Django REST 框架详解 03 | 模型建立与表设计

一、设计表

假设需求，图书管理系统：
Book: name, price, img, authors, publish, is_delete, create_time
Publish: name, address, is_delete, create_time
Author: name, age, is_delete, create_time
AuthorDetail: mobile, author, is_delete, create_time

为什么要加 is_delete 字段？

只要入库的数据，永远不会被删除

如果主键 id 自增时，随便删除数据，会导致 id 不连续，查询时，会遗漏数据

只要该数据在入库了，就代表该数据有利用价值

为什么 Author， AuthorDetail 要拆分为两张表？

Author 的查询频率高，如果字段太多会影响查询效率。AuthorDetail 只在需要详情时，才会用到

这两张表一般是一对一的关系

二、表关系

1.表关系设置

Book - Publish：多对一
publish = models.ForeignKey(to='Publish', on_delete=models.CASCADE)
Book - Author：多对多
authors = models.ManyToManyField(to='Author')
Author - AuthorDetail：一对一
author = models.OneToOneField(to='Author', on_delete=models.CASCADE)

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2.断开表关联

断关联：db_constraint=True
断开关联后，可以用编程逻辑来实现表的数据同步，这样会增加效率

class Book(BaseModel):
    name = models.CharField(max_length=64)
    price = models.DecimalField(max_digits=5, decimal_places=2)
    img = models.ImageField(upload_to='img', default='img/default.jpg')
    publish = models.ForeignKey(to='Publish', db_constraint=True, on_delete=models.CASCADE)
    authors = models.ManyToManyField(to='Author')

    class Meta:
        db_table = 'book'
        verbose_name = '书籍'
        verbose_name_plural = verbose_name

    def __str__(self):
        class Book(BaseModel):
    name = models.CharField(max_length=64)
    price = models.DecimalField(max_digits=5, decimal_places=2)
    img = models.ImageField(upload_to='img', default='img/default.jpg')
    publish = models.ForeignKey(to='Publish', db_constraint=True, on_delete=models.CASCADE)
    authors = models.ManyToManyField(to='Author')

    class Meta:
        db_table = 'book'
        verbose_name = '书籍'
        verbose_name_plural = verbose_name

    def __str__(self):
        return self.name

book 与 author 外键关系断开

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class AuthorDetail(BaseModel):
    mobile = models.CharField(max_length=11)
    author = models.OneToOneField(
        to='Author',
        db_constraint=False,  # 不断开表连接
        on_delete=models.CASCADE,  # 删除 AuthorDetail 不会影响 Author 表，但是如果删除 Author，AuthorDetail就会被一起删除
        related_name='detail'  # 正向查返回 name, 反向返回设置的 related_name
    )

    class Meta:
        db_table = 'author_detail'
        verbose_name = '作者详情'
        verbose_name_plural = verbose_name

    def __str__(self):
        return f'class AuthorDetail(BaseModel):
    mobile = models.CharField(max_length=11)
    author = models.OneToOneField(
        to='Author',
        db_constraint=False,  # 不断开表连接
        on_delete=models.CASCADE,  # 删除 AuthorDetail 不会影响 Author 表，但是如果删除 Author，AuthorDetail就会被一起删除
        related_name='detail'  # 正向查返回 name, 反向返回设置的 related_name
    )

    class Meta:
        db_table = 'author_detail'
        verbose_name = '作者详情'
        verbose_name_plural = verbose_name

    def __str__(self):
        return f'{self.author}的详情'

author 与 author_detail 表关系断开

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三、级联操作

1.CASCADE

作者删除，详情删除：models.CASCADE
models.py

class AuthorDetail(BaseModel):
    mobile = models.CharField(max_length=11)
    author = models.OneToOneField(
        to='Author',
        db_constraint=False,
        related_name='detail',
        on_delete = models.CASCADE,
    )

    class Meta:
        db_table = 'author_detail'
        verbose_name = '作者详情'
        verbose_name_plural = verbose_name

    def __str__(self):
        return f'class AuthorDetail(BaseModel):
    mobile = models.CharField(max_length=11)
    author = models.OneToOneField(
        to='Author',
        db_constraint=False,
        related_name='detail',
        on_delete = models.CASCADE,
    )

    class Meta:
        db_table = 'author_detail'
        verbose_name = '作者详情'
        verbose_name_plural = verbose_name

    def __str__(self):
        return f'{self.author}的详情'

