ORM简介
对象关系映射（Object Relation Mapping）实现了关系和数据库之间的映射，隐藏了关系数据访问的细节，不需要再编写SQL语句
创建模型
在models.py的文件中创建类 继承models.Model
from django.db import models
class BookInfo(models.Model):
title = models.CharField(max_length=20)
pub_date = models.DateField()
数据迁移
1生成迁移文件：根据模型类生成创建表的迁移文件。执行命令python3 manage.py makemigrations
python3 manage.py makemigrations
Migrations for 'books':
books/migrations/0001_initial.py
- Create model BookInfo
此时会在book文件下生成migrations/0001_initial.py迁移文件
from django.db import migrations, models
class Migration(migrations.Migration):
initial = True
dependencies = [
]
operations = [
migrations.CreateModel(
name='BookInfo',
fields=[
('id', models.AutoField(auto_created=True, primary_key=True, serialize=False, verbose_name='ID')),
('title', models.CharField(max_length=20)),
('pub_date', models.DateField()),
],
),
]
2执行迁移：根据第一步生成的迁移文件在数据库中创建表。执行命令：python3 manage.py migrate
python3 manage.py migrate
Operations to perform:
Apply all migrations: admin, auth, books, contenttypes, sessions
Running migrations:
Applying contenttypes.0001_initial... OK
Applying auth.0001_initial... OK
Applying admin.0001_initial... OK
Applying admin.0002_logentry_remove_auto_add... OK
Applying admin.0003_logentry_add_action_flag_choices... OK
Applying contenttypes.0002_remove_content_type_name... OK
Applying auth.0002_alter_permission_name_max_length... OK
Applying auth.0003_alter_user_email_max_length... OK
Applying auth.0004_alter_user_username_opts... OK
Applying auth.0005_alter_user_last_login_null... OK
Applying auth.0006_require_contenttypes_0002... OK
Applying auth.0007_alter_validators_add_error_messages... OK
Applying auth.0008_alter_user_username_max_length... OK
Applying auth.0009_alter_user_last_name_max_length... OK
Applying books.0001_initial... OK
Applying sessions.0001_initial... OK
Django默认采用sqlite3数据库,最终会生成如下数据表，其中自定义的表命名规则是<app_name><model_name>（应用名称模型类名）
DATABASES = {
'default': {
'ENGINE': 'django.db.backends.sqlite3',
'NAME': os.path.join(BASE_DIR, 'db.sqlite3'),
}
}
image.png
外键数据处理
class HeroInfo(models.Model):
name = models.CharField(max_length=20)
gender = models.BooleanField(default=False)
comment = models.CharField(max_length=128)
book = models.ForeignKey(BookInfo, on_delete=models.DO_NOTHING)
django 升级到2.0之后,表与表之间关联的时候,必须要写on_delete参数,否则会报异常:
TypeError: init() missing 1 required positional argument: 'on_delete'
on_delete参数的各个值的含义:
on_delete=None, # 删除关联表中的数据时,当前表与其关联的field的行为
on_delete=models.CASCADE, # 删除关联数据,与之关联也删除
on_delete=models.DO_NOTHING, # 删除关联数据,什么也不做
on_delete=models.PROTECT, # 删除关联数据,引发错误ProtectedError
# models.ForeignKey('关联表', on_delete=models.SET_NULL, blank=True, null=True)
on_delete=models.SET_NULL, # 删除关联数据,与之关联的值设置为null（前提FK字段需要设置为可空,一对一同理）
# models.ForeignKey('关联表', on_delete=models.SET_DEFAULT, default='默认值')
on_delete=models.SET_DEFAULT, # 删除关联数据,与之关联的值设置为默认值（前提FK字段需要设置默认值,一对一同理）
on_delete=models.SET, # 删除关联数据,
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