标签: m2m

我正在努力保存相同的表格两个表 - 有一个m2m的关系.我没有成功,我的错误仍然存​​在于以下内容:无法在指定中间模型的ManyToManyField上设置值.使用会员经理而不是会员资格是我的'直通表'.

我的代码:

def save_classroom(request):
   classroom_instance = Classroom()
   if request.method == 'POST':
        form = ClassroomForm(request.POST, request.FILES, user = request.user) 
        if form.is_valid():
           new_obj = form.save(commit=False)
           new_obj.user = request.user 
           new_obj.save()
           membership = Membership(member = request.user,classroom=new_obj)
           membership.save() 
           form.save_m2m()
           return HttpResponseRedirect('.')    
   else:
           form = ClassroomForm(user = request.user)     
   return render_to_response('classroom/classroom_form.html', {
           'form': form,

           }, 
          context_instance=RequestContext(request))  

我的模特:

class Classroom(models.Model):
     user = models.ForeignKey(User, related_name = 'classroom_creator')
     classname = models.CharField(max_length=140, unique = True)
     date = models.DateTimeField(auto_now=True)
     open_class = models.BooleanField(default=True)
     members = models.ManyToManyField(User,related_name="list of invited members", through = …

我有 2 张桌子：餐厅和食物，第三张桌子 restaurant_foods 存储两张桌子之间的多对多关系

restaurants_foods = db.Table('restaurants_foods',
    db.Column('restaurant_id', db.Integer, db.ForeignKey('restaurants.id'), primary_key=True),
    db.Column('food_id', db.Integer, db.ForeignKey('foods.id'), primary_key=True),
    db.Column('food_price', db.Float)
)

class Food(Model):
    __tablename__ = "foods"

    id = db.Column(db.Integer, primary_key=True, autoincrement=True)    
    name = db.Column(db.String(255), nullable=False)
    description = db.Column(db.String(255), nullable=True)


class Restaurant(Model):
    __tablename__ = "restaurants"

    id = db.Column(db.Integer, primary_key=True, autoincrement=True)    
    name = db.Column(db.String(255), nullable=False)
    foods = db.relationship('Food', secondary=restaurants_foods)

现在，当我查询 Restautant.query.get(1).foods 时，我希望它包含 restaurant_foods 关联表中的 food_price 列

我是Django的新手,没有找到关于这个问题的任何参考.当我在django模型(models.py)中使用多对多字段时,我收到此错误.我想问题是从窗体(forms.py)中查看视图(views.py)中的m2m.如何在视图中分配m2m字段.
Django版本2.O python 3.5

models.py

class User(AbstractUser):
 username=models.CharField(max_length=20)
 email = models.EmailField(_('email address'), unique=True)


class Setupuser(models.Model):
 organization=models.CharField(max_length=200,blank=False,null=True)
 emails_for_help = models.ManyToManyField(User)

views.py

class Set_user(FormView):
 template_name="pkm_templates/set_up_user.html"
 form_class = Set_User_Form
 success_url = '/thanks/'
 def form_valid(self, form):
    org = form.cleaned_data.get('organization')
    emails = form.cleaned_data.get("emails_for_help")
    instance = Setupuser(organization=org,emails_for_help=emails)
    instance.save()
    return redirect("/")

forms.py

class Set_User_Form(ModelForm):
  emails_for_help = 
 forms.ModelMultipleChoiceField(queryset=User.objects.all(),
 widget=forms.CheckboxSelectMultiple)
 class Meta:
    model=Setupuser
    fields=["organization","emails_for_help"]

我在保存m2m数据方面遇到了麻烦,其中包含一个"通过"类表.我想在直通表中保存所有选定的成员(在表单中选择).但我不知道如何在视图中初始化"通过"表.

我的代码:

class Classroom(models.Model):
     user = models.ForeignKey(User, related_name = 'classroom_creator')
     classname = models.CharField(max_length=140, unique = True)
     date = models.DateTimeField(auto_now=True)
     open_class = models.BooleanField(default=True)
     members = models.ManyToManyField(User,related_name="list of invited members", through = 'Membership')

class Membership(models.Model): 
      accept = models.BooleanField(User)
      date = models.DateTimeField(auto_now = True) 
      classroom = models.ForeignKey(Classroom, related_name = 'classroom_membership')
      member = models.ForeignKey(User, related_name = 'user_membership')

并在视图中:

def save_classroom(request):
   classroom_instance = Classroom()
   if request.method == 'POST':
        form = ClassroomForm(request.POST, request.FILES, user = request.user) 
        if form.is_valid():
           new_obj = form.save(commit=False)
           new_obj.user = request.user 
           new_obj.save()
           membership …

当我保存相关模型时,我正试图让多个模型更新.这应该是可以使用m2m_changed信号(它可以工作!但不在管理员？)例如

# i want the references field to update when related model is saved.
# so just call count_references

class Tag(models.Model):
    """Group everything into categories"""
    # stuff stuff stuff
    references = models.IntegerField(default=0, editable=False)

    def count_references(self):
        # just add up references each time to save headaches
        self.references = 0
        # search for reverse managers
        sets = re.compile('^\w+_set$')
        for rel_set in [method for method in dir(self) if sets.match(method)]:
            self.references += getattr(self, rel_set).count()
        self.save()

class Entry(models.Model):
    """Blog entry"""
    # stuff stuff …

我最近开始在我的Django项目中使用信号(v.1.3)并且它们都工作正常,除了我无法弄清楚为什么m2m_changed信号永远不会在我的模型上被触发.通过在django管理表单上添加/删除PageChild内联实例来编辑Section实例.

