HLockRecNum (Function)

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Modifying the type of lock for a record
Effect of lock mode
Lock failure
Number of locks
SQL Server Native Connector: Lock in write mode only
Managing locks in OLE DB
Persistence of lock

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HLockRecNum (Function)

In french: HBloqueNumEnr

Not available with these kinds of connection

Locks a record and restricts the access to this record for all the other applications. Then, the record can be unlocked by HUnlockRecNum.

Note: After executing function HLockRecNum, several cases may arise:

Registration already blocked by another application: blocking cannot be performed.
The data file containing the record is blocked in its entirety: blocking cannot be performed.

An automatic management of lock errors and modification conflicts is performed by default (except in the code of stored procedures). This assisted management of errors can be customized or disabled at any time by HOnError.

HErrorLock returns True if a lock problem occurs.

Caution: This HLockRecNum function must be used with caution: when blocked, the recording is not replayed.. Therefore, it may have been deleted or modified since the last access to this record. It is recommended to use HRead with a lock option.

This function is available for HFSQL data files only. It is not available for the data files accessed by JDBC.

Example

// Lock a record in the Customer data file
HLockRecNum(Customer, hCurrentRecNum, hLockReadWrite)
// Process on the record
...
// Restore access to the record
HUnlockRecNum()

Syntax

<Result> = HLockRecNum([<Data file> [, <Record to lock>]] [, <Lock>])

<Result>: Boolean

True if the operation was performed,
False if a problem occurs. HError is used to identify the error.

<Data file>: Optional character string

Name of the data file used.
If this name is not specified, HLockRecNum will use the last data file used by the last HFSQL function (function starting with "H").

<Record to lock>: Optional integer

Number of the record to lock.
If this parameter is not specified, HLockRecNum will handle the current record.
HLockRecNum locks the current record only. You cannot specify a record number other than the current one (to specify the current record number, use the hRecNumCurrent constant).

<Lock>: Optional integer constant

Used to define the type of lock set on the record.
hLockNo No lock: the recording can be played back or modified by another application.
hLockReadWrite Read/write block: data file record cannot be read or modified by another application.
The other application will not be able to lock the record or the data file.
hLockWrite
(default value) Write block: data file record can be read by another application but cannot be modified by another application.
The other application will not be able to lock the record or the data file.

Remarks

Modifying the type of lock for a record

To modify the type of record lock, call HLockRecNum and specify the requested type of lock. There is no need to unlock the record beforehand.

Effect of lock mode

If the data file lock mode is set to hModeMono (see HMode), HLockRecNum has no effect.

Lock failure

If the record is already locked, the lock request is retried HNbRetry times (50 by default).

If the data file cannot be locked after H.NbRetry attempts, HErrorLock returns True. The H.Level variable indicates whether the record or the data file is locked.

Number of locks

The number of records that can be individually locked in a data file is unlimited.

SQL Server Native Connector: Lock in write mode only

HLockRecNum locks the record in write mode, not in read-only. Therefore, HLockRecNum prevents the record from being modified by another computer.

HLockRecNum used on a locked record does NOT return a lock error (because only a read operation is performed).

However, HModify will return a lock error on the locked record.

Managing locks in OLE DB

HLockRecNum is not supported. This function generates the non-fatal error "Invalid operation for this type of database".

Persistence of lock

With the Native SQLServer and Sybase Connectors, re-reading a record that was locked by HLockRecNum unlocks the record.

Component: wd300hf.dll