1 1 00:00:01,650 --> 00:00:02,800 Hi and welcome back. 2 2 00:00:02,800 --> 00:00:05,040 In this video we're going to talk about 3 3 00:00:05,040 --> 00:00:08,170 something you can do to prevent this warning here 4 4 00:00:08,170 --> 00:00:10,250 for self. _id. 5 5 00:00:10,250 --> 00:00:13,488 And also a small change to this line, 6 6 00:00:13,488 --> 00:00:17,270 in order to modify its meaning slightly 7 7 00:00:17,270 --> 00:00:19,990 while still keeping you safe. 8 8 00:00:19,990 --> 00:00:23,560 Or at least while helping you get rid of warnings. 9 9 00:00:23,560 --> 00:00:27,020 The reason why we put collection = models here 10 10 00:00:27,020 --> 00:00:32,020 is to tell Python that the model class and its subclasses 11 11 00:00:33,210 --> 00:00:36,466 will have a collection attribute. 12 12 00:00:36,466 --> 00:00:39,240 Now there is another thing 13 13 00:00:39,240 --> 00:00:42,110 that doing collection = models does 14 14 00:00:42,110 --> 00:00:47,060 and that is that if we have a model, such as alert, 15 15 00:00:47,060 --> 00:00:50,157 and we don't put collection = alert, 16 16 00:00:50,157 --> 00:00:53,510 whenever we save it to MongoDB 17 17 00:00:53,510 --> 00:00:56,920 it's going to go into the models collection. 18 18 00:00:56,920 --> 00:01:00,393 That's because the parent class has this defined. 19 19 00:01:01,410 --> 00:01:04,010 And, in some cases, that can be good. 20 20 00:01:04,010 --> 00:01:04,843 For example, 21 21 00:01:04,843 --> 00:01:07,900 if you wanna make 100% sure that you never lose any data 22 22 00:01:07,900 --> 00:01:10,890 even if you make a mistake in your application 23 23 00:01:10,890 --> 00:01:13,886 then you can have something like this. 24 24 00:01:13,886 --> 00:01:17,310 And then all your models that don't fit 25 25 00:01:17,310 --> 00:01:19,760 or don't have a collection property 26 26 00:01:19,760 --> 00:01:21,390 are going to go into this models class 27 27 00:01:21,390 --> 00:01:22,700 when you realise your bug, 28 28 00:01:22,700 --> 00:01:24,940 which you will do pretty rapidly, 29 29 00:01:24,940 --> 00:01:27,660 then you go and move them from the models collection 30 30 00:01:27,660 --> 00:01:30,670 into your alerts collection or somewhere else. 31 31 00:01:30,670 --> 00:01:31,560 However, there are some cases 32 32 00:01:31,560 --> 00:01:34,230 where you just want your application to crash 33 33 00:01:34,230 --> 00:01:37,130 if you forget to set the collection. 34 34 00:01:37,130 --> 00:01:38,500 And the way you do that 35 35 00:01:38,500 --> 00:01:39,418 is you can tell Python 36 36 00:01:39,418 --> 00:01:43,202 this property collection will be defined 37 37 00:01:43,202 --> 00:01:45,116 and it will be a string 38 38 00:01:45,116 --> 00:01:47,550 but it doesn't have a value at the moment. 39 39 00:01:47,550 --> 00:01:51,460 And the way you do that is you use type hinting to do this. 40 40 00:01:51,460 --> 00:01:52,893 Collection: str. 41 41 00:01:53,830 --> 00:01:56,031 And what this says is collection is a string 42 42 00:01:56,031 --> 00:01:58,663 and it doesn't have a value right now. 43 43 00:01:59,550 --> 00:02:03,364 If you then don't put collection = alert here, 44 44 00:02:03,364 --> 00:02:07,790 as soon as your try to use self.collection or cls.collection 45 45 00:02:07,790 --> 00:02:11,270 like we do here and here, 46 46 00:02:11,270 --> 00:02:13,732 then you will get a type error and say 47 47 00:02:13,732 --> 00:02:17,302 collection doesn't have a value, it is not defined. 48 48 00:02:17,302 --> 00:02:20,300 For _id, we can do the same thing. 49 49 00:02:20,300 --> 00:02:22,930 And the reason why we absolutely prefer 50 50 00:02:22,930 --> 00:02:24,380 to this for _id 51 51 00:02:24,380 --> 00:02:26,110 is at this point and time, 52 52 00:02:26,110 --> 00:02:28,245 we don't have an _id property 53 53 00:02:28,245 --> 00:02:32,030 and we cannot reasonably give one 54 54 00:02:32,030 --> 00:02:33,860 because the _id properties 55 55 00:02:33,860 --> 00:02:37,502 are created by the init method in each model. 56 56 00:02:37,502 --> 00:02:40,181 So what we wanna say is this is going to exist 57 57 00:02:40,181 --> 00:02:43,060 but we don't have a value yet. 58 58 00:02:43,060 --> 00:02:46,580 And this property here will be a class property. 59 59 00:02:46,580 --> 00:02:47,500 But you know, 60 60 00:02:47,500 --> 00:02:50,040 you can access them as instance properties as well, 61 61 00:02:50,040 --> 00:02:51,890 if each object has its own one. 62 62 00:02:51,890 --> 00:02:52,800 So this works 63 63 00:02:52,800 --> 00:02:55,541 for both instance properties and class properties, 64 64 00:02:55,541 --> 00:02:58,750 which means it is good for what we wanna do here. 65 65 00:02:58,750 --> 00:02:59,760 It gets rid of the warning. 66 66 00:02:59,760 --> 00:03:01,124 You still get the error 67 67 00:03:01,124 --> 00:03:04,410 if you don't define it in the subclass. 68 68 00:03:04,410 --> 00:03:07,323 So it's sort of a win win situation here. 69 69 00:03:08,355 --> 00:03:11,394 If you know Python from the past, 70 70 00:03:11,394 --> 00:03:13,260 and you've used abstract classes, 71 71 00:03:13,260 --> 00:03:14,790 you've used these meta classes, 72 72 00:03:14,790 --> 00:03:18,940 you may be aware of using the abstract property decorator 73 73 00:03:18,940 --> 00:03:21,923 to define abstract properties like these. 74 74 00:03:21,923 --> 00:03:26,500 It doesn't really get rid of the warning in many situations. 75 75 00:03:26,500 --> 00:03:28,790 And I'm not going to go into detail 76 76 00:03:28,790 --> 00:03:29,860 about using abstract properties, 77 77 00:03:29,860 --> 00:03:31,450 first of all because they are deprecated 78 78 00:03:31,450 --> 00:03:32,610 and you shouldn't use it anymore, 79 79 00:03:32,610 --> 00:03:35,796 and the new way of using abstract properties, 80 80 00:03:35,796 --> 00:03:40,796 which is using this abstract method decorator, 81 81 00:03:40,860 --> 00:03:43,430 still doesn't fix the warning that we've got here. 82 82 00:03:43,430 --> 00:03:46,960 So this is the best way to fix the warning, 83 83 00:03:46,960 --> 00:03:48,770 while still getting the error 84 84 00:03:48,770 --> 00:03:51,833 if you forget to define the property. 85 85 00:03:52,900 --> 00:03:54,280 Alright, that's it for this video. 86 86 00:03:54,280 --> 00:03:55,630 Thank you for joining me. 87 87 00:03:55,630 --> 00:03:57,080 I'll see you on the next one.