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23.

Quantity: Updating Data & Saving to the Server

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When we change the quantity input, the ShoppingCartList component is now emitting an updateQuantity event. In ShoppingCart, let's listen to that!

Up in the template, find where we render shopping-cart-list. Then add @updateQuantity= and make this execute a new method called, how about, updateQuantity.

101 lines | assets/pages/shopping-cart.vue
<template>
<div :class="[$style.component, 'container-fluid']">
<div class="row">
// ... lines 4 - 5
<div class="col-xs-12 col-lg-9">
// ... lines 7 - 8
<div class="content p-3">
// ... lines 10 - 11
<shopping-cart-list
// ... lines 13 - 14
@updateQuantity="updateQuantity"
/>
</div>
</div>
</div>
</div>
</template>
// ... lines 22 - 101

Copy that, go down to the methods section... here it is... and add that new function.

Object Destructing the Event Args

We know that this will receive an event object... and because we are the ones emitting that event, we know the object will have productId, colorId and quantity keys.

In the new method, let's use object destructuring on the first argument to grab those values and set them onto variables. Do it with {}, productId, colorId and quantity:

101 lines | assets/pages/shopping-cart.vue
// ... lines 1 - 31
export default {
name: 'ShoppingCart',
// ... lines 34 - 76
methods: {
// ... lines 78 - 83
updateQuantity({ productId, colorId, quantity }) {
// ... lines 85 - 86
},
},
};
</script>
// ... lines 91 - 101

Let's console.log() all 3 values to make sure everything is hooked up:

101 lines | assets/pages/shopping-cart.vue
// ... lines 1 - 22
<script>
// ... lines 24 - 31
export default {
name: 'ShoppingCart',
// ... lines 34 - 76
methods: {
// ... lines 78 - 83
updateQuantity({ productId, colorId, quantity }) {
console.log(productId, colorId, quantity);
// ... line 86
},
},
};
</script>
// ... lines 91 - 101

At the browser... change the quantity on the inflatable sofa. Yes! The product IRI, color IRI and quantity do log.

Saving the new Quantity to the Server

Inside this function, we need to do two things. First, we need update the quantity on the cart data, which lives in this component thanks to the mixin. And second, we need to make an AJAX call to the server to save the updated cart.

Fortunately, the cart-service module, that we copied into our project earlier, has a function that does both. Down in updateQuantity, say updateCartItemQuantity() and hit tab to auto-complete this so that PhpStorm adds the import on top. Pass this the cart - this.cart - then productId, colorId and quantity.

101 lines | assets/pages/shopping-cart.vue
// ... lines 1 - 22
<script>
import { updateCartItemQuantity } from '@/services/cart-service';
// ... lines 25 - 31
export default {
name: 'ShoppingCart',
// ... lines 34 - 76
methods: {
// ... lines 78 - 83
updateQuantity({ productId, colorId, quantity }) {
console.log(productId, colorId, quantity);
updateCartItemQuantity(this.cart, productId, colorId, quantity);
},
},
};
</script>
// ... lines 91 - 101

That's it! But let's see what that function really does: hold Command or Ctrl and click the updateCartItemQuantity to jump into it.

149 lines | assets/services/cart-service.js
// ... lines 1 - 107
/**
* Updates the quantity of a product already in the cart
*
* @param {CartCollection} cart
* @param {string} productId
* @param {string} colorId
* @param {number} quantity
* @return {Promise}
*/
export async function updateCartItemQuantity(cart, productId, colorId, quantity) {
const cartItemIndex = findItemIndex(cart, productId, colorId);
if (cartItemIndex === -1) {
throw new Error(`Invalid product+color combination: ${productId}, ${colorId}`);
}
cart.items[cartItemIndex].quantity = quantity;
const response = await axios.put(getCartIri(), cart);
return { items: response.data.items };
}
// ... lines 130 - 149

Setting Data from Outside a Component?

This is pretty simple stuff: it takes the cart, finds the array index of that item in the cart by using the productId and colorId, then sets the quantity to the new quantity. It finishes by making an AJAX request back to the server to save this.

Simple, right? Yep! But... I do want to highlight one thing. This function actually modifies the cart object... which means it's actually changing the cart data! Changing data is usually something that we do directly inside a component, specifically whatever component that piece of data belongs to. But if you pass a piece of data from Vue - like cart - to an outside function... and that function changes a property on that data, then that will - of course - cause the data to be changed!

I think this is okay. After all, the most important thing is that we're changing data... we're not accidentally changing a prop like we did earlier. But you should be aware that this is happening, be careful, and ultimately, make sure that the data is being updated, not a prop.

If we wanted to be more clear, we could rewrite this function into two pieces. The first piece would simply update the cart data: we could even put that inside the component or mixin. The second would take the already-updated cart object and save it via AJAX. That might feel less convenient, but it's a more "pure" way to do things.

Anyways, because this function does both things we need... I think this should work! Let's try it! Back at the browser, change the quantity and... yea! The price and total are changing! The header count is not changing yet... but we will fix that soon. Most importantly, when we refresh... the new quantity sticks. This was saved back to the server!

Next: there's a small improvement, kind of a "clean up", that I want to make related to how we emit the event. Once we make that improvement, we'll use this same strategy to get the remove button working. Fully functional cart here we come!