PRB: No Error Message When Creating a Cyclic Relation

• Microsoft Visual FoxPro for Windows, versions 3.0 and 3.0b

SYMPTOMS

In the Database Container (DBC), a table can be related to itself to create a cyclic relationship. No error message is displayed when the relation is drawn between two tags of the same table. On the other hand, the SET RELATION command returns an error message when a cyclic temporal relation is created.

CAUSE

The cyclic relation is not a correct "SET RELATION" relation, but is used in permanent relations for referential integrity purposes.

Relational theory allows a table to be related to itself. For example, in an employee table, a whole division needs to be deleted. If the table is related to itself, you can use a cascade rule when deleting the whole division by deleting the division head.

STATUS

This behavior is by design.

MORE INFORMATION

Steps to Reproduce Behavior

1. Create a .dbc file with a table that has two tags of the same type.

2. Type MODIFY DATABASE in the Command window.

3. Click one of the index tags, and drag the tag to the second index tag in the same table. A cyclic relation is created.