WEBVTT 1 00:00:00.360 --> 00:00:01.950 Hi guys and welcome back. 2 00:00:01.950 --> 00:00:04.530 In this video we are going to be separating our code 3 00:00:04.530 --> 00:00:08.400 into models so that we can code more easily. 4 00:00:08.400 --> 00:00:10.520 Basically we're going to be creating classes 5 00:00:10.520 --> 00:00:14.060 out of the entities that our code deals in 6 00:00:14.060 --> 00:00:17.080 so that when we are dealing with those things in our code 7 00:00:17.080 --> 00:00:18.050 it becomes a little bit easier. 8 00:00:18.050 --> 00:00:20.482 We're gonna explain everything that goes on with that 9 00:00:20.482 --> 00:00:21.650 throughout the video. 10 00:00:21.650 --> 00:00:22.903 So, let's get to it. 11 00:00:24.900 --> 00:00:28.460 At the moment, we have our app.py 12 00:00:28.460 --> 00:00:31.910 dealing with certain things. 13 00:00:31.910 --> 00:00:34.910 Those things are, for example, polls 14 00:00:34.910 --> 00:00:39.080 options, votes, potentially even users. 15 00:00:39.080 --> 00:00:40.850 And often, in programming, 16 00:00:40.850 --> 00:00:43.250 when we're dealing with entities, 17 00:00:43.250 --> 00:00:44.560 as we call them, 18 00:00:44.560 --> 00:00:47.370 it can be helpful to create classes for them 19 00:00:47.370 --> 00:00:49.710 so that thinking about those things 20 00:00:49.710 --> 00:00:52.863 as individual entities can become a little bit easier. 21 00:00:53.730 --> 00:00:58.070 So, models are things that our programme deals with internally 22 00:00:58.070 --> 00:01:00.084 and the purpose of them is to make it easier 23 00:01:00.084 --> 00:01:02.920 for different parts of our application to communicate 24 00:01:02.920 --> 00:01:05.750 and also to make it easier for us to read 25 00:01:05.750 --> 00:01:07.880 and reason about the code. 26 00:01:07.880 --> 00:01:09.250 At the moment, 27 00:01:09.250 --> 00:01:10.980 this poll's variable for example, 28 00:01:10.980 --> 00:01:13.160 the database.get polls, 29 00:01:13.160 --> 00:01:17.750 is a list of tuples, it's not a list of objects 30 00:01:17.750 --> 00:01:19.520 that we can interact with 31 00:01:19.520 --> 00:01:22.420 and potentially ask them to do stuff for us 32 00:01:22.420 --> 00:01:24.250 by running methods and stuff like that. 33 00:01:24.250 --> 00:01:27.270 So, that's what we're going to do throughout this video. 34 00:01:27.270 --> 00:01:28.540 In my code I'm going to create 35 00:01:28.540 --> 00:01:31.390 model classes for poll and option. 36 00:01:31.390 --> 00:01:33.970 I consider votes to be sufficiently simple 37 00:01:33.970 --> 00:01:35.840 and encapsulated within options 38 00:01:35.840 --> 00:01:37.670 that they don't need their own class 39 00:01:37.670 --> 00:01:39.760 and our use of users at the moment 40 00:01:39.760 --> 00:01:41.530 is reserved to the username string 41 00:01:41.530 --> 00:01:42.620 attached to a vote 42 00:01:42.620 --> 00:01:45.330 and we're not gonna create a model class for that either. 43 00:01:45.330 --> 00:01:48.310 If we were storing more information about users or votes 44 00:01:48.310 --> 00:01:50.350 and we wanted to do a few more things with them 45 00:01:50.350 --> 00:01:52.130 then we might reconsider this. 46 00:01:52.130 --> 00:01:55.690 But for now, let's go ahead and create our models. 47 00:01:55.690 --> 00:01:57.240 Python directory. 48 00:01:57.240 --> 00:01:59.153 We're gonna call it models. 49 00:02:00.130 --> 00:02:05.130 And in here we're going to create our poll.py Python file. 50 00:02:05.340 --> 00:02:06.683 So we'll do poll. 51 00:02:08.570 --> 00:02:10.560 So let's begin writing a class 52 00:02:10.560 --> 00:02:13.570 to represent everything that our application 53 00:02:13.570 --> 00:02:15.130 wants to do with polls, 54 00:02:15.130 --> 00:02:18.000 including the data stored by a poll. 55 00:02:18.000 --> 00:02:20.130 I'll create the poll class, 56 00:02:20.130 --> 00:02:22.530 and by the way let me just hide away this project there. 