WEBVTT 00:02.100 --> 00:02.640 Okay. 00:02.970 --> 00:06.150 We have our application almost ready. 00:06.180 --> 00:15.330 Our API is very functional at this point, but there is thing that I would like to do for our backend 00:15.330 --> 00:17.380 to be more functional. 00:17.400 --> 00:25.010 So basically what we have here is we might have a ratings and we have might have a movies here. 00:25.020 --> 00:28.290 So if I will use this, we have a movie. 00:28.290 --> 00:36.090 But basically what I will need to do is to get some information about the ratings for that specific 00:36.090 --> 00:36.690 movie. 00:36.720 --> 00:46.680 So what we can do is we can do what we've done in our previous section is to include that rating in 00:46.680 --> 00:54.030 the sorry here in the movie Serializer, include that ratings and do related name here. 00:54.030 --> 01:03.460 But in fact, I don't need to see all the stars object in our serializer because if I will see a list 01:03.460 --> 01:10.000 of ratings here and let's say star two and half to one and a half and so on and so on, that's not really 01:10.000 --> 01:10.540 useful. 01:10.540 --> 01:20.020 What we would like to see here or display on the page is to display how many ratings we have and also 01:20.020 --> 01:23.890 what is the average rating for that specific movie. 01:23.890 --> 01:26.380 So how can we achieve that? 01:26.410 --> 01:34.660 We need to create our own function and we can do it in many places and we've done it already in the 01:34.660 --> 01:35.020 views. 01:35.020 --> 01:37.000 That's our function and we use it. 01:37.000 --> 01:41.950 But also we can go to the models and we can use a function here. 01:41.950 --> 01:45.130 We can create our function and refer to that function. 01:45.130 --> 01:48.400 Also, we can do the same for the serializer. 01:48.790 --> 01:55.750 Let's do it in models and I will show you how easily we can create a new function and how we can use 01:55.750 --> 01:56.950 it in serializer. 01:56.950 --> 01:58.360 So let's say. 01:59.180 --> 02:03.920 We would like to have a function for a number of ratings. 02:03.950 --> 02:04.940 Number. 02:06.390 --> 02:07.020 Of. 02:08.820 --> 02:10.620 Ratings like that. 02:10.740 --> 02:16.170 And then we have a self and that self will refer to the current movie. 02:16.170 --> 02:22.440 So if we'll call that function on the movie, then it the self will be the movie itself. 02:22.440 --> 02:31.050 So what we need to do, we will need to get a ratings and then we need to check how many ratings we 02:31.050 --> 02:35.430 have for that specific movie so we can do ratings here. 02:35.460 --> 02:40.200 That's a local variable and then we'll do rating. 02:42.850 --> 02:45.730 And then I can do objects. 02:49.150 --> 02:49.930 Filter. 02:52.300 --> 02:55.620 By movie is equal to self. 02:56.630 --> 03:06.160 So what I'm doing here is I'm selecting all ratings in our database that have movie like this movie. 03:06.170 --> 03:12.080 So that means for each movie we will run this function and the self is that specific movie. 03:12.080 --> 03:15.140 So we will filter for each movie here. 03:15.140 --> 03:23.330 And then what I can do is I can return length, which is length of, of an array. 03:23.360 --> 03:25.310 Length of rating. 03:26.830 --> 03:27.730 Like that. 03:29.100 --> 03:37.830 So if I will save it now, our function is ready now, so we'll copy that and I can go to serializers 03:37.830 --> 03:40.620 and I can include it here. 03:40.620 --> 03:45.360 So number of writing, it's a function available on our movie. 03:45.390 --> 03:49.230 That function will be available for us in The Serializer. 03:49.230 --> 03:52.020 So let's go back here and test it now. 03:53.380 --> 03:57.700 And you can see here number of rating one, number of rating one. 03:57.710 --> 03:59.770 So if I will go. 04:01.850 --> 04:04.550 To ratings like that. 04:07.080 --> 04:09.750 And we need to use cat. 04:11.090 --> 04:12.610 So we have two ratings. 04:12.620 --> 04:15.080 Let's remove this rating for. 04:15.120 --> 04:20.780 So we'll do rating for Slash, and then I will use method lead. 04:22.030 --> 04:26.620 Removing that we have only supposed to have only one rating now. 04:34.130 --> 04:36.200 And indeed, we have one rating. 04:36.200 --> 04:42.500 So let's come back here, refresh it, and we can see a number of ratings for this movie is zero, a 04:42.500 --> 04:45.200 number of rating for this, it's one. 04:45.560 --> 04:53.900 So in that very easy way, we could include extra information and that's very custom information that 04:53.920 --> 04:56.570 we've created manually here. 04:56.570 --> 05:03.290 So we don't need to stick with the methods that are available for serializer or for the other models. 05:03.290 --> 05:05.180 We can create our own. 05:05.180 --> 05:09.710 So let's do another function and use something similar. 05:09.710 --> 05:13.280 So definition and we can do average. 