How does loadByCode() works in magento - magento

Question

How does loadByCode() works? I have been adding a module to my new project and don't know how to use model uses loadByCode method with a given code.

Answer 1

When you look at magento model class it extends Mage_Core_Model_Abstract which intern extends Varien_Object.
The class Mage_Core_Model_Abstract has function like getId(), load(), save(), delete() etc...
Mysql4 resource files are used to perform database queries on tables.
Suppose we have the file Keyur_Test_Model_Mysql4_Test resource file.
<?php
class Keyur_Test_Model_Mysql4_Test extends Mage_Core_Model_Mysql4_Abstract
{
public function _construct()
{
$this->_init('test/test', 'test_id');
}
public function loadByField($field,$value){
$table = $this->getMainTable();
$where = $this->_getReadAdapter()->quoteInto("$field = ?", $value);
$select = $this->_getReadAdapter()->select()->from($table,array('test_id'))->where($where);
$id = $this->_getReadAdapter()->fetchOne($sql);
return $id;
}
}
And here is the model file Keyur_Test_Model_Test
<?php
class Keyur_Test_Model_Test extends Mage_Core_Model_Abstract
{
public function _construct()
{
parent::_construct();
$this->_init('test/test');
}
public function loadByField($field,$value){
$id = $this->getResource()->loadByField($field,$value);
$this->load($id);
}
}
In this file there are many new functions which have been used. Let’s take them one by one. In our model file, we have used this function -
$id = $this->getResource()->loadByField($field,$value);
$this->getResource() function returns the resource model’s object. So we are simply calling the loadyByField($field,$value) function in the resource model.
getTable() function
Now in our Mysql4 file, in the loadByField() function we have used $table = $this->getMainTable(); .This function returns the table name of the current model, i.e the one defined in the class’s constructor. If you want to get table name of another sql table in magento, we need to the getTable() call e.g
$table = $this->getTable(‘newsletter/subscribe’);
_getReadAdapter() function
Next we have:
$where = $this->_getReadAdapter()->quoteInto(“$field = ?”, $value);
Here the first function too see is the $this->_getReadAdapter() function. This function return an object which has function to perform database query, like fetch(), fetchAll(), query(), etc.
_quoteInfo() function
Another function we have used is quoteInto(): This function is used to create our where conditions.
In this the actual value is substituted into the question mark we have written. For e.g $this->_getReadAdapter()->quoteInto(“user_id = ?”, 3); translates to “user_id = 3″.
Another frequently used variation of quoteInfo() is
$where = $this->_getReadAdapter()->quoteInto("$field IN(?)", array(1,2,3));
this translates to “field in (1,2,3)”
Getting deeper into the quoteInto() function: If we have multiple where conditions we can use
$where = $this->_getReadAdapter()->quoteInto("$field = ? AND ", $value).$this->_getReadAdapter()->quoteInto("$field1 = ? OR ", $value1).$this->_getReadAdapter()->quoteInto("$field2 = ?", $value2);
Continuing on the loadByField function in our resource model, next we have
$select = $this->_getReadAdapter()->select()->from($table,array(‘test_id’))->where($where);
Here we have created the select query using the select(), and on that called the from() function.
from() function
The from() function takes many different parameters, if you want to fire a simple select * query, you need to only pass the table name like from($table).
But right now, I wanted to select just a single column that is test_id, so I passed an array with column name to
select. i.e array(‘test_id’).
If we want to select multiple column, we need to array(‘test_id’,’col1’,’col2’).
This will create a sql like “select test_id,col1,col2 from $table”.
But support we want a sql query like “select test_id as id,col1 as column1 from $table” , i would call -
from($table,array('id'=>'test_id','column1'=>'col1'));