WEBVTT 00:00.870 --> 00:01.440 Okay. 00:01.560 --> 00:06.430 We know how to create 1 to 1 and one to many relationship in databases. 00:06.450 --> 00:09.150 Let's do a many to many. 00:09.150 --> 00:10.360 So many to many. 00:10.380 --> 00:17.100 That means we'll have a set of records on one side and a set of records on another side, and we might 00:17.100 --> 00:18.480 have multiple. 00:19.290 --> 00:21.120 Connections in between them. 00:21.120 --> 00:27.380 So in our example that we use book, the perfect example will be author. 00:27.390 --> 00:36.570 So author might have a lot of books, so books will be written by one author, author, and that author 00:36.570 --> 00:38.820 might have more than one book. 00:38.820 --> 00:40.980 So we can create that. 00:43.640 --> 00:44.390 Class. 00:46.320 --> 00:47.100 Outer. 00:48.150 --> 00:55.950 And the same way models model, just this is just another model and then we can say name. 00:57.470 --> 00:58.520 Let's actually. 01:02.790 --> 01:03.600 Copy that. 01:03.630 --> 01:07.930 We are not really interested in these models to have them really precise. 01:07.950 --> 01:11.580 We just want to demonstrate what what is happening. 01:11.580 --> 01:16.350 So what we can have is we can have maybe name and surname here. 01:16.350 --> 01:17.070 So. 01:20.800 --> 01:23.560 Surname and then we'll have it like that. 01:23.560 --> 01:32.620 So to create a many to many, we'll need to have our reference in between the author and the book. 01:34.560 --> 01:37.590 We can add another field books. 01:40.060 --> 01:45.580 Models and then we can have many to many field. 01:47.040 --> 01:48.600 Then we need to decide. 01:48.600 --> 01:49.350 What. 01:50.160 --> 01:55.140 Class will use their what model? 01:55.140 --> 01:56.910 And I will use book. 01:57.940 --> 01:58.750 Like that. 01:59.050 --> 02:09.610 So once we have that added here, what we also need to do is I will first do my migrations and then 02:09.610 --> 02:10.480 migrate. 02:11.740 --> 02:13.120 So we have that. 02:13.120 --> 02:24.400 Now we go to admin and then we will register another model, which is our author. 02:27.310 --> 02:28.600 We need to import it. 02:30.580 --> 02:35.110 And the server is running so we can go here. 02:35.980 --> 02:42.670 And we have our outers here so we don't have any outer in the database. 02:42.670 --> 02:44.170 So let's create one. 02:44.770 --> 02:50.140 So j r r token. 02:50.140 --> 02:54.910 And you can see here the user interface is different for many to many. 02:54.910 --> 02:59.950 I can actually pick many of them here or I can add another one here. 02:59.950 --> 03:06.070 So this outer is actually will have a relationship with this book and with this book. 03:06.070 --> 03:07.570 So I will save it here. 03:08.020 --> 03:12.760 And we have one outer that will be in this. 03:14.510 --> 03:16.610 And then we can save it here. 03:16.940 --> 03:20.210 So we have our outer object there. 03:22.460 --> 03:27.380 And we can add it also in our serializer. 03:27.380 --> 03:29.020 So let's come back here. 03:29.030 --> 03:32.270 We have our character Serializer. 03:32.490 --> 03:39.620 I'll duplicate it here and then we'll do our outer outer serializer. 03:39.830 --> 03:47.930 Also, we need to use outer here and import it from from the top, from the model. 03:47.930 --> 03:52.310 And we can use ID, we can use name. 03:52.310 --> 03:56.540 And also we had a surname surname there. 03:56.990 --> 04:02.930 So we have outer serializer and we need to do a similar thing, what we've done with our characters 04:02.930 --> 04:06.530 basically that will be outdoors. 04:19.320 --> 04:21.410 And then we need to do outdoors. 04:22.800 --> 04:23.880 Add it here. 04:24.690 --> 04:29.940 So outdoors and then coming back to our postman, I will send it. 04:30.060 --> 04:35.270 And you can see we are having the same kind of error we had before. 04:35.280 --> 04:37.140 We already know how to solve it. 04:37.140 --> 04:42.150 So we go back to the models and then we do related. 04:43.420 --> 04:44.920 Related name. 04:45.760 --> 04:48.610 And then we can do ours. 04:49.360 --> 04:50.920 So I save it again. 04:51.040 --> 04:53.260 Go on, postman, refresh it. 04:53.260 --> 04:57.970 And you can see here we have different relationships. 