1. Routing

2. 2 purposes of Routing
2 purposes of Routing
1) maps Requests to Controller Action methods
2) generation of URLs
●
To be used as arguments to methods like
link_to, redirect_to

3. 1.) Mapping HTTP Requests to
Controller-Actions

4. Lifecycle of a HTTP Request

5. routes.rb
●
config/routes.rb
●
specify 'Routing Rules' a.k.a 'Routes' here
●
Order is important
Rules are applied in the order in which they
appear
●
To list all routes:
rake routes
●
To filter routes :

6. routes.rb (contd.)
NOTE
●
Whatever URLs have to work, have to be
EXPLICITLY specified in routes.rb
–
Unless the .html file exists in “public” folder
i.e. Even if we create Controller, ControllerAction, View →
if there is no route for the URL in routes.rb, then
that URL will NOT work

7. routes.rb (contd.)
●
A website may have many, many, URLs that
need to work…
so,
how to specify all of them in routes.rb ?
●
In routes.rb, when we create 'routing rules', we
can specify patterns for permitted URLs
(Next few slides talk about the Syntax used for
specifying those 'routing rules')

8. Legacy way that does Not work
●
Legacy way of supplying controller and action
parameters prior to Rails 3 does not work
anymore
# DOES NOT WORK
match 'products/:id', :controller => “product”, :action =>
“show”

9. Regular Syntax
●
Regular syntax
●
●
use :to
match [URL Pattern],
:to => Controller#Action
E.g.
match 'products/:id', :to => 'products#show'

10. ShortCut – drop “:to”
●
Full Syntax
match 'products/:id' , :to => 'products#show'
●
Shortcut
match 'products/:id' => 'products#show'
We can drop - , :to

11. Another Shortcut Syntax –
when path already has controller &
action names
●
Full Syntax
match “/projects/status”, :to => “projects#status”
●
Shortcut
match “/projects/status”
●
“projects” controller
●
“status” action

12. Constraining Request Methods
and Shortcut
●
To limit the HTTP method :via parameter
match 'products/show', :to => 'products#show', :via
●
Shortcut:
get “/products/show”
=> :get

13. Segment Keys
●
match 'recipes/:ingredient' => “recipes#index”
“:ingredient” – segment key
http://example.com/recipes/biryani
In Controller code:
we can get “biryani” from
params[:ingredient]

14. Passing additional parameters via
segment keys
●
Possible to insert additional hardcoded parameters
into route definitions
match 'products/special' => 'products#show',
true
●
Accessed in Controller code via
●
params[:special]
:special =>

15. Optional Segment Keys
●
Parentheses are used to define optional
segment keys
match ':controller(/:action(/:id(.:format)))

16. Segment Key Constraints
match 'products/:id' => 'products#show', :constraints => {:id
=> /d+/}
Shortcut:
match 'products/:id' => 'products#show', :id => /d+/

17. Segment Key Constraints
- More Powerful constraints checking
●
For more powerful constraints checking
–
We can pass a 'block' to “:constraints”

18. Redirect Routes
●
Possible to redirect using the redirect method
match “/google”, :to => redirect(“http://google.com/”)

19. Route Globbing
●
To grab more than 1 component
●
●
Use *
E.g.
/items/list/base/books/fiction/dickens
match 'items/list/*specs' => 'items#list'
●
In Controller code -
params[:specs]

20. 2.) Generating URLs

21. Generating URLs
●
Original way (and simplest to understand) to
generate a URL ●
we have to supply values for the segment keys
using a Hash
Example :
link_to “Products”,
:controller => “products”,
:action => “show”,
:id => @product.id

22. Generating URLs (contd.)
●
More common way nowadays
●
using Named Routes

23. Named Routes
●
Created using :as parameter in a rule
●
Example:
match “item/:id” => “items#show”, :as => “item”

24. Named Routes – Behind the scenes
●
What actually happens when we name a route ?
2 New methods get defined
–
<name>_url , <name>_path
Example :
match “item/:id” => “items#show”, :as => “item ”
→ above line creates 2 new methods
●
●
item_path, item_url
These methods are used with link_to
●
to Generate Urls

25. Example
●
Scenario:
Suppose we have a Auction Site , and have Items
data
Goal - To display details of a particular Item
●
Starting Point
In routes.rb, we will already have
match “item/:id” => “items#show”

26. Example contd.
●
In the View (i.e .html.erb file) link_to “Auction of #{item.name}”,
:controller => “items”,
:action => “show”,
:id => item.id
How can the above code be improved by using
Named Routes ?

27. Example contd.
Let us make the following change in routes.rb
●
Original Route match “item/:id” => “items#show”
●
Append :as parameter to create Named Route match “item/:id” => “items#show”, :as => “item”

28. Example contd.
View code will change as follows:
●
Original “link_to” statement
link_to “Auction of #{item.name}”,
:controller => “items”,
:action => “show”,
:id => @item.id
●
Using named route
link_to “Auction of #{item.name}”,
item_path (:id => @item.id)

29. Shortcuts when using Named Routes
●
The Named route we created can further be
shortened :
FROM
link_to “Auction of #{item.name}”, item_path (:id =>
@item.id)
TO
Rails - “id” is default parameter, so we can drop “id”
wherever possible
link_to “Auction of #{item.name}”, item_path (@item.id)
link_to “Auction of #{item.name}”, item_path (@item)

30. More complicated Named Routes
●
Many Auctions and each Auction has Many
Items URL of Item details page /auction/5/item/1
●
Starting Point
We will probably already have
match “auction/:auction_id/item/:id” =>
“items#show”

31. More complicated Named Routes
(contd.)
●
Let us create a named route
by using :as
match “auction/:auction_id/item/:id” =>
“items#show” , :as => “item”

32. ●
“link_to” statement changes
FROM:
link_to “Auction of #{item.name}”,
:controller => “items”,
:action => “show”,
:auction_id => @auction.id,
:id => @item.id
TO
link_to “Auction of #{item.name}”,

33. RESTful “resources” & Named Routes
●
resources :auctions
Above line in routes.rb creates 7 Routes out of
which 4 are Named Routes

34. RESTful “resources” & Named Routes
(contd.)
●
resources :auctions
resources :items
end

35. Scoping Routing Rules

36. “public” folder and Routing

37. Root route & “public” folder
●
In a newly generated Rails application
–
In routes.rb ●
–
root route is commented out
How is a page shown for the root URL ?
http://localhost:3000/

38. Root Route (contd.)
“public” folder
●
http://localhost:3000
=
http://localhost:3000/index.html
●
“public” folder in the root of our application
<=> root-level URL
●
That folder contains a “index.html”

39. “public” folder
●
Files in this folder will be scanned before
looking at of routing rules
●
Static content is usually put here
●
Cached content will be placed here