Django ORM多对多查询方法(自定义第三张表&ManyToManyField)

框架(架构)  /  管理员 发布于 7年前   162

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.pyclass 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.pydef 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.pyfrom django.db import modelsclass 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.pydef 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.pyclass 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.pydef 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。