Sharing basic knowledge about Magento EAV System. Using raw sql and ORM to build a query base on EAV Model.

1. Magento EAV System
The EAV system is one of the most complex part of Magento system.
TRUONG DINH KHOA
Email: mrkhoa99@gmail.com

2. Do you know?
 MySQL has a hard limit of 4096 columns per table.
 Oracle has even less: 1000.
 Microsoft SQL Server offers up to 30,000 columns.

3. Traditional model
 In a traditional database model, tables have a fixed number of columns
products
product_id
name
price
atribute_1
……
product_id name price attribute_1 … …
000001 T-Shirt 16.9 Value 1 … …
000002 EAV Book 19 Value 2 … …

4. EAV Model
 However, if entities have a huge of possible attributes? What happens? E.g. a
product has a lot of attribute: price, name, color, image, tax, manufacturer , attribute_1…
attribute_n, etc..

5. EAV Model
 The problem can be addressed by EAV (row modelling).
 Traditional model : adding more attributes => more columns.
 EAV model: adding more attributes => more rows.
 EAV stands for entity, attribute and value.
 Many cloud computing platforms (Amazon, Google, Microsoft, etc.) offer EAV
Model as featuring data stores.

6. EAV Model
 “E” in EAV stands for Entity. In Magento case, they are such as product,
customer, category, order, etc.
 “A” stands for Attribute. These are the individual properties of each of the
entities, e.g. name, weight, email address, etc.
 “V” stands for Value. The value of any particular attribute.

7. EAV Model
 Magento Model Entity Model
EAV Attribute
Value Table
(varchar)
Value Table
(text)
Value Table
(int)
Value Table
(etc)

8. EAV Model
 For example : Catalog Product
catalog_product_entity
(entity_type_id)
eav_attribute
(entity_type_id,
attribute_id)
catalog_product_entity_attribute_varchar
(entity_type_id, attribute_id)
catalog_product_entity_attribute_text
(entity_type_id, attribute_id)
catalog_product_entity_attribute_int
(entity_type_id, attribute_id)
catalog_product_entity_attribute_etc
(entity_type_id, attribute_id)

9. Creating simple raw sql
 SELECT a list of product
 3 tables:
catalog_product_entity ,
eav_attribute,
catalog_product_entity_varchar

10. Creating simple raw sql
-eav_attribute:
+attribute_id: unique identifier and primary key of table.
+entity_type_id: relates each attribute to a EAV model type.
+attribute_code: the name or key of attributes.
+….
-catalog_product_entity:
+entity_id: unique identifier of product.
+entity_type_id: identifies each type of EAV model type.
+….

11. Creating simple raw sql
-catalog_product_entity_varchar
+value_id: unique identifier and primary key
+entity_type_id: this value belongs to product entity.
+attribute_id: a foreign key- references to attribute_id on eav_attribute
+…

12. Creating simple raw sql
Raw SQL:
SELECT
p.entity_id AS product_id,
var.value AS product_name,
p.sku AS product_sku
FROM
catalog_product_entity p,
eav_attribute eav,
catalog_product_entity_varchar var
WHERE p.entity_type_id = eav.entity_type_id
AND var.entity_id = p.entity_id
AND eav.attribute_code = 'name'
AND eav.attribute_id = var.attribute_id
ORDER BY `name` ASC

13. What’s next?
 Creating a raw sql shows a small piece. It is easy to understand for new
Magento developers. But for customizing and maintaining purpose, what
programming technique is used?
 In a big picture, we need to do more for our software => Magento used Object
Relational Mapping (ORM) system.

14. Magneto ORM System
 Object-relational mapping (ORM, O/RM, and O/R mapping) in computer
software is a programming technique for converting data between
incompatible type systems in object-oriented programming languages. This
creates, in effect, a "virtual object database" that can be used from within
the programming language.
https://en.wikipedia.org/wiki/Object-relational_mapping

15. Magento ORM System
 Building a simple query to retrieve products listing:
//Instantiate a product collection:
$collection = Mage::getModel('catalog/product')->getCollection();
//Select an attribute:
$collection->addAttributeToSelect('name');
//Sort the collection:
$collection->setOrder('name', 'asc');
//Load the collection:
$collection->load();
//Print the collection
echo $collection->getSelect();

16. Magento ORM System
SELECT
`e`.*,
IF(at_name.value_id > 0, at_name.value, at_name_default.value) AS
`name`,
`price_index`.`price`, `price_index`.`tax_class_id`,
`price_index`.`final_price`,
IF(
price_index.tier_price IS NOT NULL,
LEAST(
price_index.min_price,
price_index.tier_price
),
price_index.min_price
) AS `minimal_price`,
`price_index`.`min_price`, `price_index`.`max_price`,
`price_index`.`tier_price`
FROM
`catalog_product_entity` AS `e`
LEFT JOIN `catalog_product_entity_varchar` AS `at_name_default`
ON (`at_name_default`.`entity_id` = `e`.`entity_id`)
AND (`at_name_default`.`attribute_id` = '71')
AND `at_name_default`.`store_id` = 0
LEFT JOIN `catalog_product_entity_varchar` AS `at_name`
ON (`at_name`.`entity_id` = `e`.`entity_id`)
AND (`at_name`.`attribute_id` = '71')
AND (`at_name`.`store_id` = 1)
INNER JOIN `catalog_product_index_price` AS `price_index`
ON price_index.entity_id = e.entity_id
AND price_index.website_id = '1'
AND price_index.customer_group_id = 0
ORDER BY `name` ASC

17. Magento ORM System
 Some differences in comparison with a raw sql:
-There are many columns.
-Getting products in current store: at_name_default`.`store_id` = 0
-Add more conditions: e.g. IF(at_name.value_id > 0, at_name.value,
at_name_default.value)
-etc.

18. Magento ORM System
The most useful collection methods
 addAttributeToSelect: adding an attribute to entities in a collection
 addAttributeToFilter: using to filter a collection of
EAV entities with the specified conditional parameters.
 addFieldToFilter: using also to filter a collection, but for non-EAV models, this
function is used regularly.
 addAttributeToSort: adding an attribute to sort order
 etc.

19. EAV-Advantages
 Flexibility.
 Don’t need to change database schema when adding new attributes.
 Quick to implement.

20. EAV-Disadvantages
 Performance problem: a lot of tables are required when making a query with
EAV Model.
 Find more…

21. Thanks you!

22. Khoa Truong Dinh
mrkhoa99@gmail.com
 http://www.boolfly.com/
 https://github.com/mrkhoa99
 https://vn.linkedin.com/in/truongdinhkhoa
 http://stackoverflow.com/users/5179786/khoa-truongdinh