57 00:02:22.530 --> 00:02:24.840 I'll create a poll class and then we're gonna add 58 00:02:24.840 --> 00:02:26.150 the init method in it 59 00:02:27.070 --> 00:02:29.350 and the polls have three properties: 60 00:02:29.350 --> 00:02:31.660 a title, which is a string, 61 00:02:31.660 --> 00:02:33.268 an owner, which is a string as well, 62 00:02:33.268 --> 00:02:36.720 and potentially they have an ID property. 63 00:02:36.720 --> 00:02:39.360 I'm gonna call it underscore ID, which is an integer 64 00:02:39.360 --> 00:02:41.000 and defaults to none. 65 00:02:41.000 --> 00:02:42.350 The reason it defaults to none 66 00:02:42.350 --> 00:02:44.920 is that if it doesn't get passed in 67 00:02:44.920 --> 00:02:47.150 when we create a poll object, 68 00:02:47.150 --> 00:02:49.510 we're going to assume that this poll 69 00:02:49.510 --> 00:02:51.880 hasn't been saved to the database yet 70 00:02:51.880 --> 00:02:53.640 and we're still waiting for the database 71 00:02:53.640 --> 00:02:56.690 to generate the ID for us. 72 00:02:56.690 --> 00:02:58.870 So we'll do self.id equals underscore ID, 73 00:02:58.870 --> 00:03:02.880 self.title equals title, self.owner equals owner. 74 00:03:02.880 --> 00:03:04.000 Often for these classes 75 00:03:04.000 --> 00:03:06.920 we want to create a repr dunder method 76 00:03:06.920 --> 00:03:08.650 so that when we are debugging 77 00:03:08.650 --> 00:03:09.970 and when we're printing stuff out 78 00:03:09.970 --> 00:03:11.330 it's a little bit easier to see 79 00:03:11.330 --> 00:03:13.920 what the object that we create represents. 80 00:03:13.920 --> 00:03:15.630 So we'll do a repr, 81 00:03:15.630 --> 00:03:17.490 and what this is gonna return is an f string 82 00:03:17.490 --> 00:03:19.980 with the poll and then the self.name. 83 00:03:19.980 --> 00:03:20.900 And what I'm gonna do here 84 00:03:20.900 --> 00:03:22.980 is I'm gonna put an exclamation mark r 85 00:03:22.980 --> 00:03:25.340 and that is gong to print out self.name 86 00:03:25.340 --> 00:03:28.500 but it's gonna make sure that it looks like 87 00:03:28.500 --> 00:03:30.570 what it would have to look like 88 00:03:30.570 --> 00:03:33.760 for the string to be valid in Python code. 89 00:03:33.760 --> 00:03:34.780 Basically, it's gonna put 90 00:03:34.780 --> 00:03:37.093 the quotation marks around it as well. 91 00:03:37.950 --> 00:03:39.620 Then we'll do self.owner. 92 00:03:39.620 --> 00:03:42.550 And by the way that should be self.title, not self.name 93 00:03:42.550 --> 00:03:43.860 so I will fix that in a moment. 94 00:03:43.860 --> 00:03:44.940 And self.id. 95 00:03:46.653 --> 00:03:50.620 (drawn out) self dot ID and r 96 00:03:50.620 --> 00:03:52.760 There we go, just like that. 97 00:03:52.760 --> 00:03:54.960 This should be self.title. 98 00:03:54.960 --> 00:03:57.100 Now what this is gonna print out essentially 99 00:03:57.100 --> 00:04:02.100 is poll and then the title, the owner, and the ID, 100 00:04:02.920 --> 00:04:05.400 which may be like, I don't know, one. 101 00:04:05.400 --> 00:04:07.430 And you can see that this here, 102 00:04:07.430 --> 00:04:11.240 we can use to recreate any poll object, 103 00:04:11.240 --> 00:04:14.620 and that is the purpose of the repr method. 104 00:04:14.620 --> 00:04:16.210 It should return a string 105 00:04:16.210 --> 00:04:20.010 that can be used to recreate the object it represents. 106 00:04:20.010 --> 00:04:22.530 Next up, we're gonna add the methods for the main things 107 00:04:22.530 --> 00:04:24.540 that we want to do with a poll. 108 00:04:24.540 --> 00:04:26.130 And one of those things might be 109 00:04:26.130 --> 00:04:28.270 to save it to the database. 110 00:04:28.270 --> 00:04:30.040 So we'll do save 111 00:04:30.040 --> 00:04:32.330 and then we're gonna do connection equal 112 00:04:32.330 --> 00:04:33.700 and we're gonna have a function 113 00:04:33.700 --> 00:04:35.200 called create connection here, 114 00:04:35.200 --> 00:04:37.150 I'll code it in just a moment. 