HReadSeek (Function)

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Generic search/Exact-match search
Exact-match search in Access
Performing a search on a composite key
Search on an array item
Search and filter
Looping through records that match a condition
Optimizing iterations
Previous versions

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HReadSeek (Function)

In french: HLitRecherche

Not available with this kind of connection

Positions on the first file record whose value for a specific item is greater than or equal to a sought value (generic search). The record is read and the corresponding HFSQL variables are updated.

In most cases, HReadSeek sets the position in the data file to loop through the records that match a condition. HReadNext is used to read the next record corresponding to the condition.Several cases may occur after the call to HReadSeek:

a record corresponding to the condition was found, locked (if necessary) and loaded in memory: HFound returns True.
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 HOut returns True.

This function can be used with the data files, HFSQL views or queries.

Remarks:

By default, HReadSeekFirst and HReadSeekLast are used to perform exact-match searches.
By default, HReadSeek is used to perform a generic search on strings. This search is not generic on integers, reals, dates, currencies, etc.

Example

See additional examples

// Find the first record
// for which the CUSTOMER name is MOORE
HReadSeek(CUSTOMER, NAME, "MOORE")
IF HFound() THEN
Trace("Customer MOORE found")
ELSE
Trace("Customer MOORE not found")
END

Syntax

<Result> = HReadSeek(<Data file> , <Item> , <Search value> [, <Options>])

<Result>: Boolean (optional)

Corresponds to:
True if the sought record was found and read. The file buffer is loaded with the data of the record found. In this case, HError is set to 0 and HFound is set to True.
False in the following cases:
error while accessing the file (unable to read for example). HError returns an error code. HErrorInfo returns more details about the error. In this case, HFound cannot be used.
the access to the file was performed but no record was found. In this case, HError is set to 0 and HFound is set to False.
Caution: In this case, the file buffer cannot be used.

<Data file>: Character string

Name of data file, HFSQL view or query used.

<Item>: Character string

Name of item on which the search will be performed.
For an exact-match search, this parameter can correspond to a non-key item.
To perform generic searches on a composite key, all the components of the composite key must be text components. Otherwise, an exact-match search is performed.

<Search 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.
hIdentical Exact-match search (see the Notes)
A generic search is performed by default (constant not specified).
Access by JDBC: This constant is not available.
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 search key optimized for the filter.
Caution: in this case, performance issues may arise for large files.
This variable cannot be used.
hLimitParsing
The iteration will stop when the last searched 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.
This constant is recommended when performing a simple search (without looping through the found elements).
This constant is not available.
hLockNo No lock: the record can be read or modified by another application during the reading.
The management of locks is not available.
Access by JDBC: This constant is not available.
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.
Lock in write-only. Operating mode equivalent to the hLockWrite constant.
The management of locks is not available.
Access by JDBC: This constant is not available.
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.
The management of locks is not available.
Access by JDBC: This constant is not available.
hNoRefresh
HReadSeek does not refresh the content of the table or query. If possible, the query is not re-run. All the saved positions are stored.
The lock options will have no effect if the locks are not supported by the OLE DB provider or by the Native Connector.
Access by JDBC: Locks cannot be managed in databases accessed by JDBC.

Remarks

Generic search/Exact-match search

A generic search or an exact-match search will be performed according to <Sought value>.

Generic search: search for all the records that start with the specified value
To perform a generic search, the desired value must be specified in <Sought value>.
Remark: For backward compatibility with WINDEV 5.5, the generic search of an empty string ("") is equivalent to the use of HReadFirst.
Exact-match search: search for all the records that exactly correspond to the specified value.
To perform an exact-match search, the size of the search argument must be exactly the same as the size of the key. To perform an exact-match search, you also have the ability to use the hIdentical constant.
To perform an exact-match search, you also have the ability to use HReadSeekFirst.

Caution: If you are using Hyper File 5.5 files or files in Hyper File 5.5 format migrated to HFSQL Classic, the implementation of generic searches and exact-match searches may change. For more details, see the Hyper File 5.5 and HFSQL Classic: How to manage the space characters in the searches? table

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.

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,

1. Using a list of values

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

HReadSeek(<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
HReadSeek(CUSTOMER, LASTNAME_FIRSTNAME, ["MOORE","Vince"])

WHILE HFound(CUSTOMER)
// Process
HReadNext(CUSTOMER, LASTNAME_FIRSTNAME)
END

2. Using HBuildKeyValue

If the sought item is a composite key, the value to find can be built by HBuildKeyValue.

To perform generic searches on a composite key, all the components of the 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 with index 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 filter is taken into account by the search only if the key used is identical.

Looping through records that match a condition

In most cases, HReadSeek sets the position in the data file to loop through the records that match a condition. HReadNext and HReadPrevious 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:

Optimizing iterations

To optimize the first iterations on a data file, use HOptimize on this data file.

Previous versions

This function replaces HReadSeekLock and HReadSeekNoLock, which were kept for compatibility with WINDEV 5.5.

Component: wd300hf.dll