django-一对一、一对多、多对多操作、常用方法

准备表
一对一操作
一对多操作
多对多操作
常用方法
了不起的双下划线
准备表

创建如下几张表

from django.shortcuts import HttpResponse, render, redirect
from django.db import models

class Class(models.Model):
id = models.AutoField(primary_key=True)
cname = models.CharField(max_length=32)
cdata = models.DateField()

def __str__(self):
return "%s" % [self.__class__, self.cname]

class Student(models.Model):
id = models.AutoField(primary_key=True)
sname = models.CharField(max_length=32)

# 一对多
# cid = models.ForeignKey(to="Class",to_field="id",related_name="student")
cid = models.ForeignKey(to="Class", to_field="id")

# 一对一
detail = models.OneToOneField("StudentDetail", to_field="id")
# 等同于如下的代码
# detail = models.ForeignKey(to="StudentDetail",to_field="id",unique=True)

def __str__(self):
return "%s" % [self.sname]

# #建立多对多 第一种方法
# class Teacher(models.Model):
# id = models.AutoField(primary_key=True)
# tname = models.CharField(max_length=32)
#
#
# class Teacher2Class(models.Model):m
# id = models.AutoField(primary_key=True)
# tid = models.ForeignKey(to="Teacher",to_field="id")
# cid = models.ForeignKey(to="Class",to_field="id")
#
# class Meta:
# unique_together = ("tid","cid")

# 建立多对多 第二种方法
class Teacher(models.Model):
id = models.AutoField(primary_key=True)
tname = models.CharField(max_length=32)
cid = models.ManyToManyField(to="Class",name="teacher")

# 建立多对多 第3种方法
# class Teacher(models.Model):
# id = models.AutoField(primary_key=True)
# tname = models.CharField(max_length=32)
# cid_tid = models.ManyToManyField(to="Class",
# through="Teacher2Class",
# through_fields=("tid", "cid"))
#
# class Teacher2Class(models.Model):
# id = models.AutoField(primary_key=True)
# tid = models.ForeignKey(to="Teacher", to_field="id")
# cid = models.ForeignKey(to="Class", to_field="id")
#
# class Meta:
# unique_together = ("tid", "cid")

class StudentDetail(models.Model):
id = models.AutoField(primary_key=True)
height = models.PositiveIntegerField()
email = models.EmailField()
memo = models.CharField(max_length=128)
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需要注意的如下：

# 一对多
# cid = models.ForeignKey(to="Class",to_field="id",related_name="student")
cid = models.ForeignKey(to="Class", to_field="id")

# 一对一
detail = models.OneToOneField("StudentDetail", to_field="id")
# 等同于如下的代码
# detail = models.ForeignKey(to="StudentDetail",to_field="id",unique=True)
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来看下几个表的表名、字段名
app01_class班级表：

app01_student学生表：

app01_studentdetail学生信息表：

app01_class老师表：

app01_teacher2class班级老师表：

以上的app01_teacher2class表是通过第3种方法创建的，我们来看下第一种、第二方法创建的表名、字段名是怎样的？

通过方法1 创建班级-老师对应表如下：

通过方法2 创建班级-老师对应表如下：

 

一对一操作

正向查询（由学生信息表查询学生详情表）

stu = models.Student.objects.first()
stu.detail.email
'1@qq'
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反向查询（由学生详情表反向查询学生信息表）

detail = models.StudentDetail.objects.get(id=1)
detail.student.sname
'小一
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一对多操作

正向查询（由学生表查询班级表）

from app01 import models
stu = models.Student.objects.first()
stu.cid_id
1
stu.cid.cname
'全栈1期'
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反向查询（由班级表查询学生表）

cls = models.Class.objects.first()
cls.student_set.all()
<QuerySet [<Student: ['小一']>, <Student: ['小二']>]>
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注意：

