ORA-42721
Cannot create JSON-relational duality view 'string'. The _id field at root level is not mapped to identifying key (primary or unique) of the root table.
Cause
An attempt is being made to create a duality view with a _id field at root level not mapped to identifying key of the root table, which is not allowed.
Action
Map the _id field at root level to the identifying key of the root table