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From: Derek Downey on 3 Mar 2010 10:49
Hi,
I would like to set up an application that utilizes a MySQL Master/
Slave replication scheme. My application would write to the master and
read from the slave. The application is currently using
PEAR::DB_DataObject as its data abstraction layer. The app also has an
abstract connector class that handles extra application-specific
processing (such as tracking).

I noticed that DB_DO has the ability to use multiple databases, so I
started playing with it. Here's my database configuration:

[DB_DataObject]
database_read = mysqli://USER:PASS(a)readDB.example.com/appDB
database_write = mysqli://USER:PASS(a)writeDB.example.com/appDB
.....
....


The only way I found to switch the databases was the 'database'
function. Unfortunately, this doesn't seem to switch out the DSN that
matches the database and establish a new connection (or find a cached
connection).

I am able to accomplish what I want by overwriting the database()
function to clear out the _database_dsn_md5 value, forcing DB_DO to
generate a new md5 based on the selected database. Then I override the
find/query methods to use $this->database("read"); and the insert/
update/delete methods to use $this->database("write");.

So my questions:
Has anyone else run into a similar scenario?
How did you accomplish it?
Is there a reason not to have the DB_DataObject::database()
automatically clear out the md5 to force it to get the correct DSN?


Here's a brief example of what I did using the above ini configuration.:


BASIC APP DataObject
abstract class SomeBase extends DB_DataObject {
...

// OVERRIDE DB_DO FUNCTIONALITY //
public function database() {
$firstArg = func_get_arg(0);
// NO POINT GOING FURTHER IF DATABASE IS ALREADY SET TO WHAT WE
HAVE //
if ($this->_database!=$firstArg) {
// reset md5 to force _connect to generate new based on
database
$this->_database_dsn_md5 = '';
parent::database($firstArg); // PASS ON FIRST ARGUMENT //
}
}

public function insert() {
$this->database("write");
...// DO OTHER STUFF //
parent::insert();
}

public function update() {
$this->database("write");
...// DO OTHER STUFF //
parent::update();
}

public function delete() {
$this->database("write");
...// DO OTHER STUFF //
parent::delete();
}

public function find($fetchFirst=false) {
$this->database('read');
return parent::find($fetchFirst);
}

public function query($stmt) {
$this->database('read');
return parent::query($stmt);
}
}

class Person extends SomeBase {
...
}

and here is a script that uses the classes:

<?php
$person = new Person();
$person->name = 'FOO';
$person->insert();

$person2 = new Person();
$person2->name = 'FOO';
$person2->find(true);
?>

Thanks in advance for any comments,
Derek Downey, DBA/Web Developer


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