Django 模型
A Django model is a table in your database.
Django 模型
Up until now in this tutorial, output has been static data from Python or HTML templates.
Now we will see how Django allows us to work with data, without having to change or upload files in the prosess.
In Django, data is created in objects, called Models, and is actually tables in a database.
Create Table (Model)
To create a model, navigate to the models.py
file in the /members/
folder.
Open it, and add a Member
table by creating a Member
class
, and describe the table fields in it:
my_tennis_club/members/models.py
:
from django.db import models
class Member(models.Model):
firstname = models.CharField(max_length=255)
lastname = models.CharField(max_length=255)
The first field, firstname
, is a Text field, and will contain the first name of the members.
The second field, lastname
, is also a Text field, with the member's last name.
Both firstname
and lastname
is set up to have a maximum of 255 characters.
SQLite Database
When we created the Django project, we got an empty SQLite database.
It was created in the my_tennis_club
root folder, and has the filename db.sqlite3
.
By default, all Models created in the Django project will be created as tables in this database.
Migrate
Now when we have described a Model in the models.py
file, we must run a command to actually create the table in the database.
Navigate to the /my_tennis_club/
folder and run this command:
py manage.py makemigrations members
Which will result in this output:
Migrations for 'members':
members\migrations\0001_initial.py
- Create model Member
(myworld) C:\Users\Your Name\myworld\my_tennis_club>
Django creates a file describing the changes and stores the file in the /migrations/
folder:
my_tennis_club/members/migrations/0001_initial.py
:
# Generated by Django 4.1.2 on 2022-10-27 11:14
from django.db import migrations, models
class Migration(migrations.Migration):
initial = True
dependencies = [
]
operations = [
migrations.CreateModel(
name='Member',
fields=[
('id', models.BigAutoField(auto_created=True, primary_key=True, serialize=False, verbose_name='ID')),
('firstname', models.CharField(max_length=255)),
('lastname', models.CharField(max_length=255)),
],
),
]
Note that Django inserts an id
field for your tables, which is an auto increment number
(first record gets value 1, the second record 2 etc.), this is the default behavior of Django, you can override it by describing your own id
field.
The table is not created yet, you will have to run one more command, then Django will create and execute an SQL statement, based on the content of the new file in the /migrations/
folder.
Run the migrate command:
py manage.py migrate
Which will result in this output:
Operations to perform:
Apply all migrations: admin, auth, contenttypes, members, sessions
Running migrations:
Applying members.0001_initial... OK
(myworld) C:\Users\Your Name\myworld\my_tennis_club>
Now you have a Member
table in you database!
View SQL
As a side-note: you can view the SQL statement that was executed from the migration above. All you have to do is to run this command, with the migration number:
py manage.py sqlmigrate members 0001
Which will result in this output:
BEGIN;
--
-- Create model Member
--
CREATE TABLE "members_member" ("id" integer NOT NULL PRIMARY KEY AUTOINCREMENT, "firstname" varchar(255) NOT NULL, "lastname" varchar(255) NOT NULL); COMMIT;