HTransactionCancel (Function)

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Help / WLanguage / Managing databases / HFSQL / Managing transactions / WLanguage functions

Location and access to data files
Detecting an error
Tip: Restoring the consistency of the database
Error cases
Transactions and independent HFSQL context
OLE DB and Native Connectors

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HTransactionCancel (Function)

In french: HTransactionAnnule

Not available with this kind of connection

If a transaction is in progressrolls back all operations performed on data files in transactions since the start of the transaction. In this case, the transaction is canceled without interrupting the program execution.

If no transaction is in progressrestores database consistency and rolls back a failed transaction (e.g. in the event of a power failure).
Note: A failed transaction can be rolled back by any program..
The transaction file is automatically destroyed if it is not shared. The records locked by the write operations performed during the transaction are unlocked.

Note The HTransactionFree function transforms all records "in transaction" into "normal" records if they do not belong to a transaction currently in progress.

The management of transactions is available for HFSQL Client/Server databases.

Example

MaConnexion is Connection

// Début de la transaction sur les fichiers de données associés à la connexion MaConnexion
HTransactionStart(MaConnexion)
Ajout_Commande()
WHEN EXCEPTION IN
	// Ajout de la commande
	HAdd(Commande) 
	// Validation de l'ajout
	HTransactionEnd(MaConnexion)
DO
	// Suppression des lignes de commandes
	HTransactionCancel(MaConnexion)
END

// Début de la transaction sur les fichiers de données Commande et LigneCde
HTransactionStart("C:\Temp\Transaction.trs", "Commande, LigneCde, -Client")
Ajout_Commande()
WHEN EXCEPTION IN
	// Ajout de la commande
	HAdd(Commande) 
	// Validation de l'ajout
	HTransactionEnd()
DO
	// Suppression des lignes de commandes
	HTransactionCancel()
END

// Début de la transaction sur les fichiers de données Commande et LigneCde
HTransactionStart("Commande,LigneCde,-Client")
Ajout_Commande()
WHEN EXCEPTION IN
	// Ajout de la commande
	HAdd(Commande)
	// Validation de l'ajout
	HTransactionEnd() 
DO
	// Suppression des lignes de commandes
	HTransactionCancel() 
END

Syntax

Canceling a current transaction or an interrupted transaction on a Client/Server connection Hide the details

<Result> = HTransactionCancel(<Connection>)

<Result>: Boolean

True if the transaction was canceled,
False if a problem occurs. HErrorInfo returns more details about the error.
Caution:
If a transaction is in progress on the connection, it is canceled.
If no transaction is in progress, the interrupted transactions are canceled for the specified connection.

<Connection>: Character string or Connection variable

Connection to use. This connection corresponds to:
the name of the connection defined in the data model editor or with HDescribeConnection or HOpenConnection.
the name of a variable of type Connection.
If this parameter corresponds to the constant hAccessHF7the transaction is rolled back on HFSQL Classic (ISAM) data files.

Canceling a current transaction or an interrupted transaction on all connections (HFSQL Classic or Client/Server) Hide the details

<Result> = HTransactionCancel([<Transaction file>])

<Result>: Boolean

True if the transaction was canceled,
False if a problem occurs. HErrorInfo returns more details about the error.
Caution:
If the <Transaction file> parameter is not specified, the current transaction is canceled.
If a transaction is in progressALL transactions in progress are rolled back (HFSQL Classic transactions and/or HFSQL Client/Server transactions).
If there is no transaction in progressALL interrupted transactions are rolled back (in HFSQL Classic and Client/Server).

<Transaction file>: Optional character string

Name and path of transaction file to cancel:
This parameter must be identical to the name specified in HTransactionStart (or in HTransaction).
If this parameter is not specified and if no transaction is in progress, the default transaction file is taken into account.
If a transaction is in progress, this transaction is canceled and the name of transaction file is ignored.
This parameter is ignored.

Canceling an interrupted transaction on a Client/Server database (to be used if no transaction is in progress) Hide the details

<Result> = HTransactionCancel(<Connection> , <Database>)

<Result>: Boolean

True if the transaction was canceled,
False if a problem occurs. HErrorInfo returns more details about the error.
Caution:
Only the interrupted transactions on the specified database are canceled.
The transactions in progress are not canceled.