115 00:04:37.150 --> 00:04:41.950 The new poll ID is gonna be database.create poll 116 00:04:41.950 --> 00:04:45.770 we're gonna pass in this connection self.title, self.owner 117 00:04:46.800 --> 00:04:48.882 then we're gonna close this connection 118 00:04:48.882 --> 00:04:53.100 and we're gonna set self ID to be equal to the new poll ID 119 00:04:53.100 --> 00:04:54.250 that we get from the database. 120 00:04:54.250 --> 00:04:57.030 Of course we have to import database, 121 00:04:57.030 --> 00:04:59.370 and we're also gonna have to 122 00:04:59.370 --> 00:05:01.800 import this create connection function, 123 00:05:01.800 --> 00:05:03.410 but we're gonna look at that in just a moment. 124 00:05:03.410 --> 00:05:06.120 For now, just assume that it connects to psycopg2 125 00:05:06.120 --> 00:05:08.040 and it gives us a connection back 126 00:05:08.040 --> 00:05:09.040 and at the end we close it. 127 00:05:09.040 --> 00:05:10.930 So we're gonna be using this function 128 00:05:10.930 --> 00:05:12.130 in a few different places here 129 00:05:12.130 --> 00:05:14.510 to create new connections as we need them. 130 00:05:14.510 --> 00:05:17.110 Whenever working with polls, polls have options 131 00:05:17.110 --> 00:05:20.200 so therefore it's possible to add options to a poll. 132 00:05:20.200 --> 00:05:24.190 That is why we're gonna have a method called add option 133 00:05:24.190 --> 00:05:26.910 that takes in an option text, which is a string. 134 00:05:26.910 --> 00:05:28.740 And all this does is it creates 135 00:05:28.740 --> 00:05:32.750 an option model class or object as in the option text, 136 00:05:32.750 --> 00:05:37.320 and the poll ID, and also calls save on it. 137 00:05:37.320 --> 00:05:39.990 The option model class is gonna be pretty similar 138 00:05:39.990 --> 00:05:41.480 to the poll model class. 139 00:05:41.480 --> 00:05:44.507 So, by calling .save in the option object 140 00:05:44.507 --> 00:05:46.570 then that will save it to the database 141 00:05:46.570 --> 00:05:49.010 in a similar way to what the poll does. 142 00:05:49.010 --> 00:05:50.720 As well as adding options, 143 00:05:50.720 --> 00:05:53.940 we also have to have a way of retrieving options. 144 00:05:53.940 --> 00:05:55.040 So what we're gonna do here 145 00:05:55.040 --> 00:05:57.840 is we're gonna define an options method here 146 00:05:57.840 --> 00:06:00.740 that returns a list of option models 147 00:06:00.740 --> 00:06:04.590 and this, again, is going to be the same class 148 00:06:04.590 --> 00:06:05.530 as we're using there, 149 00:06:05.530 --> 00:06:06.470 we haven't written it yet 150 00:06:06.470 --> 00:06:07.930 but we're gonna write it in a moment. 151 00:06:07.930 --> 00:06:09.460 This comes from the typing module, 152 00:06:09.460 --> 00:06:12.650 so we're gonna do from typing, import list. 153 00:06:12.650 --> 00:06:16.180 We'll also do from models, import option. 154 00:06:16.180 --> 00:06:17.260 Which at the moment doesn't exist, 155 00:06:17.260 --> 00:06:19.990 but it does get rid of these red underlines down there. 156 00:06:19.990 --> 00:06:22.540 What this has to do is, again, create a connection 157 00:06:22.540 --> 00:06:25.890 so we're gonna do connection equal create connection, 158 00:06:25.890 --> 00:06:27.780 then grab the options from the database 159 00:06:27.780 --> 00:06:31.720 so we'll do options equal database.get poll options, 160 00:06:31.720 --> 00:06:35.760 passing the connection and passing self.id. 161 00:06:35.760 --> 00:06:37.360 By the way, misspelt that. 162 00:06:37.360 --> 00:06:39.390 Self.id is the ID of the poll 163 00:06:39.390 --> 00:06:40.680 that we're currently working with 164 00:06:40.680 --> 00:06:43.470 so, this will give us the poll options. 165 00:06:43.470 --> 00:06:45.780 Notice that in this database call here, 166 00:06:45.780 --> 00:06:49.410 we're just gonna get the options for a poll. 167 00:06:49.410 --> 00:06:52.220 So we're not going to get the poll rows, 168 00:06:52.220 --> 00:06:55.490 as well as the options rows, as we have now with a join, 169 00:06:55.490 --> 00:06:58.210 we're just concerned here with the options themselves. 