[<<Previous Entry]
[^^Up^^]
[Next Entry>>]
[Menu]
[About The Guide]
DBSETFILTER()
Set a filter condition
------------------------------------------------------------------------------
Syntax
DBSETFILTER(<bCondition>, [<cCondition>]) --> NIL
Arguments
<bCondition> is a code block that expresses the filter condition in
executable form.
<cCondition> stores the filter condition as a character string for
later retrieval by the DBFILTER() function. If you omit this optional
parameter, the DBFILTER() function will return an empty string for the
work area.
Returns
DBSETFILTER() always returns NIL.
Description
DBSETFILTER() sets a logical filter condition for the current work area.
When a filter is set, records which do not meet the filter condition are
not logically visible. That is, database operations which act on
logical records will not consider these records.
The filter expression supplied to DBSETFILTER() evaluates to true (.T.)
if the current record meets the filter condition; otherwise, it should
evaluate to false (.F.).
The filter expression may be a code block (<bCondition>) or both a code
block and equivalent text (<cCondition>). If both versions are
supplied, they must express the same condition. If the text version is
omitted, DBFILTER() will return an empty string for the work area.
DBSETFILTER() performs the same function as the standard SET FILTER
command. For more information, refer to the SET FILTER command.
Notes
. Logical records: DBSETFILTER() affects the logical visibility
of records (see above).
. Side effects: Setting a filter condition is only guaranteed to
restrict visibility of certain records as described above. The
filter expression is not necessarily evaluated at any particular
time, by any particular means, or on any particular record or series
of records. If the filter expression relies on information external
to the database file or work area, the effect is unpredictable. If
the filter expression changes the state of the work area (e.g., by
moving to a different record or changing the contents of a record),
the effect is unpredictable.
. Evaluation context: When the filter expression is evaluated,
the associated work area is automatically selected as the current
work area before the evaluation; the previously selected work area is
automatically restored afterward.
Examples
. This example limits data access to records in which the Age
field value is less than 40:
USE Employee NEW
DBSETFILTER( {|| Age < 40}, "Age < 40" )
DBGOTOP()
Files Library is CLIPPER.LIB.
See Also:
DBCLEARFIL()
DBFILTER()
SET DELETED
SET FILTER
This page created by ng2html v1.05, the Norton guide to HTML conversion utility.
Written by Dave Pearson