<Connection variable>.Transaction (Function)

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Locking records
Error cases
Handling records during a transaction
Transactions and independent HFSQL context
OLE DB and Native Connectors

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<Connection variable>.Transaction (Function)

In french: <Variable Connexion>.Transaction

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, <Connection variable>.Transaction 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 <Connection variable>.TransactionStart.

Example

MyConnection1 is Connection

// Start transaction on data files associated with MyConnection1
MyConnection1.Transaction()
Add_Order()
WHEN EXCEPTION IN
// Add the order
Order.Add()
// Validate the addition
MyConnection1.TransactionEnd()
DO
// Delete the order lines
MyConnection1.TransactionCancel()
END

Syntax

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

<Result> = <Connection>.Transaction([<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>: Connection variable

Name of the Connection variable that describes the connection to use.

<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 Hide the details

<Result> = <Connection>.Transaction(<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>: Connection variable

Name of the Connection variable that describes the connection to use.

<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 <Connection variable>.TransactionEnd or <Connection variable>.TransactionCancel.
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.

Remarks

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 <Connection variable>.Transaction in 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 mode is not "Read Uncommitted".

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 <Connection variable>.Transaction 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