Liberating the data layer with services is an important step in converting a monolithic system to one that conforms to Service Oriented Architecture(SOA). WSO2 Data Services Server[1] is a solution targeted at this very requirement. In the past exposing a data-source(such as a RDBMS) as a service involved configuring the data source and mapping service operations(SOAP) or resources to predefined SQL queries(time consuming). With DSS version 3.5.0 onwards you can use Odata to provide more flexibility to data access and reduce the need of specialized SQL queries/operations.
Open Data is a protocol that specifies how data can be exposed conforming to RESTful architecture and how it can be queried using HTTP calls.
The anatomy of an Odata service URL
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extracted from the Odata Spec[2]
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Creating The Service
1) Create a Carbon Data-source
Navigate to
Configure > Datasources > New Datasource and fill in the RDBMS
details appropriately to create a data-source[3].
2) Generate a service and enable Odata
Generate a service[4]
using the data-source created in step 1 . Edit the generated service, enable Odata from the datasource configuration page and publish the
service. The Entity Model will be generated and the odata service
will be available at,
https://<host>:<https
port>/odata/<service name>
find the sql scripts and data service file used in this example here[5]
Consuming the service
The service is in
conformance with the ODATA Protocol(version 4). You can access entities [6]
and use query options[7] to filter and query the data as needed
according to the protocol spec.
Example Invocations using CURL[8]
Select all data items belonging to BOOK resource.
curl -X GET -H 'Accept: application/json' 'https://localhost:9443/odata/RestaurantOfTheMindService/default/BOOK' -k
Select a single data item belonging to BOOK resource by PK,
curl -X GET -H 'Accept: application/json' 'https://localhost:9443/odata/RestaurantOfTheMindService/default/BOOK(1)' -k
Remove a data item belonging to BOOK resource by PK,
curl -X DELETE -H 'Accept: application/json' 'https://localhost:9443/odata/RestaurantOfTheMindService/default/BOOK(1)' -k
Select all data items belonging to BOOK resource where TITLE equals Cook.
curl -X GET -H 'Accept: application/json' 'https://localhost:9443/odata/RestaurantOfTheMindService/default/BOOK?$filter=TITLE%20eq%20%27Cook%27' -k
Select all data items belonging to BOOK resource where TITLE contains Coo.
curl -X GET -H 'Accept: application/json' 'https://localhost:9443/odata/RestaurantOfTheMindService/default/BOOK?$filter=contains(TITLE%2C%27Coo%27)' -k
Select all data items belonging to BOOK resource where TITLE contains Coo, result limited to 9 and ordered by TITLE
curl -X GET -H 'Accept: application/json' 'https://localhost:9443/odata/RestaurantOfTheMindService/default/BOOK?$filter=contains(TITLE%2C%27Coo%27)&$orderby=TITLE&$top=9' -k
note that the HTTP requests must be appropriately URL encoded.
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