[MUSIC] 0:00 [SOUND] Most of this stage is going to concentrate on area of models 0:04 that we haven't talk about before, inheritance. 0:07 If you played around with object oriented Python, which I'm assuming you 0:10 have because you've come this far, then this should be pretty comfortable to you. 0:13 Model inheritance lets us define some fields, methods, attributes, etc, in 0:18 one model, and then reuse those in another model without having to repeat them again. 0:22 Django models really are just Python classes. 0:27 Where this matters, though, is your actual database. 0:31 Sometimes you want more tables, sometimes you don't. 0:34 Let's start with model inheritance that doesn't make a new table. 0:37 We call this abstract inheritance, and 0:40 we call the models that don't have a database table abstract models. 0:43 Django has two main types of inheritance, abstract and multi-table. 0:47 Let's look at abstract first. 0:52 In abstract inheritance, we have a model that's marked as abstract. 0:54 We'll call ours User. 0:58 This user model won't actually have a database table and 1:00 can't be used for quires. 1:04 So how's this useful? 1:05 This model can be used for a starter for other models. 1:07 Maybe we have Students and Staff. 1:11 These are both users but we don't want to have to look up a user and 1:13 then a student or vice versa. 1:16 Since our User model is abstract, we can make both Student and 1:19 Staff extend from User. 1:22 Each of them get all of the fields of User and they get their own tables. 1:24 Our queries are simpler. 1:28 Our database design is nicer. 1:30 And our models file is still pretty easy to understand and dry. 1:31 Let's go to workspaces and make this abstract concept a bit more concrete. 1:35 So, I'm now inside of courses, models.py where all of our models are. 1:40 And we need to see about making an abstract model. 1:45 And the model that makes the most sense to make abstract at the moment is Step. 1:49 We're gonna have multiple types of steps later on, right? 1:54 We may have text based steps, we might have video based steps, we're 1:57 gonna have quizzes, eventually we'd have code challenges, all this kind of stuff. 2:01 So we wanna make it to where this is as adaptable as possible. 2:06 So some things are gonna be the same in all of these different types of steps, and 2:10 some things are gonna be different step to step. 2:15 I think content is one that is not gonna be the same in every singe step. 2:18 So it's probably one we would take take out. 2:24 First though, let's come down here and 2:26 to make Step abstract, we have to say that it's abstract. 2:29 So we say abstract = True. 2:34 Now, that means that we're basically gonna get rid of the table. 2:38 And we just got an error here. 2:43 It tried to restart and it's like, oh, you can't have abstract models in admin. 2:45 We're gonna fix that in just a minute. 2:48 So then, let's take content. 2:51 Oops, let's take content out. 2:53 And I'm gonna cut that instead of just deleting it, 2:57 cuz I need to use it again in a minute. 2:59 And let's make our new class. 3:02 And so this class is gonna be called Text. 3:06 This will represent our text steps. 3:08 And since Text will be a step, we're gonna have it inherit from Step. 3:10 And then, we'll put our content field back in there, okay? 3:16 Cuz we want to have a content field. 3:20 And that should be it. 3:24 Everything else is gonna come from Step. 3:27 We're gonna get this dunder __str__. 3:28 We're gonna get the ordering. 3:31 We're gonna get all that stuff from Step. 3:32 The only thing that's not gonna happen is Step won't be in the database. 3:35 So let's save that. 3:38 And let's come down here and we're gonna have to make some migrations. 3:40 So python manage.py makemigrations courses. 3:45 Now, we wanna be sure and we need to pay attention to this one. 3:51 So we're gonna do that and, oh, sorry, we're gonna go fix our admin real quick. 3:56 Let's go over here to admin, and 4:02 let's come down here and let's not register step. 4:05 And let's take off that inline as well. 4:12 All right. 4:15 So now let's give it a try. 4:16 There you go, okay. 4:23 Cool, all right, [LAUGH] so now this asked us a very important question. 4:27 Did you rename the courses.Step model to Text? 4:31 And we did. 4:34 We want all of our existing steps that we created in Django basics, 4:35 we want all of those to still be in here. 4:39 We just wanted to move them over to the Text table. 4:42 So we're gonna answer y, press Return, and now we get this migration and 4:44 we have rename model Step to text. 4:49 And I wanna actually look at this migration because this is 4:52 an important one. 4:54 So if we look here and we look through here, 4:56 we see that we renamed the model Step to Text, and that's really all we did. 5:00 That's it, because that's really what we wanted to do. 5:05 We wanted Step to become abstract. 5:07 We don't want step to exist anymore. 5:08 But we want all the data that's in Step to move over to this new table called Text. 5:11 So now let's go ahead and run that, python mange.py migrate courses. 5:16 Press Return, and then now its asking us, 5:21 do we still have the content type of Step that belongs to Courses? 5:24 And we don't, it's now called Text its no longer called Step so that doesn't exist. 5:29 So we're gonna type yes to tell Django to get rid of it. 5:34 And then let's go ahead and run our server. 5:38 And let's go fix our admin. 5:43 All right, everything's up and running. 5:45 Close that migration. 5:48 And up here inside of Step we wanna bring in Text. 5:50 And let's change this over to TextInline, even though we probably wanna get rid of 5:54 these inlines and come up with something a little better later on. 5:58 And we're actually gonna build a lot of this out as a little CMS in a bit. 6:02 TextInline, and we'll register Text. 6:08 All right, cool. 6:13 And now if we come look at our Site administration, we had Steps. 6:14 So let's refresh that, we should now have Texts. 6:18 And if we look in our Texts, we still have the couple that we made before. 6:21 And if we look at Courses and we look inside here, 6:27 we still have the ability to create Texts from inside of the admin. 6:30 So everything's still good. 6:35 So, let's go look at our model again. 6:36 Turning this to True, 6:40 all it really did in this case was it got rid of the table that we already had. 6:41 Mot of the time your gonna do this without having an existing table. 6:45 But it's good to know how to do it if you have a table and you're gonna go back and 6:48 refactor, and rework through how things work. 6:52 Abstract models are an amazingly handy tool when you need to be able to diversify 6:57 your models without creating a ton of tables or 7:01 requiring complex joins in the SQL that Django generates for you. 7:03 Later in this stage, we'll look at the other type of model inheritance Django 7:07 offers, but first, let's start our quizzes. 7:10