Magento 2 : Totals collection explained

What is it?

Quote Totals collection is an important process in magento.

This process also exists on Invoice and Creditmemo objects but we will only look into detail how it is implemented for the Quote object which is the one you will be more frequently interacting with. This process is very frequent in magento. Basically, it is executed every time a change is done on the cart. It can be:

• in Quote Model afterLoad event
• at order placing \Magento\InstantPurchase\Model\PlaceOrder::placeOrder
• when saving a quote item \Magento\Quote\Model\Quote\Item\Repository::save
• and many more places...

What is it for?

The objective of that process is (as it is well named) to collect the totals for the Quote object.
The Quote object is a complex and holds many prices information (grand_total, subtotal, subtotal_with_discount, etc.).
The value of these different prices are calculated using specific rules and are impacted differently.
This is what the total collection does.

How is it implemented?

The Quote instance is the main actor but he is not alone. There is also a TotalsCollector object and many TotalCollector objects that play their role.

Let's see what object owns what and what they are responsible for.

• The Quote object has a TotalsCollector.
• The TotalsCollector object has a list of TotalCollector.

The TotalsCollector is responsible for :

• looping on addresses (in many cases, 2 addresses, one billing and one shipping), see \Magento\Quote\Model\Quote\TotalsCollector::collect.
• executing a list of total collectors for each address, see \Magento\Quote\Model\Quote\TotalsCollector::collectAddressTotals.

Let's go a little more in detail.

The TotalsCollector initiates a global Total object (\Magento\Quote\Model\Quote\Address\Total).

<?php

/** @var \Magento\Quote\Model\Quote\Address\Total $total */
$total = $this->totalFactory
    ->create(\Magento\Quote\Model\Quote\Address\Total::class);
    

For each address, the TotalsCollector will get a new Total object that will come to "enrich" the global Total object.

This is done by calling the collect method of each TotalCollector, the resulting Total contains the data for the current address.

These are the data :

• shipping_amount
• base_shipping_amount
• shipping_description
• subtotal
• base_subtotal
• subtotal_with_discount
• base_subtotal_with_discount
• grand_total
• base_grand_total

Depending on the type of each data, it can be used to either increment the same data on the main Total object. This is the case for subtotal for example :
$total->setSubtotal((float)$total->getSubtotal() + $addressTotal->getSubtotal());

Or to either simply replace the same data in the main Total object. This is the case for shipping_amount for example :
$total->setShippingAmount($addressTotal->getShippingAmount());

There is the list of TotalCollector object that the TotalsCollector natively holds :

• Magento\Quote\Model\Quote\Address\Total\Subtotal
• Magento\Tax\Model\Sales\Total\Quote\Subtotal
• Magento\Weee\Model\Total\Quote\Weee
• Magento\SalesRule\Model\Quote\Discount
• Magento\Quote\Model\Quote\Address\Total\Shipping
• Magento\Tax\Model\Sales\Total\Quote\Shipping
• Magento\SalesRule\Model\Quote\Address\Total\ShippingDiscount
• Magento\Tax\Model\Sales\Total\Quote\Tax
• Magento\Weee\Model\Total\Quote\WeeeTax
• Magento\Quote\Model\Quote\Address\Total\Grand

How is it configured?

The list of TotalCollector is loaded from xml config.
See \Magento\Quote\Model\Quote\Address\Total\Collector::__construct
and \Magento\Sales\Model\Config\Ordered::_initCollectors.

Evertything happens in sales.xml file.
You will find a node element like this one : <section name="quote">

In Magento_Quote module :

<section name="quote">
	<group name="totals">
		<item name="subtotal" instance="Magento\Quote\Model\Quote\Address\Total\Subtotal" sort_order="100"/>
		<item name="shipping" instance="Magento\Quote\Model\Quote\Address\Total\Shipping" sort_order="350"/>
		<item name="grand_total" instance="Magento\Quote\Model\Quote\Address\Total\Grand" sort_order="550"/>
	</group>
</section>

And then in Magento_SalesRule module :

<section name="quote">
    <group name="totals">
        <item name="discount" instance="Magento\SalesRule\Model\Quote\Discount" sort_order="300"/>
        <item name="shipping_discount" instance="Magento\SalesRule\Model\Quote\Address\Total\ShippingDiscount" sort_order="400"/>
    </group>
</section>

