【Django学习笔记 - 13】：关联查询日期查询、一对一查询、一对多查询、多对多查询

Django配置数据库utf-8编码

1. settings.py文件中配置数据库

DATABASES = {
    'default': {
        'ENGINE': 'django.db.backends.mysql',
        'NAME': 'dj2022',
        'HOST': '127.0.0.1',
        'PORT': 3306,
        'USER': 'root',
        'PASSWORD': '1064865165QAF',
        'TEST': {
            'CHARSET': 'utf-8',
            'COLLATION': 'utf-8_general_ci'
        }
    }
}

SESSION_ENGINE = 'django.contrib.sessions.backends.db'

2.在Navicat中输入如下命令

CREATE DATABASE 数据库名 DEFAULT SET utf8;

一、日期查询

添加日期字段：
DateTimeField(verbose_name=‘’,auto_now=True)
auto_now 表示以现在的时间作为其值

日期字段的添加

1. 创建一个模型类

2、进行数据库的迁移后，在终端中进入shell环境，添加字段值

3、在Navicat中进行数据的添加

日期字段的查询

1、查询生日为1993-12-14

>>> Husband_1.objects.filter(birthday='1993-12-14')
<QuerySet [<Husband_1: Husband_1 object (1)>]>

2、查询1991年后的数据

>>> Husband_1.objects.filter(birthday__gt='1991-01-01')
<QuerySet [<Husband_1: Husband_1 object (1)>, <Husband_1: Husband_1 object (3)>, <Husband_1: Husband_1 object (4)>, <Husband_1: Husband_1 object (5)>]>

3、只根据年代或月份查询

>>> Husband_1.objects.filter(birthday__year__gt='1991')
<QuerySet [<Husband_1: Husband_1 object (1)>, <Husband_1: Husband_1 object (5)>]>

>>> Husband_1.objects.filter(birthday__month__gt='8')
<QuerySet [<Husband_1: Husband_1 object (1)>, <Husband_1: Husband_1 object (4)>]>

二、F、Q对象

F对象

F对象，用于属性与属性之间进行比较
导包：from django.db.models import F
语法：filter(字段名_运算符=F(‘字段名’))

• 例：查询身高大体重两倍的数据

>>> from django.db.models import F
>>> Husband_1.objects.filter(weight__lt=F('height')/2)
<QuerySet [<Husband_1: Husband_1 object (1)>, <Husband_1: Husband_1 object (2)>, <Husband_1: Husband_1 object (4)>]>

Q对象

Q对象，用于逻辑运算操作，与、或、非
导包：from django.db.models import Q

1. 例1：查询大于1993年或小于1992年的数据

>>> Husband_1.objects.filter(Q(birthday__year__gt='1993')|Q(birthday__year__lt='1992'))
<QuerySet [<Husband_1: Husband_1 object (2)>, <Husband_1: Husband_1 object (3)>]>

2. 查询除了1993年的所有数据

>>> Husband_1.objects.filter(~Q(birthday__year__gt='1993'))
<QuerySet [<Husband_1: Husband_1 object (1)>, <Husband_1: Husband_1 object (5)>]>

3. 查询大于1992年且年龄为33的数据

>>> Husband_1.objects.filter(Q(birthday__year__gt='1992')&Q(age=33))
<QuerySet [<Husband_1: Husband_1 object (1)>, <Husband_1: Husband_1 object (5)>]>

或

>>> Husband_1.objects.filter(Q(birthday__year__gt='1992',age=33))
<QuerySet [<Husband_1: Husband_1 object (1)>, <Husband_1: Husband_1 object (5)>]>

三、关联查询

一对一关系

1. 添加模型类

class Wife_1(models.Model):
    name = models.CharField(verbose_name='姓名', max_length=8)
    age = models.IntegerField(verbose_name='年龄')
    height = models.FloatField(verbose_name='身高')
    weight = models.FloatField(verbose_name='体重', null=None)
    husband = models.OneToOneField(Husband_1, verbose_name='丈夫', on_delete=models.CASCADE)

    class Meta:
        db_table = 'Wife_1'

models.OneToOneField(Husband_1,verbose_name=‘丈夫’,on_delete=models.CASCADE)
on_delete，设置表与表之间的级联
级联：将表与表之间进行联系，当主表中的数据删除时，子表中的数据也会被删除，在进行一对一的关联时，必须添加上on_delete参数

