HSeekLast (Function)

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Generic search/Exact-match search

Performing a search on a composite key

Search on an array item

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Generic search/Exact-match search
Performing a search on a composite key
Search on an array item
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HSeekLast (Function)

In french: HRechercheDernier

Not available with this kind of connection

Sets the position on the last data file record whose value for a specific item is less than or equal to a sought value. The record is not read.
The number of the current record is modified when it is returned by HRecNum. For the functions that handle the current record number (HDelete, HRead, HModify, ...), the value of this number is not updated: you must use HRecNum(). For example: not to do:

HDelete(Customer)

but

HDelete(Customer, HRecNum())

The reading is performed from the lowest to the greatest value of the browse item (see the 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, HSeekLast sets the position in the data file to browse through the records that correspond to a condition. HNext is used to position on the next record corresponding to the condition.

Several cases may occur after the call to HSeekLast:

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, HSeekLast is used to perform a generic search.

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

The reading is performed from the lowest value to the greatest value of search item (see the notes 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, HSeekLast sets the position in the data file to browse through the records that correspond to a condition.

Several cases may occur after the call to HSeekLast:

a record corresponding to the condition was found, locked (if necessary) and loaded in memory: HFound returns True.
the data file is empty or there is no record corresponding to the condition: HOut returns True.
the function tries to lock a record that is already locked in read-only: HErrorLock returns True and HOut returns True.

Remark: the search can be canceled by HCancelSeek.

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

Example

// Find the last record for which the Customer name is Moore
HSeekLast(Customer, Name, "Moore")

// This example is used to find all the customers
// whose turnover is less than a specific value.
HSeekLast(Customer, Turnover, X)
WHILE NOT HOut(Customer)
AddCustomerList()
HPrevious(Customer, Turnover)
END

Syntax

<Result> = HSeekLast(<Data file> , <Key item> , <Sought value> [, <Options>])

<Result>: Boolean

True if the positioning was performed (corresponds to the value of HFound).
False if a problem occurred. This problem can be caused by:
a positioning problem (empty data file, ...): HFound returns False and HError returns 0.
an error: HError returns an integer other than 0. HErrorInfo returns more details.

<Data file>: Character string (with or without quotes)

Name of HFSQL data file used.

<Key item>: Character string (with or without quotes)

Name of key item on which the search will be performed.

<Sought value>: Type corresponding to the value

Value of sought item.

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

Configures:
the lock mode applied to the sought record
the type of search performed.
hLockReadWrite Lock in read/write: the record cannot be read or modified by another application.
Lock in write-only. Operating mode equivalent to the hLockWrite constant.
hLockWrite Lock in write mode: the record can be read by another application but it cannot be modified by another application.
hLockNo No lock (even if HStartLock was called): the record can be read or modified by another application during the reading.
hGeneric Generic search (see the Notes)
An exact-match search is performed by default (constant not specified).
hLimitParsing The browse will stop as soon as the last sought value is found. The current record will correspond to this last record found.
HFound will be set to False and HOut will be set to True.
This constant is used to optimize the search speed in Client/Server mode.
hKeepFilter The filter implemented 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.
This variable cannot be used.
By default, the browse performed after HSeekLast ignores the filter.
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 HSeekLast will remain effective during the calls to HPrevious and HNext.
To modify the lock mode, you must use:
HSeekFirst or HSeekLast,
HLast or HFirst.

Remarks

Generic search/Exact-match search

Generic search (mainly on the Character String items): Finds all records starting with the specified value.
For example: When a generic search is performed on "Smith" (for the NAME item), all records whose Name item starts with "Smith" will match the search. Therefore, the record containing "Smither" will correspond to the search (HFound returns True).
Exact-match search: Finds all records that exactly correspond to the specified value.
For example: When an exact-match search is performed on "Smith" (for the NAME item), HFound returns True for the records whose item exactly matches "Smith".
Examples or searches performed on CUSTOMER file sorted by name:


Sought value	Options	HSeekLast sets the position on the record	HFound returns	HOut returns	Explanations
Durand		6	True	False	Durand exists. The beginning of data file was not reached yet.
Dupuis		5	False	False	Dupuis does not exist. Positioning on the first lower value (Moore). The beginning of data file was not reached yet.
Moor	hGeneric	5	True	False	Moor does not exist but the search is generic, and Moore is found (among others). The beginning of data file was not reached yet.
Moor		The record was not found (no move)	False	False	Moor does not exist. The beginning of data file was not reached yet.
Bernard		The record was not found (no move)	False	True	Bernard does not exist. Positioning on the first lower value (this value does not exist): The beginning of data file was reached.

Performing a search on a composite key

Several methods can be used to perform a search on a composite key:

Using a list of values.
Using HBuildKeyValue.
Using HConvert.

Using a list of values

The following syntax is used to perform a search on a composite key:

HSeekLast(<File name>, <Name of composite key>, ...
[<Search value of first element of composite key>,
<Search value of first element of composite key>, ...])

Example:

// Find the record
HSeekLast(Customer, LastName_FirstName, ["Moore", "Vince"])

To perform generic searches on a composite key, all the components of composite key must be Text components. Otherwise, an exact-match search is performed.

Search on an array item

The search is performed on the first array element (element whose subscript is 1). To perform a search on the other array elements, use the filters or queries.

Search and filter

If a filter is enabled (HFilter), the search takes the filter into account.

If a filter is enabled, the filter is ignored by the search.

Locks

The locks apply only when a record was found.

By default (no lock mode specified in <Options>), the record is not locked.

If a lock is requested (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 set by HStartLock, use the hLockNo constant.

Reminder: A locked record can be unlocked by HUnlockRecNum.

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

Component : wd250hf.dll