HFirst (Function)

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Read operation based on a key
Checking password
Miscellaneous
Comparison between HReadFirst and HFirst
Locks

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HFirst (Function)

In french: HPremier

Not available with this kind of connection

Sets the position on the first record of a data file according to the specified 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 ascending order (for more details, see the remarks).

Caution: The record loaded into memory is not modified. HFSQL variables (e.g. Client.Name, i.e. the Nom field in the Clientfile) 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 there is no record corresponding to the filter (defined by function HFilter): function HOut returns True.
the function attempts to block a record already blocked in playback: function HErrorLock returns True and function HOut returns True.
JDBC access: lock management is not supported for databases that are accessed through JDBC.

Example

HFirst(Customer, Name)
WHILE HOut() = False
	// Process the record
	HNext(Customer, Name)
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:
or a positioning problem (empty data file, etc.): function HFound returns Faux 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 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:
hKeepFilter The filter set by HFilter will be taken into account, even if the search key is not optimized for the filter. Reminder: HFilter returns the optimized search key for the filter.
Caution: In this case, on large data files, performance problems may occur..
This variable cannot be used.
hLockNo No blocking: the recording can be played back or modified by another application.
JDBC access: This constant is not available.
hLockReadWrite Lock in read/write mode: the selected record cannot be read or modified by another application..
Lock in write mode: the selected record can be read by another application, but cannot be modified by another application.. Equivalent to hLockWrite.

JDBC access: This constant is not available.
hLockWrite Lock in write mode: the selected record can be read by another application, but cannot be modified by another application..
JDBC access: This constant is not available.
hNoRefresh
The table or query content will not be refreshed. All the saved positions are stored. If this parameter is not specified, function HFirst resets the browse for the specified item: the contents of the table or query are refreshed with data from the OLE DB database.. All the saved positions are lost. The position will be restored according to the value of best item.
Note: Routes and positions saved on other browse items are never assigned.
JDBC access: lock management is not supported for databases that are accessed through JDBC.
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 mode specified by HFirst 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.
Oracle: a different blocking 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).
The lock options are ignored. Use the lock functions (HLockRecNum) kept for backward compatibility.

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.

Checking password

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

The function HFirst function does not play the recording: the HFirst is therefore faster than function HReadFirst.

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: wd300hf.dll