Modeling

Models in peewee are Python classes. 0:00 Each column in the table, each aspect that we want to remember about our thing. 0:02 Is an attribute on the Model Class. 0:06 To demonstrate this, let's make a model to represent a student here at Treehouse. 0:08 So, let's start by creating a new file that we're going to call, Students.py. 0:12 And I'm going to hold all of our information about 0:19 the different students in a dictionary. 0:22 But before I do that, I need to go ahead and make the database and 0:24 the model and all of that stuff. 0:29 You know, cart before the horse kind of thing. 0:31 So, to do most of this, I need to import the stuff that I need from peewee. 0:35 But unlike most of the platform that we've been writing, 0:40 we're going to be using a lot of different stuff in peewee. 0:43 And so, the convention for that is, to actually go ahead and 0:46 just import everything. 0:48 I don't really like doing this, it's not my favorite technique. 0:52 But this is the convention for working with peewee and 0:57 it's pretty important to stick to conventions. 0:59 Because that way your code, looks like other people's code. 1:01 Everybody can make assumptions and just work. 1:05 So we're going to import everything. 1:08 So now, let's make our database. 1:09 We're going to be using SQLite so we wanna make a SQLite connection. 1:12 Peewee will create the database for 1:17 us if it doesn't exist, at least when we're using SQLite. 1:18 So, Sqlitedatabase, and 1:21 I'm going to call it Students.db. 1:25 The .db is kind of a bit of a convention, because it says, hey, this is a database. 1:29 You don't have to, of course, if you don't want to. 1:35 And you can name the file anything you want. 1:38 If you don't want to call it students, if you want to call it people, whatever. 1:39 Go for it. 1:44 But now, we need our model. 1:45 Models in peewee are classes, but they inherit from the model class. 1:48 So let's do, class Student and it inherits from Model. 1:53 And we always name our models with a singular name. 1:58 Notice how I'm using Student and not Students. 2:03 So, why it that? 2:06 Well, it's because a model represents a single 2:07 item in the database, theoretically. 2:09 It wouldn't make sense then, to give them a plural name. 2:12 You'll see this convention used all over the place with peewee. 2:15 And you'll also see this used everywhere in Django. 2:18 Now, our model needs some attributes. 2:22 These attributes will become the fields or columns in the database table. 2:24 Let's just hold onto two things. 2:28 We're going to hold onto the student's username. 2:29 CharField. 2:33 And let's hold onto their points. 2:40 So, what's up with these? 2:45 Well, a CharField is a field that holds characters. 2:49 Somebody will say, CareField but I always find that really hard to say. 2:53 In sequel terminology, this is a VarChar field. 2:56 Because it has a variable length, VarChar variable character. 3:00 We have to tell it the maximum number of characters that we want to store. 3:05 So we're gonna set this to 255. 3:09 That should hold pretty much any username that we're going to ever come across. 3:10 The unique attribute, 3:16 the second argument there, says that we want the usernames to be unique. 3:17 We don't wanna have multiple records for the same student. 3:23 Our points attribute which is an integer field. 3:26 You probably guessed, integer fields hold integers. 3:29 And what we've said with this default keyword argument here, 3:33 is that if we don't supply a points. 3:37 Then it should just default it to zero. 3:40 Now, we didn't set a default on the user name field. 3:43 So, if we don't provide a user name we're going to get an error. 3:46 The last thing that we have to do is, 3:49 we have to tell the model what database it belongs to. 3:50 And we do that, by defining a class inside of our class that's called Meta. 3:54 Yeah, you can have classes inside of classes. 4:00 Now, metaclasses are something you're going to hear about 4:03 a lot of different places. 4:06 And they're a huge part of programming, but this isn't a metaclass. 4:07 This is just a class that's called meta. 4:11 It's describing the class that it belongs to. 4:13 The name has some meaning, but 4:15 it doesn't necessarily mean the thing that the name reflects on. 4:17 I know that's a little weird, but again, 4:21 this is a convention you're going to see in peewee and in Django. 4:23 So, we can use the metaclass to define all sorts of things. 4:27 Like which fields should be indexed, 4:31 how things should be ordered by default, all that stuff. 4:33 But for right now, 4:36 we're just going to stick to one attribute which is the database attribute. 4:37 And we're going to set database as being equal to DB. 4:40 which is our SQLite database we created up on line three. 4:44 Okay so, we have a database and we have a model that's been described. 4:49 We should use them. 4:54 So, let's add some code in here. 4:55 That if our file is run directly and not imported. 4:59 That it will go ahead and connect to our database. 5:06 And it will create tables and the tables we want it to create is, or are student. 5:10 We only have one table. 5:17 But something we want to do is, going to be sure and say safe equals true. 5:19 The reason we have to pass in the safe equals true keyword argument. 5:23 Is so, that if we run this multiple times toward the database that's 5:29 already been created. 5:32 And the table has already been created, peewee won't freak out and break. 5:32 It'll just go, okay, cool, everything's there. 5:37 Let's move on. 5:40 Okay, let's try and run this. 5:42 We come down here, python students.py. 5:46 And then I should be able to run this a second time with no problems. 5:49 Yay! 5:55 All right, so let's do an ls, and there's our students.db. 5:55 We're not going to talk about everything in SQL lite. 5:59 But let's use SQL lite real quick, to look inside there and see what's going on. 6:02 So, we can do SQL lite 3, students.db. 6:06 That'll connect to our database. 6:10 We can do .tables and that will show us all of our tables. 6:12 So, we have a student table. 6:17 And we can do say ,select * from student. 6:19 And we get back nothing, because we haven't put anything in there. 6:24 And then we can do .exit, and that'll go ahead and leave SQL lite. 6:27 Great, we're now ready to go build something. 6:31 Connecting to a database and creating a model are both pretty simple. 6:35 Most of that is thanks to peewee's API. 6:38 Now that we have a table, let's insert some data into it and 6:40 see about getting that data back out. 6:43