Create 3. Demonstrate ability to customize the shopping cart.md

Author: unicoder88

8. Customizing the Checkout Process/3. Demonstrate ability to customize the shopping cart.md

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+# Demonstrate ability to customize the shopping cart
+
+## Describe how to implement shopping cart rules.
+DB tables:
+- `salesrule`
+  * name, description, is_active, is_rss
+  * from_date, to_date, conditions_serialized, is_advanced, sort_order, product_ids
+  * actions_serialized, simple_action, discount_amount, discount_qty, discount_step, apply_to_shipping
+  * stop_rules_processing, uses_per_customer, times_used
+  * coupon_type, use_auto_generation
+- `salesrule_label` - label translation
+  * rule_id, store_id, label
+- `salesrule_product_attribute`
+  * rule_id, website_id, customer_group_id, attribute_id
+
+Multiple selection:
+- `salesrule_website`
+- `salesrule_customer_group`
+
+- `salesrule_coupon`
+  * rule_id, code, usage_limit, usage_per_customer, times_used, expiration_date, is_primary, created_at, type
+
+Usage tracking:
+- `salesrule_coupon_usage`
+  * coupon_id, customer_id, times_used
+- `salesrule_customer`
+  * rule_id, customer_id, times_used
+- `salesrule_coupon_aggregated`, `salesrule_coupon_aggregated_updated`, `salesrule_coupon_aggregated_order` - reporting stuff
+
+- ui component `sales_rule_form`
+- conditions - html content block - *generic form* Edit\Tab\Conditions
+- conditions fieldset renderer \Magento\Rule\Block\Conditions.render
+- `$element->getRule()->getConditions()->asHtmlRecursive();`
+- Magento\SalesRule\Model\Rule extends Magento\Rule\Model\AbstractModel
+  + store labels
+  + coupon generation
+- Conditions model instance - \Magento\SalesRule\Model\Rule\Condition\Combine, extends getNewChildSelectOptions:
+  + \Magento\SalesRule\Model\Rule\Condition\Product\Found - Product attribute combination
+  + \Magento\SalesRule\Model\Rule\Condition\Product\Subselect - Products subselection
+  + Conditions combination - self, recursion
+  + \Magento\SalesRule\Model\Rule\Condition\Address - Cart Attribute:
+    base_subtotal, total_qty, weight, shipping_method, postcode, region, region_id, country_id
+
+what is:
+- `is_advanced` column - not used
+- `product_ids` column - not used
+- `salesrule_product_attribute` table - attributes currently used in conditions and actions of rule.
+
+  Used in plugin to \Magento\Quote\Model\Quote\Config::`getProductAttributes` to ensure all needed
+  attributes are loaded with quote.
+  * quote.load()
+  * quoteResource.`_assignProducts`
+  * product collection `->addAttributeToSelect($this->_quoteConfig->getProductAttributes())`.
+
+
+## What is the difference between sales rules and catalog rules?
+- Catalog rules update product final price, they are visible in all catalog - category listing, product page.
+- Sales rule is visible only in checkout and can require a coupon.
+- Sales rules can affect shipping price
+- Sales rules can trigger on products combination
+
+
+## How do sales rules affect performance?
+Performance is not affected, all calculation happens in totals collectors.
+
+## What are the limitations of the native sales rules engine?
+Only one coupon can be applied.
+
+
+Implementing rules:
+- Rule model
+  * getConditionsInstance - will be used in form as `$model->getConditions()->asHtmlRecursive()`.
+    Usually starting conditions are composite - selector [all/any] and sub-conditions selection.
+- Composite conditions model
+  * getNewChildSelectOptions - used by Consition\Combine.getNewChildElement
+
+
+## Describe add-to-cart logic in different scenarios.
+
+### Add to cart
+cart model - used only on frontend, marked deprecated.
