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)