**Collection & Member routes**
- A member route requires an ID, because it acts on a member. 
- A collection route doesn't require an ID because it acts on a
  collection of objects 
:member creates path with pattern /:controller/:id/:your_method
:collection creates path with the pattern /:controller/:your_method
For example :
map.resources :users, :collection => { :abc => :get } => /users/abc
map.resources :users, :member => { :abc => :get } => /users/1/abc
**Scopes & Namespaces routes**
namespace and scope in the Rails routes affect the controller
  names, URIs, and named routes.
The scope method gives you fine-grained control:
scope 'url_path_prefix', module: 'module_prefix', as: 'named_route_prefix' do
  resources :model_name
end
For Example :
scope 'foo', module: 'bar', as: 'baz' do
  resources :posts
end
produces routes as :
  Prefix Verb         URI Pattern                  Controller#Action
    baz_posts GET    /foo/posts(.:format)          bar/posts#index
              POST   /foo/posts(.:format)          bar/posts#create
 new_baz_post GET    /foo/posts/new(.:format)      bar/posts#new
edit_baz_post GET    /foo/posts/:id/edit(.:format) bar/posts#edit
     baz_post GET    /foo/posts/:id(.:format)      bar/posts#show
              PATCH  /foo/posts/:id(.:format)      bar/posts#update
              PUT    /foo/posts/:id(.:format)      bar/posts#update
              DELETE /foo/posts/:id(.:format)      bar/posts#destroy
The namespace method is the simple case — it prefixes everything.
namespace :foo do
  resources :posts
end
produces routes as :
   Prefix Verb        URI Pattern                  Controller#Action
    foo_posts GET    /foo/posts(.:format)          foo/posts#index
              POST   /foo/posts(.:format)          foo/posts#create
 new_foo_post GET    /foo/posts/new(.:format)      foo/posts#new
edit_foo_post GET    /foo/posts/:id/edit(.:format) foo/posts#edit
     foo_post GET    /foo/posts/:id(.:format)      foo/posts#show
              PATCH  /foo/posts/:id(.:format)      foo/posts#update
              PUT    /foo/posts/:id(.:format)      foo/posts#update
              DELETE /foo/posts/:id(.:format)      foo/posts#destroy
**Constraints & Redirect**
Rails routes are executed sequentially, you can mimic conditional
  login in the following manner:
match '/route' => 'controller#action', :constraints => Model.new
match '/route' => 'user#action'
The first line checks whether the conditions of the constraint are met (i.e., if the request is emanating from a Model domain). If the constraint is satisfied, the request is routed to controller#action.
We can add constraints to routes for multiple uses like for ip-matching, params matching, restrict format parameter, request-based restrictions etc as :
- ip-matching
   => resources :model, constraints: { ip: /172\.124\.\d+\.\d+/ }
- filtering id params
   => match 'model/:id', to: 'model#show' ,constraints: { id: /\d+/}, via: :get
- restrict format params
   => match 'model/:id', to: 'model#show' ,constraints: { format: 'json' }, via: :get
- request-based constraints
   => get 'admin/', to: 'admin#show', constraints: { subdomain: 'admin' }