+
+- checkout/cart/add [product, qty, related_product]
+  * cart model.addProduct
+    + filter request here, can register own via argument for \Magento\Checkout\Model\Cart\RequestInfoFilter
+    + by default filtered out `form_key` and `custom_price`
+  * quote.addProduct
+  * product type instance.`prepareForCartAdvanced`
+  * get same quote item or create new
+  * \Magento\Quote\Model\Quote\Item\Processor::prepare
+    + quote item.addQty
+    + support request.customPrice -> quote item.customPrice
+  * event `checkout_cart_product_add_after`
+  * checkout session.setLastAddedProductId
+  * cart.save
+    + quote collect totals
+    + event `checkout_cart_save_after`
+    + reinitialize state - remove addresses and payments
+  * event `checkout_cart_add_product_complete`
+
+- checkout/cart/updatePost
+  * cart.suggestItemsQty => \Magento\CatalogInventory\Model\StockStateProvider::suggestQty - qty increments, min/max qty
+  * cart.updateItems
+    + events `checkout_cart_update_items_before`, `checkout_cart_update_items_after`
+    + quote item.setQty -- triggers stock validation
+  * cart.save
+
+### *controller checkout/cart/add*:
+- cart.addProduct:
+  * quote.addProduct: type.`prepareForCartAdvanced`, event `sales_quote_product_add_after`
+  * event `checkout_cart_product_add_after`
+- event `checkout_cart_add_product_complete` -- this event only when normal add to cart
+  * withlist observer, marked to be deleted
+
+
+### *add to withlist* `wishlist/index/add`:
+- same buy request
+- cart candidates = type instance.processConfiguration -> `_prepareProduct`. Same as with add to cart.
+- create/update qty withlist item, just like quote item
+- event `wishlist_product_add_after`
+- event `wishlist_add_product`
+
+### *add to cart from wishlist* `withlist/index/cart`:
+
+Can override original buyRequest when adding to cart.
+NO event _checkout_cart_add_product_complete_.
+
+- load withlist item and options
+- merge buy request - saved and current.
+- wishlist item.addToCart
+- `cart.addProduct` with merged buyRequest:
+  * events `sales_quote_product_add_after`, `checkout_cart_product_add_after`
+- cart.save
+  * event `checkout_cart_save_before`
+  * event `checkout_cart_save_after`
+- quote.collectTotals
+- \Magento\Wishlist\Helper\Data::calculate
+  * write to customer session
+  * event `wishlist_items_renewed`
+
+### *merge quotes* controller `customer/account/loginPost`:
+
+Cart model is not used at all.
+
+- \Magento\Customer\Model\Session::setCustomerDataAsLoggedIn
+- event `customer_login`
+- \Magento\Checkout\Observer\LoadCustomerQuoteObserver
+- checkout session.`loadCustomerQuote`:
+  * event `load_customer_quote_before`
+  * finds existing customer quote
+  * detects that guest quote <> customer quote
+  * customer quote.`merge`(guest quote):
+    + event `sales_quote_merge_before`
+    + for each quote item.`compare` - product id, options same
+    + if items same, qty++
+    + if guest item is new, clone quote item, quote.addItem, event `sales_quote_add_item`
+    + event `sales_quote_merge_after`
+  * *delete guest quote*
+
+### *reorder* controller `sales/order/reorder`:
+
+Like normal add to cart, but NO event _checkout_cart_add_product_complete_.
+
+- load order, ensure can view
+- for each order item, `cart.addOrderItem` - converts order item to quote item:
+  * load product
+  * get item option buyRequest
+  * `cart.addProduct` with old buy request
+    + events `sales_quote_product_add_after`, `checkout_cart_product_add_after`
+
+
+## Describe how to customize the process of adding a product to the cart.
+- plugin over product type `prepareForCartAdvanced`
+- event `catalog_product_type_prepare_full_options` - custom options in `_prepareOptions`
+- plugin over \Magento\Quote\Model\Quote\Item\Processor::prepare - qty, custom price
+- event `checkout_cart_product_add_after`
+
+## Which different scenarios should you take into account?
