HReadPrevious (Function)

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Read operation according to a key item or not
Looping through records that match a condition
Locks
Memos
Miscellaneous

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HReadPrevious (Function)

In french: HLitPrécédent

Not available with this kind of connection

Positions on the previous file record according to a browse item. The record is read and the HFSQL variables are updated (Customer.Name for example, which means the Name item of Customer file).

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

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

Several cases may occur after the call to HReadPrevious:

the data file is empty or there is no record corresponding to the filter (defined by function HFilter): no read is performed and function HOut returns True.
the function attempts to block a record already blocked for playback: no playback is performed, function HErrorLock returns True and function HOut returns True.
The management of locks is not available.
JDBC access: lock management is not supported for databases that are accessed through JDBC.

This function can be used with the data files, HFSQL views or queries.

Example

HReadLast(Client, Nom)
WHILE HOut() = False
	// Traitement de l'enregistrement
	HReadPrevious(Client, Nom)
END

Syntax

<Result> = HReadPrevious([<Data file> [, <Browse item>] [, <Options>]])

<Result>: Boolean

True if the previous record was read,
False in case of error (block, end of data file, etc.): the record is not read. This problem can be caused by:
or a positioning problem (empty file, etc.): function HFound returns False and function HError returns 0.
an error: HError returns an integer other than 0. HErrorInfo returns more details.

<Data file>: Optional character string

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

<Browse item>: Optional character string

Name of item used to loop through the data file. If this name is not specified, HReadPrevious will use:
In the case of a data file: the last browse item used on this file by the last HFSQL management function (function beginning with the letter H).. If this item does not exist, the best browse item is automatically used.
In the case of a query ORDER BY of the query if it exists, otherwise according to the last field used.
In the case of a view In the case of a view: the view sort item (if available), otherwise on the last used sort item.

<Options>: Optional constant (or combination of constants)

Used to configure:
the lock set on the record read by HReadPrevious.
the management of duplicates. By default, all duplicates are iterated over.
hDistinct If duplicates are found, this constant allows you to read a single record among the duplicates. This parameter is taken into account only if the iteration is performed on a key item.
hLockNo No blocking: the Record can be played back or modified by another application during playback.
hLockReadWrite Read/write lock: the record being read cannot be read or modified by another application.
hLockWrite Write lock: the record currently read can be read by another application but it cannot be modified by another application.

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 HReadPrevious will be ignored. The lock mode specified by HReadFirst or HReadLast will remain effective when HReadPrevious and HReadNext are called.
To change the lock mode, use:
HReadSeekFirst or HReadSeekLast,
HReadFirst or HReadLast.
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 locking read functions (HReadPreviousLock) kept for backward compatibility.
This parameter is ignored.
Access through JDBC: This parameter is ignored.

Remarks

Read operation according to a key item or not

If the item is a key, HReadPrevious reads the record with the greatest key value. The sort order taken into account is the one specified in the analysis for this key.

If the item is not a key, HReadPrevious reads the previous active record. When browsing the data file, the records will be sorted according to their record number.
In this case, the selected browse item will appear in red in the code editor and a warning will be displayed in the "Code" pane.

Note: The automatic completion only offers the key items.

Looping through records that match a condition

In most cases, HReadSeek, HReadSeekFirst and HReadSeekLast are used to position in the data file to perform a browse loop among the records corresponding to a condition. HReadNext and HReadPrevious are used to read the next or previous record corresponding to the condition:

if the item is a key, HReadPrevious reads the previous records corresponding to the values less than or equal to the sought value.
if the item used is not a key, HReadPrevious will read the next records corresponding to the values equal to the sought value.

To ignore the search while going to the next or previous record, use one of the following functions:

Locks

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

If a lock is erquested (hLockWrite or hLockReadWrite constant), the record will be read only if this record is not already locked.

The lock options will have no effect if the locks are not supported by the OLE DB provider or by the Native Connector.

Memos

The memos associated with the record can be automatically read (or not) when reading the record. HSetMemo is used to customize this automatic read operation.

If the memos are supported, the associated text memos are read when the record is read. The binary memos are read only when they are explicitly used (HExtractMemo).

Miscellaneous

HRecNum returns the current record number.
HChangeKey changes the search key while keeping the position on the current record.
To optimize the first iterations on a data file, use HOptimize on this data file.
This function replaces HReadPreviousLock and HReadPrevious, which were kept for compatibility with WINDEV 5.5.

Component: wd300hf.dll