WEBVTT 00:02.220 --> 00:02.760 Okay. 00:02.940 --> 00:07.110 We know already how to do 1 to 1 relationship in our database. 00:07.140 --> 00:11.100 Let's do a one to many relationship now. 00:11.100 --> 00:13.260 So let's go back to the models here. 00:13.380 --> 00:19.070 And we have the previous setup as we finish in the last video. 00:19.080 --> 00:25.860 So the example we can use for a one to many will be characters in a book. 00:25.860 --> 00:31.130 So each book has a characters in a books. 00:31.140 --> 00:40.710 And for example, in the in The Hobbit, we might have a Frodo or any other character and we can register 00:40.710 --> 00:42.900 that in in our database. 00:42.900 --> 00:50.190 But one book might have and probably will have more than one, like in the example of the book number, 00:50.190 --> 00:51.840 that's only 1 to 1. 00:51.840 --> 00:55.020 But book will have many characters. 00:55.020 --> 01:04.420 So instead of putting that field on the book, we can create another model and we can reference that 01:04.420 --> 01:05.890 model to the book. 01:05.890 --> 01:08.290 So let's see how we can do that. 01:09.010 --> 01:21.610 I will do character, which is just a book character, so models and then model, same as we've done 01:21.610 --> 01:22.240 before. 01:22.720 --> 01:33.070 So we can have character, let's say name and then models and char field. 01:35.800 --> 01:40.120 And we can do a max length, let's say 30. 01:40.630 --> 01:46.270 It doesn't really matter that much, but we'll have that character we might have here more, I don't 01:46.270 --> 01:46.570 know. 01:46.570 --> 01:55.150 H or whatever we need to store in this, but now we need to connect this character with this model. 01:55.150 --> 02:03.790 As I said, we might have a lot of characters so we can say book and that will be a reference to our 02:03.790 --> 02:04.330 book. 02:04.330 --> 02:09.190 And then we do models and then we use foreign key. 02:09.430 --> 02:13.600 Foreign key is a connection between this and this. 02:13.600 --> 02:25.150 So we need to also pass this book class name here and then we do the same as we've done on delete and 02:25.150 --> 02:30.010 then models cascade like that. 02:33.010 --> 02:35.140 So I will leave it like that. 02:35.140 --> 02:35.750 Now. 02:35.750 --> 02:43.760 And we have another character so we can create new characters and we can assign them to a specific book 02:43.790 --> 02:44.780 here. 02:44.780 --> 02:46.640 So I will save it now. 02:46.850 --> 02:49.010 And let's go back to terminal. 02:49.010 --> 02:57.200 We'll do our up twice, make migrations, arrow up, migrate and then that's been applied. 02:57.200 --> 03:05.510 So let's go back to the admin here and I will just duplicate it here and then add this class name. 03:05.930 --> 03:15.020 I will also need to import and register here so we have that character register in our admin section. 03:15.020 --> 03:20.690 So let's come back here and we can go home and we have our characters here. 03:20.690 --> 03:28.460 So let's add a character here so we can do Frodo and then we can decide it. 03:28.460 --> 03:32.060 Oh, that's Frodo is in The Hobbit, so I will save it. 03:32.600 --> 03:34.520 And this has been added. 03:34.520 --> 03:36.470 What I can do is I can. 03:37.830 --> 03:38.490 Added. 03:39.190 --> 03:42.880 Actually, I don't think Frodo was in The Hobbit anyway. 03:43.000 --> 03:49.690 Bilbo and I can also decided to to apply that in The Hobbit. 03:50.980 --> 03:52.600 So let's correct the first one. 03:52.600 --> 03:57.760 Frodo wasn't there, so let's do Gandalf. 04:03.860 --> 04:08.000 So we have one Gandalf and one Hob, one Bilbo. 04:08.090 --> 04:10.970 And both of them are in the book. 04:11.390 --> 04:16.310 So we have two characters in the book in The Hobbit here. 04:16.310 --> 04:21.860 But as you can see here, nothing is available or visible, visible here. 04:21.890 --> 04:29.810 The reason for that is because we actually have the reference to our book from the characters, not 04:29.810 --> 04:32.870 from the from the book itself. 04:32.870 --> 04:41.540 But if we go to the serializers here now and I will just create another serializer, I duplicate this. 04:41.540 --> 04:45.350 So this time we do character. 04:49.470 --> 04:51.540 Also we need to import it 04:54.900 --> 04:58.980 and use it here and we have just name. 05:00.180 --> 05:02.790 So we have that character here. 05:03.120 --> 05:12.240 But I can't really use the character here on the Book Serializer because I have no reference from this 05:12.240 --> 05:12.860 book. 05:12.870 --> 05:20.400 So what we can do is I will show you if I will use the similar style as I've used here character. 05:21.180 --> 05:28.860 And then let's include that here, uh, like that. 05:28.860 --> 05:34.230 And then we'll use the cargo character serializer. 05:34.230 --> 05:37.830 And in this case, I will say many true. 05:38.340 --> 05:43.320 So what I'm doing here, I have a new serializer. 05:43.350 --> 05:45.660 That's for a new model I have created. 05:45.660 --> 05:50.170 And then I have a new variable here, which is character. 05:50.170 --> 05:51.730 And then this. 05:51.730 --> 05:58.840 Actually, it should be characters like that and it will use the character serializer and will pass 05:58.840 --> 05:59.980 it many through. 05:59.980 --> 06:05.830 And then this characters are also included in our fields there. 06:06.070 --> 06:10.420 But as I said, we don't have that available on the book Serializer. 06:10.420 --> 06:17.800 So if I will go now here and send it, you will see we'll get an error because the characters is not 06:17.800 --> 06:19.090 available on the book. 06:19.090 --> 06:25.510 So what we can do is we go to the models and we don't add it here like 1 to 1. 06:25.510 --> 06:32.500 But what we can do is on the book with the foreign key, foreign key on that field, what we can do 06:32.500 --> 06:42.340 is we can do related name and in the related name I will put it on another line related name. 06:42.340 --> 06:44.470 We can pass that name. 06:44.470 --> 06:46.150 So if we save it now. 06:48.110 --> 06:51.200 We can come back here and refresh it. 06:51.350 --> 06:54.860 And in this case, we can see characters here. 06:54.860 --> 06:59.980 That's an array in this case because we specify in the serializer it's many. 06:59.990 --> 07:00.760 True. 07:00.770 --> 07:09.560 So the in the serializer here we specify many true for the characters and many false for the book number. 07:09.590 --> 07:17.360 So coming back here, you can see the number is just a simple object and the characters. 07:17.360 --> 07:20.210 It's because many true it's an array. 07:20.540 --> 07:26.030 And inside we have one object, which is Gandalf and another object which is Bilbo. 07:26.240 --> 07:30.680 And in the case of another book, we don't have any characters. 07:30.680 --> 07:38.000 So you can clearly see here that 1 to 1, just one object per book, and this is our array. 07:38.030 --> 07:45.230 So we might have many objects inside for for that specific book. 07:45.260 --> 07:52.860 So this is how we can create a one to many relationship in our databases. 07:52.860 --> 07:58.740 And we for that we use a foreign key, as you can see here. 07:58.740 --> 08:00.720 So this is the way to connect. 08:00.720 --> 08:05.520 Also, you need to make sure that this book is registered before. 08:05.790 --> 08:10.050 So you need to remember the order of them. 08:10.050 --> 08:15.030 And you can see here you can create as many fields as you like. 08:15.030 --> 08:17.760 You don't you are not restricted to only one. 08:17.760 --> 08:24.300 So it might be another big model and you can connect with them using foreign key.