PC SOFT

ONLINE HELP
 WINDEVWEBDEV AND WINDEV MOBILE

Home | Sign in | English EN

WINDEV
WindowsLinuxUniversal Windows 10 AppJavaReports and QueriesUser code (UMC)
WEBDEV
WindowsLinuxPHPWEBDEV - Browser code
WINDEV Mobile
AndroidAndroid Widget iPhone/iPadIOS WidgetApple WatchMac CatalystUniversal Windows 10 App
Others
Stored procedures
Positions on the last record of a data file whose value for a specific item is less than or equal to a sought value (exact-match search). The record is read and the corresponding HFSQL variables are updated.
In most cases, <Source>.ReadSeekLast sets the position in the data file to loop through the records that match a condition. <Source>.ReadPrevious is used to read the previous record corresponding to the condition.
Several cases may occur after the call to <Source>.ReadSeekLast:
  • a record corresponding to the condition was found, locked (if necessary) and loaded in memory: <Source>.Found returns True.
    PHP The management of locks is not available.
    Java Access by JDBC: The management of locks is not available for databases accessed by JDBC.
  • the data file is empty or there is no record corresponding to the condition: no reading is performed and <Source>.Out returns True.
  • the function tries to lock a record that is already locked in read-only: no read operation is performed, HErrorLock is set to True and <Source>.Out returns True.
    PHP The management of locks is not available.
    Java Access by JDBC: The management of locks is not available for databases accessed by JDBC.
This function can be used with the data files, HFSQL views or queries.
Remark: the search can be canceled by <Source>.CancelSeek.
Example
// Find the last record for which
// the Customer name is MOORE
Customer.ReadSeekLast(NAME, "MOORE")
// Find all the customers whose turnover is less than a specific value
Customer.ReadSeekLast(Turnover, X)
WHILE NOT Customer.Out()
AddCustomerList()
Customer.ReadPrevious(Turnover)
END
Syntax
<Result> = <Source>.ReadSeekLast(<Item> , <Sought value> [, <Options>])
<Result>: Boolean
  • True if the record was found (corresponds to the value of <Source>.Found).
  • False if a problem occurs. This problem can be caused by:
<Source>: Type corresponding to the specified source
Name of data file, HFSQL view or query used.
<Item>: Character string
Name of item on which the search will be performed. This item can be a search key or not.
Hyper File 5.5 The search can only be performed on a key item.
<Sought value>: Type corresponding to the value
Value of the sought item.
<Options>: Optional constant (or combination of constants)
Used to configure:
  • the lock mode applied to the sought record.
  • the type of search performed.
hForwardOnly
Native Connectors (Native Accesses) Constant that can only be used with Native Accesses.
Optimizes simple iterations that do not use the following features:
  • Reading the previous record.
  • Modifying a record.
  • Saving position.
If one of these features is used, the result may differ from the expected one.
For example, this constant can be used to populate a Table control programmatically.
hGenericGeneric search (see the Notes)
An exact-match search is performed by default (constant not specified).
hKeepFilterThe filter set by <Source>.Filter will be taken into account, even if the search key is not optimized for the filter. Reminder: <Source>.Filter returns the search key optimized for the filter.
Caution: in this case, performance issues may arise for large files.
Hyper File 5.5 This variable cannot be used.
By default, the iteration performed after <Source>.ReadSeekLast ignores the filter.
hLimitParsingThe iteration will stop when the last searched value is found. The current record will correspond to this last record found.
<Source>.Found will return False and <Source>.Out will return True.
This constant is used to optimize the search speed in Client/Server mode.
hLockNoNo lock: the record can be read or modified by another application during the reading.
PHP This constant is not available.
Java Access by JDBC: This constant is not available.
hLockReadWriteLock in read/write: the record currently read cannot be read or modified by another application.
The lock mode is ignored if a query is used.
OLE DB Lock in write-only. Operating mode equivalent to the hLockWrite constant.
PHP This constant is not available.
Java Access by JDBC: This constant is not available.
hLockWriteLock in write mode: the record currently read can be read by another application but it cannot be modified.
The lock mode is ignored if a query is used.
PHP This constant is not available.
Java Access by JDBC: This constant is not available.
hNoRefresh
OLE DBNative Connectors (Native Accesses) <Source>.ReadSeekLast does not refresh the content of the table or query. If possible, the query is not re-run. All the saved positions are stored.
PHP The management of locks is not available.
Java Access by JDBC: The management of locks is not available for databases accessed by JDBC.
OLE DBNative Connectors (Native Accesses) Lock options will have no effect if the OLE DB provider or Native Connector (also called Native Access) does not support locks.
OLE DB The lock mode specified by <Source>.ReadSeekLast will remain effective during the calls to <Source>.ReadPrevious and <Source>.ReadNext.
To change the lock mode, use:
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 that contains "Smither" will match the search (<Source>.Found returns True).
    Remark: For backward compatibility with version 5.5, the generic search of an empty string ("") is equivalent to the use of <Source>.ReadLast.
  • 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), <Source>.Found returns True for the records whose item exactly matches "Smith".
  • Examples of searches on the CUSTOMER data file sorted by name:
Sought valueOptions<Source>.ReadSeekLast positions on the record.HFound returnsHOut returnsExplanations
Davon6TrueFalseDavon exists.
The beginning of data file was not reached yet.
Davo5FalseFalseDavo does not exist. Positioning on the first lower value (Moore).
The beginning of data file was not reached yet.
MoorhGeneric5TrueFalseMoor does not exist but the search is generic, and Moore is found (among others).
The beginning of data file was not reached yet.
MoorThe record was not found (no move).FalseFalseMoor does not exist.
The beginning of data file was not reached yet.
BernardThe record was not found (no move).FalseTrueBernard does not exist.
Positioning on the first lower value (this value does not exist): the beginning of data file was reached.