如果不在外键的字段中设置related_name的话，默认就用表名_set。
如果设置了related_name=”students”，反向查询时可直接使用students进行反向查询。

cls.students.all()
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多对多操作

正向查询（由老师表查询班级表）

from app01 import models
tea = models.Teacher.objects.first()
tea.cid_tid
<django.db.models.fields.related_descriptors.create_forward_many_to_many_manager.<locals>.ManyRelatedManager object at 0x05C110F0>

tea.cid_tid.all()
<QuerySet [<Class: [<class 'app01.models.Class'>, '全栈1期']>, <Class: [<class 'app01.models.Class'>, '全栈2期']>]>

first = tea.cid_tid.first()
first
<Class: [<class 'app01.models.Class'>, '全栈1期']>

first.cname
'全栈1期'

first.student_set
<django.db.models.fields.related_descriptors.create_reverse_many_to_one_manager.<locals>.RelatedManager object at 0x03283870>

first.student_set.all()
<QuerySet [<Student: ['小一']>, <Student: ['小二']>]>
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反向查询（由班级表反向查询老师表）

cls = models.Class.objects.first()
cls.student_set
<django.db.models.fields.related_descriptors.create_reverse_many_to_one_manager.<locals>.RelatedManager object at 0x03283070>

cls.teacher_set
<django.db.models.fields.related_descriptors.create_forward_many_to_many_manager.<locals>.ManyRelatedManager object at 0x03224710>

cls.teacher_set.all()
<QuerySet [<Teacher: Teacher object>, <Teacher: Teacher object>]>

cls.teacher_set.all().first()
<Teacher: Teacher object>

cls.teacher_set.all().first().cid_tid
<django.db.models.fields.related_descriptors.create_forward_many_to_many_manager.<locals>.ManyRelatedManager object at 0x032A2790>

cls.teacher_set.all().first().tname
'王老师'
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常用方法

create()

from app01 import models
import datetime
teacher = models.Teacher.objects.get(id=1)
teacher.cid.create(cname="linux2",cdata=datetime.datetime.now())
<Class: [<class 'app01.models.Class'>, 'linux2']>
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多对对

cls = models.Class.objects.get(id=1)
cls.teacher_set.create(tname="egon")
<Teacher: Teacher object>
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import datetime
cls = models.Class.objects.first()
cls.student_set.create(sname="王七",detail_id=4)
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stu = models.Student.objects.create(sname="wyf",detail_id=5,cid_id=2)
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以下方式对多对多不行！！

add()

from app01 import models
import datetime
cls = models.Class.objects.all()
models.Teacher.objects.first().cid.add(*cls)
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set\remove\clear

tea = models.Teacher.objects.first()
tea.cid.set([4,3])
tea.cid.remove(3)
tea.cid.clear()
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了不起的双下划线

 

models.Class.objects.filter(student__sname__contains="d")
<QuerySet [<Class: [<class 'app01.models.Class'>, 'python']>, <Class: [<class 'app01.models.Class'>, 'sfsdf']>]>
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models.Class.objects.values("cname")
<QuerySet [{'cname': 'linux'}, {'cname': 'python'}, {'cname': 'sfsdf'}]>

models.Class.objects.values("cname","student__sname")
<QuerySet [{'cname': 'linux', 'student__sname': 'wyf'}, {'cname': 'python', 'student__sname': 'wfdsd'}, {'cname': 'sfsdf', 'student__sname': 'fdgerter'}]>
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以下方法不可行！！

models.Class.objects.first().values("cname","student__sname")
Traceback (most recent call last):
File "<input>", line 1, in <module>
AttributeError: 'Class' object has no attribute 'values'
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models.Class.objects.all().values("cname","student__detail__email")

<QuerySet [{'cname': 'linux', 'student__detail__email': '1@qq'}, {'cname': 'python', 'student__detail
---------------------
作者：Saflyer
来源：CSDN
原文：https://blog.csdn.net/u013210620/article/details/79142376?utm_source=copy
版权声明：本文为博主原创文章，转载请附上博文链接！