ProcessEight/Anatomy of Magento 2: Layered Navigation.md

## Anatomy of Magento 2: Layered Navigation.md

      
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              Anatomy of Magento 2: Layered Navigation.md
            
          
    Anatomy of Magento 2: Layered Navigation

Points for investigation


Generate high-level overview of all the main components
How are the total item counts for each option generated?
How is the catalog updated to display the matching products?
How are options rendered?
What are the customisation points?
What events are dispatched?
What observers listen on the process?
What plugins are used?
What effect do the options in the Manage Attributes section of the admin have?
Create flowcharts
How does the logic differ between the catalog and search results pages?
How does this work with caching?

Architecture

Key concepts


\Magento\Catalog\Model\Layer\Resolver Creates a layer object of the given type ('catalog' or 'search')
\Magento\Catalog\Model\Layer Layer view model
\Magento\Catalog\Model\Layer\State State model for the layer. Manages which filters are applied to the layer.
\Magento\Catalog\Model\Layer\Filter\DataProvider\Category Provides logic to load the category and use it as a filter
\Magento\Catalog\Model\Layer\Filter\DataProvider\Decimal Provides logic to use decimal values (excluding prices) as a filter (e.g. Managing range values)
\Magento\Catalog\Model\Layer\Filter\DataProvider\Price Provides logic to use prices as a filter (e.g. Managing ranges, price steps, applying config settings)
\Magento\Catalog\Model\Layer\FilterList Manages the types of filters that can be used. Core filter types include 'category', 'attribute', 'price' and decimal'. Filters can be added or replaced by adding elements to the \Magento\Catalog\Model\Layer\FilterList::__construct(array filters) argument.
\Magento\Catalog\Model\Layer\Category\FilterableAttributeList Returns collection of attributes that can be filtered by layered navigation (Defined by setting the attribute property is_filterable to true)
\Magento\LayeredNavigation\Block\Navigation Contains logic for starting rendering process of current layer
\Magento\LayeredNavigation\Block\Navigation\State Manages state of the current layer
\Magento\Framework\Search\Response\Aggregation A collection of buckets for a layer
\Magento\Framework\Search\Response\Bucket A container for a filter and it's values

Code safari

First load of an anchor category, before selecting any options to filter by.

The controller for category pages, \Magento\Catalog\Controller\Category\View, checks if layered navigation is enabled for this category and if so, adds custom handles to the layout.
The default block for adding layered navigation to a category is catalog.leftnav.
Both Magento_Catalog and Magento_LayeredNavigation define blocks with this name, in htdocs/vendor/magento/module-catalog/view/frontend/layout/catalog_category_view_type_default.xml and htdocs/vendor/magento/module-layered-navigation/view/frontend/layout/catalog_category_view_type_layered.xml respectively.

Question: Given these blocks are added to the same container (sidebar.main), why don't these blocks conflict?

The class defined by both blocks is different


The block class for catalog.leftnav in catalog_category_view_type_default.xml resolves to a virtual type, which extends from \Magento\LayeredNavigation\Block\Navigation.

Filtering the collection


In \Magento\LayeredNavigation\Block\Navigation::_prepareLayout, applicable filters for the current layer are retrieved and then applied to the current request.

Magento\Catalog\Model\Layer\Category\FilterableAttributeList: Gets collection of filterable attributes

\Magento\Catalog\Model\Layer\FilterList: Creates the filters.


\Magento\CatalogSearch\Model\Layer\Filter\Category: Executes logic specific to category filters. Gets the category ID from the request and filters the collection of the current layer by it.

\Magento\Catalog\Model\Layer\Filter\DataProvider\Category: Returns the current category, loading it if necessary, then stores it in registry (current_category_filter).

\Magento\CatalogSearch\Model\Layer\Category\ItemCollectionProvider: Returns filtered collection of items for the category filter type
\Magento\CatalogInventory\Model\Plugin\Layer::beforePrepareProductCollection: Filters collection by stock status (defaults to hiding out-of-stock items)

\Magento\Catalog\Model\Layer\Category\CollectionFilter: Adds default product attributes, minimal price, final price, 'tax percents', URL rewrites (for this category) to collection and filters by product visibility


\Magento\Catalog\Model\Layer::$_productCollections: The filtered collection is then stored to the \Magento\Catalog\Model\Layer::$_productCollections property


This process of filtering the collection by filters passed in the request is repeated for each filter
\Magento\Catalog\Model\Layer::apply: The filters are then applied to the current layer. Gets all the filters applicable to the current state and creates a unique key for the state.


\Magento\LayeredNavigation\Block\Navigation::_prepareLayout delegates to the parent _prepareLayout, which eventually dispatches the core_layout_block_create_after event.

Displaying it


\Magento\Catalog\Block\Product\ListProduct::initializeProductCollection:

Gets the filtered collection from the layer block (\Magento\Catalog\Model\Layer\Category in this case)
Sorts the collection by applicable sort orders (Price, Position, etc)
Sets the collection to the toolbar block (to ensure that pagination, product counts are correct)


htdocs/vendor/magento/module-catalog/view/frontend/templates/product/list.phtml gets product collection

Outputs toolbar
Outputs product grid (or list)


htdocs/vendor/magento/theme-frontend-luma/Magento_LayeredNavigation/templates/layer/view.phtml:

Checks whether block can be output
Outputs number of active filters
Calls child block 'state' of type \Magento\LayeredNavigation\Block\Navigation\State

htdocs/vendor/magento/theme-frontend-luma/Magento_LayeredNavigation/templates/layer/state.phtml Renders currently applied filters


Outputs list of filters

Each filter has it's own renderer block class and accompanying template

Plugin \Magento\Swatches\Model\Plugin\FilterRenderer::aroundRender checks if this filter attribute is a swatch attribute and if so, renders a custom block


\Magento\LayeredNavigation\Block\Navigation\FilterRenderer::render calls the toHtml method to render each filter
The default template for each filter is htdocs/vendor/magento/module-layered-navigation/view/frontend/templates/layer/filter.phtml
The block class is \Magento\Catalog\Model\Layer\Filter\Item

Outputs the different options for each filter attribute
Outputs the count of each option for each filter attribute


How product counts are generated

TODO: Finish this section
Magento 2 uses the CatalogSearch module in order to generate the counts of each product.

