DEPRECATION WARNING: ActionView::Base instances should be constructed with a lookup context, assignments, and a controller

Question

I migrate an application from rails 5.2 to rails 6. There is only have one thing left to do but I don't know how.

I have this depreciation warning:

DEPRECATION WARNING: ActionView::Base instances should be constructed with a lookup context, assignments, and a controller. (called from new at /Users/xxx/xxxx/app/models/stock.rb:42)

from this code:

view = ActionView::Base.with_empty_template_cache.new(
         ActionController::Base.view_paths, 
         categories: categories, 
         periods: periods
       )

result = view.render formats: [:xlsx], 
                     handlers: [:axlsx], 
                     template: 'admin/reports/logistics/stocks_by_age'

I don't understand how to fix it. I went to see the depreciation in the source code, but it didn't help me figure out what I should do, and I didn't really find any documentation for this 'lookup'.

Please, could someone help me to understand this depreciation?

Answer 1

It looks like you are trying to render view outside of the request. Rails added a feature in the past, that simplified this. Now only thing you need to do is to call ApplicationController.render with your params. In your case it should look something like this:

ApplicationController.render(
  template: 'admin/reports/logistics/stocks_by_age',
  locals: { categories: categories, periods: periods } # maybe assigns: { ... }
  handlers: [:axlsx],
  formats: [:xlsx]
)

Also following code should work as well if you have logistics controller:

Admin::Reports::LogisticsController.render(:stocks_by_age, ...other params same as above..., handlers: [:axlsx], formats: [:xlsx])

See the following article for better description of how to do it. https://blog.bigbinary.com/2016/01/08/rendering-views-outside-of-controllers-in-rails-5.html

Answer 2

This deprecation warning appears because you passed ActionController::Base.view_paths to ActionView::Base.new as the first argument. This used to be okay but now an instance of ActionView::LookupContext is expected. If you look at the most recent version of ActionView::Base#initialize you'll see that where the message appears it calls ActionView::Base.build_lookup_context using your first argument to ActionView::Base.new. You can easily silence this warning by passing ActionView::LookupContext.new(ActionController::Base.view_paths) or ActionView::Base.build_lookup_context(ActionController::Base.view_paths) since that's what it ends up using anyways.

While ApplicationController.render is helpful for rendering a view outside of a request sometimes you need an instance of ActionView::Base by itself (in my case I use one as the view context for my presenter classes in their tests).