Object Identifiers for Object Views

6.7 Object Identifiers for Object Views

You can construct pointers (REFs) to the row objects in an object view. Because the view data is not stored persistently, you must specify a set of distinct values to be used as object identifiers. Object identifiers allow you to reference the objects in object views and pin them in the object cache.

If the view is based on an object table or an object view, then there is already an object identifier associated with each row and you can reuse them. To do this, either omit the WITH OBJECT IDENTIFIER clause or specify WITH OBJECT IDENTIFIER DEFAULT.

However, if the row object is synthesized from relational data, you must choose some other set of values.

You can specify object identifiers based on the primary key. This turns the set of unique keys that identify the row object into an identifier for the object. These values must be unique within the rows selected out of the view, because duplicates would lead to problems during navigation through object references.

Object views created with the WITH OBJECT IDENTIFIER Clause

An object view created with the WITH OBJECT IDENTIFIER clause has an object identifier derived from the primary key.

For example, note the definition of the object type dept_t and the object view dept_view described in "Single-Level Collections in Object Views".

Because the underlying relational table has deptno as the primary key, each department row has a unique department number. In the view, the deptno column becomes the deptno attribute of the object type. Once you know that deptno is unique within the view objects, you can specify it as the object identifier.
Object views created with the WITH OBJECT IDENTIFIER DEFAULT Clause

If the WITH OBJECT IDENTIFIER DEFAULT clause is specified, the object identifier is either system-generated or primary-key based, depending on the underlying table or view definition.