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 southwindThe 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.
alter table products add constraint;
(categoryid set check rlookup(products.categoryid,categories))
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.



I am a fan of the previous incarnation of the PlugComputer so I was excited to see that Marvell have unveiled a new PlugComputer dubbed imaginatively "PlugComputer 3.0."
PlugComputer 3.0 Features:
Smaller sleeker design,
More powerful CPU - 2gz Armanda 300 CPU,
120GB 1.8-inch SATA hard drive,
Wifi,
Bluetooth,
10/100/1000 wired Ethernet,
USB 2.0.
512MB of RAM
512MB of Flash memory
I for one would like to see an additional Ethernet port added to increase application flexibility, for some applications where you are using clustered plugs or even for routing, having multiple Ethernet ports is a must.
Even without multiple ethernet ports, these low power consumption devices really could have a place in SME environments, replacing large cumbersome legacy hardware with compact Linux plug servers.
More information about the PlugComputer can be found here
When you start the loadbalancer.org appliance you will see the following:
Default login:
Username: root
Password: loadbalancer
Access to webclient from an external client is:
http://192.168.1.129:9080
http://192.168.1.129:9443
You can access the web administrator using the IP and ports described onscreen.
For the sri lanka porject we are looking for performance and the network diagram indicates we are happy to have the cluster on the same subnet as the rest of the network.
Direct routing is the fasted performance possible, it has the advantage over NAT that the Loadbalancer does not become a bottleneck for incoming and outgoing packets. With DR the loadbalancer simply examines incoming packets and the servers to route the packets directly back to the requesting user.
The web interfaceis the only way to fully configure the loadbalancer vm. The console tool lbwizard will get it initiallised and any further configurations can then be done via the webinterface.
Using lbwizard for the Sri lanka configuration follow these steps.
On the first Loadbalancer:
//Start
Is this unit part for a HA Pair?
YES
Have you already setup the Slave?
NO
Is this a one-armed configuration?
YES
Enter the IP Address for the interface eth0?
Enter IP address you wish to be assigned to the SLAVE loadbalancer.
Enter the netmask for interface eth0?
Enter netmask for the subnet.
Enter the Floating IP adrress?
Enter the IP address that will be IP assosiacted the the HA-pair of loadbalancers.
//Finish
On the 2nd loadbalancer VM, run the lbwizard.
//Start
Is this unit part of an HA-Pair?
YES
Have you already set up the Slave?
YES
What is the slave units UP address?
Enter the IP which you entered when configuring the other loadbalancer VM.
Is this a one-armed configuration?
YES
Enter the IP Address for the interface eth0?
Enter the IP that will be assigned to the MASTER loadbalancer
Enter the netmask for interface eth0?
Enter the subnet netmask.
Enter the Floating IP address?
Enter the IP address that will be IP assosiacted the the HA-pair of loadbalancers.
Enter the address of the default gateway?
Enter the deafult gateway for the subnet.
Enter the IP of the nameserver?
Enter the dns server.
Enter the port for the first Virtual server?
Enter 22 for ssh
Enter the IP address of the first real server?
Enter the real IP of the first appserver
//Finish
Now this is complete we need to go to the web admin interface to configure the 2nd Real Server. As the lbwizard program will only allow you to configure 1 real server.
Now login to the web admin using the default password:
username: loadbalancer
password: loadbalancer
Note: Connect to the IP you have now set for your master loadbalancer
Goto the edit configuration tab
Now click add a real server:
Enter a label
IP address of the server plus the port of the service i.e. 192.168.1.125:22
Edit Configuration -> Virtual Servers
persistancte -> NO
Scheduler-> LC
LC - Least-Connection: assign more jobs to real servers with
fewer active jobs.
Service to check -> custom1
Check port -> 22
Forwarding Method -> DR
Feedback Method -> Agent
Arp Problem when using DR
Every real server must be configured to respond to the VIP address as well as the RIP
address.
You can use iptables (netfilter) on the real server to re-direct incoming packets destined for the virtual
server IP address.
This is a simple case of adding the following command to your start up script (rc.local):
//replace 10.0.0.21 with the Virtual Server IP
iptables -t nat -A PREROUTING -p tcp -d 10.0.0.21 -j REDIRECT
chkconfig iptables on
SET DATADIR TO [ <directory> ]This command is used to specify a directory where database tables, memos, indexes, and dictionary files are located. When a table is being opened this directory is searched first before the current directory and the file search path to locate the table and its associated files. This allows the database tables to be relocated to a different file system without the need to change an existing application.
