HTransactionStart (Function)

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

Network application (ISAM database)
Locking records
Error cases
Temporary files created during the transaction (ISAM database)
Handling records during a transaction
Transactions and independent HFSQL context
OLE DB and Native Connectors

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HTransactionStart (Function)

In french: HTransactionDébut

Not available with this kind of connection

Starts a transaction on the data files (HFSQL or accessed via a Native Connector) and creates the transaction file.

What information is saved in the transaction file? Whenever a WLanguage function modifies a data file or an index file during a transaction, the former values of the record and the operation performed are stored in the transaction file.

This function proposes two operating modes of transactions:

The transaction can be started on a connection: in this case, only the files associated with this connection are transacted. This mode is required to manage the isolation levels of transactions.
The transaction can be started on all HFSQL connections (existing ones or future ones). In this case, HTransactionStart starts both an HFSQL Classic transaction (ISAM) and an HFSQL Client/Server transaction.

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

Note: This function is equivalent to HTransaction.

Example

MaConnexion1 is Connection
// Début de la transaction sur les fichiers de données associés à la connexion MaConnexion1
HTransactionStart(MaConnexion1)
// Code permettant de préparer la commande à ajouter
// ...
WHEN EXCEPTION IN
	// Ajout de la commande
	HAdd(Commande) 
	// Validation de l'ajout
	HTransactionEnd(MaConnexion1)
DO
	// Suppression des lignes de commandes
	HTransactionCancel(MaConnexion1)
END

// Début de la transaction sur les fichiers de données Commande et LigneCde
HTransactionStart("C:\Temp\Transaction.trs", "Commande,LigneCde,-Client")

// Code permettant de préparer la commande à ajouter
// ...

WHEN EXCEPTION IN
	// Ajout de la commande
	HAdd(Commande) 
	// Validation de l'ajout
	HTransactionEnd() 
DO
	// Suppression des lignes de commandes
	HTransactionCancel() 
END

Syntax

Starting a Client/Server transaction on a specific connection Hide the details

<Result> = HTransactionStart(<Connection> [, <List of data files>])

<Result>: Boolean

True if the transaction was started,
False if a problem occurs. HErrorInfo returns more details about the error.

<Connection>: Character string or Connection variable

Name of 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, the transaction will be performed on ISAM HFSQL data files.

<List of data files>: Optional character string

List of logical names of one or more data files to take into account (or not) in the transaction (in this case, the data file name is preceded by the "-" sign).
If this parameter is not specified All data files used during the transaction will be taken into account in the transaction.
If all data files are prefixed with the "-" sign
For example: "-Customer, -Product" All data files specified in the list and used during the transaction will not be taken into account by the transaction.
All data files not specified in the list will be taken into account and used during the transaction.
If no data file on the list is prefixed with the "-" sign
For example: "Customer, Product" All data files specified in the list and used during the transaction will be taken into account in the transaction.
All data files not specified and manipulated during the transaction will be ignored in the transaction.
If some data files are prefixed with "-" and others are not
For example: "-Customer, Product" (equivalent to "Product") All data files in the list prefixed with "-" and used during the transaction will be ignored in the transaction.
All data files in the list not prefixed with "-" and used during the transaction will be taken into account in the transaction.
The files not specified in the list will be excluded from the transaction.
This parameter is ignored. All the data files associated with the connection are in transaction on the native server.

Starting a Client/Server transaction on a specific connection or an ISAM transaction Hide the details

<Result> = HTransactionStart(<Connection> , <Transaction file> , <List of data files>)

<Result>: Boolean

True if the transaction was started,
False if a problem occurs. HErrorInfo returns more details about the error.

<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 an empty string ("") or to the hAccessHF7 constant, the transaction is performed on ISAM HFSQL data files.

<Transaction file>: Character string

Full name of the transaction file (used to store the operations performed within the transaction). This file will be automatically deleted when using HTransactionEnd or HTransactionCancel.
If this name is an empty string, the transaction file will be created in the application's data file directory with the name: <Nom Projet>_$TRS_OPERATION.TRS.
This parameter is ignored. This parameter is taken into account for the HFSQL Classic transactions only (ISAM transactions).

