Rollback

Rollback is used to end a database transaction and comes back to the situation before the beginning of the transaction (Trbegin).

Syntax

  Rollback

Examples

# This subprogram debits an account ACCOUNT1 and credits and account ACCOUNT2 with an AMOUNT value
# It manages a transaction except if a transaction is already in progress
# OPERATION_STATUS returns [V]CST_AOK if the operation was successful, otherwise it returns [V]CST_AERROR.
# If a fatal error happens, OPERATION_STATUS returns [V]CST_AFATAL

Subprog TRANSFER(ACCOUNT1, ACCOUNT2, AMOUNT, RATE, OPERATION_STATUS)
Value Char ACCOUNT1(), ACCOUNT2()
Value Decimal AMOUNT,RATE
Variable Integer OPERATION_STATUS
Local Integer IF_TRANS

# Manage the exceptions
  Onerrgo ABORT_TRANS

# Start the transaction if no transaction is in progress
  Local File ACCOUNT
  If adxlog
    Trbegin ACCOUNT
    IF_TRANS=0
  Else
    # The transaction has been started by the calling program
    IF_TRANS=1
  Endif

# Debit operation (CODE is a unique index so only one database line is updated)
  Update ACCOUNT Where CODE=ACCOUNT1 With BALANCE=BALANCE-ar2(AMOUNT/RATE)
  If fstat
    # If IF_TRANS=1, the transaction must been aborted by the calling program
    If IF_TRANS=0 : Rollback : Endif
    OPERATION_STATUS=[V]CST_AERROR
    End
  Endif

# Credit operation
  Update ACCOUNT Where CODE=ACCOUNT2 With BALANCE=BALANCE+ar2(AMOUNT/RATE)
  If fstat
    # If IF_TRANS=1, the transaction must been aborted by the calling program
    If IF_TRANS=0 : Rollback : Endif
    OPERATION_STATUS=[V]CST_AERROR
    End
  Endif

# The operation is successful. If IF_TRANS=1, the transaction must been committed by the calling program
  If IF_TRANS=0 : Commit : Endif
  OPERATION_STATUS=[V]CST_AOK
End

# Error management
# This may happen for instance when RATE is 0 (division by zero)
$ABORT_TRANS
  If IF_TRANS=0 : Rollback : Endif
  OPERATION_STATUS=[V]CST_AERROR
End

Description and comments

• Rollback is used to abort a database transaction, which is a set of operations used to update the database tables including counters. A transaction is started by a Trbegin instruction.
• The tables opened before the transaction stay open, files opened by Trbegin or after Trbegin are closed, except for those redeclared using an existing abbreviation.
• Rollback can only be carried out in the script or subprogram that started the transaction. The Rollback instruction can be found in an error rerouting script called by Onerrgo.
• A unique level of transaction is supported by the SAFE X3 engine. Thus, if a subprogram that performs an autonomous transaction can be called within another transaction, the Trbegin / Commit / Rollback instruction must be executed in the calling nested level. The fact that a transaction is already in progress is defined by the value of adxlog: if a transaction is in progress, its value is 1; otherwise, the value is 0.
• Rollback releases all the locks placed on the tables and records and the symbols locked during the transaction. Rollback also releases locks placed before the start of the transaction, except from those placed on symbols.
• Rollback does not return any particular status.

Associated errors

See also

File, Trbegin, Commit, Onerrgo, Read, Write, Writeb, Rewrite, RewriteByKey, Delete, DeleteBykey, Lock, adxlog.