And then in Magento_Tax module :

<section name="quote">
    <group name="totals">
        <item name="tax_subtotal" instance="Magento\Tax\Model\Sales\Total\Quote\Subtotal" sort_order="200"/>
        <item name="tax_shipping" instance="Magento\Tax\Model\Sales\Total\Quote\Shipping" sort_order="375"/>
        <item name="tax" instance="Magento\Tax\Model\Sales\Total\Quote\Tax" sort_order="450"/>
    </group>
</section>

And then in Magento_Weee module :

<section name="quote">
    <group name="totals">
        <item name="weee" instance="Magento\Weee\Model\Total\Quote\Weee" sort_order="225"/>
        <item name="weee_tax" instance="Magento\Weee\Model\Total\Quote\WeeeTax" sort_order="460"/>
    </group>
</section>

If I cumulate these configurations, we will have that :

<section name="quote">
    <group name="totals">
        <item name="subtotal" instance="Magento\Quote\Model\Quote\Address\Total\Subtotal" sort_order="100"/>
        <item name="tax_subtotal" instance="Magento\Tax\Model\Sales\Total\Quote\Subtotal" sort_order="200"/>
        <item name="weee" instance="Magento\Weee\Model\Total\Quote\Weee" sort_order="225"/>
        <item name="discount" instance="Magento\SalesRule\Model\Quote\Discount" sort_order="300"/>
        <item name="shipping" instance="Magento\Quote\Model\Quote\Address\Total\Shipping" sort_order="350"/>
        <item name="tax_shipping" instance="Magento\Tax\Model\Sales\Total\Quote\Shipping" sort_order="375"/>
        <item name="shipping_discount" instance="Magento\SalesRule\Model\Quote\Address\Total\ShippingDiscount" sort_order="400"/>
        <item name="tax" instance="Magento\Tax\Model\Sales\Total\Quote\Tax" sort_order="450"/>
        <item name="weee_tax" instance="Magento\Weee\Model\Total\Quote\WeeeTax" sort_order="460"/>
        <item name="grand_total" instance="Magento\Quote\Model\Quote\Address\Total\Grand" sort_order="550"/>
    </group>
</section>

For order_invoice and order_creditmemo, we will find the same types of xml declarations.

For order_invoice :

<section name="order_invoice">
    <group name="totals">
        <item name="subtotal" instance="Magento\Sales\Model\Order\Invoice\Total\Subtotal" sort_order="50"/>
        <item name="discount" instance="Magento\Sales\Model\Order\Invoice\Total\Discount" sort_order="100"/>
        <item name="shipping" instance="Magento\Sales\Model\Order\Invoice\Total\Shipping" sort_order="150"/>
        <item name="tax" instance="Magento\Sales\Model\Order\Invoice\Total\Tax" sort_order="200"/>
        <item name="cost_total" instance="Magento\Sales\Model\Order\Invoice\Total\Cost" sort_order="250"/>
        <item name="grand_total" instance="Magento\Sales\Model\Order\Invoice\Total\Grand" sort_order="350"/>
    </group>
</section>

For order_creditmemo :

<section name="order_creditmemo">
    <group name="totals">
        <item name="subtotal" instance="Magento\Sales\Model\Order\Creditmemo\Total\Subtotal" sort_order="50"/>
        <item name="discount" instance="Magento\Sales\Model\Order\Creditmemo\Total\Discount" sort_order="150"/>
        <item name="shipping" instance="Magento\Sales\Model\Order\Creditmemo\Total\Shipping" sort_order="200"/>
        <item name="tax" instance="Magento\Sales\Model\Order\Creditmemo\Total\Tax" sort_order="250"/>
        <item name="cost_total" instance="Magento\Sales\Model\Order\Creditmemo\Total\Cost" sort_order="300"/>
        <item name="grand_total" instance="Magento\Sales\Model\Order\Creditmemo\Total\Grand" sort_order="400"/>
    </group>
</section>

Conclusion

The total collection is an important process in Magento and it's good to know how it works a bit because you will certainly be interacting with it at one point or another as a magento developer. It is used in magento natively to handle the things that are not the cart items but that impact the total price. This is how the shipping is handled and also the wee tax (Waste Electrical and Electronic Equipment) but you could imagine using it also for you own needs some day.