HTransaction (Function)

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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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HTransaction (Function)

In french: HTransaction

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, a transaction is started only for the data files associated to this connection. 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, HTransaction starts both a HFSQL Classic transaction (ISAM) and a HFSQL Client/Server transaction.

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

Remark: This function is equivalent to HTransactionStart.

Example

Versions 19 and later

MyConnection1 is Connection

// Start transaction on data files associated with MyConnection1
HTransaction(MyConnection1)
Add_Order()
WHEN EXCEPTION IN
// Add the order
HAdd(Orders)
// Validate the addition
HTransactionEnd(MyConnection1)
DO
// Delete the order lines
HTransactionCancel(MyConnection1)
END

New in version 19

// Start transaction on the Orders and OrdLine data files
HTransaction("C:\Temp\Transaction.trs", "Orders,OrdLine,-Customer")
Add_Order()
WHEN EXCEPTION IN
// Add the order
HAdd(Orders)
// Validate the addition
HTransactionEnd()
DO
// Delete the order lines
HTransactionCancel()
END

Syntax

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

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

<Result>: Boolean

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

<Connection>: Character string (with or without quotes) or Connection variable

Connection to use. This connection corresponds to:
the name of the connection defined in the data model editor or by HDescribeConnection or HOpenConnection.
the name of a Connection variable.
If this parameter corresponds to an empty string ("") or to the hAccessHF7 constant: The transaction is performed on the ISAM HFSQL files.

<List of data files>: Optional character string (with quotes)

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

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

<Result>: Boolean

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

<Connection>: Character string (with or without quotes) 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 Connection variable.
If this parameter corresponds to an empty string ("") or to the hAccessHF7 constant: The transaction is performed on the ISAM HFSQL files.

<Transaction file>: Character string (with quotes)

Full name of transaction file (used to store the operations performed in transaction). This file will be automatically deleted when using HTransactionEnd or HTransactionCancel.
If this name corresponds to an empty string, the transaction file will be created in the directory of application files and it will be named: <Project Name>_$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 (with quotes)

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> = HTransaction([<Transaction file> [, <List of data files>]])

<Result>: Boolean

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

<Transaction file>: Optional character string (with quotes)

Full name of transaction file (used to store the operations performed in transaction). This file will be automatically deleted when using HTransactionEnd or HTransactionCancel.
If this name is not specified or if it corresponds to an empty string, the transaction file will be created in the directory of the data files of the application and it will be named: <Project Name>_$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>: Optional character string (with quotes)

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), this file will contain information regarding the transactions performed by several computers. 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

Nesting transactions: It is not possible to nest transactions (i.e. to call HTransaction in a transaction). In this case, the 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 mode 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 deleted at the end of the transaction.

Handling records during a transaction

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

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 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 : wd250.dll