The following example connects to a Recital ODBC datasource, executes a query then outputs all the results from the resultset.
<?php
$sql = "select country from customers limit 10";
$conn = odbc_connect('Recital ODBC test', '?', '?');
$rs = odbc_exec($conn, $sql);
odbc_result_all($rs);
odbc_close($conn);
?>
Output:
<table><tr><th>Country</th></tr>
<tr><td>Germany </td></tr>
<tr><td>Mexico </td></tr>
<tr><td>Mexico </td></tr>
<tr><td>UK </td></tr>
<tr><td>Sweden </td></tr>
<tr><td>Germany </td></tr>
<tr><td>France </td></tr>
<tr><td>Spain </td></tr>
<tr><td>France </td></tr>
<tr><td>Canada </td></tr>
</table>
For information on installing and configuring the Recital Universal ODBC Driver and creating and modifying datasources, please see the Documentation section of this web site.
Note: Use of ? for the username and password on the local server is dependent on DB_LOCAL_LOGIN being enabled.
In this article Barry Mavin, CEO and Chief Software Architect for Recital provides details on how to use the Recital Universal .NET Data Provider with the Recital Database Server.
Overview
A data provider in the .NET Framework serves as a bridge between an application and a data source. A data provider is used to retrieve data from a data source and to reconcile changes to that data back to the data source.
Each .NET Framework data provider has a DataAdapter object: the .NET Framework Data Provider for OLE DB is the OleDbDataAdapter object, the .NET Framework Data Provider for SQL Server is the SqlDataAdapter object, the .NET Framework Data Provider for ODBC is the OdbcDataAdapter object, and the .NET Framework Data Provider for the Recital Database Server is the RecitalDataAdapter object.
The Recital Universal .NET Data Provider can access any data sources supported by the Recital Database Server. It is not restricted to only access Recital data. It can be used to access server-side ODBC, JDBC and OLE DB data sources also.
Core classes of the Data Provider
The Connection, Command, DataReader, and DataAdapter objects represent the core elements of the .NET Framework data provider model. The Recital Universal .NET Data Provider is plug compatible with the .NET Framework Data Provider for SQL Server. All SQL Server classes are prefixed with "Sql" e.g. SqlDataAdaptor. To use the Recital Universal Data Adaptor, simply change the "Sql" prefix to "Recital" e.g. RecitalDataAdaptor.
The following table describes these objects.
| Object | Description |
|---|---|
| RecitalConnection | Establishes a connection to a specific data source. |
| RecitalCommand | Executes a command against a data source. |
| RecitalDataReader | Reads a forward-only, read-only stream of data from a data source. |
| RecitalDataAdapter | Populates a DataSet and resolves updates with the data source. |
Along with the core classes listed in the preceding table, a .NET Framework data provider also contains the classes listed in the following table.
| Object | Description |
|---|---|
| RecitalTransaction | Enables you to enlist commands in transactions at the data source. |
| RecitalCommandBuilder | A helper object that will automatically generate command properties of a DataAdapter or will derive parameter information from a stored procedure and populate the Parameters collection of a Command object. |
| RecitalParameter | Defines input, output, and return value parameters for commands and stored procedures. |
The Recital Universal .NET Data Provider provides connectivity to the Recital Database Server running on any supported platform (Windows, Linux, Unix, OpenVMS) using the RecitalConnection object. The Recital Universal .NET Data Provider supports a connection string format that is similar to the SQL Server connection string format.
The basic format of a connection string consists of a series of keyword/value pairs separated by semicolons. The equal sign (=) connects each keyword and its value.
The following table lists the valid names for keyword values within the ConnectionString property of the RecitalConnection class.
| Name | Default | Description |
|---|---|---|
| Data Source -or- Server -or- Servername -or- Nodename |
The name or network address of the instance of the Recital Database Server which to connect to. | |
| Directory | The target directory on the remote server where data to be accessed resides. This is ignored when a Database is specified. | |
| Encrypt -or- Encryption |
false | When true, DES3 encryption is used for all data sent between the client and server. |
| Initial Catalog -or- Database |
The name of the database on the remote server. | |
| Password -or- Pwd |
The password used to authenticate access to the remote server. | |
| User ID -or- uid -or- User -or- Username |
The user name used to authenticate access to the remote server. | |
| Connection Pooling -or- Pool |
false | Enable connection pooling to the server. This provides for one connection to be shared. |
| Logging | false | Provides for the ability to log all server requests for debugging purposes |
| Rowid | true | When Rowid is true (the default) a column will be post-fixed to each SELECT query that is a unique row identifier. This is used to provide optimised UPDATE and DELETE operations. If you use the RecitalSqlGrid, RecitalSqlForm, or RecitalSqlGridForm components then this column is not visible but is used to handle updates to the underlying data source. |
| Logfile | The name of the logfile for logging | |
| Gateway |
Opens an SQL gateway(Connection) to a foreign SQL data source on the remote server.
