In a controller action, I want to respond to a POST request with some JSON. Some of the JSON is rendered HTML. There are other important fields in the JSON, so I am rendering the template manually like this:
html = File.open('app/views/shared/_my_partial.html.erb').read
template = ERB.new(html)
html = template.result(binding)
render json: {status: 'OK', html: html, other_important_stuff: foo}
However, this means that I can't use any partials in the _my_partial.html.erb, like this:
<%= render partial: 'shared/my_inner_partial', locals: {var: var}
...because this provokes the error "(Render and/or redirect were called multiple times in this action".
What is the right approach here? I'd like to render a partial with the ability to render other nested partials inside. However I would like to send this to the client as part of a JSON response, with other fields in it which I need to set in the controller action.
DoubleRenderError happens when you call controller render method multiple times, which is different from a view render helper. But because you're using ERB directly and binding to a controller you end up calling controller render twice.
The best option would be to create a dedicated template for your action and compose everything inside of it.
There is also render_to_string if you really need to render multiple things in a controller:
render json: {
status: "OK",
html: render_to_string(partial: "shared/my_partial"),
other_important_stuff: foo
}