WEBVTT 00:00.320 --> 00:05.390 Okay, now that we've got our basket entity created, I just want to add a couple of methods inside 00:05.390 --> 00:05.660 here. 00:05.660 --> 00:11.240 So it makes it easier to add and remove items from our basket items. 00:11.270 --> 00:13.700 Now we do this in the basket class itself. 00:13.700 --> 00:16.970 I'm just going to add a couple of methods inside here. 00:16.970 --> 00:18.890 The first one is going to be a public method. 00:18.890 --> 00:22.130 And we'll say public void add item. 00:22.130 --> 00:26.060 And we're going to add a type of product into our basket. 00:26.060 --> 00:30.140 So it's going to be a product and we'll call it product as the first argument. 00:30.140 --> 00:35.420 And we'll add the int and quantity as the second argument. 00:35.780 --> 00:40.070 And before we use the product, let's just add a bit of defensive code to make sure that we actually 00:40.070 --> 00:43.550 have the product before we try and use it to add something to our basket. 00:43.550 --> 00:47.120 So we're going to check to see if the product is equal to null. 00:47.570 --> 00:49.880 And we're in the context of an entity here. 00:49.880 --> 00:52.850 So the product should not be null. 00:53.240 --> 00:59.900 But if it is null then we're going to use the arguments null exception. 01:00.140 --> 01:06.780 And we're just going to use the throw if null method and pass in the product as an argument to that. 01:07.230 --> 01:13.050 So if the product is null, then we break out of this method and we throw an exception. 01:13.050 --> 01:18.750 So exceptions are exceptional and we shouldn't necessarily encounter this exception. 01:18.750 --> 01:20.520 But just for our compiler. 01:20.550 --> 01:24.450 And just in case we're just doing a bit of defensive coding there. 01:24.480 --> 01:26.460 We're also going to check the quantity as well. 01:26.460 --> 01:33.360 And we want to make sure that the quantity is not less than or equal to zero, because of course we 01:33.360 --> 01:35.160 want that to be a positive number. 01:35.190 --> 01:44.580 And if that is the case, then we're going to throw a new arguments exception and say as the message 01:44.580 --> 01:49.350 the quantity should be greater than zero. 01:50.280 --> 01:58.770 And as the second parameter here we'll use the name of and quantity for the exception. 01:58.770 --> 02:03.060 And let's just drop this down because I'm going off the edge of the screen. 02:03.090 --> 02:04.020 Okay. 02:04.440 --> 02:06.720 So there's are a couple of defensive checks. 02:06.720 --> 02:13.050 And next we'll go and get the item which could possibly already be in our basket. 02:13.050 --> 02:19.170 So if they're adding something to our basket, then possibly they're increasing the quantity or it's 02:19.170 --> 02:22.890 going to be a new product that we're adding to the basket. 02:22.890 --> 02:29.490 So we'll create a variable and we'll say var existing item equals. 02:29.490 --> 02:33.930 And we'll just use a method that we'll create to do this called find item. 02:33.930 --> 02:37.440 And we'll pass in as the argument the product ID. 02:37.440 --> 02:39.930 And we'll put our cursor inside the find item. 02:39.930 --> 02:42.930 And we'll generate the method find item. 02:42.930 --> 02:48.060 And we're going to return from this a basket item. 02:48.630 --> 02:53.160 And we're going to make this optional because it may or may not already be in our basket. 02:53.160 --> 02:58.770 So we're going to return possibly the basket item or NULL if we do not find it. 02:58.770 --> 03:07.350 And we're going to return from this method items, which is what we're using what we have called our 03:07.350 --> 03:08.880 basket items. 03:09.450 --> 03:12.330 Then we'll use the first or default method. 03:12.330 --> 03:20.080 And this method specifically it will find the first item that matches if it exists in our list of basket 03:20.080 --> 03:25.600 items, or it will return the default value for a basket item. 03:25.600 --> 03:33.160 Now, because the basket item is an object if it's not found, the default value for this is null. 03:33.160 --> 03:37.570 So that's what we would return if it doesn't exist in our basket items. 03:37.570 --> 03:39.040 So I'll specify item. 03:39.040 --> 03:40.360 Then we'll use an expression. 03:40.360 --> 03:46.540 So we use the arrow and say item dot product id is equal to product. 03:46.540 --> 03:48.160 Or I've just called it ID here. 03:48.160 --> 03:50.410 Let's call it product ID instead. 03:51.910 --> 04:00.070 And I'll specify product ID here just for clarity as our items have an ID property as well as the product 04:00.100 --> 04:00.970 ID property. 04:00.970 --> 04:04.480 So it helps to be clear what it is we're using there. 04:04.480 --> 04:10.330 So then we can check to see if our existing item which may be the basket item, or it may be null. 04:10.330 --> 04:14.110 Then we can check to see if we do have that already in our basket. 04:14.260 --> 04:22.840 So if the existing item is equal to null, then we know that we need to add this to our items. 