170 00:06:58.210 --> 00:07:00.450 So that's something that we have to code as well. 171 00:07:00.450 --> 00:07:03.120 Then we'll close the connection 172 00:07:03.120 --> 00:07:06.640 and we are going to return the option object. 173 00:07:06.640 --> 00:07:11.640 So we'll do option one, option two, option zero 174 00:07:12.050 --> 00:07:14.330 for option in options. 175 00:07:14.330 --> 00:07:16.850 The reason why we're passing these arguments 176 00:07:16.850 --> 00:07:18.710 to the option constructor, 177 00:07:18.710 --> 00:07:21.360 is because if you look at database.py, 178 00:07:21.360 --> 00:07:23.860 go to the top here for create options, 179 00:07:23.860 --> 00:07:26.660 an option has three values. 180 00:07:26.660 --> 00:07:28.880 The ID, the option text, and the poll ID 181 00:07:28.880 --> 00:07:32.210 those are gonna come back from our database. 182 00:07:32.210 --> 00:07:35.440 So here we're gonna pass them into the option constructor 183 00:07:35.440 --> 00:07:37.364 so that we can use those values from the database 184 00:07:37.364 --> 00:07:39.760 to create new objects. 185 00:07:39.760 --> 00:07:42.510 Next up, the three class methods that we're gonna need 186 00:07:42.510 --> 00:07:45.450 to get a specific poll by ID, 187 00:07:45.450 --> 00:07:47.260 we need that from app.py. 188 00:07:47.260 --> 00:07:50.960 Here we are getting specific poll information 189 00:07:50.960 --> 00:07:53.860 then we need one to get all the polls, 190 00:07:53.860 --> 00:07:55.920 for example we need that when we are trying 191 00:07:55.920 --> 00:07:58.320 to display the open polls. 192 00:07:58.320 --> 00:08:00.910 And we need one to get the latest poll, 193 00:08:00.910 --> 00:08:02.400 because we'll need that as well. 194 00:08:02.400 --> 00:08:06.503 So, we're gonna go over to poll.py and create those. 195 00:08:07.960 --> 00:08:08.820 If I leave them here, 196 00:08:08.820 --> 00:08:11.790 all of these do the same thing essentially. 197 00:08:11.790 --> 00:08:14.830 The get method takes in a poll ID 198 00:08:14.830 --> 00:08:17.350 and goes into the database and finds it. 199 00:08:17.350 --> 00:08:19.180 Notice that get poll doesn't exist yet 200 00:08:19.180 --> 00:08:20.110 but we're gonna create it. 201 00:08:20.110 --> 00:08:23.670 It essentially just retrieves a poll with that ID 202 00:08:23.670 --> 00:08:26.940 and then uses the CLS parameter, 203 00:08:26.940 --> 00:08:29.160 which is specific to class methods, 204 00:08:29.160 --> 00:08:31.970 to call the poll class, 205 00:08:31.970 --> 00:08:34.620 and it creates a new poll object 206 00:08:34.620 --> 00:08:37.030 passing in this information from the database. 207 00:08:37.030 --> 00:08:41.540 So the return type of this method is actually a poll object. 208 00:08:41.540 --> 00:08:43.390 And because we can't do this, 209 00:08:43.390 --> 00:08:46.349 we can't annotate a method of a class 210 00:08:46.349 --> 00:08:49.220 with the same class that it returns 211 00:08:49.220 --> 00:08:50.800 because by this point in time, 212 00:08:50.800 --> 00:08:52.070 when this actually runs, 213 00:08:52.070 --> 00:08:54.330 the class hasn't finished evaluating yet. 214 00:08:54.330 --> 00:08:56.320 So this is actually invalid in Python, 215 00:08:56.320 --> 00:08:58.060 we just put it as a string 216 00:08:58.060 --> 00:09:01.100 and Python knows to evaluate this return type 217 00:09:01.100 --> 00:09:04.020 after the class has finished processing. 218 00:09:04.020 --> 00:09:06.770 So that is what this returns - a poll object. 219 00:09:06.770 --> 00:09:09.560 The all method returns a list of polls 220 00:09:09.560 --> 00:09:11.960 and once again goes in and does database.get polls, 221 00:09:11.960 --> 00:09:14.120 which at the moment does exist. 222 00:09:14.120 --> 00:09:16.810 It just selects all the polls. 