Search performed on a key item or on a non-key item

The search can be performed on a key item or a non-key item.
If the search is performed on a key item:
  • the search is fast and the result is sorted.
  • if the iteration is continued by <Source>.ReadPrevious, the next records will correspond to the values less than or equal to the search value. In this case, <Source>.Out must be checked after each read operation to find out whether the beginning of the file has been reached.
If the search is performed on a non-key item:

Performing a search on a composite key

Several methods can be used to perform a search on a composite key:
1. Using a list of values
The following syntax is used to perform a search on a composite key:
HReadSeekLast(<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
Customer.ReadSeekLast(LastName_FirstName, ["MOORE","Vince"])

2. Using <Source>.BuildKeyValue
Example:
bufSoughtVal is Buffer = Customer.BuildKeyValue(LastName_FirstName, sLastName, sFirstName)
Customer.ReadSeekLast(LastName_FirstName, bufSoughtVal)
WHILE Customer.Found()
Customer.Delete()
Customer.Previous(LastName_FirstName)
END
Hyper File 5.5 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 and filter

If a filter is enabled (<Source>.Filter), the filter is taken into account by the search only if the key used is identical.
To apply this filter in the rest of the iteration (even if the search key is not optimized for the filter), use the hKeepFilter constant.
Hyper File 5.5 If a filter is enabled, the filter is ignored by the search.

Search on an array item

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

Looping through records that match a condition

In most cases, <Source>.ReadSeekLast sets the position in the data file to loop through the records that match a condition. <Source>.ReadNext and <Source>.ReadPrevious are used to read the next and previous matching records.
To ignore the search while going to the next or previous record, use one of the following functions:
WINDEVWEBDEV - Server codeReports and QueriesUser code (UMC)External languageAjaxStored proceduresOLE DB

Exact-match search in Access

To perform an exact-match search on an ACCESS database, it is recommended to use NoSpace if there are space characters at the end of the sought value.
WINDEVWEBDEV - Server codeReports and QueriesUniversal Windows 10 AppiPhone/iPadIOS WidgetMac CatalystUser code (UMC)External languageAjaxHFSQLHFSQL Client/ServerStored proceduresHyper File 5.5OLE DBNative Connectors (Native Accesses)

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 erquested (hLockWrite or hLockReadWrite constant), the record will be read only if this record is not already locked.
Reminder: A locked record can be unlocked by <Source>.UnlockRecNum.
OLE DBNative Connectors (Native Accesses) Lock options will have no effect if the OLE DB provider or Native Connector (also called Native Access) does not support locks.
WINDEVWEBDEV - Server codeReports and QueriesUniversal Windows 10 AppiPhone/iPadIOS WidgetMac CatalystUser code (UMC)AjaxHFSQLStored procedures

Optimizing iterations

To optimize the first iterations on a data file, use <Source>.Optimize on this data file.
Component: wd280hf.dll
Minimum version required
  • Version 25
This page is also available for…
Comments
Click [Add] to post a comment