jdbc

This is a simple readme describing how to compile and use the jdbc driver.

This isn't a guide on how to use JDBC - for that refer to Javasoft's web site:

	http://www.javasoft.com

or the JDBC mailing list:

	jdbc@java.blackdown.org

	http://www.blackdown.org

For problems with this driver, then refer to the postgres-interfaces email
list:

	http://www.postgresql.org

When PostgreSQL V6.4 was released, full documentation for the driver was
included in the main documentation tree (under the doc directory).

This file was finally amended on December 29 1998 to account for the major
changes made to the driver since V6.4 was released.

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COMPILING

To compile the driver, simply use make in the src/interfaces/jdbc directory.
This will compile the driver, and build a .jar file (Java ARchive).

REMEMBER: once you have compiled the driver, it will work on ALL platforms
that support the JDK 1.1 api or later.

The V6.5 driver introduced support for the JDBC2 specification (which is used
with JDK 1.2 api and later). This caused us some problems because classes
written for JDBC1 and JDBC2 are not compatible, so a large chunk of the
driver had to be re-written to accomodate this.

Running make will build a .jar file (postgresql.jar) which contains the driver.
That jar file will contain the driver for _your_ version of the JDK. That is,
if you run make using JDK 1.1.7, then you will get the JDBC1 driver. If you
run using 1.2 then you will get the JDBC2 driver.

Tip: If you want the driver to run on both JDBC1 or JDBC2, first compile under
JDK 1.1.x, then recompile under JDK 1.2.

In testing, I've done this using 1.1.6 (running under linux), and running make
on my Win95 based Laptop (CygWin B20.1 was used to get a GNUMake - and a
decent shell {bash}).

When the .jar file is built, it includes all the classes under postgresql, and
the driver automatically selects the correct classes.

That means you don't have to compile it on every platform. Believe me, I
still hear from people who ask me "I've compiled it ok under Solaris, but it
won't compile under Linux" - there's no difference.

PS: When you run make, don't worry if you see more than one or two calls to
    javac. This is normal, because the driver dynamically loads classes, and
    the Makefile ensures everything gets compiled.

I advise you don't try running javac outside of make. You may miss something.

Possible problems

You may see a message similar to:

postgresql/Driver.java:87: interface java.sql.Connection is an interface. It can't be instantiated.
    return new Connection (host(), port(), props, database(), url, this);

This is caused by not having the current directory in your CLASSPATH. Under
Linux/Solaris, unset the CLASSPATH environment variable, and rerun make.

If you are still having problems, I keep a copy of the driver (for different
versions of the backend) on my web site http://www.retep.org.uk/postgres/

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INSTALLING THE DRIVER

To install the driver, the .class files have to be in the classpath. This can be
done in two ways:

1: create a directory "postgresql" (and it must be called this) in the current
   directory (or a directory in the class path), and copy all .class files
   into it.

2: copy the postgres.jar file into a directory, and add it to the classpath.

   ie: under LINUX/SOLARIS (the example here is my linux box):

	export CLASSPATH=.:/usr/local/lib/postgresql.jar:/usr/local/jdk1.1.1/lib/classes.zip

   note: in java, .zip and .jar files hold collections of classes.

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USING THE DRIVER

To use the driver, you must introduce it to JDBC. Again, there's two ways
of doing this:

1: Hardcoded.

   This method hardcodes your driver into your application/applet. You
   introduce the driver using the following snippet of code:

	try {
	  Class.forName("postgresql.Driver");
	} catch(Exception e) {
	  // your error handling code goes here
	}

   Remember, this method restricts your code to just the postgresql database.

2: Parameters

   This method specifies the driver from the command line. When running the
   application, you specify the driver using the option:

	-Djdbc.drivers=postgresql.Driver

   eg: This is an example of running one of my other projects with the driver:

	java -Djdbc.drivers=postgresql.Driver finder.finder

   note: This method only works with Applications (not for Applets).
	 However, the application is not tied to one driver, so if you needed
	 to switch databases (why I don't know ;-) ), you don't need to
	 recompile the application (as long as you havent hardcoded the url's).

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JDBC URL syntax

The driver recognises JDBC URL's of the form:

	jdbc:postgresql:database

	jdbc:postgresql://host/database

	jdbc:postgresql://host:port/database

Also, you can supply both username and passwords as arguments, by appending
them to the URL. eg:

	jdbc:postgresql:database?user=me
	jdbc:postgresql:database?user=me&password=mypass

Previous versions you had to use an auth argument to tell the driver what
authentication scheme to use when connecting to the database.

However, this is no longer supported because the database tells the driver
what scheme it's expecting.

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That's the basics related to this driver. You'll need to read the JDBC Docs
on how to use it.

POSTGRESQL SPECIFICS
--------------------

Date datatype:

The driver now issues the "show datestyle;" query when it first connects, so
any call to ResultSet.getDate() how returns the correct date.

One caveat though: if you change the datestyle from within JDBC, you must also
issue the "show datestyle" query. Without this, the driver will not know of
the change.

ie:
	Statement s = db.createStatement();
	...
	s.executeUpdate("set datestyle='european'");
	s.executeUpdate("show datestyle");
	..
	s.close();

Please note: This may change later, so that the driver uses the same format
internally (similar to how the ODBC driver works).

			------------------

JDBC supports database specific data types using the getObject() call. The
following types have their own Java equivalents supplied by the driver:

	box, circle, line, lseg, path, point, polygon

When using the getObject() method on a resultset, it returns a PG_Object,
which holds the postgres type, and its value. This object also supports
methods to retrive these types.

	Eg: column 3 contains a point, and rs is the ResultSet:

	PG_Object o = (PG_Object)rs.getObject(3);
	PGpoint p = o.getPoint();
	System.out.println("point returned x="+p.x+", y="+p.y);

Also, when using these classes, their toString() methods return the correct
syntax for writing these to the database.

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Peter T Mount, December 29 1998
home email: pmount@retep.org.uk		http://www.retep.org.uk
work email: petermount@it.maidstone.gov.uk or peter@taer.maidstone.gov.uk

PS: Please use the home email whenever possible. If you must contact me at work
then please cc my home one at the same time.