Query parameters with url_for?

Question

url_for([:edit, @post])

is working and generating /comments/123/edit. Now I need to add a query parameter, so that instead of

Answer 1

You can use polymorphic_path

polymorphic_path([:edit, @post], :qp => 'asdf')

Answer 2

The answer from Simone Carletti indeed works, but there are times when one wants to construct the URL using objects as described in the Rails routing guide, and not rely on the _path helpers.

The answers from both Ben and Swards are attempting to describe exactly how to do this, but for me the syntax used results in an error (using Rails 4.2.2, which has the same behaviour as 4.2.4, which is the current stable release as of this answer).

The correct syntax for creating a URL/path from objects while also passing parameters should be, as opposed to a nested array, rather a flat array containing the URL components, plus a hash as the final element:

url_for([:edit, @post, my_parameter: "parameter_value"])

Here the first two elements are parsed as the components for the URL, and the hash is considered as parameter(s) for the URL.

This also works with link_to:

link_to( "Link Text", [:edit, @post, my_parameter: "parameter_value"])

When I call url_for as suggested by Ben & Swards:

url_for([[:edit, @post], my_parameter: "parameter_value"])

I get the following error:

ActionView::Template::Error (undefined method 'to_model' for #<Array:0x007f5151f87240>)

The trace shows that this is being called from polymorphic_routes.rb in ActionDispatch::Routing, via url_for from routing_url_for.rb (ActionView::RoutingUrlFor):

gems/actionpack-4.2.2/lib/action_dispatch/routing/polymorphic_routes.rb:297:in `handle_list'
gems/actionpack-4.2.2/lib/action_dispatch/routing/polymorphic_routes.rb:206:in `polymorphic_method'
gems/actionpack-4.2.2/lib/action_dispatch/routing/polymorphic_routes.rb:134:in `polymorphic_path'
gems/actionview-4.2.2/lib/action_view/routing_url_for.rb:99:in `url_for'

The problem being, that it's expecting an array of URL components (eg. symbols, model objects, etc), not an array containing another array.

Looking at the appropriate code from routing_url_for.rb, we can see that when it receives an array which has a hash as the final element, it will then extract the hash and treat as parameters, leaving then just the array with the URL components.

Which is why the flat array with a hash as the last element works, and the nested array does not.

Answer 3

You can pass params to url_for. Checkout it in the sourcecode: https://github.com/rails/rails/blob/d891c19066bba3a614a27a92d55968174738e755/actionpack/lib/action_dispatch/routing/route_set.rb#L675

Answer 4

Use named routes.

edit_post_path(@post, :qp => "asdf")