SET RELATION

SET RELATION

Relate two work areas by a key value or record number

Syntax

      SET RELATION TO [<expKey> | <nRecord> INTO <xcAlias>]
            [, [TO] <expKey2> | <nRecord2> INTO <xcAlias2>...]
            [ADDITIVE]

Arguments

TO <expKey> is an expression that performs a SEEK in the child work area each time the record pointer moves in the parent work area. For this to work, the child work area must have an index in USE.

TO <nRecord> is an expression that performs a GOTO to the matching record number in the child work area each time the record pointer moves in the parent work area. If <nRecord> evaluates to RECNO(), the relation uses the parent record number to perform a GOTO to the same record number in the child work area. For a numeric expression type of relation to execute correctly, the child work area must not have an index in USE.

INTO <xcAlias> identifies the child work area and can be specified either as the literal alias name or as a character expression enclosed in parentheses.

ADDITIVE adds the specified child relations to existing relations already set in the current work area. If this clause is not specified, existing relations in the current work area are released before the new child relations are set.

SET RELATION TO with no arguments releases all relations defined in the current work area.

Description

SET RELATION is a database command that links a parent work area to one or more child work areas using a key expression, record number, or numeric expression. Each parent work area can be linked to as many as eight child work areas. A relation causes the record pointer to move in the child work area in accordance with the movement of the record pointer in the parent work area. If no match is found in the child work area, the child record pointer is positioned to LASTREC() + 1, EOF() returns true (.T.), and FOUND() returns false (.F.).

The method of linking the parent and child work areas depends on the type of <expKey> and presence of an active index in the child work area. If the child work area has an active index, the lookup is a standard SEEK. If the child work area does not have an active index and the type of <expKey> is numeric, a GOTO is performed in the child work area instead.

Notes

. Cyclical relations: Do not relate a parent work area to itself either directly or indirectly.

. Soft seeking: SET RELATION does not support SOFTSEEK and always behaves as if SOFTSEEK is OFF even if SOFTSEEK is ON. This means that if a match is not found in the child work area, the child record pointer is always positioned to LASTREC() + 1.

. Record number relations: To relate two work areas based on matching record numbers, use RECNO() for the SET RELATION TO expression and make sure the child work area has no active indexes.

Examples

      .  This example relates three work areas in a multiple parent-
         child configuration with Customer related to both Invoices and Zip:

         USE Invoices INDEX Invoices NEW
         USE Zip INDEX Zipcode NEW
         USE Customer NEW
         SET RELATION TO CustNum INTO Invoices, Zipcode INTO Zip
         LIST Customer, Zip->City, Invoices->Number, ;
                  Invoices->Amount

      .  Sometime later, you can add a new child relation using the
         ADDITIVE clause, like this:

         USE BackOrder INDEX BackOrder NEW
         SELECT Customer

         SET RELATION TO CustNum INTO BackOrder ADDITIVE

Seealso

DBRELATION(), DBRSELECT(), FOUND(), RECNO(), SET INDEX

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