Introduction to Odata

Open Data Protocol -OData

:: Microsoft has given us a way to access data as queryable and inter-operable using Restful API under Microsoft Open Specification Promise.

It is built upon WEB API Architecture by following REST. More of, it allows user to make quarable service point. We can say re-usability features we use rather than creating separate service points..

 REST-Rules

Each resource should be identified by a URI (unique identifier).

It uses HTTP protocol with API verbose  GET, POST, PUT ,PATCH and DELETE method to perform actions.  

Representation of entity is exchanged on server using verbose to perform action.

Application may have state but client session data can’t be stored on the server.

Response can be cached at client side

Query Options

$filter

?$filter=FirstName eq 'rupesh'

$orderby

?$orderby=DateCreated desc

Default- Ordered in ascending order

desc-Descending order

asc -Ascending order

$top and $skip

?$top=2 - Selecting the top N records

?$skip=10- Skipping first N records and fetch next records 

$count

/$count - Records counts

$expand

include related resource - load them all

 

$select

?$select=FirstName, Email- Selected the columns values

$search

?$search=abc- Searched in collection and returns only matched results

Lambda Operators

?$filter=FirstName/any(s:endswith(s, 'khanna'))

OData defines two operators any and all

Any - It checks whether at least one element in a collection satisfy a specified condition if any matches returns true else false.

All- Returns true if all the elements satisfy the condition else returns false.

Functions and Actions

OData supports custom operations (Actions and Functions).

Functions -No observable side effects.

Actions- Observable side effects.

Few frequently used queries with meaning

Add        Addition                ?$filter=price add 5 lt 25

Sub         Subtraction           ?$filter=marks sub 5 gt 80

Mul         Multiplication         ?$filter=stdcount mul 2 gt 25

Div         Division                 ?$filter=avgage div 2 gt 60

Mod        Modulo                  ?$filter=numberInt mod 2 eq 0

Eq           Equal                      ?$filter=FirstName eq 'Raj'

Ne           Not equal                ?$filter=FirstName ne 'Raj'

Gt           Greater than                   ?$filter=age gt 20

Ge           Greater than or equal      ?$filter=age ge 20

Lt            Less than              ?$filter=age lt 20

Le           Less than or equal ?$filter=age le 50

And        Logical and            ?$filter=age le 50 and age gt 20

Or           Logical or              ?$filter=age le 20 or age gt 12

Not         Logical negation    ?$filter=not endswith(email,'.com')

We will cover all the operation in details in next modules 

Reference

Odata standard documents

Microsoft Odata