You can use PL/SQL object types for JSON to read and write multiple fields of a JSON document. This can increase performance, in particular by avoiding multiple parses and serializations of the data.

• Overview of PL/SQL Object Types for JSON
  PL/SQL object types allow fine-grained programmatic construction and manipulation of In-Memory JSON data. You can introspect it, modify it, and serialize it back to textual JSON data.
• Using PL/SQL Object Types for JSON
  Some examples of using PL/SQL object types for JSON are presented.