EAV and extension attributes

Magento provides two types of attributes that integrators can use to extend the functionality provided out-of-the-box:

  • Custom and EAV (Entity-Attribute-Value) attributes. Custom attributes are those added on behalf of a merchant. For example, a merchant might need to add attributes to describe products, such as shape or volume. A merchant can add these attributes on the admin panel, and these attributes can be displayed. See the merchant documentation for information about managing custom attributes.

    Custom attributes are a subset of EAV attributes. Objects that use EAV attributes typically store values in several MySQL tables. The Customer and Catalog modules have the primary models that use EAV attributes. Other modules, such as ConfigurableProduct, GiftMessage, and Tax, use the EAV functionality for Catalog.

  • Extension attributes. Extension attributes are new in Magento 2. They are used to extend functionality and often use more complex data types than custom attributes. These attributes do not appear on the GUI.

EAV and custom attributes

CustomAttributesDataInterface defines the methods that are called to get and set custom attributes, including getCustomAttributes().

A module has a set of built-in attributes that are always available. The Catalog module has several attributes that are defined as EAV attributes, but are treated as built-in attributes. These attributes include:

  • attribute_set_id
  • created_at
  • group_price
  • media_gallery
  • name
  • price
  • sku
  • status
  • store_id
  • tier_price
  • type_id
  • updated_at
  • visibility
  • weight

In this case, when getCustomAttributes() is called, the system returns only custom attributes that are not in this list.

The Customer module does not treat its EAV attributes in a special manner. As a result, the getCustomAttributes() method returns all EAV attributes.

Extension attributes

Use ExtensibleDataInterface to implement extension attributes. In your code, you must define getExtensionAttributes() and setExtensionAttributes(*ExtensionInterface param).

public function getExtensionAttributes();

Most likely, you’ll want to extend interfaces defined in the Api/Data directory of a Magento module.

Declare extension attributes

You must create an <Module>/etc/extension_attributes.xml file to define the extension attributes for a module:

<config>
    <extension_attributes for="Path\To\Interface">
        <attribute code="name_of_attribute" type="datatype">
           <resources>
              <resource  ref="permission"/>
           </resources>
           <join reference_table="" reference_field="" join_on_field="">
              <field>fieldname</field>
           </join>
        </attribute>
    </extension_attributes>
</config>

where:

Keyword Description Example

for

The fully-qualified type name with the namespace that processes the extensions. The value must be a type that implements `ExtensibleDataInterface`. The interface can be in a different module.

Magento\Quote\Api\Data\TotalsInterface

code

The name of the attribute. The attribute name should be in snake case (the first letter in each word should be in lowercase, with each word separated by an underscore).

gift_cards_amount_used

type

The data type. This can be a simple data type, such as string or integer, or complex type, such as an interface.

float
Magento\CatalogInventory\Api\Data\StockItemInterface

ref

Optional. Restricts access to the extension attribute to users with the specified permission.

Magento_CatalogInventory::cataloginventory

reference_table

The table involved in a join operation. See Searching extension attributes for details.

admin_user

reference_field

Column in the reference_table

user_id

join_on_field

The column of the table associated with the interface specified in the for keyword that will be used in the join operation.

store_id

field

One or more fields present in the interface specified in the type keyword.

You can specify the column="" keyword to define the column in the reference_table to use. The field value specifies the property on the interface which should be set.

<field>firstname</field>
<field>lastname</field>
<field>email</field>

<field column="customer_group_code">code</field>

The system uses a join directive to add external attributes to a collection and to make the collection filterable. The join element in the extension_attributes.xml file defines which object fields and the database table/column to use as the source of a search.

In the following example, an attribute named stock_item of type Magento\CatalogInventory\Api\Data\StockItemInterface added to the Magento\Catalog\Api\Data\ProductInterface.

<extension_attributes for="Magento\Catalog\Api\Data\ProductInterface">
    <attribute code="stock_item" type="Magento\CatalogInventory\Api\Data\StockItemInterface">
        <join reference_table="cataloginventory_stock_item" reference_field="product_id" join_on_field="entity_id">
            <field>qty</field>
        </join>
    </attribute>
</extension_attributes>

When getList() is called, it returns a list of ProductInterfaces. When it does this, the code populates the stock_item with a joined operation in which the StockItemInterface’s qty property come from the cataloginventory_stock_item table where the Product’s entity_Id is joined with the cataloginventory_stock_item.product_id column.

Extension attribute authentication

Individual fields that are defined as extension attributes can be restricted, based on existing permissions. This feature allows extension developers to restrict access to data. See Web API authentication overview for general information about authentication in Magento.

The following code sample defines stock_item as an extension attribute of the CatalogInventory module. CatalogInventory is treated as a “third-party extension”. Access to the inventory data is restricted because the quantity of in-stock item may be competitive information.

<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:Api/etc/extension_attributes.xsd">
    <extension_attributes for="Magento\Catalog\Api\Data\ProductInterface">
        <attribute code="stock_item" type="Magento\CatalogInventory\Api\Data\StockItemInterface">
            <resources>
                <resource ref="Magento_CatalogInventory::cataloginventory"/>
            </resources>
        </attribute>
    </extension_attributes>
</config>

In this example, the stock_item attribute is restricted to only the users who have the Magento_CatalogInventory::cataloginventory permission. As a result, an anonymous or unauthenticated user issuing a GET http://<magento_base_url>/rest/V1/products/<sku> request will receive product information similar to the following:

{
  "sku": "tshirt1",
  "price": "20.00",
  "description": "New JSmith design",
  "extension_attributes": {
    "logo size": "small"
  },
  "custom_attributes": {
    "artist": "James Smith"
  }
}

However, an authenticated user with the permission Magento_CatalogInventory::cataloginventory receives the additional stock_item field:

{
  "sku": "tshirt1",
  "price": "20.00",
  "description": "New JSmith design",
  "extension_attributes": {
    "logo size": "small",
    "stock_item" : {
      "status" : "in_stock"
      "quantity": 70
    }
  },
  "custom_attributes": {
    "artist": "James Smith"
  }
}

This only works for extension attributes (those attributes defined in an extension_attributes.xml file). There are no permission restrictions on the rest of the returned data. For example, there is no way to restrict custom_attributes.

ExtensionInterfaces

An ExtensionInterface will be empty if no extension attributes have been added. In the following example, in an unmodified installation, CustomerExtensionInterface will be generated, but will be empty:

interface CustomerExtensionInterface extends \Magento\Framework\Api\ExtensionAttributesInterface { }

However, if an extension similar to the following has been defined, the interface will not be empty.

<extension_attributes for="Magento\Customer\Api\Data\CustomerInterface">
    <attribute code="attributeName" type="Magento\Some\Type[]" />
</extension_attributes>

Web API authentication overview