HPrevious (Function)

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Ayuda / WLanguage / Administrar bases de datos / HFSQL / Funciones HFSQL

Read operation based on a key
Comparison between HPrevious and HReadPrevious
Miscellaneous
Locks

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HPrevious (Function)

No disponible con este tipo de conexión

Sets the position on the previous record of the data file according to a browse item. The record is not read.
The number of the current record is modified only when it is returned by HRecNum. For functions handling the current record number by default (functions HDelete, HRead, HModify, ...), the value of this number is not updated: you must use the HRecNum() function. For example: do not:

HDelete(Customer)

but

HDelete(Customer, HRecNum())

Values in the browse item are read in descending order (for more details, see the remarks).

Attention: Record loaded into memory is not modified. The HFSQL variables (for example Customer.Name, i.e. the Name item of the Customer file) are not updated.

Generally, HPrevious sets the position in the data file during a loop operation.

Several cases may occur after the call to HPrevious:

the data file is empty or there is no record corresponding to the filter (defined by HFilter): function HOut returns True.
the function attempts to block a record already blocked in play mode: function HErrorLock returns True and function HOut returns True.
JDBC access: lock management is not supported for databases that are accessed through JDBC.

Ejemplo

HLast(Customer, Name)
WHILE HOut() = False
	// Process the record
	HPrevious(Customer, Name)
END

Sintaxis

<Result> = HPrevious([<Data file> [, <Search key item>] [, <Options>]])

<Result>: Boolean

True if the position was set,
False if an error occurs. This problem can be caused by:
or a positioning problem (empty data file, etc.): function HFound returns False and HError returns 0.
an error: HError returns an integer other than 0. HErrorInfo returns more details.

<Data file>: Optional character string

Name of the HFSQL data file used. If this parameter corresponds to an empty string, HPrevious will use the last data file used by the last HFSQL management function (function starting with "H").

<Search key item>: Optional character string

Name of the key item used to loop through the data file. If this name is not specified, HPrevious 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 HPrevious:
hDistinct If there are any duplicates, sets the position on a single record of the duplicates. This parameter is taken into account only if the iteration is performed on a key item.
By default, all duplicates are iterated over.
hLockNo No blocking: the Record can be played back or modified by another application.
hLockReadWrite Lock in read/write mode: the selected record cannot be read or modified by another application.
hLockWrite Lock in write mode: the selected record can be read by another application, but cannot be modified by another application.

Access through JDBC: This parameter is ignored.
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 HPrevious will be ignored. The lock mode specified by HFirst or HLast will remain effective during the calls to HPrevious and HNext.
To change the lock mode, use:
HSeekFirst or HSeekLast.
HFirst or HLast.
HLockRecNum or HUnlockRecNum.
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 with the sqlCommit or sqlRollBack constant).
The lock options are ignored. Use the lock functions (HLockRecNum) kept for backward compatibility.