我试图按照文档中的描述注册回调函数,但是没有得到任何结果.

摘自我的models.py

from django.db import models
from django.db.models.signals import m2m_changed


class Section(models.Model):
    name = models.CharField(unique = True, max_length = 100)
    pages = models.ManyToManyField(Page, through = 'PageChild')

class PageChild(models.Model):
    section = models.ForeignKey(Section)
    page = models.ForeignKey(Page, limit_choices_to = Q(is_template = False, is_background = False))


@receiver(m2m_changed, sender = Section.pages.through)
def m2m(sender, **kwargs):
    print "m2m changed!"

m2m_changed.connect(m2m, sender = Section.pages.through, dispatch_uid = 'foo', weak = False)

我错过了一些明显的东西吗

我遇到了一个奇怪的问题,我希望这里的某些人能够对此有所了解.

我正在重写模型的save()方法,以便在运行super()之后向ManyToMany字段添加一些值.我的问题是,当我在Django admin中保存时,值似乎被添加到关系中,但然后再次为空.

但是,如果我这样做,manage.py shell它没有问题.

我已经在那里放了两个打印语句,无论我是通过Django admin还是通过shell运行它,它们都会产生完全相同的输出.

class Store(models.Model):
    holidays = models.ManyToManyField(StoreHoliday, blank=True)
    copy_holidays_from = models.ForeignKey('Store', blank=True, null=True)

    def save(self):
        print '====  BEFORE SAVE:', self.holidays.all()
        super(Store, self).save()
        self.copy_holidays()
        print '====  AFTER SAVE:', self.holidays.all()

    def copy_holidays(self):
        if self.pk and self.copy_holidays_from:
            self.holidays.clear()
            for h in self.copy_holidays_from.holidays.all():
                self.holidays.add( h )

这是print声明的输出:

====  BEFORE SAVE: []
====  AFTER SAVE: [<StoreHoliday: 10 Mar 2010, Chuck Norris birthday (Closed)>]

有没有人对可能导致这种情况的原因有任何建议？

编辑:当通过管理界面保存时,Django似乎丢弃了save()中m2m关系的所有手动更改.这与处理表单的方式有关吗？

我在Django中使用以下模型模式(使用Postgres).

class A(Models.model):
    related = models.ManyToManyField("self", null=True)

给定A的QuerySet,我想返回一个字典A,将QuerySet中的每个实例尽可能快地映射到id其related实例的列表.

我可以肯定地遍历每个A并查询相关字段,但是有更优化的方法吗？

Django中的多对多关系示例:

class First(models.Model):
    seconds = models.ManyToManyField(Second, through='Middle')

class Middle(models.Model):
    first = models.ForeignKey(First)
    second = models.ForeignKey(Second)

class Second(models.Model):

根据中间模型的文档,只有一个相关对的ManytoManyField模型包含上面示例中的模型First.它是否正确？

如果是这样,哪个模型应包含该ManytoManyField字段？使用任何一方的关系是否有任何差异取决于它在哪里ManytoManyField？

谢谢

编辑(我应该更清楚):

我对中介表感兴趣,因为我将有额外的数据存储在关系中.

当我说使用时,我并不是指定义模型,我的意思是使用关系(否则我会让Django做它的事情).

如果我想要所有与第一个相关的秒,它是否与获得与第二个相关的所有第一个完全相同,或者ManytoManyField通过引入任何额外的功能使一个方向比另一个方向更容易？

我对Django的信号不是很熟悉,可以使用一些帮助.

如何在保存实例之前修改pk_set？我是否必须向信号呼叫者返回一些东西(比如kwargs)？或者我保存instance自己？

作为一个简单的例子:我希望确保在pk=1保存时我的所有视频都包含类别.我该怎么做m2m_changed？

class Video(models.Model):
    category = models.ManyToManyField('Category')

def video_category_changed(sender, **kwargs):
    action = kwargs.pop('action', None)
    pk_set = kwargs.pop('pk_set', None)
    instance = kwargs.pop('instance', None)

    if action == "pre_add":
        if 1 not in pk_set:
            pk_set.update( [ 1 ] )  # adding this to the set
            # do something else?
            # profit?

m2m_changed.connect( video_category_changed, sender=Video.category.through )