Oracle Tips by Burleson

Enforcing a Cascade Update  

What do we need to enforce a cascade update? One method is to utilize data dictionary tables and views to backtrack foreign key relations and then apply updates along this path. However, this may be a lengthy process and can be cause a performance problem. A simpler method is to implement a table-based cascade update. The table would contain the information that a procedure would need to update all tables that are dependent upon a main, or master, table. Therefore, the table would have to contain the master table name, the dependent table(s), and, in case we can’t duplicate the exact column name across all of the dependent tables, the column to update. The table DDL script in Listing 4.3 meets these requirements. If required, a fourth column indicating an update order could be added, and the cursor in the UPDATE_TABLES procedure (detailed later) would have to be altered to do an ordered retrieve of the information. Listing 4.3 shows the required CREATE TABLE command.      

The table by itself would be of little use. Since the data in the table is dynamic (i.e., multiple tables and columns that would have to be addressed), we must enable our trigger to be able to dynamically reassign these values. The easiest way to do this is to create a set of procedures that utilize the DBMS_SQL Oracle-provided package to dynamically reassign our update variables. Source 4.1 shows the commented code for just such a procedure set, which consists of two procedures: UPDATE_TABLES and UPDATE_COLUMN.

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