1. 级联演示

绑定表husband_1中id为3的数据

>>> Wife_1.objects.create(name='小芳', age=30, height=168, weight=48, husband_id=3)
<Wife_1: Wife_1 object (1)>

>>> wife = Wife_1.objects.get(id=1)

>>> husband = Husband_1.objects.get(id=3)
>>> wife.husband
<Husband_1: Husband_1 object (3)>
>>> wife.husband.name
'王五'

从主表中查询子表的数据：
例如：husband.子表的模型类类名（小写）.name

>>>husband.wife_1.name
'小芳'

一对多多对一

1. 添加模型类

class Children_1(models.Model):
    Children_choice = (
        (1, '男'),
        (2, '女')
    )
    name = models.CharField(verbose_name='姓名', max_length=8)
    age = models.IntegerField(verbose_name='年龄')
    sex = models.CharField(choices=Children_choice, verbose_name='性别', max_length=2)
    father = models.ForeignKey(Husband_1, on_delete=models.CASCADE)
    mother = models.ForeignKey(Wife_1, on_delete=models.CASCADE)

    class Meta:
        db_table = 'Children_1'

2.建立连接

>>> Children_1.objects.create(name='王小五', age=10, sex='男', father_id=3, mother_id=1)
<Children_1: Children_1 object (1)>
>>> Children_1.objects.create(name='王小美', age=8, sex=2, mother_id=1)
<Children_1: Children_1 object (2)>

3.查询演示

>>> son = Children_1.objects.get(id=1)
>>> daughter = Children_1.objects.get(id=2)
>>> son.mother
<Wife_1: Wife_1 object (1)>
>>> daughter.father.name
'王五'

4. 使用_set进行一对多的查询

没有related_name参数时，从‘一‘（父母）这一方查询’多‘（孩子）的一方，需要在模型类类名小写后加上’_set‘进行查询，当查询的记过可能有多个的时候，就需要再模型类类名小写后加上’_set’进行查询

>>> mother = Wife_1.objects.get(id=1)
>>> mother.children_1.set
>>> mother.children_1_set
<django.db.models.fields.related_descriptors.create_reverse_many_to_one_manager.<locals>.RelatedManager object at 0x0000026FE5696988>
>>> mother.children_1_set.all()
<QuerySet [<Children_1: Children_1 object (1)>, <Children_1: Children_1 object (2)>]>
>>> data1 = mother.children_1_set.all()
>>> data1[0].name
'王小五'

5. 使用related_name参数

related_name参数：表示为关联的字段起一个关联名称，相当于起别名，便于开发人员进行查询

>>> wife = Wife_1.objects.get(id=1)
>>> wife.mother
<django.db.models.fields.related_descriptors.create_reverse_many_to_one_manager.<locals>.RelatedManager object at 0x00000272C5CD68C8>
>>> data = wife.mother.all() # 获取所有孩子的信息
>>> data
<QuerySet [<Children_1: Children_1 object (1)>, <Children_1: Children_1 object (2)>]>
>>> data[1].name
'王小美'
>>> data[0].name
'王小五'

多对多查询

1. 添加模型类

class Brother_1(models.Model):
    Brother_choice = (
        (1, max_length=8)
    age = models.IntegerField(verbose_name='年龄')
    sex = models.CharField(choices=Brother_choice, max_length=2)
    brother = models.ManyToManyField(Husband_1, verbose_name='兄弟')
    sister = models.ManyToManyField(Wife_1, verbose_name='姐妹')

    class Meta:
        db_table = 'brother_1'

数据库表的命名格式：模型类名小写_关联字段名 -> brother_1_brother

2. 演示如下

>>> Brother_1.objects.create(name='大海', age=35, sex='男')
<Brother_1: Brother_1 object (1)>
>>> brother = Brother_1.objects.get(id=1)
>>> husband = Husband_1.objects.get(id=1)
# 1、通过对象进行关联
>>> brother.brother.set([husband,])
# 2、通过id进行关联

原文地址：https://blog.csdn.net/Oh_Python