WEBVTT 00:01.610 --> 00:02.150 Okay. 00:02.150 --> 00:07.250 In this video, we will be talking about relationship in databases. 00:07.250 --> 00:11.540 So I will open models file here. 00:12.590 --> 00:20.540 And so far we have just one class, one model in our database, which is one table, and we will add 00:20.540 --> 00:22.810 more into our databases. 00:22.820 --> 00:29.510 We'll create new models, and I will show you how to build a relationship in between the models. 00:29.510 --> 00:31.850 So what kind of relationship we have? 00:31.880 --> 00:35.870 We have 1 to 1, one to many and many to many. 00:36.200 --> 00:43.940 And I will show you different examples where we might use different relationship type and how we can 00:43.940 --> 00:44.780 use it. 00:44.780 --> 00:53.000 So in this video, we will be doing another model that will be 1 to 1 with our book. 00:53.120 --> 00:56.500 So what will be the use case of 1 to 1? 00:56.510 --> 01:06.020 Usually when we want to have 1 to 1 is that we will have two records in our database and for each record, 01:06.020 --> 01:13.830 the one record in our example book will have just only one record of something else. 01:14.340 --> 01:22.830 So we can have multiple books, we can have multiple another objects, but each of these will have only 01:22.830 --> 01:24.540 1 to 1 relationship. 01:24.570 --> 01:31.260 Usually this kind of relationship is used to extend our model somehow. 01:31.260 --> 01:36.660 So we have basic information in our book and then we extend it with something extra. 01:36.660 --> 01:40.830 And that extension is only for that specific book. 01:40.830 --> 01:44.060 So in our case, we can represent it. 01:44.070 --> 01:47.610 I can show it using our example of book number. 01:47.610 --> 01:54.990 So let's create class book number and I will explain it in a second. 01:54.990 --> 01:59.550 So we'll do the same thing as we've done above and then model. 02:01.350 --> 02:03.900 So we have another book number here. 02:03.900 --> 02:13.320 So each book has its own ISBN, which is internal international standard book number, and that number 02:13.320 --> 02:18.840 is unique and it's given to each book that has been published. 02:18.840 --> 02:21.010 So we have two type of ISBN. 02:21.250 --> 02:22.530 ISBN. 02:23.790 --> 02:25.980 Then we can call it ten. 02:26.610 --> 02:31.980 So it will be models char field. 02:33.790 --> 02:36.430 And let's max length will be ten. 02:37.840 --> 02:42.100 And also we can do, uh, that's supposed to be ISBN. 02:43.370 --> 02:45.410 And then I will duplicate it. 02:46.640 --> 02:54.560 And another type of ISBN, I think they back in the days they had ISBN ten, which is ten characters 02:54.560 --> 03:01.040 long a string to uniquely identify the book number. 03:01.040 --> 03:07.550 But now it's ISBN at 13, so all the others will have both ten and 13. 03:07.940 --> 03:10.280 Anyway, we'll have this. 03:11.240 --> 03:20.030 So we'll have one field which is just a char field and another 113 so we can do a here. 03:20.030 --> 03:20.720 Blank. 03:21.800 --> 03:22.670 True. 03:26.060 --> 03:29.300 And we can also hear blank True. 03:30.200 --> 03:32.780 So we allow this to be blank. 03:32.780 --> 03:36.560 So we have another model registered here. 03:37.010 --> 03:37.790 At the moment. 03:37.790 --> 03:41.570 We have no relationship in between them. 03:41.930 --> 03:44.540 So how can we create a relationship? 03:44.990 --> 03:46.870 We need to create our field. 03:46.880 --> 03:50.090 In our case it will create on a book site. 03:50.720 --> 04:00.470 So we will do, let's call it number and then we'll do models and 1 to 1 field. 04:01.630 --> 04:02.260 Here. 04:02.260 --> 04:04.690 We need to provide the class name. 04:05.260 --> 04:07.590 So first argument is the class name. 04:07.600 --> 04:11.230 So 1 to 1 field and we will use the book number. 04:11.230 --> 04:14.710 And I will tell you in a second why this is underscored red. 04:14.920 --> 04:20.680 So what we need to do also we can decide that null is true. 04:23.680 --> 04:27.550 So by it will be stored as null. 04:28.420 --> 04:30.700 And then we can also say blank. 04:30.700 --> 04:31.300 True. 04:31.330 --> 04:33.190 So it's not required. 