Developers: Magento questions and answers 1

Magento Design Pattern here

What is the difference between Mage::getSingletone() and Mage::getModel() and Mage::getResourceModel() in Magento

Answer:
Mage::getSingletone() always finds for an existing object if not then create that a new object but Mage::getModel() always creates a new object.

2nd:
The difference between Mage:getSingleton() and Mage::getModel() is that the former one does not create an object if the object for same class is already created, while the later creates new objects every time for the class when it’s called.
Mage::getSingleton() uses the “singleton design pattern” of PHP. If the object is not created, it will create it.
Mage::getSingleton() is mostly used when you want to create an object once, modify it and later fetch from it. Popular example is session, you first create a session object, and then add/remove values from session across different pages, so that it retains your values (e.g. cart values, logged in customer details, etc.) and doesn’t create new session object losing your last changes.
Mage::getModel() is used when you want to have the fresh data from the database. Example is when you want to show records from database.
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Why Magento use EAV database model ?
In EAV database model, data are stored in different smaller tables rather than storing in a single table.

product name is stored in catalog_product_entity_varchar table
product id is stored in catalog_product_entity_int table
product price is stored in catalog_product_entity_decimal table

Magento Use EAV database model for easy upgrade and development as this model gives more flexibility to play with data and attributes.

Q 6. What technology used by Magento?

Ans. Magento uses PHP as a web server scripting language and the MySQL Database. The data model is based on the Entity-attribute-value model that stores data objects in tree structures, thus allowing a change to a data structure without changing the database definition.

How to improve magento performance?

Enabled magento caching

MySQL Query caching

Enable Gzip Compression

Disable any unused modules

Disable the Magento log

Optimise your images

Combine external CSS/JS into one file

Enable Apache KeepAlives: 
Make sure your Apache configuratio 
has KeepAlives enabled.

Q 8. What is benefit of namespace (package) in magento?

Ans. We can have more than one module with same name but they should be placed in different namespaces. All magento core modules are contained in mage namespace.

core/Mage/Catalog

and all custom modules are placed in

local/CustomModule

Q 9. How to include CMS block in template file(.phtml)?

echo $this->getLayout()->createBlock(‘cms/block’)->setBlockId(‘static_block_id’)->toHTML();

Q 10. How to add an external javascript/css file to Magento?

<action method="addJs"><script>js/yourfile.js</script></action>

<action method="addCss"><stylesheet>css/yourstyle.css</stylesheet></action>

<action method="addItem"><type>skin_js</type><name>js/ yourfile.js</name></action>

<action method="addItem"><type>skin_css</type><name>css/yourstyle. css</name></action>

Q. How to fetch 5 bestsellers products programmatically?

Mage::getResourceModel(‘reports/product_collection’)

->addOrderedQty()

->addAttributeToSelect(‘*’)

->setPage(1, 5)

->load();

Why magento is slow ? Which factors affect performance of magento?

1. EAV structure of magento database, even for retrieving single entity the query becomes very complex .
2. Magento’s template system involves a lot of recursive rendering
3. Huge XML trees built up for layout configuration, application configuration settings

How to run custom MySql query in Magento?

$db = Mage::getSingleton('core/resource')->getConnection('core_write');

$result=$db->query("SELECT * FROM PCDSTable");

When will you need to clear cache to see the changes in Magento?

When you have added/modified XML, JS, CSS file(s).

What are the addAttributeToFilter Conditionals in Magento? - See more at: http://virallangaliya.blogspot.com/p/magento-interview-questions-and-answers.html#sthash.pTQJ94RY.dpuf

Ans.
In Magento we can use addAttributeToFilter Conditions same as WHERE in SQL
Below are the all condtions

Equals: eq
$_products->addAttributeToFilter('status', array('eq' => 1));

Not Equals - neq
$_products->addAttributeToFilter('sku', array('neq' => 'test-product'));

Like - like
$_products->addAttributeToFilter('sku', array('like' => 'UX%'));

One thing to note about like is that you can include SQL wildcard characters such as the percent sign.

Not Like - nlike
$_products->addAttributeToFilter('sku', array('nlike' => 'err-prod%'));

In - in
$_products->addAttributeToFilter('id', array('in' => array(1,4,98)));

When using in, the value parameter accepts an array of values.

Not In - nin
$_products->addAttributeToFilter('id', array('nin' => array(1,4,98)));

NULL - null
$_products->addAttributeToFilter('description', 'null');

Not NULL - notnull
$_products->addAttributeToFilter('description', 'notnull');

Greater Than - gt
$_products->addAttributeToFilter('id', array('gt' => 5));

Less Than - lt
$_products->addAttributeToFilter('id', array('lt' => 5));

Greater Than or Equals To- gteq
$_products->addAttributeToFilter('id', array('gteq' => 5));

Less Than or Equals To - lteq
$_products->addAttributeToFilter('id', array('lteq' => 5)); - See more at: http://virallangaliya.blogspot.com/p/magento-interview-questions-and-answers.html#sthash.pTQJ94RY.dpuf

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