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So what we're going to do in this episode is just go ahead and add an item to our cart. We're going to see that in our cart. We're going to manually create a stock change to reduce the quantity. And then we should see an exception thrown if the quantity has changed.

In the next episode, we'll take that exception and we will handle syncing the quantities for multiple products just to make sure that the quantities are reduced to the amount we do have available. And this process will happen on the cart page that we can see here. It will happen on the checkout page, and it will also happen when we go through to process

the order as well. So if we order and someone has just ordered before us and reduced that quantity and that brings our quantity down for a particular product, we're going to let the user know before we process the payment. OK, let's go ahead and add a product in.

We can just work with one product for this. So let's go ahead and just choose our Nike Air Force 1s in black in size 8. Now, I'm going to bump this quantity up to, let's say, 10. So we'll go for the full 10 pairs of this.

And if we come over to our database here under stocks, we know that's the case because for this one, we have got 10. Let's remove the others just so we're a little bit clearer, and we should be good. OK, so what we're going to do is reduce this by 5.

So this is what happens when we create an order and we purchase five of these. Now, at the moment, when we refresh this, we kind of see a sort of not an error but a problem here because we have technically a 10 value for this quantity. But remember, we reduce this quantity dropdown by the amount of stock that we have.

So what we want to do at this point ideally is not do this because it kind of looks like we have one in our cart when actually, if we come over to our cart variation here, we still have 10. That's not what we want to happen.

We want this to reduce down to the maximum that we actually have available. So let's start by doing this over on our cart index controller that we are currently looking at here. Ideally, what we want to do is refresh the page and then verify these quantities.

So we're going to go ahead and bring in our cart interface in here, and we're going to call a method on our cart to verify the available quantities. So let's say verify available quantities. Let's go ahead and create this over on cart.php.

So let's do this just, well, we could do it anywhere. Let's just do it down here. So verify available quantities. And for now, let's just die dump just to make sure that this is working nicely.

There we go. So that's at the point that we want to trigger and check that we have available quantities. And if we don't for any of the products in our cart, we want to throw an exception. So we want to iterate and do this for every single product.

So let's go ahead and grab the cart instance. Let's grab the variations or we could use contents. And let's go over each one here, create our closure in here. Now, this will only detect and throw an exception for the first one that we find that has no

quantity available or less quantity available. But that's fine, because when we bring in the sync method, that's going to go ahead and sync this and reduce all of the items in our cart based on any stock. So if we have two products in our cart that both have a quantity of 10 and both are reduced

by five, these will both be reduced by five. What we won't be able to do is tell the user exactly the products that have been reduced, but we can always refact that later if we have time. OK, so we're going through each of the products in our cart.

What do we want to check in here? Let's think about this in plain English. We want to check that for each of these variations that we get through in this iteration pivot. So the pivot is going to be, say, 10.

We want to check if that is greater than the available stock for that variation. And we've got that variation here, so we can access the stock's relationship. So let's put this into an if statement. And we're just going to say variation pivot quantity.

So that's, in our case, going to be 10, because we have 10 of that in our cart. And we're going to access the stock's relationship on that variation. And we're going to sum up the amount. So we could technically, if we just come over to the variation model,

we could check if, let's have a look, stock count. So we could use this stock count. But remember, that uses the descendants themselves. So I think just doing a sum on the amount for this is going to be absolutely fine for now.

And then let's throw an exception in here and just say stock reduced. We'll be changing this to a custom exception in a moment. So let's make sure we pull that namespace in. OK, so now we should expect to see this.

And let's make sure we throw a new exception. OK, let's go over and give that a refresh. And there we go. We get a stock produced exception.

Because, of course, the stock that we've got in here, which is 10, is now 5, because we produced that by 5. Now let's create a custom exception for this so we know exactly what we're looking for. So I'm just going to create an exceptions folder out in our cart here.

And let's go ahead and create a quantity no longer available exception. And let's just scaffold this out really quickly. So the namespace here is going to be app cart exceptions. We could, of course, create a new exception by the command line with artisan.

But we'll just kind of keep this as it is for now. And quantity no longer available exception. And, of course, that's going to extend PHP's base exception, which we can go ahead and put in here.

Now we don't need to do anything in here. Technically, what you could do is pass the product in so you could show more information. But let's kind of keep this as it is. In fact, I'm going to get rid of the exception suffix on this,

because I don't really think it makes too much sense. So that should be fine. OK, so now we can go ahead and throw a quantity no longer available. And we can pick that up where we need it.

So if we just come over and give that a refresh, we get exactly the same thing here with the stock produced. But now we have something a little bit more specific to pick up. So over in our cart index controller, what we're going to do is try

and we're going to verify those available quantities. And then we're going to catch a quantity no longer available exception. And let's make sure we pull that in. And then here, we're going to go ahead and sync the products that we have in our cart

with the max quantities that are available. So that is where we've got to. The process of verifying the available quantities is done. We just need to focus on syncing these, which we're going to be doing in the next episode.