How to set the default format for a route in Rails

问题:

With the default routing, the request /posts/:id gets mapped to the "show" action with :format => "html". I am using some xhtml elements in my show action which don't get rendered correctly unless the :content_type is set to xml. I am currently getting around this by rendering show.xml.erb and setting the content_type manually as follows:

format.html { render :template => "/posts/show.xml.erb", 
             :locals => {:post => @post}, :content_type => "text/xml" }

This seems silly though. How can I change routes.rb so that /posts/:id is routed with format=>"xml"? Thanks.

回答1:

Default format for requests:

You can set the default format of a given route to xml using the defaults hash.

Examples:

# single match defaulting to XML (/plots/1 is the same as /plots/1.xml)
match 'posts/:id' => 'posts#show', :defaults => { :format => 'xml' }

# using resources, defaulting to XML (all action use XML by default)
resources :posts, :defaults => { :format => 'xml' }

# using resources and mixing with other options
resources :posts,
          :only => [:new, :create, :destroy],
          :defaults => { :format => 'xml' }

It's always a good idea to search the official Ruby on Rails routing guide, it's fairly in-depth and a very good first-stop resource for any routing issues.

回答2:

If you only want to support one format and treat all requests as that format, you could use a filter to change it:

before_filter :set_format

def set_format
  request.format = 'xml'
end

回答3:

Rails 4 and 5: In your controller (e.g. ApplicationController if all whole application uses same format) add following:

  before_action :set_default_request_format

  def set_default_request_format
    request.format = :json unless params[:format]
  end

For Rails 3 and older use before_filter instead of before_action.

回答4:

I'm finding weird behaviour in Rails 5 if you use this:

{ format: :json }

In your config/routes.rb then even if JSON isn't set in your accept header, it still coerces the request to a JSON request, including for controller tests that have the as: :html option set. It's not really a big deal for me, so I'm not going to dig into why this is, but if someone figures it out, let me know and I'll update this answer.

回答5:

If you want to set the default format for a route, use defaults option:

resources :posts, defaults: { format: 'xml' }

But if you want to enforce every request to return a specific format, use constraints option:

resources :posts, constraints: lambda { |req| req.format == 'xml' }

See the documentation: http://edgeguides.rubyonrails.org/routing.html#request-based-constraints