223 00:09:16.810 --> 00:09:20.290 And then what it does is it creates a poll object 224 00:09:20.290 --> 00:09:22.630 for each poll returned by the database 225 00:09:22.630 --> 00:09:25.270 and we end up with a list of poll objects. 226 00:09:25.270 --> 00:09:27.830 Finally, the latest method does the same thing 227 00:09:27.830 --> 00:09:29.860 but it just gets the latest poll. 228 00:09:29.860 --> 00:09:32.220 And I forgot to pass in the connection there 229 00:09:32.220 --> 00:09:34.160 so that's something that we need to pass in, 230 00:09:34.160 --> 00:09:38.020 and then simply gets the CLS return type there 231 00:09:38.020 --> 00:09:39.960 with the poll information. 232 00:09:39.960 --> 00:09:41.480 We're gonna have to change something in here 233 00:09:41.480 --> 00:09:42.410 afterwards anyway, 234 00:09:42.410 --> 00:09:45.570 because this at the moment returns a poll with option list 235 00:09:45.570 --> 00:09:48.560 and now we just want to get a single poll. 236 00:09:48.560 --> 00:09:50.040 So we do have to make those changes, 237 00:09:50.040 --> 00:09:51.680 but you can see that with the type hinting 238 00:09:51.680 --> 00:09:54.180 Python actually tells us this is probably not 239 00:09:54.180 --> 00:09:56.900 what we wanted to do with the current data types, 240 00:09:56.900 --> 00:09:59.210 but we're gonna change them in a moment. 241 00:09:59.210 --> 00:10:01.709 All right, so a lot of things new here. 242 00:10:01.709 --> 00:10:04.230 But essentially what we've done is we've created 243 00:10:04.230 --> 00:10:08.210 a class whose objects we can use 244 00:10:08.210 --> 00:10:12.810 to interact with the system in a bit of an easier way. 245 00:10:12.810 --> 00:10:15.620 Now we'll be able to, for example, create poll objects. 246 00:10:15.620 --> 00:10:17.210 I'm gonna just put it up here as an example. 247 00:10:17.210 --> 00:10:21.790 But we can say poll equal poll Flask versus Django, 248 00:10:21.790 --> 00:10:23.130 the owner can be Jose, 249 00:10:23.130 --> 00:10:25.860 and the ID let's say comes from the database and it's three, 250 00:10:25.860 --> 00:10:29.200 we can do things like poll.add option to add a new option. 251 00:10:29.200 --> 00:10:33.260 We can say Flask, and that is actually gonna go and save 252 00:10:33.260 --> 00:10:34.770 the option to the database 253 00:10:34.770 --> 00:10:37.190 without us having to do that ourselves. 254 00:10:37.190 --> 00:10:39.851 We can print poll.options for example 255 00:10:39.851 --> 00:10:41.220 and that is going to get us 256 00:10:41.220 --> 00:10:42.686 all the options from the database. 257 00:10:42.686 --> 00:10:45.900 And this is actually gonna be a list of option objects 258 00:10:45.900 --> 00:10:47.650 that we can then further interact with. 259 00:10:47.650 --> 00:10:48.790 Essentially, it allows us to be 260 00:10:48.790 --> 00:10:50.450 a little more flexible with how we're 261 00:10:50.450 --> 00:10:52.350 interacting with our system. 262 00:10:52.350 --> 00:10:55.870 By the way, I might actually make this a property, 263 00:10:55.870 --> 00:11:00.870 a decorator there, just so we can access poll.options 264 00:11:01.460 --> 00:11:04.080 instead of poll.options with the brackets. 265 00:11:04.080 --> 00:11:05.580 That's all that this allows. 266 00:11:05.580 --> 00:11:07.580 If you're not familiar with the property decorator, 267 00:11:07.580 --> 00:11:08.520 then I will leave a link 268 00:11:08.520 --> 00:11:10.680 in the resources section of this lecture. 269 00:11:10.680 --> 00:11:11.780 This is what I had in my notes, 270 00:11:11.780 --> 00:11:13.950 but I forgot to add it in earlier. 271 00:11:13.950 --> 00:11:16.530 All right, before moving on to adding the option class 272 00:11:16.530 --> 00:11:18.730 we're gonna cut it here and do this in the next video 273 00:11:18.730 --> 00:11:19.860 because this is getting a bit long. 274 00:11:19.860 --> 00:11:21.450 So, thank you guys for watching this video. 275 00:11:21.450 --> 00:11:22.973 I'll see you in the next one.