The gateway can be specified in several formats: |
Populating a DataSet from a DataAdaptor
The ADO.NET DataSet is a memory-resident representation of data that provides a consistent relational programming model independent of the data source. The DataSet represents a complete set of data including tables, constraints, and relationships among the tables. Because the DataSet is independent of the data source, a DataSet can include data local to the application, as well as data from multiple data sources. Interaction with existing data sources is controlled through the DataAdapter.
A DataAdapter is used to retrieve data from a data source and populate tables within a DataSet. The DataAdapter also resolves changes made to the DataSet back to the data source. The DataAdapter uses the Connection object of the .NET Framework data provider to connect to a data source and Command objects to retrieve data from and resolve changes to the data source.
The SelectCommand property of the DataAdapter is a Command object that retrieves data from the data source. The InsertCommand, UpdateCommand, and DeleteCommand properties of the DataAdapter are Command objects that manage updates to the data in the data source according to modifications made to the data in the DataSet.
The Fill method of the DataAdapter is used to populate a DataSet with the results of the SelectCommand of the DataAdapter. Fill takes as its arguments a DataSet to be populated, and a DataTable object, or the name of the DataTable to be filled with the rows returned from the SelectCommand.
The Fill method uses the DataReader object implicitly to return the column names and types used to create the tables in the DataSet, as well as the data to populate the rows of the tables in the DataSet. Tables and columns are only created if they do not already exist; otherwise Fill uses the existing DataSet schema.
Examples in C#:
////////////////////////////////////////////////////////////////////////
// include the references below
using System.Data;
using Recital.Data;
////////////////////////////////////////////////////////////////////////
// The following code example creates an instance of a DataAdapter that
// uses a Connection to the Recital Database Server Southwind database
// and populates a DataTable in a DataSet with the list of customers.
// The SQL statement and Connection arguments passed to the DataAdapter
// constructor are used to create the SelectCommand property of the DataAdapter.
public DataSet SelectCustomers()
{
RecitalConnection swindConn = new
RecitalConnection("Data Source=localhost;Initial Catalog=southwind");
RecitalCommand selectCMD = new
RecitalCommand("SELECT CustomerID, CompanyName FROM Customers", swindConn);
selectCMD.CommandTimeout = 30;
RecitalDataAdapter custDA = new RecitalDataAdapter();
custDA.SelectCommand = selectCMD;
swindConn.Open();
DataSet custDS = new DataSet();
custDA.Fill(custDS, "Customers");
swindConn.Close();
return custDS;
}
////////////////////////////////////////////////////////////////////////
// The following example uses the RecitalCommand, RecitalDataAdapter and
// RecitalConnection, to select records from a database, and populate a
// DataSet with the selected rows. The filled DataSet is then returned.
// To accomplish this, the method is passed an initialized DataSet, a
// connection string, and a query string that is a SQL SELECT statement
public DataSet SelectRecitalRows(DataSet dataset, string connection, string query)
{
RecitalConnection conn = new RecitalConnection(connection);
SqlDataAdapter adapter = new RecitalDataAdapter();
adapter.SelectCommand = new RecitalCommand(query, conn);
adapter.Fill(dataset);
return dataset;
} On entry to the .rsp page.
IF type( _session["state"] ) != "U"m_state = _session["state"]RESTORE DATASESSION FROM m_state
ELSE
// open up your tables for the first timeENDIF
SAVE DATASESSION TO m_state_SESSION["state"] = m_state
lslk lists information about locks held on files with local inodes on systems running linux.
Install it with:
yum install lslk
This guide will assist you in setting up an rsnapshot backup server on your network. rsnapshot uses rsync via ssh to perform unattended backups of multiple systems in your network. The guide can be found on the centos website here.
In this article Barry Mavin explains step by step how to setup a Linux HA (High Availability) cluster for the running of Recital applications on Redhat/Centos 5.3 although the general configuration should work for other linux versions with a few minor changes.