Explanation of Referential Integrity Rules for INSERT

• Microsoft Visual FoxPro for Windows, version 3.0

SUMMARY

This is a general explanation of Referential Integrity Rules for INSERT included with the Referential Integrity Builder provided with Visual FoxPro.

MORE INFORMATION

Visual FoxPro allows only "Restrict" or "Ignore" referential integrity rules for Inserts on a child table. If you choose "Restrict," Visual FoxPro prevents orphan records. If you choose "Ignore," Visual FoxPro does not protect against orphan records.

The Restrict and Ignore options on Insert are the only choices available because the rule is expressed or enforced from the child's point of view. The "Delete" and "Update" tabs provide the additional choice of Cascade because the point of view is taken from the parent. It is not possible to Cascade from the child's point of view. In other words, there is nothing below a child.

The "point of view" refers to the perspective taken from the current table in a relation. The "point of view" of each rule is expressed in highlighted text in each Tab of the Referential Integrity Builder dialog.

Because the child point of view is taken on the Insert rules it is asking, "what do you want to do when something is done/Inserted in the child table?" In referential terms, the "restrict" rule says a child record's foreign key value must be present in the parent table's primary key before the record can be added.

Both of the other referential integrity options (Update and Delete) take the point of view of the parent table; in effect, they ask, "what do you want to do when something is done in the parent?"

In referential terms this means when the primary-key value in the parent changes, you may or may not want something done to the matching foreign-key records in the child table.