- Read operation according to a key item or not
- Looping through records that match a condition
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
Values in the browse item are read in descending order (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 no record corresponds 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 read operation is performed, HErrorLock returns True and HOut returns True.
The management of locks is not available.
Access by JDBC: The management of locks is not available for databases accessed by JDBC.
WHILE HOut() = False
// Process the record
<Result> = HReadPrevious([<Data file> [, <Browse item>] [, <Options>]])
- 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.
<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:
- 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 the view (if it exists), otherwise the last item used.
<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 the duplicates are browsed.
|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.|
|hLockNo||No lock: the record can be read or modified by another application during the reading.|
|hLockReadWrite||Lock in read/write: the record currently read cannot be read or modified by another application.|
|hLockWrite||Lock in write mode: 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
will remain effective when HReadPrevious
To modify the lock mode, you must use:
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
The lock options are ignored. Use locking read functions (HReadPreviousLock
) kept for backward compatibility.
This parameter is ignored.
Access by JDBC: This parameter is ignored.
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 browse item will appear in red in the code editor and a warning will be displayed in the "Code" pane
Looping through records that match a condition
In most cases, HReadSeek
are used to position in the data file to perform a browse loop among the records corresponding to a condition. HReadNext
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:
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
- The current record number is returned by HRecNum.
- HChangeKey is used to modify the search key while remaining positioned 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.
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