Enhanced performance of product loading.

When adding a new resolved field to product interface, make sure to:

1. Understand when you are able to load it? If you can load it on collection, create a processor and register it in CompositeCollectionProcessor using DI.
2. If data is needed to be formatted, or you can not request data with collection, use DataPostProcessor. Register a processor there, and return a product (as key => value array) processing function (see example in implementations).
3. If data is impossible to request before collection load, but it is possible to append the loaded data afterwards (using the collection itself) - use CollectionPostProcessor, register the processor there in the same way as for DataPostProcessor.

• quote-graphql
• wishlist-graphql
• catalog-graphql
• reviews-graphql

CASE ONE: The data can not be requested along with product collection (only post-load is possible)

1. After collection load, checked for requested fields in schema (using $info) for each additional info category
2. If additional info was requested, the helper requested & returned the info for all products at once
3. The loop through all loaded products applying data from helpers to each specific product

CASE TWO: The data can be requested before load (field can be resolved with collection load)

This one is covered by M2 (by default) - we will just ignore this.

1. The collection processor goes through collection, it adds requested fields to a collection
2. If field requires additional work, it is formatted after collection load
3. If field needs no formatting it is automatically out-putted in resulting data array

CASE THREE: The data can be requested after collection load, but is based on the collection data, not product array.

a. The code duplicates in each of 5 places were the collection was loaded [REQUIRES ABSTRACTION] b. The data structures are common to be different from place to place, a check if field was requested or no is hard:

1. ConfigurableVariant: variants/product
2. Default: products/items
3. Cart, Wish-list: items/product
4. Orders: order_products

Class name: ScandiPWA\Performance\Model\Resolver\ResolveInfoFieldsTrait

Motivation: allows for GraphQL info parsing, can extract fields from path. By default returns array of product fields, the product field parsing can be changed by overriding getFieldContent method.

Used in:

1. ScandiPWA\Performance\Model\Resolver\Products\DataPostProcessor\Images
2. ScandiPWA\Performance\Model\Resolver\Products\DataPostProcessor\Stocks
3. ScandiPWA\Performance\Model\Resolver\Products\DataPostProcessor\Attributes
4. ScandiPWA\CatalogGraphQl\Model\Resolver\ConfigurableVariant
5. ScandiPWA\CatalogGraphQl\Model\Resolver\Products\Query\Filter
6. ScandiPWA\WishlistGraphQl\Model\Resolver\WishlistItemsResolver
7. ScandiPWA\QuoteGraphQl\Model\Resolver\ProductsResolver

Class name: ScandiPWA\Performance\Model\Resolver\Products\CollectionPostProcessor

Motivation: allows to post-process collection, for situations, where data is applied on-top of loaded collection - media gallery data, product options data, etc.

Used in:

1. ScandiPWA\CatalogGraphQl\Model\Resolver\Products\DataProvider\Product
2. ScandiPWA\CatalogGraphQl\Model\Variant\Collection

Class name: ScandiPWA\Performance\Model\Resolver\Products\DataPostProcessor

Motivation: allows for loaded product collection data post-processing. Accepts array of products, resolve info and can efficiently process the product data. Is made to prevent child fields of products to request the data in the loop. Attribute, image, stock info is moved to this resolver out of product.

Used in:

1. ScandiPWA\WishlistGraphQl\Model\Resolver\WishlistItemsResolver
2. ScandiPWA\QuoteGraphQl\Model\Resolver\GetCartForCustomer
3. ScandiPWA\CatalogGraphQl\Model\Resolver\Products\Query\Filter
4. ScandiPWA\QuoteGraphQl\Model\Resolver\ProductsResolver
5. ScandiPWA\CatalogGraphQl\Model\Resolver\ConfigurableVariant

Class name: ScandiPWA\CatalogGraphQl\Model\Resolver\Products\DataProvider\Product

Motivation: previously the collection post processor was implemented here (hard-coded). Since it was moved into separate class, the logic had to be removed from origin.

Used in:

1. ScandiPWA\QuoteGraphQl\Model\Resolver\ProductsResolver
2. ScandiPWA\CatalogGraphQl\Model\Resolver\Products\Query\Filter

Class name: Magento\CatalogGraphQl\Model\Resolver\Products\DataProvider\Product\CompositeCollectionProcessor

Motivation: The M2 implementation was OK, just added additional processors to it:

1. ScandiPWA\CatalogGraphQl\Model\Resolver\Products\DataProvider\Product\CollectionProcessor\ImagesProcessor