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What good is a database without tables? Let's build a model, connect to our database, and turn our model into a table.
New Terms
- model - A code object that represents a database table
-
SqliteDatabase- The class from Peewee that lets us connect to an SQLite database -
Model- The Peewee class that we extend to make a model -
CharField- A Peewee field that holds onto characters. It's avarcharin SQL terms -
max_length- The maximum number of characters in aCharField -
IntegerField- A Peewee field that holds an integer -
default- A default value for the field if one isn't provided -
unique- Whether the value in the field can be repeated in the table -
.connect()- A database method that connects to the database -
.create_tables()- A database method to create the tables for the specified models. -
safe- Whether or not to throw errors if the table(s) you're attempting to create already exist
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
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