HReadPrevious (Function)

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).

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

In most cases, HReadPrevious is used to position in the data file during a browse loop.

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 HFilter): no reading is performed and HOut returns True.
the function tries to lock a record that is already locked in read-only: no reading is performed, HErrorLock returns True and HOut returns True.
The management of locks is only performed on HFSQL Client/Server data files or data files handled by a native access. An HFSQL Mobile record cannot be locked. Indeed, the operating system of Pocket PC does not allow you to lock records.
The management of locks is not available.
Access by JDBC: The management of locks is not available for the databases accessed by JDBC.

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

Versions 15 and later

This function is now available for Android applications.

New in version 15

This function is now available for Android applications.

Versions 17 and later

This function is now available for iPhone/iPad applications.

New in version 17

This function is now available for iPhone/iPad applications.

Versions 18 and later

This function is now available in Android Widget mode.

This function is now available in Windows Store apps mode.

New in version 18

This function is now available in Android Widget mode.

This function is now available in Windows Store apps mode.

This function is now available in Android Widget mode.

This function is now available in Windows Store apps mode.

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

Versions 21 and later

This function is now available in Universal Windows 10 App mode.

New in version 21

This function is now available in Universal Windows 10 App mode.

Example

HReadLast(Customer, Name)
WHILE HOut() = False
// Process the record
HReadPrevious(Customer, Name)
END

Syntax

<Result> = HReadPrevious([<File name> [, <Name of browse item>] [, <Options>]])

<Result>: Boolean

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

<File name>: Optional character string (with or without quotes)

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

<Name of browse item>: Optional character string (with or without quotes)

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

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

Used to configure:
the lock performed on the record read by HReadPrevious.
the management of duplicates. By default, all the duplicates are browsed.
hLockNo No lock (even if HStartLock was called): the record can be read or modified by another application during the reading.
hLockWrite Lock in write mode: the record currently read can be read by another application but it cannot be modified by another application.
hLockReadWrite Lock in read/write: the record currently read cannot be read or modified by another application.
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 browse is performed on a key item.
The management of locks is only performed on HFSQL Client/Server data files or data files handled by a native access. An HFSQL Mobile record cannot be locked. Indeed, the operating system of Pocket PC does not allow you to lock records.
The lock options will have no effect if the locks are not supported by the OLE DB provider or by Native Access.
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 modify the lock mode, you must use:
HReadSeekFirst or HReadSeekLast,
HReadFirst or HReadLast.
HLockRecNum or HUnlockRecNum.
For Native Oracle Access, a different lock mode can be specified for each record. However, if a transaction was started by SQLTransaction before implementing the lock, the lock will only be released at the end of the transaction (SQLTransaction with sqlFin or sqlAnnule).
The lock options are ignored. Use the locking read functions (HReadPreviousLock) kept for backward compatibility.
This parameter is ignored.
Access by 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 is the one that was 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 search item will appear in red in the code editor and a warning will be displayed in the "Code" pane.

Note: The automatic completion proposes the key items only.

Browsing the records corresponding to 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), no lock operation is performed on the record.

If a lock is erquested (hLockWrite or hLockReadWrite constant), the record will be read only if this record 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 specified by HStartLock, use the hLockNo constant.

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

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).

Various

The current record number is returned by HRecNum.
HChangeKey is used to modify the search key while being positioned on the current record.
To optimize the time of the first browses performed on a data file, use HOptimize on this file.

Component : wd240hf.dll