04:22.840 --> 04:24.670 So we're going to say items add. 04:25.840 --> 04:29.290 And then we'll say new baskets item. 04:29.290 --> 04:31.660 And we'll drop down to the next line. 04:31.660 --> 04:36.760 Open curly brackets and we'll specify the product is equal to product. 04:37.450 --> 04:41.500 And the quantity is equal to quantity. 04:41.500 --> 04:44.470 And that's all we need to do when we're adding a product. 04:44.470 --> 04:46.630 And then we can add the else condition. 04:46.630 --> 04:49.510 So just below the if statement we'll specify else. 04:49.630 --> 04:51.490 Then open curly brackets. 04:51.490 --> 04:56.440 And we can say existing item and set the quantity property equals. 04:56.440 --> 05:01.900 And we can say existing item dot quantity plus quantity. 05:01.900 --> 05:04.510 And we get the little helper the ellipses here. 05:04.510 --> 05:06.250 And let's see. 05:06.280 --> 05:11.170 It tells us that for this particular expression we should use a compound assignment. 05:11.170 --> 05:12.070 That sounds interesting. 05:12.070 --> 05:15.340 Let's use the quick fix and see what this suggests. 05:15.340 --> 05:17.350 And sure, that makes a lot of sense. 05:17.350 --> 05:22.750 That's a lot more concise than the method I was showing there. 05:22.780 --> 05:23.470 So great. 05:23.470 --> 05:28.640 That's going to increase the quantity of the existing item if it was already in the basket. 05:28.640 --> 05:31.700 So that's the add item taken care of. 05:31.700 --> 05:36.650 And then we need two similar but different of course for the remove item. 05:36.650 --> 05:41.300 So we're going to say publicvoid remove item. 05:41.300 --> 05:45.470 And inside here we just need the products ID. 05:45.620 --> 05:47.750 And again we need the quantity. 05:47.750 --> 05:52.580 If they're removing or reducing the number of the items in the basket. 05:52.580 --> 05:58.340 So we're going to check once again to make sure the quantity is not less than or equal to zero. 05:58.370 --> 06:03.830 And if it is then we're going to throw a new argument exception. 06:03.830 --> 06:12.950 And we'll just use the same message and say quantity should be greater than zero. 06:13.340 --> 06:19.370 And once again we'll just pass in as a second parameter the name of quantity okay. 06:19.370 --> 06:20.990 And let's drop that down as well. 06:20.990 --> 06:23.690 So I don't go off the edge of the screen. 06:23.690 --> 06:28.370 So then we just need to get hold of the item from our basket. 06:28.370 --> 06:35.610 So we'll use var item equals and then we can use the find item method we created below and pass in the 06:35.610 --> 06:36.690 product id. 06:37.470 --> 06:43.080 And we need to check to see if the item is null because of course if we hover over the item then we 06:43.080 --> 06:47.040 can see that possibly could be null because we can see that question mark there. 06:47.250 --> 06:51.570 So if the item is equal to null, what do we do from this. 06:51.600 --> 06:53.220 Well we can't really do anything. 06:53.880 --> 06:59.280 So all we'll do is we won't throw an exception, but we'll simply return from this method and stop the 06:59.280 --> 07:02.670 execution of the removal of the item. 07:03.420 --> 07:09.150 Then we'll specify item dot quantity is minus equals quantity. 07:09.150 --> 07:14.880 And then we can check to see if the item dot quantity is equal. 07:14.910 --> 07:20.970 Or let's say less than equal to zero and equal to zero should equally do the same thing here. 07:20.970 --> 07:26.730 I'm just being maybe overly careful, but if they've got zero or less than zero items in the basket, 07:26.730 --> 07:29.940 then we just want to remove the item from the basket. 07:29.940 --> 07:34.320 So I'm going to say items remove and pass in the item. 07:34.350 --> 07:36.930 Now what's going on with these add and remove methods? 07:36.930 --> 07:40.770 By the way, when it comes to using them, we're not doing anything with the database. 07:40.770 --> 07:47.100 When we execute these, all we're doing is telling Entity Framework to track what the current state 07:47.100 --> 07:48.390 of the entity is. 07:48.390 --> 07:53.820 Because in order to use these methods, we're going to have to retrieve the entity, the basket from 07:53.820 --> 07:54.720 the database. 07:54.720 --> 08:01.920 And then we can use the basket functionality such as the add item or the remove item on that entity. 08:01.920 --> 08:07.350 And when we do use one of these methods, then we're simply going to be tracking the state of that entity 08:07.350 --> 08:08.040 in memory. 08:08.040 --> 08:14.790 At that point, nothing happens with the database until we call a save changes method in the database. 08:14.790 --> 08:16.800 But we'll come on to that when we use it. 08:16.800 --> 08:23.550 So these are helper methods that just make it easier for us to use this entity class in our code or 08:23.550 --> 08:28.260 inside our controllers when we add the endpoints for this kind of functionality. 08:28.260 --> 08:33.420 So what we're going to take a look at next is we're going to take a look at updating our DB context. 08:33.420 --> 08:39.240 And then we're going to take a look at creating a new migration so that we can update our database schema. 08:39.240 --> 08:40.890 And that's what's coming up.