This is a series of blogs detailing my introduction to using OData v4 with C# and ASP.NET WebApi.
Query Entity By Key
The previous blog showed how we could list the Airlines entity set. The AirLineCode is a key and therefore the value is unique. We can list a single entity by referencing its key.
From Postman let’s look at the Airline ‘AA’. Issue a GET request to http://services.odata.org/TripPinRESTierService/Airlines(‘AA’)
A single entity is returned along with all the properties defined in the model. We cannot filter on ‘American Airlines’ because Name is not a key.
Fetch a Single Property
From Postman let’s fetch just the Name of the Airline. Issue a GET request to http://services.odata.org/TripPinRESTierService/Airlines(‘AA’)/Name
The Name property is returned only however; the JSON has given the field the name value. You can only return a single property using this resource path.
Fetch Entities using a Navigation Path
The Person entity has three Navigation Properties. These are relationships from one entity to another.
From Postman let’s fetch a single Person entity. Issue a GET request to http://services.odata.org/TripPinRESTierService/People(‘russellwhyte’)
All the properties are return however; there is no reference to any navigation property. Lets see what trips this person has been on.
From Postman let’s fetch the trips for Russel White. Issue a GET request to http://services.odata.org/TripPinRESTierService/People(‘russellwhyte’)/Trips
Here three trips are returned. Since TripId is the key defined on the Trip entity, we can filter out a single trip.
From Postman let’s fetch the trips for Russel White. Issue a GET request to http://services.odata.org/TripPinRESTierService/People(‘russellwhyte’)/Trips(0)
Query Entity By Composite Key
Although the Trip Pin service does not define a composite key, you can define a model to have one. For example; imagine a Person entity that has two keys, FirstName and LastName. They are only unique when combined together and not unique individually.
The URL would look like http:////Person(FirstName = ‘Joe’, LastName = ‘Bloggs’)
We need to specify all the property names when two or more keys are used.
In the next blog we will actually do some coding and develop a simple service to query using single and composite keys.
Denham Coder 