|
|
|
|
|
|
|
|
|
|
- Generic search/Exact-match search
- Search performed on a key item or on a non-key item
- Performing a search on a composite key
- Search and filter
- Search on an array item
- Looping through records that match a condition
- Exact-match search in Access
- Locks
- Optimizing iterations
<Source>.ReadSeekLast (Function) In french: <Source>.LitRechercheDernier
 Not available with this kind of connection
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.
 The management of locks is not available.
 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.
The management of locks is not available.
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.
// 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.
<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 | | | hGeneric | Generic search (see the Notes)
An exact-match search is performed by default (constant not specified). | | hKeepFilter | The 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.
By default, the iteration performed after <Source>.ReadSeekLast ignores the filter. | | hLimitParsing | The 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. | | hLockNo | No lock: the record can be read or modified by another application during the reading.
| | hLockReadWrite | Lock in read/write mode: the record currently read cannot be read or modified by another application.
The lock mode is ignored if a query is used.
| | hLockWrite | Lock 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.
| | hNoRefresh | |
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:
 | | | | | | | Search value | Options | <Source>.ReadSeekLast positions on the record. | HFound returns | HOut returns | Explanations | | Davon | | 6 | True | False | Davon exists.
The beginning of data file was not reached yet. | | Davo | | 5 | False | False | Davo 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. |
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"])
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
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.
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:
This page is also available for…
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|