Create variable that can be defined and accessed in multiple controllers in Rails

Question

I'm creating an app for creating multiple to-do lists. So a user signs in, has multiple lists, and each list contains multiple items. Everything else is working, but I'm struggling to create the items.

My code for creating a new item on a list (this is found in the items_controller) is :

def create

    @list =
    @new_item = @list.items.build(params[:item])
    if @new_item.save
      flash[:success] = "Item saved!"
    end
    redirect_to root_path
  end

And the issue is, I'm not sure how to define what @list should be. I have a variable current_user (based on the session) for creating a new list, but there is only one user per session and multiple lists per session, so I can't just replicate that method.

Basically, I'm stuck on how to be able to have the item know which list it belongs to (which should be the list whose show page I was just on). In Java I'd have a static variable that I would redefine every time I went to a list, but I tried doing that and it didn't work, and I read that apparently in rails that doesn't work.

Save your users lists into the data base - even in java web apps using a static variable is not a good idea — house9
– house9, Commented Jan 7, 2012 at 22:55
The lists are in the database--the trouble is that even though each list has its own id, the item doesn't know which specific list it belongs to — user1136497
– user1136497, Commented Jan 7, 2012 at 23:01
How can that be? Doesn't a list has_many items :through something, or habtm? — Dave Newton
– Dave Newton, Commented Jan 7, 2012 at 23:10
It does, but the item hasn't been created yet, so it doesn't belong to anything... — user1136497
– user1136497, Commented Jan 7, 2012 at 23:31

David Grayson · Accepted Answer · 2012-01-07 23:50:58Z

1

Rather than storing a variable, you should keep track of the list using url parameters. You will need to modify your form to include a list_id parameter. Then in the controller when you are creating a list item, do something like:

@list = List.find params[:list_id]
@new_item = @list.items.build params[:item]

Or if you made your params include an items[list_id] parameter, then in Rails it will be accessible in params[:item][:list_id] so you should just be able to just do:

@new_item = ListItem.create params[:item]

If you do it this second way, just be sure to add a validation in the ListItem model to guarantee that list_id is present and the list it points to exists.

answered Jan 7, 2012 at 23:50

David Grayson

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user1136497 Over a year ago

That's a good idea--I should keep track of it with url parameters. But really, I think, when I link to a List show page from the main home page, and then while on the list page the list_id will be accessible from params.

heavysixer · Accepted Answer · 2012-01-07 23:10:01Z

1

The listItem should have a foreign key to the list model, and the list model should have a foreign key to the account. In this way you should be able to traverse the structure easily.

class ListItem  < ActiveRecord::Base
  belongs_to :list
end

class List <  < ActiveRecord::Base
  belongs_to :account
  has_many :list_items
end

class Account <  < ActiveRecord::Base
  has_many :lists
end

answered Jan 7, 2012 at 23:10

heavysixer

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1 Comment

user1136497 Over a year ago

That's exactly how my database is set up. However, in order to create the list item, I need to specify which list it should belong to--and I'm not sure how to specify that (@list) using the foreign key :list_id, since it doesn't belong to a list yet.

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