04:33.220 --> 04:35.170 Also, we need to do. 04:36.840 --> 04:49.650 On the lead models cascade and we can move it to another so I can do it here. 04:49.980 --> 04:56.220 So we decided that if that will be empty, we'll store it as null, then it's not required. 04:56.220 --> 04:58.950 And also on delete, we'll do models cascade. 04:58.980 --> 05:04.620 That means when we delete one another will be cascading and in being deleted as well. 05:04.620 --> 05:08.900 So we can see here this is underscore red for a reason. 05:08.910 --> 05:13.260 The way the python reads a file is from the top to the bottom. 05:13.260 --> 05:21.870 So when it reached the 15 line here, there is no way he can tell what the book number is because the 05:21.870 --> 05:26.730 book number is only available from line 21. 05:26.940 --> 05:33.150 And if I will take this and I will just cut it here and paste it there. 05:35.050 --> 05:37.690 You can see there is no errors now. 05:38.410 --> 05:40.330 And that's very important. 05:40.330 --> 05:46.570 When you design your models, you need to think about it, how to design it in order. 05:46.570 --> 05:49.360 They will be available in the file. 05:50.050 --> 05:57.100 So if you have multiple models, you need to design it the way that you don't want to do a cross reference 05:57.100 --> 06:05.320 because you might have a situation that something will needs to be available in one model but also needs 06:05.320 --> 06:06.970 to be available on another model. 06:06.970 --> 06:11.080 And the way you order the things really matters. 06:11.350 --> 06:14.650 So just pay attention to to the order. 06:14.650 --> 06:20.740 So we have our book, we have our 1 to 1 field, to the book number, which is this one. 06:21.070 --> 06:24.430 And then we decided what to do with the data. 06:24.430 --> 06:36.350 So as always, what we need to do in the terminal, we do Python manage.py make migrations. 06:37.900 --> 06:40.370 And you can see here two things happened. 06:40.390 --> 06:46.450 First, we create a new model, which is new table in our database, and then we add field number to 06:46.450 --> 06:46.780 the book. 06:46.780 --> 06:51.280 So we have that number and that's a 1 to 1 reference to our book number. 06:51.280 --> 06:53.740 And then we need to also do migrate. 06:58.020 --> 07:03.130 And that has been migrated to our database and it's available for us to use. 07:03.150 --> 07:08.670 So what we also can do is if I will go to run 07:12.210 --> 07:16.710 admin, you can see here we only see books here. 07:17.250 --> 07:24.270 So what we need to do is we need to go to admin and we can register our new model. 07:44.000 --> 07:45.440 We've done that before. 07:49.230 --> 07:57.270 So we import book number and then we do admin size register and the book here if I'll come back to this. 07:58.290 --> 07:59.580 Page and refresh. 07:59.610 --> 08:03.720 You can see book number is automatically registered there. 08:04.550 --> 08:06.050 And I can add it or change it. 08:06.050 --> 08:14.030 So what we can do is, if I will add here, I have that ISBN ten and ISBN 13 available for us and we 08:14.030 --> 08:16.760 can save it, but I don't want to do it here. 08:16.760 --> 08:24.140 What I want to do is I will show you if we go home and if we go to the books and this is how it works. 08:24.140 --> 08:32.000 So if we go to The Hobbit, you can see this is 1 to 1 field here, the number because we call it number. 08:32.000 --> 08:35.480 So if I click on this, nothing is there. 08:35.510 --> 08:43.040 That's a dropdown from all available book numbers that are available in our database, but in fact we 08:43.040 --> 08:44.960 don't have any yet. 08:44.960 --> 08:49.190 So we can do we can directly add it from here. 08:49.190 --> 08:51.650 So let's say we have. 08:52.990 --> 08:53.650 Some. 08:53.650 --> 08:55.360 One, two, three, four, five. 08:56.350 --> 08:59.710 Some one, two, three, four, five, six, seven, eight. 08:59.740 --> 09:00.730 Whatever that is. 09:00.730 --> 09:02.020 That's supposed to be ten. 09:02.050 --> 09:02.820 That's 13. 09:02.830 --> 09:03.880 It doesn't really matter. 09:03.880 --> 09:09.460 So if we save it, you can see book number here is assigned to this book. 09:09.460 --> 09:15.850 So if I will have that ISBN, real ISBN, I can assign them to this specific book. 09:15.850 --> 09:17.320 So I will save it here. 09:17.740 --> 09:19.240 And that's been added. 