<Source>.ReadLast (Function)

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Managing databases

HFSQL functions

Prefix syntax

ReadLast

Presentation

Example

Read operation according to a key item or not

Locks

Memos

Password

Miscellaneous

See also

<Source>.ReadLast (Function)

In french: <Source>.LitDernier

Not available with this kind of connection

Sets the position on the last record of a data file according to a browse item. The record is read and the HFSQL variables are updated (e. g. Customer.Name, in other words, the Name item in the Customer data file).

The highest value in the browse item is read (for more details, see remarks).

In most cases, <Source>.ReadLast is used to set the position in the data file in order to perform a read loop with <Source>.ReadPrevious.

Several cases may occur after the call to <Source>.ReadLast:

the data file is empty or no record corresponds to the filter (defined by <Source>.Filter): 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 returns 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.

Example

Customer.ReadLast(Name)
WHILE Customer.Out() = False
// Process the record
Customer.ReadPrevious(Name)
END

Syntax

<Result> = <Source>.ReadLast([<Browse item> [, <Options>]])

<Result>: Boolean

Corresponds to:
False if an error occurred. In this case, HError returns an integer other than 0. HErrorInfo returns more details about the error. The record is not read.
the value of <Source>.Found in the other cases (the record can be read, even if <Result> returns False).

<Source>: Type corresponding to the specified source

Name of data file, HFSQL view or query used.

<Browse item>: Optional character string

Name of item used to loop through the data file or the view. If this name is not specified, <Source>.ReadLast will use:
For a data file: the last browse item used on this file by the last function for HFSQL management (starting with the letter H). If this item does not exist, the best browse item is automatically used.
For a query: the ORDER BY of the query (if it exists), otherwise the last item used.
For a view: the sort item of the view (if it exists), otherwise the last item used.

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

Configures:
the lock set on the record read by <Source>.ReadLast.
whether the filter that was defined must be taken into account.
hForwardOnly
Constant that can only be used with Native Connectors (also called 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 when looping through records to populate a Table control programmatically.
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 data files.
This variable cannot be used.
hLockNo No lock: the record can be read or modified by another application during the reading.

This constant is not available.

Access by JDBC: This constant is not available.
hLockReadWrite Lock in read/write: the record currently read cannot be read or modified by another application.

Lock in write-only. Operating mode equivalent to the hLockWrite constant.

This constant 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 by another application.

This constant is not available.

Access by JDBC: This constant is not available.
hNoRefresh
<Source>.ReadLast 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.
The lock mode specified by <Source>.ReadLast will remain effective during the calls to <Source>.ReadPrevious and <Source>.ReadNext.
To modify the lock mode, you must use:
<Source>.ReadSeekFirst or <Source>.ReadSeekLast,
<Source>.ReadFirst or <Source>.ReadLast.
<Source>.LockRecNum or <Source>.UnlockRecNum.
For Native Oracle Connector, a different lock 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 with the sqlCommit or sqlRollBack constant).
The lock options are ignored. Use locking read functions (HReadLastLock) kept for backward compatibility.
The lock options are not available.
Access by JDBC: The management of locks is not available for databases accessed by JDBC.

Remarks

Read operation according to a key item or not

If the item is a key, <Source>.ReadLast reads the record with the greatest key value. The sort order is the one that was specified in the analysis for this key. If duplicates are found, <Source>.ReadLast reads the last "duplicate" record according to the sequence of record numbers.

If the item is not a key, <Source>.ReadLast reads the last active record. When browsing the data file, the records will be sorted according to their record number.
In this case, the selected browse item will appear in red in the code editor and a warning will be displayed in the "Code" pane.

Remark: The automatic completion proposes the key items only.

Locks

By default (<Options> not specified), 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.

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

Memos

The memos associated with the record can be automatically read (or not) when reading the record. <Source>.SetMemo is used to customize this automatic read operation.

If the memos are supported, the associated text memos are read when the record is read. The binary memos are read only when they are explicitly used (<Source>.ExtractMemo).

Password

If <Source>.ReadLast is the first function that handles the specified data file, the password is checked when the opening data file. If the password is incorrect, HErrorPassword returns True and <Source>.Out is set to True.

Miscellaneous

The current record number is returned by <Source>.RecNum.
<Source>.ChangeKey is used to modify the search key while remaining positioned on the current record.
To optimize the first iterations on a data file, use <Source>.Optimize on this data file.
This function replaces HReadLastLock and HReadLastNoLock, which were kept for compatibility with WINDEV 5.5.

Component: wd270hf.dll