Django ORM多对多查询方法(自定义第三张表&ManyToManyField)
对于多对多表
- 1.自定义第三张表，更加灵活
- 2.ManyToManyField 自动生成第3张表 只能 有3列数据 不能自己添加。
自定义第三张表
# models.py
class Boy(models.Model):
name = models.CharField(max_length=32)
class Girl(models.Model):
name = models.CharField(max_length=32)
class Love(models.Model):
b = models.ForeignKey('Boy')
g = models.ForeignKey('Girl')
# 创建联合唯一索引
# class Meta:
# unique_together = [
# ('b','g')，
# ]
# views.py
def test(request):
# objs = [
# models.Boy(name='summer'),
# models.Boy(name='spring'),
# models.Boy(name='autumn'),
# ]
# models.Boy.objects.bulk_create(objs,5)
# objs = [
# models.Girl(name='小于'),
# models.Girl(name='小秋'),
# models.Girl(name='小夏'),
# ]
# models.Girl.objects.bulk_create(objs,5)
# 查询和girl小于有关系的boy
# 1 通过girl表进行反向查找
obj = models.Girl.objects.filter(name='小于').first().love_set.all()
# obj = models.Girl.objects.filter(name='小于').first().love_set.select_related('b').all()
for i in obj:
print(i.b.name)
print(' '.center(60,'='))
# 2 通过Love表进行查找
obj = models.Love.objects.filter(g__name='小于').all()
for i in obj:
print(i.b.name)
# 这样进行查询性能不好，需要重新发sql请求在进行查询另外一张表中的数据
boy_list = models.Love.objects.filter(g__name='小于').values('b__name')
for i in boy_list:
print(i['b__name'])
# 这样 进行了 优化 不会重复发送sql请求，查询到的结果内是字典
boy_obj = models.Love.objects.filter(g__name='小于').select_related('b').all()
for i in boy_obj:
print(i.b.name)
# select_related('ut') 相当 于 inner join 先连成一张表再进行查询
return HttpResponse('insert ok ....')
ManyToManyField
# models.py
from django.db import models
class Boy(models.Model):
name = models.CharField(max_length=32)
# m = models.ManyToManyField('Girl')
class Girl(models.Model):
name = models.CharField(max_length=32)
m = models.ManyToManyField('Boy')
# views.py
def test(request):
# objs = [
# models.Boy(name='summer'),
# models.Boy(name='spring'),
# models.Boy(name='autumn'),
# ]
# models.Boy.objects.bulk_create(objs,5)
# objs = [
# models.Girl(name='小于'),
# models.Girl(name='小秋'),
# models.Girl(name='小夏'),
# ]
# models.Girl.objects.bulk_create(objs,5)
# ManyToManyField
obj = models.Girl.objects.filter(name='小秋').first()
# 增
# obj.m.add(3)
# obj.m.add(3,4)
# obj.m.add(*[1,2])
# 删
# obj.m.remove(3)
# obj.m.remove(3,4)
# obj.m.remove(*[1,2])
# 改
# obj.m.set([1,2,])
# boy_obj = obj.m.all()
# for row in boy_obj:
# print(row.id,row.name)
# 清除
# obj.m.clear()
# 反向查 在没有 ManyToManyField 字段的表中查
obj = models.Boy.objects.filter(name='summer').first()
girl_obj = obj.girl_set.all()
# 增删改查
obj.girl_set.set([1,2,3])
for row in girl_list:
print(row.id,row.name)
return HttpResponse('ok')
杂交(自定义第三张表+ManyToManyField)
# modles.py
class Boy(models.Model):
name = models.CharField(max_length=32)
class Girl(models.Model):
name = models.CharField(max_length=32)
m = models.ManyToManyField('Boy',through='Love',through_fields=('b','g')) # 只让其生成3张表，如果不加后面产生生成4张表
class Love(models.Model):
b = models.ForeignKey('Boy')
g = models.ForeignKey('Girl')
# views.py
def test(request):
obj = models.Girl.objects.filter(name='小于').first()
# obj.m.add(1) # 不行
# obj.m.remove(1) # 不行
# obj.m.set([1,2]) # 不行
# obj.m.clear() # 可以
# obj.m.all() # 可以
# 杂交的方法对获取查询方便点，还添加了清空功能
boy_obj = obj.m.all()
for i in boy_obj:
print(i.name)
以上这篇Django ORM多对多查询方法(自定义第三张表&ManyToManyField)就是小编分享给大家的全部内容了，希望能给大家一个参考，也希望大家多多支持【听图阁-专注于Python设计】。
