EAV Basics

Entity Attribute Value (EAV) is a framework that allows entities to have different values for its properties.

Two Main Purposes:

1. Multi-valued attributes: Different values for attributes based on scope (global, website, store)
2. Flexible data architecture: Allows extending an entity's data architecture easily

EAV is technically implemented via ResourceModel.

EAV consists of the following components:

1. Entity Types - Registered EAV entities
2. Attribute Sets - Groups of attributes
3. Attributes - Individual properties with behavior
4. Attribute Values - Stored values in type-specific tables

eav_entity_type Table

Each EAV entity must be registered as an entity type in the eav_entity_type table.

SELECT entity_type_id, entity_type_code, entity_table 
FROM eav_entity_type;

+----------------+------------------+-------------------------+
| entity_type_id | entity_type_code | entity_table            |
+----------------+------------------+-------------------------+
| 1              | customer         | customer_entity         |
| 2              | customer_address | customer_address_entity |
| 3              | catalog_category | catalog_category_entity |
| 4              | catalog_product  | catalog_product_entity  |
| 5              | order            | sales_order             |
| 6              | invoice          | sales_invoice           |
| 7              | creditmemo       | sales_creditmemo        |
| 8              | shipment         | sales_shipment          |
+----------------+------------------+-------------------------+

There are eight entity types in Magento. They come from the early days of Magento 1, and by Magento 2.4, have evolved significantly.

For example, the celebrated multi-scope functionality of EAV attributes is a core feature of the EAV framework, however it is fully implemented in the Catalog module.

Verify Customer Attributes:

SELECT attribute_id, attribute_code, backend_type, backend_table 
FROM eav_attribute 
WHERE entity_type_id=1;

Attribute sets are groups of attributes. See Topic 3.01 for comprehensive coverage of attribute sets.

Key Points:

• Stored in eav_attribute_set table
• Contain attribute groups
• Allow different products to have different attributes
• Can be created via admin or programmatically

Attribute Storage

Each eav_attribute has a lot of information associated with it, besides its values. That information can be generic or entity type specific.

While it is possible to add attributes via an admin interface, we should try to do that programmatically via a Data Patch.

Further Reading:

• How to Add a New Product Attribute
• Adding Customer EAV Attribute for Backend Only

Attributes have their own properties which define an attribute's behavior. Three models are of great importance:

1. Frontend Model - Formats/adjusts value on frontend
2. Source Model - Provides list of acceptable options
3. Backend Model - Controls how value is saved to database

Purpose

Formats or adjusts the value of the attribute on the frontend.

Implementation:

The value of the attribute's frontend_model property must be set to a class that:

• Implements Magento\Eav\Model\Entity\Attribute\Frontend\FrontendInterface
• OR extends Magento\Eav\Model\Entity\Attribute\Frontend\AbstractFrontend (more meaningful)

Key Method:

public function getValue(\Magento\Framework\DataObject $object)
{
    $value = $object->getData($this->getAttribute()->getAttributeCode());
    // Format or adjust the value here
    return $value;
}

Purpose

Provides a list of acceptable options for an attribute. The most basic example would be boolean options.

A source model must:

• Implement \Magento\Eav\Model\Entity\Attribute\Source\SourceInterface
• OR extend \Magento\Eav\Model\Entity\Attribute\Source\AbstractSource

Native Implementations:

For catalog entities, a source model may implement additional methods:

• getFlatColumns() - Used in the indexing process
• addValueSortToCollection() - Allows custom logic for sorting by this attribute

Reference Implementation:

Purpose

Controls how the attribute's value is saved to the database.

Implementation:

Backend model must:

• Implement \Magento\Eav\Model\Entity\Attribute\Backend\BackendInterface
• OR extend \Magento\Eav\Model\Entity\Attribute\Backend\AbstractBackend (more meaningful)

Methods of Interest:

Example:

Storage Tables

Values are stored in a set of tables, specific per entity type.

Example for catalog_product:

SHOW TABLES LIKE 'catalog_product_entity_%';

+-------------------------------------------------------+
| Tables_in_magento (catalog_product_entity_%)         |
+-------------------------------------------------------+
| catalog_product_entity_datetime                       |
| catalog_product_entity_decimal                        |
| catalog_product_entity_gallery                        |
| catalog_product_entity_int                            |
| catalog_product_entity_media_gallery                  |
| catalog_product_entity_media_gallery_value            |
| catalog_product_entity_media_gallery_value_to_entity  |
| catalog_product_entity_media_gallery_value_video      |
| catalog_product_entity_text                           |
| catalog_product_entity_tier_price                     |
| catalog_product_entity_varchar                        |
+-------------------------------------------------------+

Each value table stores:

• entity_id - The entity (product, category, etc.) ID
• attribute_id - The attribute ID
• value - The actual value
• store_id - Indicator for scope

Example Scenario:

Say there is a record with:

• attribute_id = 25
• store_id = 4
• value = 133

Step-by-Step Interpretation:

1. Check the scope of attribute with id 25 in eav_attribute, is_global field
2. Assume is_global = 2, which means website scope
3. So the attribute has different values on different websites
4. Its value for website with id 4 equals 133

• How to Add a New Product Attribute
• EAV and Extension Attributes
• Topic 3.01: Attribute Sets & Attributes
• Topic 3.02: Types of Attributes