04:57.970 --> 05:04.000 So we have 1 to 1, one to many and many to many. 05:04.000 --> 05:06.040 And the many to many. 05:06.040 --> 05:07.540 Here is. 05:08.250 --> 05:15.750 You have this one juror talking here and also you have the same author here. 05:15.930 --> 05:20.300 So you have authors this this one and this one. 05:20.310 --> 05:26.700 It's the same record in database, but you can see it is available on both of them. 05:26.700 --> 05:28.900 And then we have characters here. 05:28.920 --> 05:31.140 You might have more, more than one. 05:31.140 --> 05:34.890 And there will be specific for for this book. 05:34.890 --> 05:38.940 And also you have a simple. 05:39.630 --> 05:41.750 1 to 1 relationship. 05:41.760 --> 05:49.410 So that's how the relationship in Django works and that's generally all what it is to it. 05:49.710 --> 05:50.020 A. 05:51.210 --> 05:55.470 When you design your application, it's very important to think it through. 05:55.500 --> 05:57.270 What would you like to store it in? 05:57.270 --> 05:58.650 What models? 05:58.650 --> 06:03.750 How would would you like to use it and what will be the relationship in between them? 06:03.750 --> 06:11.370 Because the way you construct the A models and the serializes later on it will matter for you how you 06:11.370 --> 06:14.240 will receive the data from your database. 06:14.250 --> 06:20.070 So as you can see here, we using the serializer, we can build the very complex objects. 06:20.070 --> 06:28.260 So we are asking for books, but we get the array not for this book specific book, not just the book 06:29.010 --> 06:34.680 ID, but we also have another model, which is then another model. 06:34.680 --> 06:40.260 And we can actually include here more information than just a simple ID and name. 06:40.830 --> 06:44.070 And as you can see here, we can decide on any field that we store it. 06:44.070 --> 06:50.070 We try to keep our model very simple, but in fact, you can in the real application, they are not 06:50.070 --> 06:50.550 simple. 06:50.550 --> 06:55.180 They are full of data, real data, and they're real useful. 06:55.180 --> 07:01.690 And it's really up to you which fields you would like to include it and how you would like to structure. 07:01.690 --> 07:09.800 The one thing I haven't said yet is you don't need to have one serializer per model. 07:09.820 --> 07:16.780 So if you go to the serializer here, what you can do is you can possibly create another serializer 07:16.780 --> 07:20.350 for a book, for for a book. 07:20.380 --> 07:25.300 And you will exclude include only, for example, ID and title. 07:25.300 --> 07:28.270 And that's completely I can actually show you. 07:28.270 --> 07:33.900 So if I will copy that and then I will remove all of that data. 07:33.910 --> 07:36.010 So we'll still have a book serializer. 07:36.010 --> 07:39.340 So book mini serializer, I will name it. 07:39.340 --> 07:47.020 The name needs to be unique, but you can use the same model, so I will just keep it ID and title. 07:48.050 --> 07:50.000 So I can have it like that. 07:50.000 --> 07:52.780 And then I have this serializer. 07:52.790 --> 07:55.160 I will copy the serializer. 07:55.160 --> 08:03.950 And if I will go to the views and I have my view set, I in this view set, I use serializer class book 08:03.950 --> 08:04.640 serializer. 08:04.640 --> 08:08.120 So let's say I want to use book mini serializer. 08:08.360 --> 08:14.450 I will import that also from the serializer and I will show you that in a second how it works. 08:14.450 --> 08:19.160 So postman, if I will send it now and let's come back here. 08:19.160 --> 08:21.110 I have book mini serializer. 08:21.990 --> 08:24.630 The Serializers have been saved. 08:35.790 --> 08:39.390 And this will go here. 08:40.470 --> 08:42.270 I'll rerun the server. 08:44.810 --> 08:49.470 And you can see here I have that mini serializer in use. 08:49.490 --> 08:58.010 So what is that doing is by default, it will use that mini serializer because I decided to use it here, 08:58.010 --> 08:59.060 in my view, set. 08:59.060 --> 09:03.980 But inside here, what I can do, I will show you a little trick. 09:03.980 --> 09:08.000 If I'll go click command and click on the models here. 09:08.000 --> 09:14.450 I have different methods that are included in the view set and you can see here we have create, retrieve, 09:14.480 --> 09:17.350 update, partial update, destroy and list. 09:17.360 --> 09:23.270 So basically what we are seeing here and when we go. 09:24.480 --> 09:25.170 Here. 09:25.170 --> 09:28.800 That's a list because it's a list of all our records here. 09:28.800 --> 09:29.580 But. 09:30.840 --> 09:31.710 Also. 09:33.190 --> 09:34.900 We have retrieved one. 09:34.900 --> 09:38.680 So retrieve is just retrieving one single. 