I solved it by using @post.comments.all, which only gives me the saved models, but Rails complains that this is deprecated in Rails 4.

How do I remove the unsaved comment from the list of comments I get from @post.comments?

Answer 1

I ran into a similar issue with a Rails 5 application. This seemed like the most straightforward approach:

@comment = @post.comments.build
@comments = @post.comments.where.not(id: nil)

Answer 2

You could add a scope to the comment model to find only database rows instead of in memory data, for example:

class Comment < ActiveRecord::Base
  scope :by_post, ->(post) { where(post: post) }
end

called by: @comments = Comment.by_post(@post)

Answer 3

The most efficient way imho is just to ignore the new record in the view, instead of retrieving all comments again.

So in your view you will do something like:

= f.simple_fields_for :comments do |c|
  - unless c.object.new_record? 
    = render 'comment_fields', :f => c