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Help / WLanguage / Managing databases / HFSQL / HFSQL functions
  • Read operation based on a key
  • Password verification
  • Miscellaneous
  • Comparison between HReadFirst and HFirst
  • Locks
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Stored procedures
Positions on the first Record of a data file according to the specified route item. The record is not read.
The number of the current record is modified only when it is returned by HRecNum. For the functions that handle the current record number (HDelete, HRead, HModify, etc.), the value of this number is not updated: you must use HRecNum(). For example: not to do:
HDelete(Customer)
but
HDelete(Customer, HRecNum())
Values in the browse item are read in ascending order (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, HFirst sets the position in the data file to loop through the records that match a condition. HNext is used to position on the next record corresponding to the condition.
Several cases may occur after the call to HFirst:
  • a record corresponding to the condition was found: HFound returns True
  • the data file is empty or there is no record corresponding to the condition: HOut returns True
Remarks:
  • By default, HSeekFirst and HSeekLast are used to perform an exact-match search.
  • By default, HFirst performs a generic search.

Values in the browse item are read in ascending order (for more details, see the the remarks).
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, HFirst is used to set the position in the data file in order to perform a read loop with HNext.
Several cases may occur after the call to HFirst:
  • the data file is empty or no record corresponds to the filter (defined by HFilter): HOut returns True.
  • the function tries to lock a record that is already locked in read-only: HErrorLock returns True and HOut returns True.
Example
HFirst(Client, Nom)
WHILE HOut() = False
// Traitement de l'enregistrement
HNext(Client, Nom)
END
Syntax
<Result> = HFirst([<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:
    • a positioning problem (empty data file, etc.): 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 data file used. If this parameter is an empty string (""), HFirst manipulates the last data file used by the last HFSQL 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, HFirst will use the last browse item used on this data 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 set on the record selected by HFirst:
hKeepFilterThe filter set by HFilter will be taken into account, even if the search key is not optimized for the filter. Reminder: HFilter returns the search key optimized for the filter.
Caution: In this case, performance issues may arise for large data files.
hLockNoNo lock: the record can be read or modified by another application.
hLockReadWriteLock in read/write mode: the selected record cannot be read or modified by another application.

hLockWriteLock in write mode: the selected record can be read by another application but it cannot be modified.
hNoRefresh
Native Connectors (Native Accesses) The lock options will have no effect if the locks are not supported by the OLE DB provider or by the Native Connector.
Native Connectors (Native Accesses) Oracle: 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).
Remarks

Read operation based on a key

HFirst positions on the record with the smallest key value.
The sort order taken into account is the one specified in the analysis for this key.
If duplicates are found, HFirst sets the position on the first "duplicate" record according to the sequence of record numbers.
Universal Windows 10 AppiPhone/iPadHFSQL ClassicHFSQL Client/Server

Password verification

If HFirst is the first function that handles the specified data file, the password is checked when opening the data file.
If the password is incorrect, HErrorPassword returns True and HOut returns True.

Miscellaneous

  • HRecNum returns the current record number.
  • HChangeKey changes the search key while keeping the position on the current record.

Comparison between HReadFirst and HFirst

HFirst does not read the record: therefore, HFirst is faster than HReadFirst.
WINDEV MobileUniversal Windows 10 AppiPhone/iPadHFSQL ClassicHFSQL Client/ServerNative Connectors (Native Accesses)

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.
Component: wd290hf.dll
Minimum version required
  • Version 9
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Comments
HFILER E FILETOARRAY
O filetoarray se não tiver antes dele um hfilter coloca no array a tabela inteira e se colocar o hfilter, traz só o registro. exemplos:

//assim vai trazer só o registro atual
HFilter(RADFileA,RADFileA.IDRADFileA,gnID)
FileToArray(garr_RADFileA_Depois,RADFileA,RADFileA.IDRADFileA)

//vai trazer todos os registros
FileToArray(garr_RADFileA_Depois,RADFileA,RADFileA.IDRADFileA)

DICA:
Voce pode atribuir uma Classe de um arquivo a um array assim:

garr_RADFileA_Antes is array of CMRADFileA
garr_RADFileA_Depois is array of CMRADFileA
BOLLER
24 Feb. 2019

Last update: 07/06/2023

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