数据库迁移

python manage.py makemigrations
python manage.py migrrate

执行script.py

import os, django

os.environ.setdefault('DJANGO_SETTINGS_MODULE', 'def_proj01.settings')
django.setup()

from api import models

models.AuthorDetail.objects.filter(pk=import os, django

os.environ.setdefault('DJANGO_SETTINGS_MODULE', 'def_proj01.settings')
django.setup()

from api import models

models.AuthorDetail.objects.filter(pk=1).delete()

作者详情删除，并不会影响作者

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执行script.py

import os, django

os.environ.setdefault('DJANGO_SETTINGS_MODULE', 'def_proj01.settings')
django.setup()

from api import models

models.Author.objects.filter(pk=import os, django

os.environ.setdefault('DJANGO_SETTINGS_MODULE', 'def_proj01.settings')
django.setup()

from api import models

models.Author.objects.filter(pk=1).delete()

反之，删除作者后，详情随之删除

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2.SET_NULL

作者删除，外键置空： on_delete=models.SET_NULL
models.py

class AuthorDetail(BaseModel):
    mobile = models.CharField(max_length=11)
    author = models.OneToOneField(
        to='Author',
        db_constraint=False,
        related_name='detail',        
        null=True,
        on_delete=models.SET_NULL
    )

    class Meta:
        db_table = 'author_detail'
        verbose_name = '作者详情'
        verbose_name_plural = verbose_name

    def __str__(self):
        return f'class AuthorDetail(BaseModel):
    mobile = models.CharField(max_length=11)
    author = models.OneToOneField(
        to='Author',
        db_constraint=False,
        related_name='detail',        
        null=True,
        on_delete=models.SET_NULL
    )

    class Meta:
        db_table = 'author_detail'
        verbose_name = '作者详情'
        verbose_name_plural = verbose_name

    def __str__(self):
        return f'{self.author}的详情'

数据库迁移

python manage.py makemigrations
python manage.py migrrate

执行script.py

import os, django

os.environ.setdefault('DJANGO_SETTINGS_MODULE', 'def_proj01.settings')
django.setup()

from api import models

models.Author.objects.filter(pk=import os, django

os.environ.setdefault('DJANGO_SETTINGS_MODULE', 'def_proj01.settings')
django.setup()

from api import models

models.Author.objects.filter(pk=1).delete()

作者删除后，作者详情保留，但是外键置空

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3.SET_DEFAULT

作者删除，作者详情设置默认值： on_delete=models.SET_DEFAULT

与 models.SET_NULL 相似，只是将空换为默认值
models.py

class AuthorDetail(BaseModel):
    mobile = models.CharField(max_length=11)
    author = models.OneToOneField(
        to='Author',
        db_constraint=False,
        related_name='detail',
        default='default',
        on_delete=models.SET_DEFAULT
    )

    class Meta:
        db_table = 'author_detail'
        verbose_name = '作者详情'
        verbose_name_plural = verbose_name

    def __str__(self):
        return f'class AuthorDetail(BaseModel):
    mobile = models.CharField(max_length=11)
    author = models.OneToOneField(
        to='Author',
        db_constraint=False,
        related_name='detail',
        default='default',
        on_delete=models.SET_DEFAULT
    )

    class Meta:
        db_table = 'author_detail'
        verbose_name = '作者详情'
        verbose_name_plural = verbose_name

    def __str__(self):
        return f'{self.author}的详情'

4.DO_NOTHING

作者删除，作者详情不改变：on_delete=models.DO_NOTHING
models.py

class AuthorDetail(BaseModel):
    mobile = models.CharField(max_length=11)
    author = models.OneToOneField(
        to='Author',
        db_constraint=False,
        related_name='detail',
        default='default',
        on_delete=models.DO_NOTHING
    )

    class Meta:
        db_table = 'author_detail'
        verbose_name = '作者详情'
        verbose_name_plural = verbose_name

    def __str__(self):
        return f'class AuthorDetail(BaseModel):
    mobile = models.CharField(max_length=11)
    author = models.OneToOneField(
        to='Author',
        db_constraint=False,
        related_name='detail',
        default='default',
        on_delete=models.DO_NOTHING
    )

    class Meta:
        db_table = 'author_detail'
        verbose_name = '作者详情'
        verbose_name_plural = verbose_name

    def __str__(self):
        return f'{self.author}的详情'

四、Admin

通过 Admin 我们可以直接通过后台来编辑表

admin.py注册

from django.contrib import admin
from api from django.contrib import admin
from api import models

admin.site.register(models.Author)
admin.site.register(models.AuthorDetail)
admin.site.register(models.Book)
admin.site.register(models.Publish)