Magento Interfaces

Magento provides interfaces for all major entities.

Product interface:

use Magento\Catalog\Api\Data\ProductInterface;

$product = $this->productFactory->create();
$product->setName('My Product');
$product->setSku('MY-SKU');
$product->setPrice(29.99);
$product->setStatus(1);
$product->setVisibility(4);

Key product interface methods:

getId()
getName() / setName()
getSku() / setSku()
getPrice() / setPrice()
getStatus() / setStatus()
getVisibility() / setVisibility()
getAttributeSetId() / setAttributeSetId()
getExtensionAttributes()

Order interface:

use Magento\Sales\Api\Data\OrderInterface;

$order = $this->orderRepository->get($orderId);
$order->getIncrementId();
$order->getStatus();
$order->getGrandTotal();
$order->getItems();
$order->getShippingAddress();

Customer interface:

use Magento\Customer\Api\Data\CustomerInterface;

$customer = $this->customerRepository->getById($customerId);
$customer->getEmail();
$customer->getFirstname();
$customer->getLastname();
$customer->getGroupId();

Creating custom interfaces for your modules.

Custom entity interface:

<?php
namespace Vendor\Blog\Api\Data;

interface PostInterface
{
    const ENTITY_ID = 'entity_id';
    const TITLE = 'title';
    const CONTENT = 'content';
    const STATUS = 'status';
    const AUTHOR_ID = 'author_id';
    const URL_KEY = 'url_key';
    const CREATED_AT = 'created_at';
    const UPDATED_AT = 'updated_at';
    
    public function getId(): ?int;
    public function getTitle(): string;
    public function setTitle(string $title): self;
    public function getContent(): string;
    public function setContent(string $content): self;
    public function getStatus(): int;
    public function setStatus(int $status): self;
    public function getAuthorId(): ?int;
    public function setAuthorId(int $authorId): self;
    public function getUrlKey(): ?string;
    public function setUrlKey(string $urlKey): self;
    public function getCreatedAt(): ?string;
    public function setCreatedAt(string $createdAt): self;
    public function getUpdatedAt(): ?string;
    public function setUpdatedAt(string $updatedAt): self;
}

Interface naming conventions:

PostInterface — Data interface for entity
PostRepositoryInterface — Repository for CRUD
PostSearchResultsInterface — Search results
PostServiceInterface — Business operations
PostExtensionAttributesInterface — Extension attributes

Common patterns for using interfaces in Magento.

Type-hinting interfaces:

// GOOD: Depend on interface
public function __construct(
    private \Magento\Catalog\Api\ProductRepositoryInterface $productRepo
) {}

// BAD: Depend on concrete class
public function __construct(
    private \Magento\Catalog\Model\ProductRepository $productRepo
) {}

Repository returning interface:

public function get($id): PostInterface
{
    $post = $this->postFactory->create();
    $this->resource->load($post, $id);
    
    if (!$post->getId()) {
        throw new NoSuchEntityException();
    }
    
    return $post; // Post implements PostInterface
}

Service method with interface:

public function publish(PostInterface $post): PostInterface
{
    $post->setStatus(PostInterface::STATUS_PUBLISHED);
    $post->setPublishedAt($this->date->formatDate());
    
    return $this->postRepository->save($post);
}

Interface in di.xml:

<!-- Bind interface to implementation -->
<preference for="Vendor\Blog\Api\PostRepositoryInterface"
            type="Vendor\Blog\Model\PostRepository"/>

<!-- Override for specific area -->
<type name="Vendor\Blog\Api\PostRepositoryInterface">
    <arguments>
        <argument name="cacheEnabled" xsi:type="boolean">true</argument>
    </arguments>
</type>

Best practices for interface design.

1. Keep interfaces focused:

// BAD: Too many responsibilities
interface PostInterface
{
    // 50+ methods
}

// GOOD: Focused interface
interface PostInterface
{
    // Core data methods only
}

interface PostServiceInterface
{
    // Business operations
}

2. Return self for fluent interface:

interface PostInterface
{
    public function setTitle(string $title): self;
    public function setContent(string $content): self;
    public function setStatus(int $status): self;
}

// Usage: fluent chaining
$post->setTitle('Title')
    ->setContent('Content')
    ->setStatus(1);

3. Use nullable for optional fields:

interface PostInterface
{
    public function getId(): ?int; // Nullable
    public function getTitle(): string; // Required
    public function getAuthorId(): ?int; // Optional
}

4. Document interfaces:

/**
 * Post data interface
 *
 * @api
 */
interface PostInterface
{
    /**
     * Get post title
     *
     * @return string
     */
    public function getTitle(): string;
}

5. Don't change published interfaces:

- Adding methods: Minor version
- Changing signatures: Major version
- Removing methods: Breaking change