<Connection>: Character string or Connection variable

Connection to use. This connection corresponds to:
the name of the connection defined in the data model editor or with HDescribeConnection or HOpenConnection.
the name of a variable of type Connection.
If this parameter corresponds to the hAccessHF7 constant, only transactions interrupted in HFSQL Classic mode will be canceled.

<Database>: Character string

Name of the relevant database. An error occurs if this parameter corresponds to an empty string ("").

Canceling a transaction (to be used if no transaction is in progress) Hide the details

<Result> = HTransactionCancel(<Transaction file> , <Connection>)

<Result>: Boolean

True if the transaction was canceled,
False if a problem occurs. HErrorInfo returns more details about the error.
Caution:
If the <Transaction file> parameter is not specified, the current transaction is canceled.
If a "general" transaction is in progress, ALL the current transactions are canceled (HFSQL Classic transactions and/or HFSQL Client/Server transactions).
If a transaction is in progress on the connection, it is canceled.
If no transaction is in progress, only the interrupted transactions are canceled for the specified connection.

<Transaction file>: Character string

Name and path of transaction file to cancel.
This parameter must be identical to the name specified in HTransactionStart (or in HTransaction).

<Connection>: Character string or Connection variable

Connection to use. This connection corresponds to:
the name of the connection defined in the data model editor or with HDescribeConnection or HOpenConnection.
the name of a variable of type Connection.
If this parameter corresponds to the hAccessHF7 constant, only transactions interrupted in HFSQL Classic mode will be canceled.

Canceling a specific transaction, linked to a connection Hide the details

<Result> = HTransactionCancel(<Connection> , <Transaction to cancel>)

<Result>: Boolean

True if the transaction was canceled,
False if a problem occurs. HErrorInfo returns more details about the error.
Warning: Only interrupted transactions on the specified database are rolled back.

<Connection>: Character string or Connection variable

Connection to use. This connection corresponds to:
the name of the connection defined in the data model editor or with HDescribeConnection or HOpenConnection.
the name of a variable of type Connection.
If this parameter corresponds to the hAccessHF7 constant, only the transaction interrupted in HFSQL Classic mode will be canceled.

<Transaction to cancel>: Integer

Identifier of transaction that will be canceled for the specified connection. This identifier is returned by HTransactionList.

Remarks

Location and access to data files

Before calling HTransactionCancel, the data files handled by the canceled transaction must be:

located (HSubstDir, HChangeName, etc.).
accessible (HPass, etc..).

Detecting an error

When an error is detected by the program (management of errors with WHILE EXCEPTION for example), HTransactionCancel is used to:

restore the data files in their initial status.
cancel all the operations performed on the data files since the call to HTransactionStart (or HTransaction).

Tip: Restoring the consistency of the database

If a breakdown (power outage, reboot, ...) occurs during a transaction, the data files may become corrupted: the transaction was neither validated nor canceled. The transaction file is still found on the computer.

To restore the consistency of the database, you should propose in your application:

an option used to maintain the database consistency.
This option can for example call HTransactionCancel or HTransactionStart/HTransactionEnd.
management of error 70034 in the project initialization code via the WHEN EXCEPTION keyword.
Therefore, when the error 70034 occurs, the database consistency will be restored by HTransactionCancel, or by HTransactionStart/HTransactionEnd.

Note: this operation can take a relatively long time (depending on the number of transactions performed).

Error cases

Transaction nesting: it is not possible to nest transactions (i.e. to call function HTransactionStart or function HTransaction within a transaction).. In this case, error 70031 occurs.
A fatal error is displayed in the following cases:
- A transaction is started on all the connections while there is at least one connection in transaction.
- A transaction is started on a connection while a transaction was already started on all the connections.
- A transaction is started on all the connections while there is at least one connection whose isolation level is not "Read Uncommitted".

Transactions and independent HFSQL context

When copying a context, if a transaction is in progress on the first context, the new context is not in transaction. You must call HTransactionStart (or HTransaction) to start a transaction in the new context.

OLE DB and Native Connectors

Only syntaxes with connection are taken into account by the Native Connectors that support transactions. You can also use SQLTransaction.

Component: wd300hf.dll