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Q130236: Explanation of Referential Integrity Rules for INSERT

Article: Q130236
Product(s): Microsoft FoxPro
Version(s): WINDOWS:3.0
Operating System(s): 
Keyword(s): 
Last Modified: 10-FEB-2000

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The information in this article applies to:

- Microsoft Visual FoxPro for Windows, version 3.0 
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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.

Additional query words: VFoxWin

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Keywords          :  
Technology        : kbVFPsearch kbAudDeveloper kbVFP300
Version           : WINDOWS:3.0

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