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'This example uses the DELETE statement to remove records from an ISAM file.
'It creates a transaction with the BEGINTRANS and COMMITTRANS statements,
'and uses the SAVEPOINT function and ROLLBACK statement within the
'transaction to provide rollback of any or all of the deletions.
 
'Note: To run this program, you must load the ISAM TSR program PROISAM.EXE.
'Also, this program assumes a file called BOOKS.MDB exists in the current
'directory. BOOKS.MDB is a sample ISAM file that SETUP copies to your disk.
 
DEFINT A-Z
TYPE Borrower
    Cardnum AS LONG             'Card number.
    TheName AS STRING * 36      'Name.
    Street AS STRING * 50       'Street.
    City AS STRING * 26         'City.
    State AS STRING * 2         'State.
    Zip AS LONG                 'Zip code.
END TYPE
 
DIM People AS Borrower          'Record structure variable.
CONST Database = "BOOKS.MDB"    'Name of the disk file.
CONST Tablename = "Cardholders" 'Name of the table.
CONST viewbottom = 17, viewtop = 3, msgtxt = " *** Deleted: Savepoint "
DIM SavePts(viewbottom - viewtop + 1)
 
    TableNum = FREEFILE
    OPEN Database FOR ISAM Borrower Tablename AS TableNum
 
    'Loop until user chooses to quit.
    DO
        VIEW PRINT
        CLS : COLOR 15, 0
        PRINT SPC(34); "Card Holders"
        PRINT "Card#"; SPC(2); "Name"; SPC(13); "Street";
        PRINT SPC(20); "City"; SPC(6); "State"; SPC(2); "Zip"
        LOCATE 24, 1: PRINT "Choose a key:    ";
        PRINT "D - Delete this record    N - Next record    Q - Quit";
        MOVEFIRST TableNum
        VIEW PRINT viewtop TO viewbottom: COLOR 7, 0: CLS
        vPos = viewtop
 
        'Loop through a screenful of records.
        DO
            'For each record, display and ask user what to do with it.
            RETRIEVE TableNum, People
            LOCATE vPos, 1
            PRINT USING ("#####"); People.Cardnum;
            PRINT "  "; LEFT$(People.TheName, 15); "  ";
            PRINT LEFT$(People.Street, 25); "  ";
            PRINT LEFT$(People.City, 10); "  "; People.State; "   ";
            PRINT USING ("#####"); People.Zip
 
            'Get keystroke from user.
            validkeys$ = "DNQ"
            DO
                keychoice$ = UCASE$(INKEY$)
            LOOP WHILE INSTR(validkeys$, keychoice$) = 0 OR keychoice$ = ""
 
            'Process keystroke.
            SELECT CASE keychoice$
            CASE "D"
                IF NOT inTransaction THEN
                    inTransaction = -1
                    BEGINTRANS
                END IF
                NumSavePts = NumSavePts + 1
                SavePts(NumSavePts) = SAVEPOINT
                DELETE TableNum
                LOCATE vPos, 7: PRINT msgtxt; NumSavePts; SPC(79 - POS(0));
            CASE "Q"
                EXIT DO
            CASE "N"
                MOVENEXT TableNum
            END SELECT
            vPos = vPos + 1
        LOOP UNTIL EOF(TableNum) OR vPos = viewbottom
 
        'If user didn't delete any records, simply quit.
        IF NumSavePts = 0 THEN EXIT DO
 
        'Allow user to commit deletions, or roll back some or all of them.
        VIEW PRINT: LOCATE 24, 1: PRINT "Choose a key:    ";
        PRINT "R - Rollback to a savepoint   A - Rollback all deletions"
        PRINT SPC(17); "Q - commit deletions and Quit";
        validkeys$ = "RAQ"
        DO
            keychoice$ = UCASE$(INKEY$)
        LOOP WHILE INSTR(validkeys$, keychoice$) = 0 OR keychoice$ = ""
        SELECT CASE keychoice$
        CASE "R"
            VIEW PRINT 24 TO 25: PRINT : PRINT
            DO
                PRINT "Roll back to which savepoint ( 1 -"; NumSavePts; ")";
                INPUT RollbackPt
            LOOP UNTIL RollbackPt > 0 AND RollbackPt <= NumSavePts
            ROLLBACK SavePts(RollbackPt)
            NumSavePts = RollbackPt - 1
        CASE "A"
            NumSavePts = 0
            ROLLBACK ALL
        CASE "Q"
            EXIT DO
        END SELECT
    LOOP
 
    IF inTransaction THEN COMMITTRANS
    CLOSE
    END