Question

I’m creating a simple inventory app, there is a view that lists ‘items’. It has tables with these rows:

<tr>
<td><%= item.title %></td>
<td><%= item.desc %></td>
<td><%= item.value %></td>
<td><%= item.room.name %></td>
<td><%= item.user.username %></td>
<td>
  <%= link_to 'View', item %>
  <%= link_to 'Edit', edit_item_path(item) %>
  <%= link_to 'Delete', item, method: :delete, data: { confirm: 'Are you sure?' } %>
  <%= link_to 'Add Comment', !?????! %>
</td>
/tr>

I have a linked model for ‘comments’ set up but don’t know how to pass the 'item_id' to it when creating a new one.

Answer 1

The URL helpers actually accept the object to make a route for an association. Meaning, assuming you have a nested route for comments within items,

resources :items do
  resources :comments
end

you can link_to the new_item_comments_path(item).

The method new_item_comments_path(item) makes a string URL based on the new_item_comments route, which you feed to link_to to make an HTML <a> tag.

To be clearer, in your view you would have:

  <%= link_to 'View', item %>
  <%= link_to 'Edit', edit_item_path(item) %>
  <%= link_to 'Delete', item, method: :delete, data: { confirm: 'Are you sure?' } %>
  <%= link_to 'Add Comment', new_item_comments_path(item) #-> (instead of ???) %>

In this case, the item you are passing is the reference to your current item, which allows the URL helper to make a URL for it from the route.

The Rails guide for routing should be a useful read for you.

Now that’s assuming your Comment controller assigns the right stuff at the right place. You seemed to have figured that out, but I’ll explain for the sake of clarity (and future visitors)

class CommentsController < ApplicationController
  # GET /item/:item_id/comments/new
  def new
    @comment = Comment.new

    @item = Item.find(params[:item_id])
    @comment.item = @item
    # render
  end

  # POST /item/:item_id/comments
  def create
    @comment = Comment.new(params[:comment])

    @item = Item.find(params[:item_id])
    @comment.item = @item

    # if @comment.save blah
  end
end