+- add to cart from catalog
+- add to cart from wishlist
+- move all wishlist to cart
+- merge quote when existing customer has quote, then shops as a guest and logs in
+- admin create order
+- admin reorder
+- configure added product - change custom options
+
+
+## Render product types
+checkout cart index:
+- `<update handle="checkout_cart_item_renderers"/>`
+- `<update handle="checkout_item_price_renderers"/>`
+
+- block \Magento\Checkout\Block\Cart\AbstractCart::getItems - quote visible items
+  * can limit with *pagination*
+  * *custom_items* can override
+- abstract cart.`getItemHtml`(quote item)
+- render via abstract cart.`getItemRenderer` by product type
+  * renderer child block `renderer.list` \Magento\Framework\View\Element\RendererList
+  * renderer list block.getRenderer(type, template)
+  * finds child block by alias = product type
+  * \Magento\Checkout\Block\Cart\Item\Renderer
+  * 
+
+Customizations:
+- provide cart block data arguments `<referenceBlock name="checkout.cart.form">`:
+  * `renderer_list_name` - use custom renderer list
+  * `overriden_templates` - array by product type
+  * `renderer_template` - regardless of product type
+- in `checkout_cart_item_renderers`, `<referenceBlock name='renderer.list'>`, add child blocks by alias = product type. E.g.
+
+```xml
+<referenceBlock name="checkout.cart.item.renderers">
+    <block class="Magento\Checkout\Block\Cart\Item\Renderer" name="checkout.cart.item.renderers.default" as="default" template="Magento_Checkout::cart/item/default.phtml">
+        <block class="Magento\Checkout\Block\Cart\Item\Renderer\Actions" name="checkout.cart.item.renderers.default.actions" as="actions">
+            <block class="Magento\Checkout\Block\Cart\Item\Renderer\Actions\Edit" name="checkout.cart.item.renderers.default.actions.edit" template="Magento_Checkout::cart/item/renderer/actions/edit.phtml"/>
+            <block class="Magento\Checkout\Block\Cart\Item\Renderer\Actions\Remove" name="checkout.cart.item.renderers.default.actions.remove" template="Magento_Checkout::cart/item/renderer/actions/remove.phtml"/>
+        </block>
+    </block>
+</referenceBlock>
+```
+
+## Describe the available shopping cart operations.
+
+### Configure product in cart - controller `checkout/cart/configure`
+Product view and product configure are rendered via same helper
+\Magento\Catalog\Helper\Product\View.prepareAndRender.
+
+The only difference is params:
+- category_id - can be `false`
+- configure_mode - optional
+- buy_request - optional
+- specify_options - error message if missing options
+
+*Normal product view*:
+- params[category_id] = current
+- params[specify_options] - from product type
+- helper product view.prepareAndRender
+  * \Magento\Catalog\Helper\Product::initProduct - load product, check visible/enabled
+    + event `catalog_controller_product_init_before`
+    + event `catalog_controller_product_init_after`
+  * event `catalog_controller_product_view`
+
+*Configure product*:
+- params[`buyRequest`] = quote item.buyRequest
+- helper product view.prepareAndRender
+  * product helper.initProduct
+  * product helper.`prepareProductOptions` - set default selections from buy request, e.g. selected size=XXL
+    + product.processBuyRequest, `product type.processBuyRequest`, `product type.checkProductConfiguration`
+    + product.`setPreconfiguredValues`
+  * product.setConfigureMode -- used to show all hidden customization options instantly in edit mode
+  * event `catalog_controller_product_view`
+
+product.getPreconfiguredValues is later used:
+- default product qty = product.preconfigured values.qty
+- custom option values = product.preconfigured values.option_{$id}
+
+### How do you add a field to the shipping address?
+
+Quote address extends AbstractExtensibleModel, and so should implement `getCustomAttributesCodes()`
+to add custom attributes. Custom attributes should load and save automatically, assuming you added
+a column in migration and registered custom attribute in plugin (see below).
+
+Quote address custom attributes:
+* community \Magento\Quote\Model\Quote\Address\CustomAttributeList - empty, use plugin to add
+* EE \Magento\CustomerCustomAttributes\Model\Quote\Address\CustomAttributeList::getAttributes
+  + customer address attributes + customer attributes
+
+Alternatively, you can always register extension attribute and load/save it manually.