CopyForUpdate Procedure

This procedure allows LOB columns (BLOB, CLOB, or NCLOB) in version-enabled tables to be modified. Use this procedure only if a version-enabled table has any LOB columns.

Syntax

DBMS_WM.CopyForUpdate(
   table_name       IN VARCHAR2,
   [, where_clause  IN VARCHAR2 DEFAULT '']);

Parameters

Table 70-8 CopyForUpdate Procedure Parameters  

Parameter	Description
table_name	Name of the table containing one or more LOB columns. The name is not case sensitive.
where_clause	The WHERE clause (excluding the WHERE keyword) identifying the rows affected. Example: 'department_id = 20' The WHERE clause cannot contain a subquery. If where_clause is not specified, all rows in table_name are affected.

Usage Notes

This procedure is intended for use only with version-enabled tables containing one or more LOB columns. The CopyForUpdate must be used because updates performed using the DBMS_LOB package do not fire INSTEAD OF triggers on the versioning views. Workspace Manager creates INSTEAD OF triggers on the versioning views to implement the copy-on-write semantics. (For non-LOB columns, you can directly perform the update operation, and the triggers work.)

See the following example.

Examples

The following example updates the SOURCE_CLOB column of TABLE1 for the document with DOC_ID = 1.

  Declare 
    clob_var 
  Begin
     /* This procedure copies the lob columns if necessary, i.e., 
        if the row with doc_id = 1 has not been versioned in the 
        current version */
     vm.copyForUpdate('table1', 'doc_id = 1');

     select source_clob into clob_var
     from   table1
     where  doc_id = 1 for update;

     dbms_lob.write(clob_var,<amount>, <offset>, buff);

  End;