Magento get read or write connection for model / resource model

Question

I have 3 databases (in addition to the magento one) connected to magento with models (non-eav) defined for the tables.

They all have their read and write connections defined in the local.xml

 <cloudvm_db>
 <connection>
 <host><![CDATA[SERVER]]></host>
 <username><![CDATA[USER]]></username>
 <password><![CDATA[PASS]]></password>
 <dbname><![CDATA[cloudvm]]></dbname>
 <model>mysql4</model>
 <type>pdo_mysql</type>
 <active>1</active>
 </connection>
 </cloudvm_db>
 <cloudvm_read>
 <connection>
 <use>cloudvm_db</use>
 </connection>
 </cloudvm_read>
 <cloudvm_write>
 <connection>
 <use>cloudvm_db</use>
 </connection>
 </cloudvm_write>

then this is defined as the connection for the model in the modules config.xml

<models>
 <cloud_workervm>
 <class>Cloud_WorkerVM_Model</class>
 <resourceModel>cloud_workervm_resource</resourceModel>
 </cloud_workervm>
 <cloud_workervm_resource>
 <class>Cloud_WorkerVM_Model_Resource</class>
 <entities>
 <virtualmachine>
 <table>virtualmachine</table>
 </virtualmachine>
 </entities>
 </cloud_workervm_resource> 
 </models>
 <resources>
 <cloud_workervm_write>
 <connection>
 <use>cloudvm_write</use>
 </connection>
 </cloud_workervm_write>
 <cloud_workervm_read>
 <connection>
 <use>cloudvm_read</use>
 </connection>
 </cloud_workervm_read> 
 </resources>

what I am trying to do is write a function(s) that you can pass the name of a model e.g. "cloud_workervm/cloudvm" and return the name of (or an object of) the read connection and the write connection

Answer 1

Please follow bellow steps

Config.xml

 <?xml version="1.0"?>
<config>
 <modules>
 <AR_Externaldb>
 <version>0.1.0</version>
 </AR_Externaldb>
 </modules>
 <frontend>
 <routers>
 <externaldb>
 <use>standard</use>
 <args>
 <module>AR_Externaldb</module>
 <frontName>externaldb</frontName>
 </args>
 </externaldb>
 </routers>
 <layout>
 <updates>
 <externaldb>
 <file>externaldb.xml</file>
 </externaldb>
 </updates>
 </layout>
 </frontend>
 <admin>
 <routers>
 <externaldb>
 <use>admin</use>
 <args>
 <module>AR_Externaldb</module>
 <frontName>externaldb</frontName>
 </args>
 </externaldb>
 </routers>
 </admin>
 <adminhtml>
 <layout>
 <updates>
 <externaldb>
 <file>externaldb.xml</file>
 </externaldb>
 </updates>
 </layout>
 </adminhtml>
 <global>
 <models>
 <externaldb>
 <class>AR_Externaldb_Model</class>
 <resourceModel>externaldb_mysql4</resourceModel>
 </externaldb>
 <externaldb_mysql4>
 <class>AR_Externaldb_Model_Mysql4</class>
 <entities>
 <vehicle><table>BaseVehicle</table></vehicle>
 </entities>
 </externaldb_mysql4>
 </models>
 <resources>
 <!-- End DB -1 --> 
 <externaldb_write>
 <connection>
 <use>externaldb_database</use>
 </connection>
 </externaldb_write>
 <externaldb_read>
 <connection>
 <use>externaldb_database</use>
 </connection>
 </externaldb_read>
 <externaldb_setup>
 <connection>
 <use>core_setup</use>
 </connection>
 </externaldb_setup>
 <externaldb_database>
 <connection>
 <host><![CDATA[localhost]]></host>
 <username><![CDATA[testsql]]></username>
 <password><![CDATA[test123]]></password>
 <dbname><![CDATA[database-1]]></dbname>
 <model>mysql4</model>
 <type>pdo_mysql</type>
 <active>1</active>
 </connection>
 </externaldb_database>
 <!-- End DB-1 --> 
 <!-- DB -2 -->
 <pcdb_write>
 <connection>
 <use>pcdb_database</use>
 </connection>
 </pcdb_write>
 <pcdb_read>
 <connection>
 <use>pcdb_database</use>
 </connection>
 </pcdb_read>
 <pcdb_setup>
 <connection>
 <use>core_setup</use>
 </connection>
 </pcdb_setup>
 <pcdb_database>
 <connection>
 <host><![CDATA[localhost]]></host>
 <username><![CDATA[test]]></username>
 <password><![CDATA[test123]]></password>
 <dbname><![CDATA[database-2]]></dbname>
 <model>mysql4</model>
 <type>pdo_mysql</type>
 <active>1</active>
 </connection>
 </pcdb_database>
 <!-- End DB -2 -->
 </resources>
 <blocks>
 <externaldb>
 <class>AR_Externaldb_Block</class>
 </externaldb>
 </blocks>
 <helpers>
 <externaldb>
 <class>AR_Externaldb_Helper</class>
 </externaldb>
 </helpers>
 </global>
</config>

Bellow Read & write function use in model or resource

<?php
class AR_Externaldb_Model_Test extends Mage_Core_Model_Abstract
{
protected $_readAdaptor;
protected $_readPcdbAdaptor;
protected $_writeAdaptor;
public function readAdaptor()
{
 if(empty($this->_readAdaptor)) {
 $this->_readAdaptor = Mage::getSingleton('core/resource')->getConnection('externaldb_read');
 }
 return $this->_readAdaptor;
}
public function writeAdaptor()
{
 if(empty($this->_writeAdaptor)) {
 $this->_writeAdaptor = Mage::getSingleton('core/resource')->getConnection('externaldb_write');
 }
 return $this->_writeAdaptor;
}
public function readPcdbAdaptor()
{
 if(empty($this->_readPcdbAdaptor)) {
 $this->_readPcdbAdaptor = Mage::getSingleton('core/resource')->getConnection('pcdb_read');
 }
 return $this->_readPcdbAdaptor;
}

}

• Conrad Jones: the layout update and router is unnecessary. I added a getReadAdapter and getWriteAdapter to each model resource in the end, I was trying to avoid having to modify each class. There must be a way to get it from the config xml,

Answer 2

For getting resource read collection try this:

Mage::getResourceModel('cloud_workervm/virtualmachine')->getReadConnection()

Format:

Mage::getResourceModel('ModelPrefix/entityname')->getReadConnection()

For getting resource write collection try this:

Mage::getResourceModel('cloud_workervm/virtualmachine')->getConnection('write')

Format:

Mage::getResourceModel('ModelPrefix/entityname')->getConnection('write')