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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.

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Each Recital table can have one or more data dictionaries to provide a central repository for constraints and other metadata. 

Here's how to set up field validation based on dynamic values from another table.

Using the products.dbf table from the southwind sample database, validation can be added to the categoryid field to ensure it matches an existing categoryid from the categories.dbf table.
open database southwind
alter table products add constraint;
(categoryid set check rlookup(products.categoryid,categories))
The rlookup() function checks whether an expression exists in the index (master or specified) of the specified table .  An attempt to update categoryid with a value not in the list will give an error: Validation on field 'CATEGORYID' failed.

If you have access to the Recital Workbench, you can use the modify structure worksurface to add and alter your dictionary entries, including a customized error message if required.

validation


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There is a good article here this describes agile software development techniques. This is what we have always been doing but it's nice to see it defined formally.

We use this technique ourselves on our development portal.
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Recital is a dynamic programming language with an integrated high performance database particularly well suited for the development and deployment of high transaction throughput applications.  Recital 10 further enhances Recital with extensive features and functionality to facilitate its use in fault tolerant high availability systems. Much of the development of Recital 10 was concentrated on performance optimizations and cluster aware functionality to provide an application platform that can be scaled as needed without any application changes. 

Key features of Recital 10 include:

  • Cluster aware database engine that works transparently with drbd, heartbeat, glusterfs and samba
  • High degree of fault tolerance with self healing indexes
  • Massive performance improvements 
  • Extensive internals overall and modernization with superior object-oriented capabilities
  • Chronological data versioning with database timelines
  • SmartQuery caching
  • Database Administration Tools
  • Code and Data Profiling
  • Better integration with unix/linux command shell
  • Incorporates a range of new built-in functions compatible with those in the PHP core libraries
  • Built-in support for outputting data in HTML, XML, and JSON format
  • Seamless SQL command integration into the Recital scripting language
  • Much improved Microsoft FoxPRO language compatibility
  • Numerous extensions and improvements (see below for details)
  • Very large file support (2^63)
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Recital on Linux 64 bit requires certain 32 bit libraries for installation and/or operation.  It also needs to be installed and configured as the root user, or using sudo for those systems without a root login.

For systems that do not have the xterm libraries installed, please install these to use xterm, or set the DB_TERM environment variable to start Recital from a terminal:
DB_TERM=gnome-terminal; export DB_TERM

This setting can be added to the /opt/recital/conf/recital.conf (text) file to make it available system-wide.

Please note that the Recital ODBC Driver for Linux requires a 32 bit ODBC Driver Manager.

Centos 6:

sudo yum install zlib-devel.i686 pam-devel.i686
(and accept dependencies)
Then run the installer in text mode
sudo ./recital-10.0.3-linux32.bin --mode text
Run Recital with sudo the first time, to set the system filetype compatiblity settings.
sudo recital
After saving the compatibility settings, quit to exit, then run Recital as your preferred user.
> quit
$ recital

RedHat / Fedora family:

sudo yum install zlib-devel.i686 pam.i686
(and accept dependencies)
Then run the installer in text mode
sudo ./recital-10.0.3-linux32.bin --mode text
Run Recital with sudo the first time, to set the system filetype compatiblity settings.
sudo recital
After saving the compatibility settings, quit to exit, then run Recital as your preferred user.
> quit
$ recital

 Ubuntu family:

sudo apt-get install ia32-libs 
In later versions of Ubuntu, ia32-libs is obsolete. The following package should be installed:
sudo apt-get install lib32z1
Ubuntu 12.04 and above also require the following:
sudo apt-get install libpam0g:i386
Then run the installer in text mode
sudo ./recital-10.0.3-linux32.bin --mode text
Run Recital with sudo the first time, to set the system filetype compatiblity settings.
sudo recital
After saving the compatibility settings, quit to exit, then run Recital as your preferred user.
> quit
$ recital

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I am pleased to finally report that the Centos release of Redhats 5.3 has been built and is available for download from http://www.centos.org/

The highlights of this release can be found at the following URL: http://www.redhat.com

The main areas of interest in my opinion excluding critical secirty fixes are:

  • Updated hardwaresupport support for the new Intel Core i7 (Nehalem) chips
  • Beefed up virtualiseation support increasing CPU and Ram limits of Virtual machines.
  • Inclusion of the fully open sourced OpenJDK. This makes Red Hat Enterprise Linux 5.3 the first enterprise-ready solution with a fully open source Java stack when combined with JBoss Enterprise Application Platform.


For those who already have Centos 5.2 installed you can simply receive the update via Yum.

Before you do the following, check that  you do not have 3rd party repo's and the Centos-testing repo enabled.

You can display the currently enabled repo's using the following command.

$ yum repolist



Then as root at the prompt type:

$ yum update

 

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If you use Eclipse Ganymede with large projects on linux you may run out of memory. To prevent this happening, you can specify the amount of memory to be allocated to Eclipse in the eclipse.ini file which is located in the eclipse directory.

Specifying this seems to reslove the problem:

-Xmx512m
-XX:MaxPermSize=512m

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Use iptables to restrict access to Recital Web only from localhost.

iptables -I INPUT -j ACCEPT -p tcp --destination-port 8001 -i lo
iptables -A INPUT -j DROP -p tcp --destination-port 8001 -i eth0


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We are pleased to announce the release of Recital 10.0.3.

Here is a brief list of features and functionality that you will find in the 10.0.3 release.

  • New Commands:
    - SET TMPNAMPATH ON|OFF
    - REMOVE TABLE
  • New Functions:
    - CURSORGETPROP()
    - CURSORSETPROP()
    - CURVAL()
    - GETFLDSTATE()
    - OLDVAL()
    - TABLEREVERT()
    - TABLEUPDATE()
    - SETFLDSTATE()
  • Enhanced Functions:
    - TMPNAM() - additional parameter to specify the return of basename only
    - MAILATTACH() - parameter changed from array to filename to allow directory and file extension to be specified
  • Enhancements:
    - DO level increased from 32 to 64.
  • Fixes:
    - Delay exiting Recital after SYS(3) or SYS(2015)
    - SET SOFTSEEK issue when search key above first record in index
    - Compilation error with REPLACE command after UDF call
    - FETCH INTO memvars error
    - END TRANSACTION at command prompt error
    - ROLLBACK locking error
    - Linux ODBC Driver undefined symbol error
    - RELEASE variable with same name as variable in calling program issue
    - SQLCODE() issue on non-gateway data access
    - Issuing two SQLEXEC() calls error
    - LASTSEQNO() in workareas > 1 error
    - SET RELATION to detail table in workarea 1 issue
    - LIST STATUS on empty table delay
    - SET AUTOCATALOG alias entries error
    - ADD OBJECT in DEFINE CLASS error
    - DEACTIVATE WINDOW error
    - SORT error
    - Other reported bugs
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TIP
The Recital Oracle Gateway requires the Oracle libclntsh.so shared library.  If this file is unknown to ld.so.conf, add it using the ldconfig command. 
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