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脚本之家。