Hi all,
we have discovered a way how to realize master/slave support with cake
(also with multiple slaves).
This old post is completely depricated:
http://groups.google.com/group/cake-php/browse_thread/thread/58ea010f930fab6c
Because Model::find() and Model::save() create the $db-handle lines
before it calles the callbacks 'beforeFind' and 'beforeSave'.
The way we realized is to overwrite the save() and updateAll()
methodes and to set the default db-config in the AppModel::__construct
().
Note: One thing remains: It's not possible to do a bindModel in the
'beforeSave' and 'afterSave' callbacks, because they get the wrong db-
config... If you find a way to do it, please let us know!
1. Define your Database-Configs in app/config/database.php. You should
have master and as much slaves you want to have:
class DATABASE_CONFIG {
var $master = array(
driver' => 'mysql',
'persistent' => false,
'host' => 'localhost',
'login' => 'login',
'password' => 'password',
'database' => 'database',
'encoding' => 'utf8'
);
// Config for Slave #1
var $slave1 = array(
driver' => 'mysql',
'persistent' => false,
'host' => 'slave1',
'login' => 'login',
'password' => 'password',
'database' => 'database',
'encoding' => 'utf8'
);
// Config for Slave #2
var $slave2 = array(
driver' => 'mysql',
'persistent' => false,
'host' => 'slave2',
'login' => 'login',
'password' => 'password',
'database' => 'database',
'encoding' => 'utf8'
);
...
}
2. Create/Alter app/models/app_model.php and create/alter the
constructor '__construct' of it like the following:
class AppModel extends Model {
public function __construct($id = false, $table = null, $ds = null)
{
/**********************************
* USED FOR MASTER/SLAVE MECHANIC *
**********************************/
// If a datasource is set via params, use it and return
if((is_array($id) && isset($id['ds'])) || $ds) {
parent::__construct($id, $table, $ds);
return;
}
// Use a static variable, to only use one connection per page-call
(otherwise we would get a new handle every time a Model is created)
static $_useDbConfig;
if(!isset($_useDbConfig)) {
// Get all available database-configs
$sources_list = ConnectionManager::enumConnectionObjects();
// Find the slaves we have
$slaves = array();
foreach($sources_list as $name => $values) {
// Slaves have to be named "slave1", "slave2", etc...
if(preg_match('/^slave[0-9]+$/i', $name) == 1) {
$slaves[] = $name;
}
}
// Randomly use a slave
$_useDbConfig = $slaves[rand(0, count($slaves) - 1)];
$this->_usedSlave = $_useDbConfig;
}
$this->useDbConfig = $_useDbConfig;
parent::__construct($id, $table, $ds);
}
...
}
This method uses a local static variable to save the db-config
application-wide. It collects all configs from the database.php that
start with "slave#" and selects a random one for it. This is now the
"default"-config for the application that is used with every query
done via the Model-class UNTIL we do the next step:
3. We now overwrite the Model::save() and Model::find() methods to use
another database-config for write-queries!
Note: We discovered, that it's not enough to just overwrite Model::save
(), because Model::updateAll() doesn't use the callbacks, neither the
Model::save() method.
function save($data = null, $validate = true, $fieldList = array())
{
// Remember the old config
$oldDb = $this->useDbConfig;
// Set the new config
$this->setDataSource('master');
// Call the original Model::save() method
$return = parent::save($data, $validate, $fieldList);
// Reset the config/datasource
$this->setDataSource($oldDb);
return $return;
}
function updateAll($fields, $conditions = true) {
$oldDb = $this->useDbConfig;
$this->setDataSource('master');
$return = parent::updateAll($fields, $conditions);
$this->setDataSource($oldDb);
return $return;
}
Now you should have full master/slave support within your cake-
application.
The way it works:
When your application is called, the AppModel will be called the first
time and realizes, that the local $_useDbConfig variable is not set.
So it randomly selects one of your slave-configs and sets this to the
default used database-config (AppModel::useDbConfig). Every further
instance of AppModel will recognize that the local $_useDbConfig
variable already exists and will use the same config.
Now every query you do will use this slave-config, EXCEPT all save's
and updateAll's, because you've overwritten these methods to use your
master-config.
Hope this tutorial was helpful to you!
Greetings,
Andreas Hofmann!
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