09:39.550 --> 09:42.250 I will copy that from this is Django code. 09:42.250 --> 09:44.800 I will copy that here and I will come back to the view. 09:44.800 --> 09:49.720 So we have that retrieve method available in the view set. 09:49.720 --> 09:53.710 But if I will include it here, that means I would like to use my own. 09:53.710 --> 09:56.770 I just copy the one from the from the view set. 09:56.770 --> 09:59.980 So it is at this point it is the same. 09:59.980 --> 10:04.000 So you can see here response is not imported. 10:04.000 --> 10:05.890 So we need to import response here. 10:09.020 --> 10:11.030 From rest. 10:12.270 --> 10:13.830 Rest framework. 10:15.940 --> 10:16.730 Response. 10:16.750 --> 10:19.630 Import response like that. 10:19.930 --> 10:25.810 And here we have get serializer, which is this serializer class. 10:25.810 --> 10:26.830 We will get it. 10:26.830 --> 10:31.090 But instead of that, I can use the serializer. 10:31.090 --> 10:33.700 We had the full serializer. 10:33.700 --> 10:34.840 We had it here. 10:34.840 --> 10:37.240 So I will go back to the view set. 10:37.480 --> 10:42.910 I'm kind of doing that very fast now, but I will explain it once again. 10:43.730 --> 10:46.490 In a second, so we'll go serializer. 10:48.390 --> 10:49.260 Like that. 10:50.830 --> 10:55.240 So what I am doing here is for method retrieve. 10:55.270 --> 10:59.020 I will use the same method as it was built in there. 10:59.260 --> 11:02.860 And for this one I would like to use the book serializer. 11:02.860 --> 11:08.050 So the default one, the serializer class for an entire view set is the mini one. 11:08.680 --> 11:11.290 Which contains only ID and title. 11:11.290 --> 11:16.230 And as you can see here, so we have that mini one. 11:16.240 --> 11:24.940 But if we will use the retrieve, which is one specific record from database, we will use the book 11:24.940 --> 11:28.360 serializer, which is the full serializer for all the data. 11:28.360 --> 11:29.380 So let's test it. 11:29.380 --> 11:34.690 Now we go to the postman and I will send it again and see here. 11:34.690 --> 11:41.860 It's just a mini serializer shown, but if I will go book ID one, which is hobbit and then I will send 11:41.860 --> 11:42.340 it. 11:42.640 --> 11:46.360 You can see I have all the data available for this. 11:46.360 --> 11:51.040 So if you would like to optimize your database queries. 11:51.040 --> 11:55.360 And for example, we have just a page with a title on it. 11:55.390 --> 12:01.990 What you can do is you can have mini serializer for this because that will what you will need on your 12:02.560 --> 12:03.310 page. 12:03.310 --> 12:10.730 But if someone will click on this ID, you will take this ID from here and you will pass it to your 12:10.730 --> 12:16.910 URL like that, and then you will load it and you will have all the data available for this book. 12:16.940 --> 12:22.640 In that way, you don't need to have all the data for all books in your system. 12:22.640 --> 12:29.420 You will just ask for the data you will need for a certain part of your application and that's very 12:29.420 --> 12:30.050 optimized. 12:30.050 --> 12:31.910 You don't overload it with the data. 12:31.910 --> 12:32.510 You will. 12:32.510 --> 12:36.080 You might never use it and that's how you can create it. 12:36.080 --> 12:45.590 So doing that again in the serializers you can actually have more than one serializer for the same class. 12:45.590 --> 12:50.690 You might decide which one will have how many fields here and. 12:52.120 --> 12:55.030 This is the way we can actually decide it. 12:55.030 --> 13:02.410 For each method that are available in the model view that we can override it and we can decide it. 13:02.410 --> 13:07.480 What serializer will be used for that certain one and that will be the default one. 13:08.450 --> 13:09.110 Okay. 13:09.530 --> 13:14.180 And that's about it for our Django in the introduction. 13:15.080 --> 13:23.720 I hope at this point you kind of understand how it all work and we are kind of ready to start building 13:23.720 --> 13:27.740 our API and that will be our first project. 13:27.860 --> 13:33.080 So we'll go again from the beginning and we'll create our mini application. 13:33.080 --> 13:35.330 That will be our backend API.