ASP.NET MVC 4 - Routing Internals

Routing Internals
Łukasz Łysik
ASP.NET MVC 4 Study Group

Agenda
• Routes Registration
• Routes Registration for Areas
• How routing works?
• Generating URLs
• Debugging routes

Routes Registration Overview
Are there any
restrictions here?

Routes Registration MapRoute
RouteCollectionExtensions:

Routes Registration Route class

MySite/{controller}-{action}/{id}
Routes
Registration
Route class ParsedRoute
ParsedRoute
ContentPathSegment
LiteralSubsegment
(„MySite”)
SeparatorPathSegment ContentPathSegment
ParameterSubsegment
{controller}
LiteralSubsegment „-”
ParameterSubsegment
{action}
SeparatorPathSegment ContentPathSegment
ParameterSubsegments
{id}

Routes
Registration
Route class Constraints

Routes
Registration
Route class
Custom
Constraints
Problem: We want to have mechanism which closes our web site for
maintenance for specified period of time.
Inputs:

Routes
Registration
Route class
Custom
Constraints
Coding

Routes
Registration
Route class
Custom
Constraints

Routes
Registration
Route class DataTokens
• Contain values associated with the route that are not used when ASP.NET
routing determines whether a route matches a request.
• Custom data tokens can be defined and used by custom logic in route
handler, controller, action, etc.
• Predefined DataTokens are related to Areas.

Routes Registration for Areas Overview

Routes Registration for Areas Overview
Problem: Multiple controllers with the same names

Routes Registration for Areas MapRoute

Routes Registration for Areas DataTokens collection
Area
Current area name.
Namespaces
Namespaces to search for
controllers.
UseNamespaceFallback
Set to „false” to disable searching
in other namespaces.
Q: In which part of request pipeline these two DataTokens are used?
A: In DefaultControllerFactory.

Routes Registration for Areas Usage of DataTokens
DefaultControllerFactory:

Route 1
URL 1
ParsedRoute 1
Defaults 1
Constraints 1
DataTokens 1
RouteHandler 1
Route 2
URL 2
ParsedRoute 2
Defaults 2
Constraints 2
DataTokens 2
RouteHandler 2
… Route n
URL n
ParsedRoute n
Defaults n
Constraints n
DataTokens n
RouteHandler n
How Routing Works? RouteTable.Routes

How Routing Works? Routing Process (1)
UrlRoutingModule RouteTable.Routes
Do you have any routes
for this context?
Route 1 Route 2 Route n
. . .
ParsedRoute matches current URL?
Do I have any constraints?
Process constraints.
Constraints satisfied?
Return null.Build and return RouteData.
No
No
No
Yes
Yes

How Routing Works? Routing Process (2)
UrlRoutingModule
RouteData
(based on Route 2)
Give me IRouteHandler
IRouteHandler
Give me IHttpHandler
Tell IIS to use
IHttpHandler which I
got from matched
Route.

How Routing Works? Route.ProcessConstraint

How Routing Works? Route.GetRouteData

URL Generation Matching Algorithm
RouteCollection.GetVirtualPath(Supplied values)
Does Route have required parameters?
Did the call to GetVirtualPath specify a value for
each required parameter?
Does Route have default values that do not
correspond to URL parameter?
Does true value for that default, if specified,
match the specified value?
Process constraints
Yes
Yes
Yes
No
Required = with no default value
No match!
No
No
URL: “todo/{action}”
Defaults:
controller=home
action=index
No match!
No
Yes

• Possible problems:
– Routes don’t work.
– URL is routed to wrong controller/action.
– DataTokens values are missing (are wrong).
– Constraints don’t work.
• What we need?
– Tool that will tell us which routes are being
matched, what RouteData parameters and
DataTokens are.
Debugging Routes Problems

Debugging Routes How?
Q: How to write a tool that will debug routes?
Q: What is the name of static class which stores routes?
Q: Which request pipeline element uses RouteTable.Routes?
A: RouteTable.Routes
A: UrlRoutingModule

Demo
Debugging Routes Coding session

Debugging Routes Coding session

• RouteDebugger by Phil
Haack:
– http://haacked.com/archive/20
11/04/12/routedebugger-
2.aspx
• How it works:
– Registers own HTTP module.
– Attach to Request_End event.
– Writes route data at the bottom
of each view.
Debugging Routes RouteDebugger 2.0

References
Professional ASP.NET MVC 4
(http://www.amazon.co.uk/Professional-ASP-NET-MVC-Wrox-Guides/dp/111834846X)

ASP.NET MVC 4 - Routing Internals

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