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All right.
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So we are now on to the last item in CRUD which is how do you delete data from your persistent container
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using Core Data.
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So let's try that out over here as well.
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So, what if instead of checking items off by just having the accessories show up, what if instead we just
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remove the item from a persistent container?
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So I'm going to comment out this line which is, of course, toggling the done attribute from true to false.
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And instead, I'm going to tap into that itemArray,
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and I'm going to use the method remove at a particular index, and the index is, of course, indexPath.row
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which is the current selected index.
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Now, remember this line does nothing for our Core Data.
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It merely updates our itemArray which is used to populate our table view so that when we reload the
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table view, we're able to refresh the latest items.
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Now, the method that will need to remove the data from our context is context.delete, and we can specify
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an NSManagedObject to delete, and that is, of course, going to be itemArray
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at indexPath.row,
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so the NSManagedObject at the current selected row here.
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Now, just saying delete to our context is not enough,
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remember, this is the temporary area. And unless we save that context and we commit those changes to our
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persistent container, then this line would have done nothing at all.
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So, now we're going to save that context using that same saveItem's method and that's going to take
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the current state of the context, and it's going to try and commit it to our persistent container.
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At the end of all of that, it's going to reload the table view and show us the latest data.
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Now the order which you call these two methods, one, is removing the current item from the itemArray
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which is used to load up the table view data source ,and the other one is removing the data from our permanent
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stores.
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The order matters a huge deal.
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And if we run our app, we'll see what happens
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when we don't take care of that.
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If we run our app as it is right now and we click on the last item in our table view, so remember, there
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are item array at the moment only contains three NSManagedObjects and they are at index 0, 1, and 2.
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Now when I click on the third row here or index equals 2, the first thing that's going to trigger is
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that I'm going to remove that item from our itemArray.
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So, now I only have two items in our itemArray. And if I click here, then our app is going to crash because
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indexPath.row at the moment equals 2.
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And once we remove the item at index 2 and then we try to access it to try and delete it from our context,
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then this is why we have an index out of range error. And if we try to run the app without clicking on
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the last item, if we try to click maybe the first item, then you can see there are  app also behaves rather strangely
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and it removes the second to last item.
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And this is all because of the order of our methods.
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So what we have to do is we have to call context.delete first to remove this NSManagedObject
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from our context before we try to remove it from our itemArray because we're using the itemArray here
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to try and grab that object.
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So, now if we run an app with this new order, then you can see that when we try to delete something, our
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app works as expected.
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So all of these work exactly as we want it to.
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So I think deleting our items outright when we click on it is a little bit dramatic.
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And to be honest, I think I prefer the user experience where we have a checkmark next to the ones that
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are done.
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So I'm going to comment out these two lines.
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But before we end this lesson, it's a good point to remind ourselves that to delete items from our context,
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all we need to do is just call context.delete, and then specify the item that we want removed.
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But that's not enough,
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as with everything using Core Data and trying to do CRUD on it, we have to also save the context and
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commit the current status to our persistent container.
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So other than read, everything else creates update or destroy.
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Basically, whenever you need to change the data inside the persistent store, you always need to call
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context.save to commit those changes.
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Now, when you're reading or as we've done inside loadItems, we don't call saveItems or context.save
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here because we don't need to change the persistent container.
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And instead, we're just fetching it and looking at the current version.
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Now, in the next lesson, we're going to see some more fancy stuff that we can do using Core Data,
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and I'm going to show you how you can query items using Core Data, so that we can create a search bar
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inside our to-do list app, so that if we have a whole bunch of to-dos like 20, we can search and look
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for the ones that we're interested in.
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So for all of that and more, I'll see you on the next lesson.