In this article Barry Mavin, CEO and Chief Software Architect for Recital, details how to work with Triggers in the Recital Database Server.

Overview

A trigger is a special kind of stored procedure that runs when you modify data in a specified table using one or more of the data modification operations: UPDATE, INSERT, or DELETE.

Triggers can query other tables and can include complex SQL statements. They are primarily useful for enforcing complex business rules or requirements. For example, you can control whether to allow a new order to be inserted based on a customer's current account status.

Triggers are also useful for enforcing referential and data integrity.

Triggers can be used with any data source that is handled natively by the Recital Database Engine. This includes Recital, FoxPro, FoxBASE, Clipper, dBase, CISAM, and RMS data,

Creating and Editing Triggers

To create a new Trigger,  right-click the Procedures node in the Databases tree of the Project Explorer and choose Create. To modify an existing Trigger select the Trigger in the Databases Tree in the Project Explorer by double-clicking on it, or select Modify from the context menu. By convertion we recommend that you name your Stored Procedures beginning with "sp_xxx_", user-defined functions with "f_xxx_", and Triggers with "dt_xxx_", where xxx is the name of the table that they are associated with.

Associating Triggers with a Table

Once you have written your Triggers as detailed above you can associate them with the operations performed on a Table by selecting the Table tab.

The Tables tab allows you to select a Trigger procedure by clicking on the small button at the right of the Text field.

Types of Triggers

As can be seen from the Tables tab detailed below, The Recital Database Server handles 6 distinct types of Triggers.

Open Trigger

The Open Trigger is called after is a table is opened but before any operations are performed on it. You can use this trigger to record a log of table usage or provide a programmable means of checing security. If the Trigger procedure returns .F. (false), then the table is not opened. You can use a TRY...CATCH block around the associated command to inform the user.

Close Trigger

The Close Trigger is called just prior to a table being closed. In this trigger you may find it useful to get transaction counts by using the IOSTATS() built-in 4GL function, and record these values in a transaction log.

Update Trigger

The Update Trigger is called prior to a record update operation being performed. You can use this trigger to perform complex application or data specific validation. If the Trigger procedure returns .F. (false), then the record is not updated. You can use inform the user from within the Trigger procedure the reason that the data cannot be updated.

Delete Trigger

The Delete Trigger is called prior to a record delete operation being performed. You can use this trigger to perform complex application or data specific validation such as cross-table lookups e.g. attempting to delete a customer recortd when there are still open orders for that specific customer. If the Trigger procedure returns .F. (false), then the record is not deleted.

Insert Trigger

The Insert Trigger is called prior to a record insert (append) operation being performed. You can use this trigger to perform such tasks as setting up default values of columns within the record. If the Trigger procedure returns .F. (false), then the record is not inserted.

Rollback Trigger

The RollbackTrigger is called prior to a rollback operation being performed from within a form. If the Trigger procedure returns .F. (false), then the record is not rolled back to its original state.

Testing the Trigger

To test run the Trigger, select the Trigger in the Databases Tree in the Project Explorer by double-clicking on it. Once the Database Administrator is displayed, click the Run button to run the Trigger.

The Openfiler NAS/SAN Appliance (NSA) is a Storage Management Operating System / NAS Appliance distribution. It is powered by the Linux 2.6 kernel and Open Source applications such as Apache, Samba, LVM2, ext3, Linux NFS and iSCSI Enterprise Target. Openfiler combines these ubiquitous technologies into a small, easy to manage solution fronted by a powerful web-based management interface. Openfiler allows you to build a Network Attached Storage (NAS) and/or Storage Area Network (SAN) appliance, using industry-standard hardware, in less than 10 minutes of installation time.

Building upon the popularity of server virtualization technologies such as VMware, Virtual Iron, and Xen, Openfiler can also be deployed as a virtual machine instance or on  a bare metal machine.

This deployment flexibility of Openfiler ensures that storage administrators are able to make the best use of system performance and storage capacity resources when allocating and managing networked storage in a multi-platform environment.

Openfiler is ideally suited for use with High Availability Recital applications as it incorporates:

• Heartbeat cluster manager
• drbd disk replication
• CIFS
• NFS
• Software and hardware RAID
• FTP
• rsync
• HTTP/DAV
• iSCSI
• LVM2
• Multiple NIC bonding for High Availability
• Powerful web-based GUI

 

IF type( _session["state"] ) != "U"
    m_state = _session["state"]
    RESTORE DATASESSION FROM m_state
ELSE
    // open up your tables for the first time 
ENDIF

SAVE DATASESSION TO m_state
_SESSION["state"] = m_state

Hdparm can be used to view or set many hardware characteristics of IDE or SATA drives including optical drives (and even some SCSI drives).  For example, the read-lookahead feature can be enabled or disabled.  Also of interest is that the on board write caching can be disabled.  This may or may not be of use when trying to optimize the writing of data to the drive especially when the operating system and/or file system itself may also perform write caching.

Some options of hdparm are dangerous and are generally listed as such in the man page.

Hdparm is available from SourceForge and there is even a version for Windows.