Practical OData

Vagif Abilov
Miles AS
vagif.abilov@gmail.com
@ooobject
github: object
http://bloggingabout.net/blogs/vagif/

 OData and REST
 WCF Data Services
 OData feed in 5 minutes: EF + MS SQL
 The power of ObjectContext
 Using reflection provider
 Using custom providers and NoSQL
 Extending OData services
 Performance and diagnostics
 A song about OData

Are you familiar with OData?

Have you used OData in your projects?

Do you have components on your machine
that use OData communication?

 The Open Data Protocol (OData) is a Web
protocol for querying and updating data
 Consumers query a datasource over HTTP
and get results back in formats like
AtomPub, JSON or plain XML
 OData follows many of the principles of
REST

Querying NuGet feed with LINQPad

Importing data from OData feed into
Microsoft Excel using PowerPivot

 Command content specified in URIs
 Use of HTTP verbs (GET, POST, PUT,
DELETE)
 Use of HTTP status codes
 Response sent as XML (AtomPub) or
JSON
 Related content specified using link
elements

Method Safe Idempotent
GET Yes Yes
POST No No
PUT No Yes
DELETE No Yes

http://localhost:50555/InMemory.svc/
Customers('ALFKI')

Customers()?$filter=CompanyName eq
'Alfreds Futterkiste„

Customers()?$expand=Orders

http://localhost.:50555/InMemory.svc/
Customers
<entry term="Northwind.InMemory.Customers" />
<content type="application/xml">
<m:properties>
<d:CompanyName>My
Company</d:CompanyName>
<d:CustomerID>TEMP</d:CustomerID>
</m:properties>
</content>
</entry>

Customers(„TEMP')
<entry term="Northwind.InMemory.Customers" />
<content type="application/xml">
<m:properties>
<d:CompanyName>My New
Company</d:CompanyName>
<d:CustomerID>TEMP</d:CustomerID>
</m:properties>
</content>
</entry>

Customers(„TEMP')

Request: a company with non-existing
CompanyName

Response: an empty collection

Request: a company with non-existing
CompanyID

Response: 404 Not Found

var ctx = new NorthwindContext("http://localhost.:50555/InMemory.svc");
ctx.IgnoreResourceNotFoundException = true;
var customers =
from c in ctx.Customers
where c.CustomerID == "XYZ"
select c;

 Formerly ADO.NET Data Services
 Codename “Astoria”
 OData provider library for .NET
 Not to be confused with WCF RIA Services
designed specifically for end-to-end
Silverlight and ASP.NET applications

 Using Entity Framework provider
• EF model first+ MS SQL – trivial
• EF code first, different DB vendors – easy
 Using reflection provider
• Any context exposing a set of IQueryable
properties – easy
• Implementing IUpdatable for updatable OData
feeds – easy
 Using custom provider
• OData provider toolkit usually helps – still complex

public class EntityFrameworkModelFirstMsSql :
DataService<NorthwindMsSqlContext>
{
public static void InitializeService(DataServiceConfiguration config)
{
config.SetEntitySetAccessRule("*", EntitySetRights.All);
config.SetServiceOperationAccessRule("*", ServiceOperationRights.All);
config.DataServiceBehavior.MaxProtocolVersion =
DataServiceProtocolVersion.V2;
}

protected override NorthwindMsSqlContext CreateDataSource()
{
return new NorthwindMsSqlContext(/* connection string */);
}
}

 As simple as with MS SQL assuming EF
provider for the respective vendor is
available
 Proven choice: Devart dotConnect product
family:
• Oracle
• MySQL
• PostgreSQL
• SQLite

 Not supported by tools
 EDMX is just an XML file with 3 main
sections:
• Conceptual model (CSDL)
• Storage model (SSDL)
• Mapping (MSL)
 You can author your own EF model:
• Support for n database vendors
• 2n + 1 XML sections (1 CSDL + n SSDL + n MSL)

 DbContext class, wraps ObjectContext
 Model is generated from entities
 Database can be generated from the
model
 Convention over configuration reduces
configuration code to bare minimum
 No more trick to share conceptual model
between databases from different vendors

public class NorthwindContextBase : DbContext
{
public ObjectContext ObjectContext
{
get { return (this as IObjectContextAdapter).ObjectContext; }
}
}

public class EntityFrameworkCodeFirstMsSql : DataService<ObjectContext>
{
protected override ObjectContext CreateDataSource()
{
var ctx = new NorthwindContext("NorthwindContext.EF.CF.MsSql");
return ctx.ObjectContext;
}
}

