<Source>.Previous (Function)

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Read operation according to a key

Comparison between <Source>.Previous and .LitPrécédent

Various

Locks

See also

<Source>.Previous (Function)

In french: <Source>.Précédent

Not available with this kind of connection

Positions on the previous file record according to a browse item. The record is not read.
The number of the current record is modified when it is returned by <Source>.RecNum. For the functions that handle the current record number (<Source>.Delete, <Source>.Lit, <Source>.Modifie, ...), the value of this number is not updated: you must use <Source>.RecNum(). For example: not to do:

Customer.Delete()

but

Customer.Delete(Customer.RecNum())

The reading is performed from the lowest to the greatest value of the browse item (see the remarks for more details).

Caution: The record loaded in memory is not modified. The HFSQL variables (Customer.Name for example, which means the Name item of Customer file) are not updated.

In most cases, <Source>.Previous sets the position in the data file to browse through the records that correspond to a condition. <Source>.Next is used to position on the next record corresponding to the condition.

Several cases may occur after the call to <Source>.Previous:

a record corresponding to the condition was found: <Source>.Found returns True
the data file is empty or there is no record corresponding to the condition: <Source>.Out returns True

Remarks:

By default, <Source>.SeekFirst and <Source>.SeekLast are used to perform an exact-match search.
By default, <Source>.Previous is used to perform a generic search.

Remark: From version 19, HFSQL is the new name of HyperFileSQL.

The read operation is performed from the greatest to the lowest value of the browse item (see remarks for more details).

Caution: The record loaded in memory is not modified. The HFSQL variables (Customer.Name for example, which means the Name item of Customer file) are not updated.

In most cases, <Source>.Previous is used to position in the data file during a browse loop.

Several cases may occur after the call to <Source>.Previous:

the data file is empty or no record corresponds to the filter (defined by <Source>.Filter): <Source>.Out returns True.
the function tries to lock a record that is already locked in read-only: HErrorLock returns True and <Source>.Out returns True.

Remark: From version 19, HFSQL is the new name of HyperFileSQL.

Example

Customer.Last(Name)
WHILE Customer.Out() = False
// Process the record
Customer.Previous(Name)
END

Syntax

<Result> = <Source>.Previous([<Search key item> [, <Options>]])

<Result>: Boolean

True if the position was set,
False if an error occurred. This problem can be caused by:
a positioning problem (empty data file, ...): <Source>.Found returns False and HError returns 0.
an error: HError returns an integer other than 0. HErrorInfo returns more details.

<Source>: Type corresponding to the specified source

Name of HFSQL data file used.

<Search key item>: Optional character string (with or without quotes)

Name of key item used to browse the data file. If this name is not specified, <Source>.Previous will use the last browse item used on this file by the last HFSQL management function (function starting with "H"). If this item does not exist, the best browse item is automatically used.

<Options>: Optional constant

Configures the lock and the management of duplicates performed on the record selected by <Source>.Previous:
hLockWrite Lock in write mode: the selected record can be read by another application but it cannot be modified by another application.
hLockReadWrite Lock in read/write: the selected record cannot be read or modified by another application.
hLockNo No lock (even if HStartLock was called): the record can be read or modified by another application.
hDistinct If duplicates are found, it is used to position on a single record among the duplicates. This parameter is taken into account only if the browse is performed on a key item.
By default, all the duplicates are browsed.
The lock options will have no effect if the locks are not supported by the OLE DB provider or by the Native Connector.
The lock options specified by <Source>.Previous will be ignored. The lock mode specified by <Source>.First or <Source>.Last will remain effective during the calls to <Source>.Previous and <Source>.Next.
To modify the lock mode, you must use:
<Source>.SeekFirst or <Source>.SeekLast.
<Source>.First or <Source>.Last.
<Source>.LockRecNum or <Source>.UnlockRecNum.
For Native Oracle Connector, a different lock mode can be specified for each record. However, if a transaction was started by SQLTransaction before setting the lock, the lock will only be released at the end of the transaction (SQLTransaction associated with sqlCommit or sqlRollBack).
The lock options are ignored. Use the lock functions (<Source>.LockRecNum) kept for backward compatibility.

Remarks

Read operation according to a key

<Source>.Previous sets the position on the record with the greatest key value.

The sort order is the one that was specified in the analysis for this key.

Comparison between <Source>.Previous and <Source>.LitPrécédent

<Source>.Previous does not read the record: therefore, <Source>.Previous is faster than <Source>.LitPrécédent.

Various

The current record number is returned by <Source>.RecNum.

<Source>.ChangeKey is used to modify the search key while remaining positioned on the current record.

Locks

By default (<Options> not specified), the record is not locked.

If a lock is requested (hLockWrite or hLockReadWrite constant), the position will be set on the record only if it is not already locked.

There is no need to specify a lock parameter if the data file is locked by HStartLock: the lock specified by HStartLock is automatically taken into account. To ignore the lock set by HStartLock, use the hLockNo constant.

Component : wd250hf.dll