Json response on rails 6 from url with queries - ruby-on-rails

Question

Only on Rails 6 when:
I receives a json response on pages with url like:
www.site.com/foo
and not when url is like:
www.site.com/foo?q=x
to reproduce:
rails new todo
rails scaffold Todo task:string
rails db:migrate
rails server
Create a task
In file show.json.jbuilder you'll see:
json.partial! "todos/todo", todo: #todo
Go to show page (todo/1)
Type on browser's console to se json response:
$.ajax({
url: window.location.href + ".json",
dataType: 'json',
async: false
});
When your url is "todo/1" jbuilder loads ok:
Started GET "/todos/1.json" for ::1 at 2019-10-28 13:55:54 -0300
Processing by TodosController#show as JSON
Parameters: {"id"=>"1"}
Todo Load (0.3ms) SELECT "todos".* FROM "todos" WHERE "todos"."id" = ? LIMIT ? [["id", 1], ["LIMIT", 1]]
↳ app/controllers/todos_controller.rb:67:in `set_todo'
Rendering todos/show.json.jbuilder
Rendered todos/_todo.json.jbuilder (Duration: 1.0ms | Allocations: 125)
Rendered todos/show.json.jbuilder (Duration: 2.2ms | Allocations: 306)
Completed 200 OK in 10ms (Views: 3.9ms | ActiveRecord: 0.3ms | Allocations: 1565)
But if your url is "todo/1?q=foo" you have no data:
Started GET "/todos/1?q=foo.json" for ::1 at 2019-10-28 13:55:44 -0300
Processing by TodosController#show as JSON
Parameters: {"q"=>"foo.json", "id"=>"1"}
Todo Load (0.2ms) SELECT "todos".* FROM "todos" WHERE "todos"."id" = ? LIMIT ? [["id", 1], ["LIMIT", 1]]
↳ app/controllers/todos_controller.rb:67:in `set_todo'
Rendering todos/show.html.erb within layouts/application
Rendered todos/show.html.erb within layouts/application (Duration: 0.7ms | Allocations: 89)
Completed 200 OK in 25ms (Views: 21.3ms | ActiveRecord: 0.2ms | Allocations: 6547)
Obs: I opened this rails github issue

Answer 1

In order to work in rails 6.0.0 we need to explicitly tell to use json format when the url has queries:
todos_controller.rb
change from:
def show
end
to:
def show
respond_to do |format|
format.html
format.json
end
end

Answer 2

This is because the request must be in the following form:
www.site.com/foo.json?q=x
If you want to pass parameters to the request, you can use the data parameter of ajax.
For instance:
$.ajax({
url: "/todos",
type: "GET",
data: {
id: 1,
q: "x"
},
success: function (response) {
console.log(response.data)
}
})