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今天在分析Magento源代码的时候,在文件app/code/core/Mage/Catalog/Model/Resource/Eav/Mysql4/Config.php 中追踪到下面的函数 getAttributesUsedInListing()

/**
* Retrieve Product Attributes Used in Catalog Product listing
*
* @return array
*/
public function getAttributesUsedInListing() {
$select = $this->_getReadAdapter()->select()
->from(array(’main_table’ => $this->getTable(’eav/attribute’)))
->join(
array(’additional_table’ => $this->getTable(’catalog/eav_attribute’)),
‘main_table.attribute_id = additional_table.attribute_id’,
array()
)
->joinLeft(
array(’al’ => $this->getTable(’eav/attribute_label’)),
‘al.attribute_id = main_table.attribute_id AND al.store_id = ‘ . (int) $this->getStoreId(),
array(’store_label’ => new Zend_Db_Expr(’IFNULL(al.value, main_table.frontend_label)’))
)
->where(’main_table.entity_type_id=?’, $this->getEntityTypeId())
->where(’additional_table.used_in_product_listing=?’, 1);

– $sql = $select->assemble();
– echo $sql;

return $this->_getReadAdapter()->fetchAll($select);
}
Magento 操作数据库是在 Zend DB(Zend Framework)的基础上简单的做了下封装了。Zend DB 有自己的一套规则,来组合生成最终的SQL查询语句,可以看到上面的代码中有 from() join() joinLeft() where() 等函数,乱七八糟的一大堆东西,需要对 Zend DB的规则非常熟悉,才能知道实际执行的SQL语句,有没有办法直接打印出SQL语句?找了下,还真有,就是assemble()函数。在上面代码中最后部分可以看到。顺被把SQL也附上来:

SELECT `main_table`.*,
IFNULL(al.value, main_table.frontend_label) AS `store_label`
FROM `eav_attribute` AS `main_table`
INNER JOIN `catalog_eav_attribute` AS `additional_table`
ON main_table.attribute_id = additional_table.attribute_id
LEFT JOIN `eav_attribute_label` AS `al`
ON al.attribute_id = main_table.attribute_id AND al.store_id = 1
WHERE (main_table.entity_type_id=’4′)
AND (additional_table.used_in_product_listing=1)