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DBRELATION()
Return the linking expression of a specified relation
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Syntax
DBRELATION(<nRelation>) --> cLinkExp
Arguments
<nRelation> is the position of the desired relation in the list of
current work area relations. The relations are numbered according to
the order in which they were defined with SET RELATION.
Returns
DBRELATION() returns a character string containing the linking
expression of the relation specified by <nRelation>. If there is no
RELATION SET for <nRelation>, DBRELATION() returns a null string ("").
Description
DBRELATION() is a database function used with DBRSELECT() to determine
the linking expression and work area of an existing relation created
with the SET RELATION command.
DBRELATION() returns the linking expression defined by the TO clause.
DBRSELECT() returns the work area linked as defined by the INTO clause.
By default, DBRELATION() operates on the currently selected work area.
It will operate on an unselected work area if you specify it as part of
an aliased expression (see example below).
Notes
. Declared variables: A character string returned by
DBRELATION() may not operate correctly when recompiled and executed
using the macro operator (&) if the original expression contained
references to local or static variables, or otherwise depends on
compile-time declarations.
Examples
. This example opens three database files, sets two child
relations from the parent work area, and then displays the linking
expression to the second child work area:
USE Invoices INDEX Invoices NEW
USE BackOrder INDEX BackOrder NEW
USE Customer INDEX Customer NEW
SET RELATION TO CustNum INTO Invoices, OrderNum ;
INTO BackOrder
//
? DBRELATION(2) // Result: OrderNum
. Later you can query the same linking expression from an
unselected work area by using an aliased expression like this:
USE Archive NEW
? Customer->(DBRELATION(2)) // Result: OrderNum
. This example is a user-defined function, Relation(), that
returns the results of both DBRELATION() and DBRSELECT() as an array:
FUNCTION Relation( nRelation )
RETURN { DBRELATION(nRelation), ;
ALIAS(DBRSELECT(nRelation)) }
Files Library is CLIPPER.LIB.
See Also:
DBFILTER()
DBRSELECT()
SET RELATION
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