05:14.970 --> 05:15.750 Rating. 05:16.770 --> 05:18.030 Same 12. 05:18.630 --> 05:23.310 And then what we need to do, we need to copy this. 05:23.760 --> 05:24.720 So. 05:31.450 --> 05:32.110 I like that. 05:32.130 --> 05:39.420 We'll select all our ratings and then we'll create another variable and I will call it sum, which is 05:39.420 --> 05:41.100 at the beginning, it's zero. 05:41.100 --> 05:46.170 So what we will do is we will loop through the ratings and we will sum it up. 05:46.380 --> 05:56.730 So for rating in ratings, we'll do a loop here and then I will do some. 06:00.050 --> 06:03.510 Add rating like that. 06:03.530 --> 06:11.300 So basically what I'm doing here is I set up some to zero at the beginning, so it will be zero. 06:11.300 --> 06:19.160 And then I select as before method, I select all the ratings for that specific movie, and then I loop 06:19.160 --> 06:20.180 through all of them. 06:20.180 --> 06:25.730 So this ratings here is an array of all the ratings for that movie, and we loop through them, and 06:25.730 --> 06:32.660 every time I loop, I have a local variable rating available and I just add this rating to the sum. 06:32.660 --> 06:37.160 So basically every single time we loop it and we add it here. 06:37.160 --> 06:45.200 So at the end of this line, I have already summed up the result here. 06:45.770 --> 06:47.240 So this is the sum. 06:47.240 --> 06:50.570 But in fact I would like to see an average. 06:50.570 --> 06:57.740 So average I can do return sum divide it by. 07:00.080 --> 07:00.770 Length. 07:02.300 --> 07:03.130 Rating. 07:04.730 --> 07:10.520 So I will have some and I divide it by number of ratings we have in our system. 07:10.670 --> 07:19.790 But that might throw an error because if the length is zero, then I am not allowed to divide by zero 07:19.790 --> 07:20.300 here. 07:20.300 --> 07:23.870 So what I need to do is I need to check it if. 07:32.930 --> 07:38.930 Is bigger than zero, then I can do this. 07:43.280 --> 07:43.970 Hulls. 07:48.380 --> 07:55.370 Return zero or whatever, we we can return null or whatever we have here. 07:55.670 --> 07:59.090 So basically that's what we have here. 07:59.090 --> 08:03.800 So once again, I set up assume a zero. 08:03.800 --> 08:11.660 Then I select all the ratings, I loop through them and add each rating to the sum, and then I return 08:11.690 --> 08:15.680 sum divided by number of ratings for that specific movie. 08:15.680 --> 08:21.350 And I do only that when we have at least one rating. 08:21.380 --> 08:23.300 Otherwise I just return zero. 08:23.300 --> 08:28.790 Because if I will have zero divided by zero then it will throw an error. 08:28.790 --> 08:30.500 So I will save it. 08:30.500 --> 08:34.640 Now let's come back to our postman and test how it works. 08:37.590 --> 08:44.640 Uh, actually, actually, I forgot to put average rating in our serializer, so we need to go here 08:44.640 --> 08:46.230 in the serializer. 08:46.290 --> 08:47.400 Another field. 08:47.850 --> 08:49.020 Average rating. 08:50.260 --> 08:52.570 Coming back here, Postman. 08:53.820 --> 08:57.480 Sending again so unsupported operand. 08:57.960 --> 09:09.510 I use Add like this for a rating, but in fact I should do if I go back to the models, I'm adding rating 09:09.510 --> 09:09.870 here. 09:09.870 --> 09:12.210 But that's the rating is an object rating. 09:12.210 --> 09:16.320 But we would like to add rating stars. 09:16.590 --> 09:23.970 So stars is the real rating rating has more things like movie and user. 09:23.970 --> 09:28.440 But we would like to use the stars for some some of the average rating. 09:28.440 --> 09:33.000 So we'll save it once again and then test it. 09:33.360 --> 09:37.620 And you can see average rating, three, average rating zero. 09:38.040 --> 09:45.180 So we have our two methods here and that object is very optimized for our front end. 09:45.210 --> 09:49.410 We'll ask for the list of movies and you can see here a list of movies. 09:49.410 --> 09:53.710 This one movie will contain ID title. 09:53.710 --> 10:00.730 We can actually exclude this ID if we like, but we have title description number of ratings and average 10:00.730 --> 10:05.290 rating here so we can actually display that on the on the screen. 10:05.290 --> 10:10.270 And we will we can do that using only one query to our database. 10:10.270 --> 10:12.540 So we don't need to query a. 10:13.360 --> 10:17.940 Movies and then ask for ratings and calculate that on the front end. 10:17.950 --> 10:19.590 That would be also possible. 10:19.600 --> 10:27.490 But this is more optimized and using one query, we can get all that data coming back to us. 10:27.670 --> 10:29.770 So this is now functional. 10:29.770 --> 10:33.120 We have ratings, we have movies, we have all the information we need. 10:33.130 --> 10:42.340 In the next videos, we will focus on doing our user login and logout and registering new users.