In this article Barry Mavin, CEO and Chief Software Architect for Recital, details on how to use the Client Drivers provided with the Recital Database Server to work with local or remote server-side JDBC data sources.
Overview
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 JDBC Driver provides the same functionality for java applications.
The Recital Universal ODBC Driver provides the same functionality for applications that use ODBC.
Each of the above Client Drivers use a connection string to describe connections parameters.
The basic format of a connection string consists of a series of keyword/value pairs separated by semicolons. The equals sign (=) connects each keyword and its value.
The following table lists the valid names for keyword/values.
| Name | Default | Description |
|---|---|---|
|
Data Source |
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 |
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 | The user name used to authenticate access to the remote server. | |
|
Connection Pooling |
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.
servertype@nodename:username/password-database e.g. oracle@nodename:username/password-database mysql@nodename:username/password-database postgresql@nodename:username/password-database -or- odbc:odbc_data_source_name_on_server oledb:oledb_connection_string_on_server jdbc:jdbc_driver_path_on_server;jdbc:Recital:args |
To connect to a server-side JDBC data source, you ue the gateway=value key/value pair in the following way.
gateway=jdbc:jdbc_driver_path_on_server;jdbc:Recital:args
You can find examples of connection strings for most ODBC and OLE DB data sources by clicking here.
Example in C# using the Recital Universal .NET Data Provider:
////////////////////////////////////////////////////////////////////////
// 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, and a gateway to
// Recital Southwind database. It then populates a DataTable
// in a DataSet with the list of customers via the JDBC driver.
// The SQL statement and Connection arguments passed to the DataAdapter
// constructor are used to create the SelectCommand property of the
// DataAdapter.
public DataSet SelectCustomers()
{
string gateway = "jdbc:/usr/java/lib/RecitalJDBC/Recital/sql/RecitalDriver;"+
"jdbc:Recital:Data Source=localhost;database=southwind";
RecitalConnection swindConn = new
RecitalConnection("Data Source=localhost;gateway=\""+gateway+"\");
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;
}
Example in Java using the Recital Universal JDBC Driver:
//////////////////////////////////////////////////////////////////////// // standard imports required by the JDBC driver import java.sql.*; import java.io.*; import java.net.URL; import java.math.BigDecimal; import Recital.sql.*; ////////////////////////////////////////////////////////////////////////
// The following code example creates a Connection to the Recital // Database Server, and a gateway to the Recital Southwind database. // It then retrieves all the customers via the JDBC driver. public void SelectCustomers() { // setup the Connection URL for JDBC String gateway = "jdbc:/usr/java/lib/RecitalJDBC/Recital/sql/RecitalDriver;"+ "jdbc:Recital:Data Source=localhost;database=southwind"; String url = "jdbc:Recital:Data Source=localhost;gateway=\""+gateway+"\";
// load the Recital Universal JDBC Driver new RecitalDriver(); // create the connection Connection con = DriverManager.getConnection(url); // create the statement Statement stmt = con.createStatement(); // perform the SQL query ResultSet rs = stmt.executeQuery("SELECT CustomerID, CompanyName FROM Customers"); // fetch the data while (rs.next()) { String CompanyID = rs.getString("CustomerID"); String CompanyName = rs.getString("CompanyName"); // do something with the data... } // Release the statement stmt.close(); // Disconnect from the server con.close(); }
Specifying this seems to reslove the problem:
-Xmx512m -XX:MaxPermSize=512m
The REQUIRE() statement includes and executes the contents of the specified file at the current program execution level.
When a file is included, the code it contains inherits the variable scope of the line on which the include occurs. Any variables, procedures, functions or classes declared in the included file will be available at the current program execution level.
The REQUIRE_ONCE() statement is identical to the REQUIRE() statement except that Recital will check to see if the file as already been included and if so ignore the command.
The full syntax is:
REQUIRE( expC ) REQUIRE_ONCE( expC ) e.g. REQUIRE_ONCE( "myapp/myglobals.prg" )
// determine how many Recital users are on the system
nusers = pipetostr("ps -ef | grep db.exe | wc -l")
- edit the .vmx file and add the following line
uuid.action = "keep"
- set the virtual machine to power off when vmware is stopped. Do not set this to "suspend" or it will not restart on the backup machine.
Many motherboards nowadays have integrated gigabit ethernet that use the Realtek NIC chipset.
The Realtek r8168B network card does not work out of the box in Redhat/Centos 5.3: instead of loading the r8168 driver, modprobe loads the r8169 driver, which is broken as can be seen with ifconfig which shows large amounts of dropped packets. A solution is to download the r8168 driver from the Realtek website and install it using the following steps:
Check whether the built-in driver, r8169.ko (or r8169.o for kernel 2.4.x), is installed.
# lsmod | grep r8169
If it is installed remove it.
# rmmod r8169
Download the R8168B linux driver from here into /root.
Unpack the tarball :
# cd /root
# tar vjxf r8168-8.012.00.tar.bz2
Change to the directory:
# cd r8168-8.012.00
If you are running the target kernel, then you should be able to do :
# make clean modules
# make install
# depmod -a
# insmod ./src/r8168.ko (or r8168.o in linux kernel 2.4.x)
make sure modprobe knows not to use r8169, and that depmod doesn’t find the r8169 module.
# echo "blacklist r8169" >> /etc/modprobe.d/blacklist
# mv /lib/modules/`uname -r`/kernel/drivers/net/r8169.ko \ /lib/modules/`uname -r`/kernel/drivers/net/r8169.ko.bak
You can check whether the driver is loaded by using the following commands.
# lsmod | grep r8168
# ifconfig -a
If there is a device name, ethX, shown on the monitor, the linux driver is loaded. Then, you can use the following command to activate it.
# ifconfig ethX up
After this you should not see any more dropped packets reported.
Unfortunately java does not support __FILE__ and __LINE__ but you can get the same functionality with this code which can be placed in one of your libraries.
public static void showTrace(String msg)
{
if (msg.length() > 0) System.out.println(msg);
System.out.println("Trace: " +
"file " + new Throwable().getStackTrace()[1].getFileName() +
" class " + new Throwable().getStackTrace()[1].getClassName() +
" method " + new Throwable().getStackTrace()[1].getMethodName() +
" line " + new Throwable().getStackTrace()[1].getLineNumber());
}
APPEND FROM <table-name>Before when appending into a shared Recital table each new row was locked along with the table header, then unlocked after it was inserted. This operation has now been enhanced to lock the table once, complete inserting all the rows from the table and then unlock the table. The performance of this operation has been increased by using this method. All the database and table constraints are still enforced.
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.
