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REST and Application Express: Filtering

Carsten Czarski
Consulting Member of technical Staff

More and more Application Express developers are faced with the requirement to integrate REST services or HTTP/JSON data feeds into their applications. Application Express provides great support for SOAP web services, but for REST services using JSON to exchange data, the built-in functionality is limited. For instance, all the JSON parsing has to be done manually by employing PL/SQL code or SQL functions.

During the last weeks, we released a few articles describing how to access a REST service from within Application Express, how to leverage the REST Client Assistant packaged application and how to deal with REST services providing large result sets ...

In the previous articles, we always fetched all response data from the REST service - either all at once or page-wise, depending on REST service capabilities. But in practice, it's often required to get only a subset of the response data - we want to filter the response based on some end user criteria.

"So that's easy" might be your first thought - since all JSON parsing is done with SQL functions. In the SQL query, both XMLTABLE and JSON_TABLE act as a row source, so its result can be treated like rows from a table or view. Thus we can simply amend the WHERE clause of the SQL query, which has been generated be the REST Client Assistant packaged application. 

But imagine a REST service returning a huge amount of data (thousands or even millions of rows). As learned in the Work with REST services returning large result sets page-wise article, these services return their data page-wise. So, in order to apply a SQL filter, we would first have to fetch all data, walking though all the response pages. 

For REST services provided by Oracle REST Data Services (ORDS), a filter syntax is provided: Filter criteria can be passed to ORDS with the REST request and will be executed server-side returning only the final (and limited) amount of rows.

This article shows how the response of a  REST service invocation can be filtered either using SQL or a filtering syntax provided by the REST service. Have a read, how this can be used in your own Application Express applications.