<List of data files>: Character string

List of logical names of one or more data files to take into account (or not) in the transaction (in this case, the data file name is preceded by the "-" sign).
If this parameter is not specified All data files used during the transaction will be taken into account in the transaction.
If all data files are prefixed with the "-" sign
For example: "-Customer, -Product" All data files specified in the list and used during the transaction will not be taken into account by the transaction.
All data files not specified in the list will be taken into account and used during the transaction.
If no data file on the list is prefixed with the "-" sign
For example: "Customer, Product" All data files specified in the list and used during the transaction will be taken into account in the transaction.
All data files not specified and manipulated during the transaction will be ignored in the transaction.
If some data files are prefixed with "-" and others are not
For example: "-Customer, Product" (equivalent to "Product") All data files in the list prefixed with "-" and used during the transaction will be ignored in the transaction.
All data files in the list not prefixed with "-" and used during the transaction will be taken into account in the transaction.
Data files not specified in the list will be excluded from the transaction.
This parameter is ignored. All the data files associated with the connection are in transaction on the native server.

Starting an ISAM and/or Client/Server transaction on all the HFSQL Client/Server connections (existing ones or future ones) Hide the details

<Result> = HTransactionStart([<Transaction file> [, <List of files>]])

<Result>: Boolean

True if the transaction was started,
False if a problem occurs. HErrorInfo returns more details about the error.

<Transaction file>: Optional character string

Full name of the transaction file (used to store the operations performed within the transaction). This file will be automatically deleted when using HTransactionEnd or HTransactionCancel.
If this name is not specified or is an empty string, the transaction file will be created in the application's data file directory with the name: <Nom Projet>_$TRS_OPERATION.TRS.
This parameter is ignored. This parameter is taken into account for the HFSQL Classic transactions only (ISAM transactions).

<List of files>: Optional character string

List of logical names of one or more data files to take into account (or not) in the transaction (in this case, the data file name is preceded by the "-" sign).
If this parameter is not specified All data files used during the transaction will be taken into account in the transaction.
If all data files are prefixed with the "-" sign
For example: "-Customer, -Product" All data files specified in the list and used during the transaction will not be taken into account by the transaction.
All data files not specified in the list will be taken into account and used during the transaction.
If no data file on the list is prefixed with the "-" sign
For example: "Customer, Product" All data files specified in the list and used during the transaction will be taken into account in the transaction.
All data files not specified and manipulated during the transaction will be ignored in the transaction.
If some data files are prefixed with "-" and others are not
For example: "-Customer, Product" (equivalent to "Product") All data files in the list prefixed with "-" and used during the transaction will be ignored in the transaction.
All data files in the list not prefixed with "-" and used during the transaction will be taken into account in the transaction.
Data files not specified in the list will be excluded from the transaction.

Remarks

Network application (ISAM database)

In network, the transaction file can be created on a local disk or on a network drive.

If the transaction file is installed on a local computer, this file will contain information regarding the transactions performed by the current computer. In this case, the transaction file is deleted when the transaction is ended.
If the transaction file is installed on a network drive (recommended), the transaction file will contain transaction information for several workstations.. Each computer is identified by a unique number. In this case, the transaction file is deleted when the last transaction is ended.

Locking records

The added, modified or deleted records in a transaction are locked in write mode.

Error cases

Transaction nesting: It is impossible to nest transactions (i.e. to call the function HTransactionStart 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".

Temporary files created during the transaction (ISAM database)

During the transaction, temporary files (".TRX" extension) are created in the directory containing the data files (".FIC" files). These temporary files must not be deleted. Otherwise, the data handled by the transaction could be damaged.

Remark: These temporary files are automatically destroyed at the end of the transaction.

Handling records during a transaction

During a transaction, some rules must be complied with when handling the records. For more details, see Transactions: Handling the records during a transaction.

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 to start a transaction in the new context.

OLE DB and Native Connectors

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

Component: wd300hf.dll