Introduction to WCF Data service and ODATA

Dhananjay Kumar
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WCFDataServiceWebApplication.zip

You can see video tutorial of this article

Creating WCF Data Service

Consuming WCF Data Service

WCF Data Service, Project Astoria, OData and ADO.Net Data Service are same thing.

What is ODATA?

ODATA is HTTP or web protocol to querying or manipulating data.
ODATA uses HTTP, JOSN or ATOM.
ODATA can be implemented through any platform supports, HTTP, XML or JSON.
ODATA can expose data/information from relational database, File systems, Web sites, services etc.
ODATA specification available under Microsoft's Open Specification Promise (OSP) so third parties, including open source projects, can build Open Data Protocol clients and services.

What is WCF Data Service?

WCF Data service framework provides an API that allows data to be created and consumed over HTTP using RESTful service.
WCF Data service supports all database operations using URI.
WCF Data service can expose an entity model via an URI.
WCF Data service is RESTful service to support CRUD operations on database.
WCF Data service could be consumed by any type of client like Windows, SilverLight, Web, AJAX and console.

Block diagram explaining working of WCF Data Service

Create a Data Access layer using ADO.Net Entity model or LINQ.
Make sure Data model is implementing IQueryable and IUpdateable .
Expose the data model as REST service using WCF Data service.

CRUD Operations and HTTP verb

Supported Message Format

Sample on WCF Data Service

Let us say, we have a table called Student of below structure below in our database

In Student table RollNumber is a primary key.

Let us create WCF Data Service which will expose the above table as REST service

Step 1: Create a Web Application

Create a new project and select ASP.Net Web Application project template from Web tab. Give a meaning full name to the web application.

Step 2: Create a Data Model

We can create a Data Model, which can be exposed as WCF Data Service in three ways

Using ADO.Net Entity model.
Using LINQ to SQL class.
Custom Data Model.

For our purpose, I am going to use ADO.Net Entity model to create the data model. So to create an entity model

Right click on web application and add a new item
Select ADO.Net Entity model from Data tab.
Since we have table in data base. so we are going to choose option , select from database.
Either choose the data base from drop down or create a new data connection.

In above connection string StudentDBEntities is name of the connection string. If we want, we can change this connection string as per our requirement. If your required data base is not listed in drop down then, you can create a new data connection. To create new data connection click on New Connection.

You can give the data base server name and press refresh. After pressing Refresh, you can choose the data base from the drop down. After selecting the data base click on Test Connection to test connection established successfully or not?
Select tables, views and stored procedure from data base you want to make as the part of your data model. Since we are having only one table so we are selecting one table.

If you want you can change name of the data model. By default it is name of the data base appended by the term model. Click on Finish button to complete and create the data model.
Now we can see that StudentDataModel.edmx has been created in the designer.

Since there is only one table, so there is only one table model at design surface.

Now we have created the data model which can be exposed as WCF Data Service. Now you can see in solution explorer, you have StudentModel.edmx and StdentModel.Designer.cs files.

Step 3: Creating WCF Data Service

Right click on Web Application project and add a new item.
Select WCF Data Service from Web tab. Give any meaningful name. I am leaving the default name here.
After adding the WCF Data Service, we can see a service file with extension .svc has been added to the solution explorer. When we click on .svc.cs file, we can see the code generated for us.

Very first we need to put data source name. To do so uncomment the first commented line and put the data source name. In our case name of the model, which we created in 2nd step is the data source. Our data source name is StudentDBEntities

Now we need to set access rules for entity or entity set. Since we have only one table, so either we can give name of the table explicitly or if we want to set the same access rule for all the table in the data model or data source we could put *.

So we are setting the access rule that, on the entity in data source perform all the operations.

Step 4: Run the WCF Data Service

Just press F5 to run the WCF Data Service. Data Service will be hosted in the default ASP.Net server called Cassini.

On running you can see, one table is listed. That table is Student

The above is the data in ATOM message format.

Note: If your browser is not showing the expected result, make sure Feed reading of browser is off. To do from menu of IE and select tool and then Internet Option then Content

MetaData

One feature of WCF data service is that, they provide operation to retrieve Metadata about the service and offer of the service.
This is very useful in determining structure before requesting them.
WCF Data service provides metadata accessible.
Metadata expose all the resource and custom services.
Metadata could be accessed by appending $metadata to service URI.

So, the URI to access metadata is

http://localhost:29409/WcfDataService1.svc/$metadata

URI Query options

We can perform various queries in the browser itself using the URI query options.

Options

Options	Descriptions
expand	Request set of related entities to be retrieved.
orderby	Indicates the sequence entity to be retrieved
skip	Skip number of data items.
top	At most returns top number of data items
filter	Applies the filtering condition

Operators

Options	Descriptions
eq	Equal
ne	Not Equal
gt	Greater Than
ge	Greate than or equal to
lt	Less than
le	Less than or equal to
and	Logical AND
or	Logical OR
not	Logical NOT

Math Operators

Operators	Descriptions
add	add
sub	Subtract
mul	multiply
div	Division
mod	remainder

Various queries

Fetch all the records from the table Student

URI: http://localhost:29409/WcfDataService1.svc/Students

Result
Fetch the student details with roll number 1

URI: http://localhost:29409/WcfDataService1.svc/Students?$filter=RollNumber eq'1'
Fetch top 2 record from the student table

URI: http://localhost:29409/WcfDataService1.svc/Students?$top =2
Fetch the records of the student with roll number 1 or 3

URI: http://localhost:29409/WcfDataService1.svc/Students?($filter=RollNumber eq'1')or($filter=rollnumber eq '3')

Different Access rules on the entity set

Enumerator	Descriptions
All	All Read and Write are permitted
AllRead	All Read permitted
AllWrite	All Write is permitted
None	No access is permitted
ReadMultiple	Reading multiple row is permitted
ReadSingle	Reading a single row is permitted
WriteAppend	Creating New data is permitted
WriteDelete	Deleting data is permitted
WriteMerge	Merge updating is permitted
WriteReplace	Replace updating is permitted

As we discussed above we can set access rule for a particular entity or whole entity set in data source.

config.SetEntitySetAccessRule("*", EntitySetRights.All);

This will permit all right access on all entity set.

config.SetEntitySetAccessRule("Students", EntitySetRights.AllWrite);

This will permit all write access on Student entity set.

Creating a client to consume WCF Data Service

Step 1

Add a new project in the same solution of type console application.

Step 2

Add the service reference of WCF Data Service. To add right click on the console project and add a service reference. Since WCF Data Service and client project in the same solution , click on Discover to discover the service in the solution.

Add the reference of System.Data.Service.Client in client project also.

Step 3

Add namespaces

Step 4

Need to create instance of DataContext and StudentDBEntities. These two classes take as parameter in their constructor. Parameter is base URI of the WCF Data Service.