Rails%203%20In%20Action

236 CHAPTER 9 File uploading
When you pass the :locals option to render, you can set local variables that can be
used in the partial. Local variables in views are usable only in the views or partials in
which they’re defined unless you pass them through by using this :locals. You pass
through the number of your file field and the asset object provided by fields_for
:assets.
To get the new action to render this partial, you can use the same code in the new
action in FilesController but with a small change:
def new
asset = Asset.new
render :partial => "files/form",
:locals => { :asset => asset }
end
Here you must pass the name of the partial using the :partial option so the controller
will attempt to render a partial. If you left it without the option, the controller
would instead try to render the template at app/views/files/form.html.erb, which
doesn’t exist.
Before this line, you need to set up the asset variable that you reference. Add
these two lines directly above the first line inside the new action:
@ticket = Ticket.new
asset = @ticket.assets.build
Because the Ticket object for your form is only a new record, it isn’t important precisely
what object it is: all new Ticket objects are the same until they’re saved to the
database and given a unique identifier. You can exploit this by creating another
Ticket object and building your new asset from it.
It makes sense to do this because in your app/views/files/_form.html.erb file, you
still reference the now-nonexistent f variable, which came from form_for @ticket in
app/views/tickets/new.html.erb. Again, you can exploit the fact that all new Ticket
objects are the same and use a fields_for instead of a form_for in this partial to get
it to give the file field a proper name. Without this fields_for, the name of the field
would be something like asset[asset], and you need it to be something more like
ticket[asset_attributes][0][asset]. Now change the app/views/files/_form
.html.erb partial to look like the following listing.
Listing 9.15 app/views/files/_form.html.erb
number do |asset| %>
The @ticket object here could either be from the new action in the Tickets-
Controller or from the new action in the FilesController: it doesn’t matter.