09:19.240 --> 09:22.090 So this hobbit has that. 09:22.660 --> 09:32.080 If I go if I go back here to the books and you can see lots of the ring here, if I will try to pick 09:32.080 --> 09:38.620 something like that, which is the same book number I've created for a Hobbit and save it, You can 09:38.620 --> 09:42.610 see there is an error book with this number already exist. 09:42.610 --> 09:45.580 And the reason I see that error is. 09:47.220 --> 09:49.470 This specific thing. 09:49.470 --> 09:54.560 So 1 to 1 can only have one per book. 09:54.570 --> 10:02.820 So if you will try to assign a the same one to the book, it will throw an error like this. 10:02.820 --> 10:09.030 So if you want to see that book, you need to add a new one with new ISBNs. 10:09.600 --> 10:12.360 Okay, so we have that sorted out. 10:12.360 --> 10:16.560 Let's come back to the postman and see what we will see here. 10:16.560 --> 10:21.750 So we have our books here, list of books, and now we've added extra fields. 10:21.750 --> 10:26.070 So what we can do here is test it and nothing is there. 10:26.070 --> 10:32.160 So the reason for that is because we haven't add anything in serializer. 10:32.160 --> 10:36.210 So we have ID title description price published and is published. 10:36.210 --> 10:48.460 So if I will take a new field we have created and put it here on Serializers, that's like that if I 10:48.490 --> 10:49.630 refresh it now. 10:51.820 --> 10:54.400 Going back to Postman and then. 10:55.120 --> 10:59.620 You can see here, number one and number null. 10:59.620 --> 11:01.000 And what is that? 11:01.240 --> 11:06.610 Well, basically, that's ID of our book number reference in our database. 11:06.610 --> 11:11.290 And this is Null because we haven't added anything to Lords of the Ring. 11:11.290 --> 11:12.460 And this is one. 11:12.460 --> 11:19.090 Well that's not really useful for us that much because if we have ISBN, we'd like to see ISBN here. 11:19.090 --> 11:30.940 So what we can do is we can copy entire serializer, paste it here and what I will do is I will have 11:30.940 --> 11:34.900 another serializer, create a new one number. 11:35.050 --> 11:37.360 So we'll have book number serializer. 11:37.360 --> 11:39.370 It will use the model Serializer. 11:39.370 --> 11:42.940 In our case, it's a book number. 11:42.970 --> 11:58.270 We need to also import it here and then inside we will have ID, then we have ISBN, then an ISBN 13. 11:58.300 --> 12:02.350 That's what we have available on our model like that. 12:02.350 --> 12:07.960 So we have another serializer here and we have number here. 12:07.960 --> 12:11.320 So what we can do in the serializer, we can connect them. 12:11.320 --> 12:27.550 So I can say number is our book number serializer like that, and then I can provide many faults. 12:29.110 --> 12:33.220 So what I'm saying, this will be always one record, not an array. 12:33.220 --> 12:35.620 So many, many faults. 12:35.620 --> 12:45.820 And then instead of a simple ID for for this record in a database, we'll use the whole serializer and 12:45.820 --> 12:47.920 that whole serializer will give us ID. 12:48.250 --> 12:49.120 ISBN. 12:49.150 --> 12:52.630 ISBN So let's test it now. 12:52.630 --> 12:58.310 I will save it and come back to Postman and we send it again. 12:58.310 --> 13:04.910 And you can see here now, number is not just an ID, it's a whole object inside object. 13:04.940 --> 13:07.460 This one is null, so nothing is there. 13:07.460 --> 13:12.560 But this is what we have added a moment ago in our admin page. 13:12.560 --> 13:17.000 So you can see that some and something here along with ID. 13:17.300 --> 13:24.140 So this is the way to have nested serializers one inside another. 13:24.140 --> 13:28.670 And then you can do inside this, you can have another nested serializer. 13:28.670 --> 13:32.210 So we can keep on going and going with this. 13:32.480 --> 13:39.380 And I also show you how we can actually create another model and how we can connect with them so we 13:39.380 --> 13:43.280 know how to do, how to do 1 to 1 in the next video. 13:43.280 --> 13:45.800 We will I will show you how to do one to many.