 Suitable for most of scenarios with static
resource set information (schema known
at compile time)
 Resource sets exposed as IQueryable<T>
properties of the context class
 DataServiceKey attribute specifies entity
key
 Optional support for IUpdatable

OData feed exposing
in-memory data collection

OData feed using
NHibernate to access
MS SQL database

 Entity Framework provider is the quickest
way to add OData feed on the top of a
popular SQL database
 Reflection provider covers most of other
scenarios when the data schema is known
up-front
 Custom provider is needed when the
schema is discovered at runtime or data
don‟t have fixed types

 If the content of NoSQL database is known
at compile time, reflection provider can be
used
 If the content of NoSQL database is
divided into collections of fixed types, the
resource sets can be built at runtime
 If the content is untyped, OData feed can
still be built using open types

Creating OData feed for MongoDB
using WCF Data Services
and OData Provider Toolkit

 OData data model supports open types for
Entries. An entry of an open type may
have extra properties (dynamic properties)
in addition to those statically declared in
metadata
 WCF Data Services framework takes care
of transforming the incoming requests into
an expression tree. Custom code is
responsible for evaluation expression tree
against the data store

 Custom service operations can only use
HTTP GET and POST
 Generated client context code does not
include custom service operations – it has
to be added manually
 Default webHttpBinding settings may not
be sufficient for large payload
(send/receiveTimeout, maxBufferSize and
maxStringContentLength often need to be
increased)

[WebInvoke(Method = "POST")]
public void DeleteProductsByNamePattern(string namePattern)
{
this.CurrentDataSource.ExecuteStoreCommand(
string.Format("DELETE FROM Products WHERE
ProductName LIKE '{0}%'", namePattern));
}

public void DeleteProductsByNamePattern(string namePattern)
{
HttpWebRequest request = (HttpWebRequest)WebRequest.Create(
string.Format("{0}/DeleteProductsByNamePattern?namePattern={1}",
this.BaseUri, namePattern));
request.Method = "POST";
request.Accept = "application/atom+xml,application/xml";
request.ContentType = "application/atom+xml";
request.ContentLength = 0;
HttpWebResponse response = (HttpWebResponse)request.GetResponse();
}

 OData design goal is to provide data
publishing protocol for services, not for
low-level components
 Don‟t use OData to implement cascaded
updates and deletes of large number of
dependent entities
 Understand the difference between client-
side and server-side operations

 LINQPad (LINQ to OData)
 Fiddler
 RedGate .NET Reflector Pro (to step-in to
WCF Data Services code)
 Oren Eini‟s profilers (EF Profiler,
NHibernate Profiler)
 Elmah logging framework (install it using
NuGet, it will update your web.config)

 Don‟t reinvent the wheel, don‟t come with
your own standards
 Consider OData to expose data sources
on the Web
 Don‟t treat OData as a SQL database
publisher
 Writing OData feeds is easy

 Code examples for this presentation:
https://github.com/object/
NorthwindOData
 Open Data Protocol:
http://www.odata.org/
http://www.odata.org/mailing-list
 WCF Data Services forum:
http://social.msdn.microsoft.com/Forums/e
n/adodotnetdataservices/

 WCF Data Services Toolkit:
http://wcfdstoolkit.codeplex.com/
 Microsoft WCF Data Services March 2011
CTP 2 for .NET Framework 4 and
Silverlight 4:
http://www.microsoft.com/downloads/en/de
tails.aspx?FamilyID=60fb0117-8cea-4359-
b392-6b04cdc821be

OData! Please relieve me
AtomPub is what I‟m gonna need
Believe me when I tell you:
AtomPub is what I‟m gonna need

JSON‟s what I want in JavaScript
JSON‟s what I want in JavaScript

When you told me:
“Internal error 500”
Oh well you know,
I nearly broke down and cried

When you told me:
“Internal error 501”
Oh well you know,
I nearly broke down and died

I want to live a RESTful life
I want to live a RESTful life

 Vagif Abilov
 Miles AS
 vagif.abilov@gmail.com
 @ooobject
 github: object
 http://bloggingabout.net/blogs/vagif/

Practical OData

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