Gaining the Knowledge of the Open Data Protocol (OData)

Gaining the Knowledge of the Open Data Protocol (OData)

Chris WoodruffDirector, Perficient

Level: Intermediate

Who I am?

Chris Woodruff

MVP, Visual C#

Director at Perficient

Co-host of Deep Fried Bytes Podcast

@cwoodruff / cwoodruff@live.com / Skype: cwoodruff

You will learn:

• Understand the background of OData• Have an understanding of the OData

protocol• How to produce an OData feed using

WCF Data Services• How to produce an OData feed using

ASP.NET Web API• How to consume an OData feed using

LINQ

BACKGROUNDKnowledge of OData

Today, the tools for capturing data both at the mega-scale and at the milli-scale are just dreadful. After you have captured the data, you need to curate it before you can start doing any kind of data analysis, and we lack good tools for both data curation and data analysis.

Jim Gray

Quote

Problem: Data APIs frequently create more problems than solutionsTHIS TALK IS ABOUT ONE SOLUTION.

Survey

…knows what the web is

…are comfortable w/ HTTP and XML? JSON?

…have a basic understanding of the term REST

…have created a Data API

Is there really a problem?What is it?QUIZ TIME

Facebook: What fields will I get when I read a post?

Facebook: How do you like a post?

How do developers know what to do?

SO GIVEN THAT NOBODY KNEW THE ANSWERS TO THESE QUESTIONS,

I guess they use docs

So is there really a problem?YesDEVELOPERS DON’T HAVE TIME TO ACTUALLY READ THE DOCS

Can OData Magically cure the problem? No, but it can help.LET’S SEE HOW

THE PROTOCOLKnowledge of OData

The Basics of OData

Feeds, which are Collections of typed Entities

OData services can expose Actions and Functions (v4), Services (v3)

OData services expose all these constructs via URIs

OData service may also expose a Service Metadata Document

Full SQL like Query “Language”

HTTP Command (Verb)

SQL Command

GET SELECT

PUT UPDATE

POST INSERT

DELETE DELETE

The $metadata endpoint

URL Conventions

http://services.odata.org/OData/OData.svc

\_______________________________________/

|

service root URI

http://services.odata.org/OData/OData.svc/Category(1)/Products?$top=2&$orderby=name

\_______________________________________/ \__________________/ \_________________/

| | |

service root URI resource path query options

URL Conventions

$filter/Suppliers?$filter=Address/City eq 'Redmond‘

$orderby/Products?$orderby=ReleaseDate asc, Rating desc

$top and $skip/Products?$top=5&$skip=2

$select and $expand/Products?$select=*,Category/Name&$expand=Category

Combining UEL Conventions

• http://.../Players/–?$skip=10–&$top=2–&filter=substringof(‘Wood',nameLast)–&$orderby=nameLast%20desc–&$select=nickname,yearBorn,nameFirst–&$format=json

Payload Conventions

• Success and error Codes– 200 OK, 201 Created, 415 Unsupported Media Type,

etc

• Overall Format– JSON– AtomPub– JSON Verbose

• Nuances– PATCH, Null payloads, etc

JSON Format

• Friendly to Javascript• 90% more compact than AtomPub• Reads like a custom API• Very little OData “gunk”

Atom Format

• Atom parsers exist in many frameworks• Element fields can be mapped to their

Atom counterparts• A good example of OData interoperability

What else can you do with OData?

• Actions and Functions allow hypermedia-based method calls (non-CRUD operations)

• Defined conventions for PATCH and deep insert

• Vocabularies

OData isn’t always the best fit

• OData may not be a good fit for highly opinionated APIs laden with developer intent

• OData may not be a good fit for bulk data transfer

• OData may not be a good fit for the APIs that dramatically different in shape than the backend

OData does not support all queries

• OData doesn’t currently support aggregation– You can’t ask for customers that have at least 2

orders

• OData doesn’t currently support filters expansions– You can’t ask for a customer and only their orders

placed in 2013

• OData doesn't support “graph” queries– You can ask friend-of-a-friend type queries, but there

are limitations

OData is becoming a standard

• OASIS, ISO• ETA early 2014

Who uses OData?

What does OData give me and my organization?

Empower Internal Power Users

Empower Existing and Future Customers

Monetize Data for untapped Revenue

CREATING FEED W/ WCF DATA SERVICES

Knowledge of OData

WCF DATA SERVICESDEMO

CREATING FEED W/ ASP.NET WEB API

Knowledge of OData

ASP.NET WEB APIDEMO

OData Best Practices (Producer)

• Always design your OData feed will server-side paging if your entity collections hold large amounts of data.

• Looks at server-side validation of queries and data updates based on the user credentials sent through HTTP

CONSUMING ODATAKnowledge of OData

What if Data API’s were like…

LINQ?• What are the last 50 invoices we sent?

– context.Invoice.OrderByDescending(i=>i.PostedAt).Take(50);

• What are the invoices from the last 24 hours?– context.Invoice.Where(i=>i.PostedAt > DateTime.Now.AddDays(-1));

• How many $1M invoices have we sent?– context.Invoice.Where(i=>i.TotalAmount >= 1000000);

CONSUMING ODATA WITH LINQ

DEMO

OData Best Practices (Consumer)

• Use Query Projection to only bring back the entity properties you or your app needs.

• Think about client-side paging even if their exists server-side paging.

• Design and implement a client-side data caching function in your app (unless sensitive data).

Why are we excited!!

WRAP-UPKnowledge of OData

The demo projects can be found at:

github.com/cwoodruff/

Resources

RESThttp://www.ics.uci.edu/~taylor/documents/2002-REST-TOIT.pdf

OData

http://odata.org

http://odataprimer.com

Contact Me

Chris “Woody” Woodruffcwoodruff@live.com

Twitter @cwoodruff

Skype cwoodruff

http://chriswoodruff.com

http://deepfriedbytes.com