Model Upgrades

Our models and 0:00 their corresponding database tables are the backbone of any queries that we make. 0:01 They're what the ORM actually uses to get all the information that we ask for. 0:05 Over the past few Django courses, we've created and modified just a few models. 0:09 In this course, we're not going to introduce any new models, but 0:13 we do need to make a change or two to our course model. 0:15 Let's hop into Workspaces to see how our models are and 0:18 what changes we're going to make. 0:21 Okay, before we get to the meat of this course, I need to do a few things. 0:24 We need to add a new field to our course model, so that we can tie it to a teacher. 0:28 I wanna just use the user model that Django gave us, 0:31 there's no reason to reinvent that particular wheel just yet. 0:35 So let's go to our models inside of courses. 0:39 All right, so first we need to import the user model, 0:44 Django has a module named contrib. 0:48 So from django.contrib and inside contrib, there is a lot of useful, 0:50 but not required features. 0:55 It's where they all live, auth is one of those features. 0:56 So our import is from django.contrib.auth.models import User. 1:00 It's a pretty handy import to memorize, 1:06 there's a good chance that you'll use it in most of your projects. 1:07 Okay, so now we need to add the foreign key to our model. 1:11 So right down here, we're gonna do teacher = models.ForeignKey, 1:17 and that's going to go to User. 1:22 All righty, so since we've added something to our model, we need to do a migration. 1:24 So let cd into learning_site, 1:31 and then manage.py makemigrations courses. 1:34 And so you can see here that we're adding those non-nullable field teacher to 1:39 the course without a default, and we can't do that, we had to provide something. 1:43 So I know I have one user in here, which is me, and I'm the teacher for 1:47 all the courses that are currently in there, so I'm just gonna do one, and 1:51 I'm gonna enter in 1. 1:55 Now before we run this migration though, I wanna change one more thing. 1:57 I wanna add a character field into the course model, and 2:02 this is gonna hold on to what the subject of the course is. 2:06 So let's just say subject = models.Charfield, 2:10 default is a blank string, and the max length is 100. 2:15 Now there's a really good chance, like 99 point and 2:20 then as many 9s as you wanna type, that if I was doing this for 2:23 an actual commercial product or an actual project I was building, 2:26 I would have another model here that represents the subject. 2:30 Or I'd have some sort of taxonomy system, so 2:34 I could have multiple subjects, whatever. 2:36 For what we're doing here though, both of those are a little bit overkill. 2:38 And so I'm not gonna do them, but you should definitely feel free to try and 2:41 do those changes yourself. 2:45 So I wanna forcefy the default because just like with the teacher, 2:47 I have to have a value to put into our existing ones. 2:51 And yeah, I think we're good. 2:53 Let's go ahead and make one more migration. 2:56 And then let's run our migrations, 3:00 manage.py migrate courses. 3:04 All right, so our migrations have been made, and 3:08 we're ready to assign courses the teachers and subjects. 3:12 I don't wanna do all that on camera though, and 3:16 I don't wanna make you do it yourself. 3:18 So I've actually included a json file right here, fixtures.json, 3:20 that has all of the data already in it. 3:25 It's called a fixture file because it has fixed data that's going to get imported, 3:27 and so I wanna just show you how to use this. 3:32 I mean, it's full of json data, and 3:35 every item in here relates to a single database row. 3:37 There's a fields key here, and inside of each of these is the column and the value. 3:40 And then at the end of that where, there it is, model, 3:47 we have the app and model that it belongs to. 3:51 Django will read all of this, and it can create objects for 3:54 us based on what's inside of here. 3:57 It's a good way to set up starter data, that's really about it though. 3:59 You don't wanna use this for migrating from one database to another, 4:02 unless you're really, really careful. 4:06 All right, so let's go ahead and 4:08 load this with the appropriately named loaddata command. 4:10 Loaddata, and it's fixtures.json. 4:16 Cool, so it installed 89 objects from our one fixture. 4:21 Wow, that was a pretty quick review of our models, and 4:26 that fixture data is there waiting for you if you want to use it. 4:29 The database in the workspace should already have the data loaded though. 4:32 If you wanna make your own fixtures, you can use the dump data management command. 4:36 I'll put a link to docs about it in the teacher's notes. 4:39 Take a little break, and when you come back, 4:42 we'll talk about a really handy tool for evaluating your Django code. 4:44