RESTREpresentational State Transfer

REST - Theory

Resources Representations Verbs Links Headers HTTP Status Codes

Resources

A resource is identified by a Uri.

Uri’s are considered Opaque.

http://localhost/api/customershttp://localhost/api/customers/1

Representations

Fetching a resource returns a Representation.

Representations have a content type i.e. text/xml, application/json, text/html etc.

<customer> <self>http://localhost/api.svc/customers/12</self> <organisation>DevDefined</organisation> <id>1</id> <orders> http://localhost/api.svc/customers/12/orders </orders></customer>

Verbs

Conceptual SQL HTTP (REST)

Find SELECT GET

Create INSERT POST ... Or PUT

Update UPDATE PUT

Destroy DELETE DELETE

HTTP Verbs are used to operate on resources.

GET must be Side Effect Free PUT must be Idempotent.

Links

Links are returned in representations.

Clients follow links, allowing them to transition state.

Using Links can provide elegant ways to scale out or integrate 3rd party services.

Headers

If-Modified-Since Etag Cache-Control Accept Content-Type Authorization

HTTP Status Codes (Just a few...)

Code Name Description

200 OK Successful Request.

201 Created New resource created, returns Uri.

202 Accepted Request accepted, but resources haven’t been created yet.

304 Not Modified Conditional get, resource is unchanged (so we can use a previously cached resource)

400 Bad Request Error in request(i.e. request failed validation)

404 Not Found Resource was not found.

405 Method Not Allowed

i.e. If you try to delete a read-only resource, or the whole resource container.

500 Internal Server Error

Something else went wrong (default status for errors in WCF).

Demos

WCF – Building a Simple Rest Service

Linq & REST – ADO.Net Data Services▪Entity Framework▪Custom classes

MVC meets REST - MonoRail OAuth – RESTful Authorization

Demo #1

WCF Demo - A quick tour of a WCF REST service. webHttpBinding WebGet vs WebInvoke UriTemplates GET, POST, PUT, & Delete Changing the representation.

Fresh to Fiddler?

Fiddler is very useful when developing REST services.

There are some catches for first time users: Disable IPV6 in Fiddler when using Cassini (it

doesn’t like the ::1 loopback address) Use “.” after localhost when testing with IE 7

to stop proxy being bypassed.▪ i.e. http://localhost.:8080/api.svc/customers/

FireFox users - you need to manually configure proxy settings.

WCF Gotchas

Exceptions end up as 500 errors on client. ▪ You need to explicitly set status for non-server errors (i.e. For

invalid requests) Uri Templates are fussy▪ Trailing slashes will cause a match to fail, contrary to many

peoples expectations. HTTP Method names are case-sensitive.▪ Using “Post” instead of “POST” can make for confusing 405

errors The input/output Representation format is defined at

the contract operation level.▪ Targeting multiple representations “across the board” is ugly.

Support for linking resources is non-existent.

Demo #2

ADO.Net Data Services (Was Astoria) Building Service using ADO.Net Entity

Framework. Exploring Query Syntax.

Entity Framework

Using EF - Out of scope However... Provides easy way to quickly play with Astoria. Add Item -> Entity Model

Use AdventureWorks database, just the tables should do, call it “AdventureWorks”

Add Item -> ADO.Net Data Service Edit the .cs file, set entities class for service to

AdventureWorksModel.AdventureWorksEntities. Alter InitializeService method to look like this

(Don’t do this for production use)

public static void InitializeService(IDataServiceConfiguration config){ config.SetEntitySetAccessRule("*", EntitySetRights.All); config.SetServiceOperationAccessRule("*", ServiceOperationRights.All);}

Querying -Simple

Uri Conceptual

/ List of types / tables - “Workspace” in AtomPub.

/Employee List of instances / rows - “Collection” or “Feed’ in AtomPub.

/Employee(1) Instance / Row by Key(s) – Collection “Member” or “Entry” in AtomPub

/Employee(1)/Contact Foreign Key / Relationship

/Employee(1)/Gender Property / Column

/ProductProductPhoto(ProductID=332,ProductPhotoID=160)

Instance (Composite Key)

/Product?$orderby=Name Order the results by the Name property.

/Product?$orderby=ListPrice desc, Name

Order by ListPrice in descending Order, then Name ascending.

Querying – Advanced

Uri Conceptual

/Product?$filter=contains(Name,'wheel')

All products matching filter:.Select(p=>p.Name.Contains(“wheel’))

/Shift(1)/EmployeeDepartmentHistory?$filter=EmployeeID eq 30

Navigated Relationship with clause, same as:

Shifs.Select(s => s.Id == 1).SelectMany(s => s.EmployeeDepartmentHistory).Where(history => history.EmployeeID == 30)

/Product(528)?$expand=BillOfMaterials

Will expand the Navigation Property in-line instead of linking to it.

/Product?$top=20 Top 20 results, same as: .Take(20)

/Product?$skip=20&$take=10 Display page 3 (with page size of 10) same as: .Skip(20).Take(10)

Custom Objects – Demo #3

ADO.Net Data Services isn’t limited to the EF.

Anything implementing IQueryable interface will work too.

Let’s try!

Implementation

ADO.Net Data Entities - Client

Entities comes with a .Net Client.▪ Found in the System.Data.Services.Client assembly.

Client allows Linq -> Uri -> Linq -> Whatever.▪ With different Types on the client and Server!▪ Client types can be POCO objects, even if the server side

representations are not.▪ [DataServiceKey(...)] attribute required to support non-GET

requests. Client implements a “unit of work” like pattern,

allowing changes to be collected and then persisted at once.

Changes can be batched in a single request (though this can be viewed as a perversion of HTTP principles).