Django-ORM多对多查询 (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)