django ORM多对多正向查询时查询返回结果为None

Posted 2020-11-28 hbyang

表

class Books(models.Model):
    ‘‘‘书籍‘‘‘
    id = models.AutoField(primary_key=True)
    name = models.CharField(verbose_name=‘书籍名‘, max_length=32)class Writer(models.Model):
    ‘‘‘作者‘‘‘
    id = models.AutoField(primary_key=True)
    name = models.CharField(verbose_name=‘名字‘, max_length=32)
    Email = models.EmailField(verbose_name=‘邮件‘)
    phone = models.CharField(verbose_name=‘手机号‘, max_length=32)
    book = models.ManyToManyField(verbose_name=‘书籍‘, to=Books)

按照我们的理解

print(obj.book.name)

None

问题解决

注意：要说明的是多对多的查询用.all，查单个的时候用.values或者values_list，不要用obj.book.name，这样查到的会是None，反向查询也是如此。

总结：不管是一对多，还是多对多，要是查询多得一方就得用all()

print(obj.book.values)

<bound method BaseManager._get_queryset_methods.<locals>.create_method.<locals>.manager_method of <django.db.models.fields.related_descriptors.create_forward_many_to_many_manager.<locals>.ManyRelatedManager object at 0x03F8A950>>

print(obj.book.values(‘name‘))
<QuerySet [{‘name‘: ‘鬼吹灯‘}, {‘name‘: ‘择天记‘}, {‘name‘: ‘大主宰‘}, {‘name‘: ‘名族的重建‘}]>