\Magento\Catalog\Block\Product\ListProduct::initializeProductCollection dispatches event catalog_block_product_list_collection

This is observed by \Magento\Review\Observer\CatalogBlockProductCollectionBeforeToHtmlObserver, which loads the collection
In \Magento\CatalogSearch\Model\ResourceModel\Fulltext\Collection::_renderFiltersBefore, search criteria is created and passed to the search instance, \Magento\Search\Api\SearchInterface, which in turn queries the configured search engine, \Magento\Search\Model\SearchEngine


For filter type 'category'


\Magento\LayeredNavigation\Block\Navigation::canShowBlock triggers a process which initialises all filter options

\Magento\Catalog\Model\Layer\Category\AvailabilityFlag::isEnabled tries to load all filters
\Magento\Catalog\Model\Layer\Category\AvailabilityFlag::canShowOptions cycles through all filters and loads the item count for each one.

That loop eventually calls \Magento\Catalog\Model\Layer\Filter\AbstractFilter::_initItems
\Magento\CatalogSearch\Model\Layer\Filter\Category::_getItemsData: Gets collection from layer model, calls getFacetedData

\Magento\CatalogSearch\Model\ResourceModel\Fulltext\Collection::getFacetedData: Renders filters of layer product collection; Returns faceted data from faceted search result for filter

Gets aggregations from searchResult; Loops through buckets in aggregations


\Magento\Catalog\Block\Product\ListProduct::initializeProductCollection dispatches event catalog_block_product_list_collection

This is observed by \Magento\Review\Observer\CatalogBlockProductCollectionBeforeToHtmlObserver, which loads the collection
In \Magento\CatalogSearch\Model\ResourceModel\Fulltext\Collection::_renderFiltersBefore, search criteria is created and passed to the search instance, \Magento\Search\Api\SearchInterface, which in turn queries the configured search engine, \Magento\Search\Model\SearchEngine


For filter type 'attribute'


\Magento\LayeredNavigation\Block\Navigation::canShowBlock triggers a process which initialises all filter options

\Magento\Catalog\Model\Layer\Category\AvailabilityFlag::isEnabled tries to load all filters
\Magento\Catalog\Model\Layer\Category\AvailabilityFlag::canShowOptions cycles through all filters and loads the item count for each one.

That loop eventually calls \Magento\Catalog\Model\Layer\Filter\AbstractFilter::_initItems
\Magento\CatalogSearch\Model\Layer\Filter\Category::_getItemsData: Gets collection from layer model, calls getFacetedData

\Magento\CatalogSearch\Model\ResourceModel\Fulltext\Collection::getFacetedData: Renders filters of layer product collection; Returns faceted data from faceted search result for filter

Gets aggregations from searchResult; Gets buckets for this attribute from aggregations
Buckets contains Metrics. Metrics are a count of how many times the filter option (i.e. attribute value) appeared in the search result. These are the counts which are eventually displayed beside each option in the layered navigation block.


Gets all frontend attribute options and generates filter options/items from them

\Magento\CatalogSearch\Model\Layer\Filter\Attribute::buildOptionData Detects whether this option reduces the number of products displayed. If not, the filter option is not rendered. If so, a new filter item is created and added to an internal array. This array is built up to contain the frontend label, attribute value and product count for each filter option of this attribute.


For filter type 'price'


htdocs/vendor/magento/theme-frontend-luma/Magento_LayeredNavigation/templates/layer/view.phtml:33 eventually calls

\Magento\Catalog\Model\Layer\Filter\AbstractFilter::_initItems

\Magento\CatalogSearch\Model\Layer\Filter\Category::_getItemsData: Gets collection from layer model, calls getFacetedData

\Magento\CatalogSearch\Model\ResourceModel\Fulltext\Collection::getFacetedData: Renders filters of layer product collection; Returns faceted data from faceted search result for filter

Gets aggregations from searchResult; Gets buckets for this attribute from aggregations
Buckets contains Metrics. Metrics are a count of how many times the filter option (i.e. attribute value) appeared in the search result. These are the counts which are eventually displayed beside each option in the layered navigation block.


Checks that there is more than one 'facet' (attribute option) (in order to generate a valid range)

Each 'facet' contains a value representing the price steps (e.g. 100-200), a count of how many products fit this facet and 'from' and 'to' values representing the upper and lower bounds of the range.


\Magento\Catalog\Model\Layer\Resolver:


Is used to determine the type of layer to use for this request: 'category' or 'search'.


The types are defined in \Magento\Catalog\Model\Layer\Resolver


The types are added to a layersPool argument which is populated in htdocs/vendor/magento/module-catalog/etc/di.xml:490 and injected by di.


Which opens the possibility of creating a custom type?


The resolver returns a layer object of the configured type


Both of the default types extend from \Magento\Catalog\Model\Layer.


Rendering starts in \Magento\LayeredNavigation\Block\Navigation::_prepareLayout


How does the logic differ between the catalog and search results pages?

There are separate layers for both:
htdocs/vendor/magento/module-catalog/etc/di.xml:490